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SuzukiSavage.com
/cgi-bin/YaBB.pl General Category >> Rubber Side Down! >> Why get a 36mm carb instead of a 40mm? /cgi-bin/YaBB.pl?num=1352365571 Message started by Cavi Mike on 11/08/12 at 01:06:11 |
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Title: Why get a 36mm carb instead of a 40mm? Post by Cavi Mike on 11/08/12 at 01:06:11 The more and more I look around, the more and more I realize that a 36mm should just be too small for a 650cc bike. 36mm carbs are on 400cc 4-strokes and 250cc 2-strokes. I even saw a 36mm flat-slide on a 125 smoker. 650cc is over 50% bigger than a 400 - so why exactly should I be using a carb that's the same size? I'm about the drop the hammer on a carb right this second but I'm really thinking it's the TM40 I should be getting - not the TM36. Unless someone can make a real good argument, I may just have to get the 40. |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by ToesNose on 11/08/12 at 03:39:05 Seeing how I don't get alot of free time for riding I haven't jumped into modding or even researching towards performance upgrades, I'd rather be riding then wrenching at this point. But it would be nice to hear what some of the folks who have done performance mods have to say on this Mike. |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by Drifter on 11/08/12 at 04:12:27 A 36 or even smaller would work on this low tech low HP engine and get better mileage. For a larger carb to work as intended you need more air flow higher lift and longer duration cam, open exhaust and more rpm,higher compresion. At lower rpm a big carb does not work as well as a smaller one due to the venturi effect and fuel atomization. This engine already has a very short intake, a large carb would just make this worse. Small and long intake runners produce more torque along with small diameter header pipes. I cant see much advantage of a big carb on this engine without lots of expensive mods....i have a ninja that takes care of my need for speed. |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by Cavi Mike on 11/08/12 at 04:28:46 Don't care about your Ninja and it's a no-brainer that a smaller carb will offer greater fuel economy - it's like someone putting a throttle-stop on your bike. Can't use more gas if you can't get it in the bike. And low-tech doesn't have anything to do with how much air an engine draws in. Didn't answer my question at all. If anything, you made an argument in favor of a larger carb. Suzuki DRZ400 has a 39mm carb if anyone was curious... |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by Drifter on 11/08/12 at 04:52:04 Did you read what i said....look up the basics of an ICE, what i said was correct. If you want to go fast get another bike, wanting speed from this bike is like cutting steak with a butter knife....far better tools for the job. If you did not want opinions why ask the question? No reason to be rude to someone answering your question. |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by rfw2003 on 11/08/12 at 04:52:17 Cavi, Lancer is the man to talk to. He has tried all sorts and sizes of carbs on the Savage. I can't find the post right now but he was saying the at least in the round slide style carbs thee 36mm was the best performer. R.F. |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by Dave on 11/08/12 at 05:02:19 The carb needs to be sized to work with the engine. This includes port size, valve size, cam duration and lift, exhaust flow, etc. If you have an engine that flow lots of air - then it can use a larger carb. The Savage has a very mild cam, relatively small ports and valves, a restrictive exhaust system, mild compression, and it is designed to run smoothly at cruising speeds. This means that the air flow is relatively low most of the time, and a smaller carb is better because the airflow through the smaller carb is at a high enough speed to create a nice vacuum and pull fuel out of the jets well. If you put too big of a carb on without making other changes to improve the flow of air through the engine - then the speed of air flow through the carb becomes low and the carb does not work well atomizing or metering the fuel at low throttle settings. The carb may work well when the engine is revved up - but that is not where the cam, valves, ports, exhaust are designed to work well on the Savage. Too big of a carb....and you will end up with an engine that runs badly until you have the engine running at full speed. It will be a very frustrating bike to ride. With a stock engine the 36mm is supposed to be best, and with modificaitons you can move up to a 38mm. |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by Cavi Mike on 11/08/12 at 05:12:46 71475C53415047350 wrote:
Who said I want to go fast? You said that, not me. Just because one isn't looking for speed doesn't mean they should put a small carb on their bike. I did read what you said and you're arguing a point not relevant to this topic. And as I said, you didn't answer my question because you answered a question you made up. |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by ZAR on 11/08/12 at 06:11:56 7D4B505F4D5C4B390 wrote:
Kind of like buying a 100hp John Deere tractor and 20' bush hog to mow a 1/4 acre yard then......... The only way to make use of the extra size and power is to expand the yard........by several acres ;D ! |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by Gyrobob on 11/08/12 at 07:38:08 This is simply a matter of matching flow rates. The carb should flow just a little more than the max the motor would ever need. All other considerations are just details. |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by Cavi Mike on 11/08/12 at 16:28:24 0E1506540 wrote:
Because wanting to maximize volumetric efficiency is EXACTLY like mowing your lawn! Didn't you know?! *facepalm* Thank you to Dave and Gyrobob. I think I'm gonna dig into the motor a little bit - most likely with a bunch of Lancer parts. |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by LANCER on 11/09/12 at 05:37:25 Yep, it is about FLOW RATE. That is the name of the game. The stock CV carb is designed for economy and minimal emissions, not performance. Look down the throat of the CV carb ... what do you see ? The mount end of the carb does have a 40mm ID but there is a butterfly valve in the way and beyond that the middle of the throat narrows Considerably, both of which impedes flow. Then look down the throat of a VM carb and what do you see ? It is wide open. In both cases I've assumed that the slide is up and out of the way. The slide in the CV is moved up only by engine vacuum which builds in a LAG in the response time. The slide in a VM carb is moved directly by the throttle cable which enables faster response. The difference is function, response and ultimate performance is dramatic. That is why a 36mm VM with absolutely outperform a 40mm CV from idle to WOT. |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by Gyrobob on 11/09/12 at 06:02:23 737E717C7A6D2D281F0 wrote:
I agree,... with a sense of awesome totalness. I would speculate, though, that for a VM carb to be so responsive, getting the jetting (I made a rhyme, eh?) spot on is a perty big thang. |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by Gyrobob on 11/09/12 at 06:12:04 Here's a 36mm VM carb on amazon: http://www.amazon.com/Mikuni-Round-Slide-Series-Carburetor/dp/B000GZK7LG The description says: Bore Size : 36mm Spigot Mount : 43mm Main Jet : 310 Pilot Jet : 35 Needle Jet : Q-5 Throttle Valve : 2.5 Jet Needle : 6FJ6 Air Jet : 2.0 ~ $100 seems like a reasonable price to be able to start with something factory new. Is this a good place to start? |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by Cavi Mike on 11/09/12 at 08:44:02 I'm not willing to spend $100 on something that I know I'm going to want to change out shortly - it's not like I can get that money back. I also want a flat-slide. Most likely I'm going to get the TM40-6 pumper and start saving for Lancer's 97mm bore kit and cam. |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by Gyrobob on 11/09/12 at 09:33:23 7557405F7B5F5D53360 wrote:
What's the advantage of a flat slide? |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by verslagen1 on 11/09/12 at 10:04:24 Better flow thru the venturi. similar to adding the uniflo to the VM |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by Gyrobob on 11/09/12 at 11:54:56 415245445B5650525906370 wrote:
Okay,.. I'll accept better flow through the venturi. What difference would that make? Would swapping out a stock CV Savage carb for a properly sized flat slide carb give any of these things? -- more power -- more responsiveness -- better mileage for a given amount of power -- lowered operating expense -- less backfiring, popping, etc. -- longer engine life -- neater sound from the intake side of the engine -- better looking engine -- cool factor when hanging out -- more reliability If a few or several of those factors listed above happen when switching to a flat slide carb, I'll try it. |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by verslagen1 on 11/09/12 at 12:04:32 -- more power=captain? -- more responsiveness=anythings better than the cv -- better mileage for a given amount of power=you want more power or what? -- lowered operating expense=mpg? -- less backfiring, popping, etc.=fuel map you want? -- longer engine life=think natural gas -- neater sound from the intake side of the engine=the unmuffled sounds of a savage heart -- better looking engine=what? you don't think 10 miles of ducting look cool? -- cool factor when hanging out = you wanna go fast or talk fast? -- more reliability = think natural gas, how cool would a nat. gas tank look? |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by LANCER on 11/09/12 at 12:12:30 372433322D2026242F70410 wrote:
A 36mm VM with the UFO installed will outflow a 36mm TM in the low and midrange, making more power, and equal the TM in the high range. It does take some time and effort to get it dialed in correctly but the result is worth it. |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by dr1445 on 11/10/12 at 19:41:13 if you are going with a tm40-6, which i recall is a harley carb, you will need to change the ap nozzle jet to around a #40 or 45. thats about 1/2 the size of the nozzle jet for the harley. if i recall the slow jet is about right to start with and a main around 150 is good starting point. you need a smaller intake boot to fit the carb to engine and the air filter side does not fit the stock intake hose. details! |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by swing69 on 11/10/12 at 19:57:45 so my question would be: I have a 86 650; all stock. I want to add a slightly better flowing / slightly louder muffler. In addition, Im thinking of tossing the stock carb. Without modifying any internals. what is the best bolt on spec. carb for smooth running and slightly better performance. Please specify the carb and jetting please. thanks |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by justin_o_guy2 on 11/10/12 at 21:06:03 Im not tryin to lower the boom on ya here, but, th way Im readin your post, youre actually wanting more than you realize. Its just not that easy, to just spit out a carb & the jetting, even IF someone knew exactly what exhaust you want & what elevation you live at, Its more of a "Change this, create a bit of a jetting issue, chase it down & solve it" kinda thing,,, M<aybe someone will come along & kikk me to the curb, I could be wrong,, hang around & wait on the smart guys.,. |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by Cavi Mike on 11/11/12 at 21:35:41 584E0D0808093C0 wrote:
Mikuni is not made by Harley, it's made by Mikuni. At best - the HS40 is a licensed copy that Harley produces and puts on their bikes but the TM40 is a Mikuni carb through and through and they're made in Japan. |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by LANCER on 11/12/12 at 02:42:32 The TM 40 WAS one of the primary after market carbs used on Harleys when the stock carbs were replaced. Now days the MARKETING is for the newer 42, 45 & 48mm versions. Why ? Because they sell for more $$ and because the engines keep getting bigger. The TM 40 can certainly be made to work on the LS650 engine, it has been done before, but the throat size will result in poorer performance vs a 36mm VM or Amal or Keihin or TM because of slower air velocity in the throat. If you swap the stock carb for a performance carb then go with a 36mm, it is the best size for this engine. It just WORKS. In any state of tune from stock to max mod that is still STREETABLE, it is the best size carb for best performance for this engine. I choose the 36mm VM for the Performance Carburetor Kits because it was the best bang for the buck, parts and jets are plentiful/available, and our engine likes it. The Mikuni VM is the most popular performance carb in the world for single cylinder engines, both 2 &4 stroke. |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by kamelryttarn on 07/27/19 at 13:39:11 Maybe a little bit off topic, but what would happen if you put a smaller VM than the 36 on a 650cc Savage? Like a VM34 or even VM32? |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by LANCER on 07/27/19 at 13:52:55 293B2B7978283E2B2A4C0 wrote:
A 34mm VM will work fine on a stock engine and would perform very well in the low-mid range, high range not so much. I would not go smaller than a 34mm though, i think a 32 is just too small. I’ve never tried to run one so cannot say for sure. |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by batman on 07/27/19 at 21:33:34 [/quote] Who said I want to go fast? You said that, not me. Just because one isn't looking for speed doesn't mean they should put a small carb on their bike. Cavi, I got it! Your putting a larger carb on it and talking to Lancer about 97mm pistons because your NOT looking for speed - makes perfect sense to me. ::) |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by hotrod on 07/28/19 at 06:34:18 It seems like if you go too small with a carb you still have a lot to work with, but if you go too big you might end up with a big fat zero. If the carb has a accelerator pump you may be able to hide low end response problems , but that's really not tuning. |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by LANCER on 07/28/19 at 11:08:38 With the type of engine that we have, a slow turning single, it does not respond quickly when the throttle is turned anyway so what’s the point of having an accelerator pump ? At one time I had a 36mm TM on my engine but removed it because it just did not add anything useful in my opinion. There is a very slight pause with the VM if you go WOT instantly, but but as mentioned the engine just does not respond quickly anyway. With a little practice when you install a VM it is easy to get a pretty darn quick response. This is assuming you are talking about going from idle to WOT, but after that there is virtually no difference between a VM & TM on the road. |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by DragBikeMike on 07/28/19 at 15:31:35 I am lovin this post. It's a nugget of gold. The best carb is the carb YOU like best. When I was a young man, I spent hours lusting over the hotrods that the cool guys drove. Back in the day, the coolest cars had certain qualities that were unmistakable. They all idled about 1500. They all made this awesome induction sound when the eight barrels opened up. They were all a handful to drive around town, lurching along, heavy clutches that wore your leg out, flat tappet cams ticking away in a sweet cadence that mesmerized the young wannabes. Some things you just can't shake. I can't shake my affection for a hotrod, warts & all. In addition to my Savage, I have a Burgman. That thing is sweet. It always starts on the first tap of the starter button, immediately settles in to a silky smooth idle, fuels perfectly under ALL conditions, has tons of power, is comfy as a Barcalounger, keeps me dry in the rain, has loads of trunk capacity, stops on a dime, carves corners like its on rails. But, it ain't nearly as much fun as my Savage. Now that I put the 40mm S&S carburetor on, to me the Savage is even more fun. It's my hotrod. Sure its a little choppy here and there, but screw on that throttle and the old engine gets an instant erection. It's like Viagra for that 40 inch mill. I've been testing and tuning for the last 1500 miles or so. Logged countless hours in the saddle sorting out the stock carb on my Stage II ported head. That head doesn't utilize bigger valves so it only flows about It's like hoppin out of a new Camaro with all the performance options and climbing into a 55 Chevy with a hopped up 409 and traction bars. The thing is a handful but oh the smile on my face. Its significantly faster than the stock carb, and also significantly less sophisticated. But I love this thing. It not only makes loads of top end power, but it also has excellent torque. Roll it on, any gear, and it goes. It actually likes WOT way better than cruise. IMO, the stock carb can pretty much handle any flow requirements demanded by the stock cylinder head. It's a typical metric mixer, pretty much flawless once correctly jetted, and flows more than enough air to support stock head flow regardless of exhaust, cam, compression, etc. Bump up your head flow and it's time to invest in a carburetor that can keep up with the head. If you are curious about the flow capabilities of the carbs in question, check out this old post on carb flow tests. http://suzukisavage.com/cgi-bin/YaBB.pl?num=1552860080 I'm not suggesting that everyone go out and round up an S&S Super-E and slap it on your Savage. It's waaaaay to much trouble. But for me, having a thirty year-old piece of nostalgia hangin off my intake port is simply the coolest. Takes me back to my younger days. Yep! The best carb is the carb YOU like best. 8-) |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by hotrod on 07/28/19 at 18:23:51 Carbs are like dogs. They are all different . They just need to be housebroken. ;D |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by ohiomoto on 07/29/19 at 07:04:10 And just like dogs, they will pee on the floor at some point. :) |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by batman on 07/29/19 at 08:45:47 DragBikeMike , Some of us don't have the benefit of a second bike, and must "get it right the first time" not after 1500 miles of tuning. Where Cavi Mike 's logic is a bit shaky , is that he's buying a carb and then building the motor to fit it. I'm thinking that's bass ackwards, the piston and of course the cam will determine the character and needs of the motor ,and the carb should be tuned to match them later. DMB ,you stated that your bike runs better at WOT ,why wouldn't it? the rest of the time the carb is to big. How many main jet sizes did you drop to get the SS carb to work on the savage? I rebuilt the same carb for a friend 's Sportster this spring and had to drop one size , and it's 1000cc bike. Cavi Mike remarks that smaller bikes have larger carbs but doesn't take into consideration that they have redlines that may be twice as high ,a 300 cc Ninja flows more fuel(twice as fast) at 11,000 rpm than a Savage at 5800 rpm ,so needs larger throats (2x 32mm FI 's) Cavi Mike won't spend $100 on a VM 36/38 that he might not like (but could sell to members on this site) but he'll spend $233 on a TM -40 pumper that might be to big ,that no one will want for the same reason , were is the logic? But to each his own . |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by DragBikeMike on 07/29/19 at 13:30:05 Correct, to each his own. The intent of my reply was to show that a souped up head can use a 40mm carb. That 1500 miles of test & tune weren’t spent exclusively on the S&S. Most of that time was spent sorting out the stock carb, then sorting out the exhaust system, then sorting out the stock carb again. After I was satisfied that things were optimized for the Stage II head, I embarked on the S&S. Essentially, I spent a lot of time, and learned a whole bunch. It was fun, and I like the results. Now I have a good foundation for the next phase of the project, the Stage III head with bigger valves. That 40mm mixer will be absolutely necessary for the Stage III. I made it a point to state “I'm not suggesting that everyone go out and round up an S&S Super-E and slap it on your Savage. It's waaaaay to much trouble”. I also made the point “IMO, the stock carb can pretty much handle any flow requirements demanded by the stock cylinder head. It's a typical metric mixer, pretty much flawless once correctly jetted, and flows more than enough air to support stock head flow regardless of exhaust, cam, compression, etc.” If I wanted to get things just right the first time, I’d leave the bike alone. |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by batman on 07/29/19 at 20:33:36 Mike ,you have a lot of talent , just the fact that you improved the head flow by as much as you did is very impressive ,but I'm not sure most of the rest of us could do that, so I would try to steer them and myself to Lancer's advice , to insure a more positive outcome . Even you progressed to changing the carb last which was one of the points I was trying to make. Lancer made the point that the carb might be to large to flow as well as a smaller one , and without your higher head flow , I think that's a valid point as well. I just thought your comment might mislead someone to think that bigger is always better. Cavi Mike seems to be leaning that way. |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by kamelryttarn on 07/29/19 at 23:30:59 The reason I resurrected a ~7 year old thread was that I liked the idea of putting a Mikuni VM on my Savage when I start to convert it to a bobber. It runs GREAT with the stock carburetor so I thought I could put that aside the way it is so that I have something to go back to if I encounter any problems with the VM. I rarely pass 50mph so I thought I might be able to go with a smaller VM than the 36. From what I understand when I read about carburetors for this bike, if I get a too big there wont be enough air flow through it. This will probably be a winter project for this or perhaps next winter and I will use an O2 sensor to help with tuning of the carburetor. |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by DragBikeMike on 07/30/19 at 11:27:08 Kamelryttarn, what is your motivation for switching to the VM? Are you looking to make this torque monster even more torquey? The stock carburetor is a "constant velocity" carburetor (CV). The VM is a "variable venturi" carburetor (VV). The CV carb is designed to keep the velocity of the air flowing through the venturi at a constant velocity (flow rate). The intent is to maintain the highest vacuum signal at the discharge of the emulsion tube. The design accomplishes this by utilizing a vacuum operated slide to adjust the venturi size to match the flow rate through the carb. The vacuum applied to the slide is venturi vacuum, not manifold vacuum. It is a sophisticated design and awfully hard to beat for the kind or riding you do. The VV carb is designed to vary the size of the venturi based on throttle position. Once again, the intent is to maintain higher vacuum at the emulsion tube. The position of the slide is dependent on throttle position so the carburetor does not automatically adjust the venturi size to match flow. While significantly superior (in all aspects, venturi sizes being equal) to a conventional fixed-venturi carb (like my S&S), it is only superior to the CV carburetor when it comes to WOT operation. Set up properly, the CV carburetor will provide the best throttle response, low end power, general drivability, and fuel economy. If you are looking for better acceleration and WOT performance, the VV will outperform the CV (venturi sizes being equal) because there is less junk in the flow path to restrict flow. In general, a 2mm smaller VV carb will have the equivalent WOT flow of a CV (i.e. a 34mm VV should flow about the same as a 36mm CV). If you are looking for better low end pulling power, I doubt that a 34mm or 32mm VM will work better than the stock CV, because the stock CV automatically adjust the venturi size based on what the engine is currently doing. So with the CV, the venturi size will always be as small as reasonably achievable to suit the current operating condition. The stock mixer is an excellent carburetor and awfully hard to beat for general day-to-day fun. BTW, is it possible that you might be leaning toward the VM for aesthetics? The exterior dimensions are a bit smaller than the stocker so it has a cleaner look. |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by kamelryttarn on 07/30/19 at 12:16:43 Aesthetics is definitely a big part of it. Also the Mikunis has been around for ages and are used for so many different engines, you can find information and spare parts everywhere. One of my goals is to tune the AF ratio to almost perfection and without any proof of it I suspect it's easier to find jets for the Mikuni than the stock carburetor. The difference between CV and VV was new to me and probably something I have to consider. The stock CV carb feels a bit more "Japanese/over engineered" and maybe not as robust as the Mikuni. |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by DragBikeMike on 07/31/19 at 13:12:27 Kamelryttarn, actually, the stock carburetor is a Mikuni too. Main jets and pilot jets are plentiful and easily procured. The needle and needle jet are special and are not readily available in different sizes. The stocker is easy to dial in just right on a stock or mildly modified engine. You shouldn't need to alter any jets other than the Main Jet and Pilot Jet. But if its the look you are after, the only solution is to switch to a different carburetor. I apologize to all members about the screwy Google adds that keep showing up in my last reply. I have no clue why they are there. I've tried to remove them several times but they just keep showing up. If anyone knows how to fix it please LMK. |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by batman on 08/01/19 at 17:47:12 I hate to beat this topic to death ....But I love the stock CV carb ! after 24 seasons It has never been a problem. I have done a few mods to it that have made it much better than it was completely stock- the only purchase being a 150 main jet . my motor from carb to exhaust header is stock ,the only custom piece being an unmolested HD Dyna muffler . I run a tuned intake runner using about 5"of 1 1/2 "PVC pipe inside a gutted stock air box ,with custom Oldfeller filters moved to it's exterior ( they can't be seen , the bike appears stock) . These simple low cost mods have raised hP from 30 to approx. 34 . max rpm from 5800 to 6146 . top speed from 87 to 92mph( a stock bike would reach redline a 97.5mph) , and increased acceleration through the entire speed range , all on E87 pump gas. avg 51.5 mpg at 60-70mph. I couldn't ask for more . It also means if any of running gear brakes down I can visit a Suzuki dealer anywhere in the world by a stock part, and the bike will run as well or nearly so and get me home, making reliability as high as possible. To each his own. |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by kamelryttarn on 01/27/20 at 00:38:26 Let's say for arguments sake that I have put a too small Mikuni VM carb on a Suzuki Savage but the jets are all optimized. What would happen? Will the engine stall at a low ( perhaps ~4000 ) rpm ? I guess that air speed through the venturi will be quite high (a good thing?) but eventually the carb wont be able to supply enough air/fuel mixture to keep up or even raise the rpm? |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by batman on 01/27/20 at 01:51:35 No ,your motor will run normally until you reach very high rpm or WOT. That's where the carb may limit your speed. Too small a carb hurts higher speeds by not being able to supply fuel fast enough ,too large a carb hurts lower speeds , caused by the air velocity being to low. |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by Dennisgb on 01/27/20 at 16:49:52 There is usually an overlap in carb sizes given a controlled air flow. Somewhere there are calculations for this. The difference between a VM34 and a VM36 would be minimal if even measurable. The difference would be in jetting to get the same fuel flow with the slightly higher velocity of the VM34. I’ve experienced better throttle response in some cases with the next smaller carb. The one caveat would be the long stroke and slow response of a thumper and the time between intake strokes. |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by batman on 01/27/20 at 19:37:14 Dennisgb , you maybe half right, a smaller carb may well perform better in some bikes not because of it's size but because of the design of the entire head ,the total intake and exhaust passages. the flow in AND out of the motor needs to be balanced. Most bike's today run a balanced cam with intake and exhaust lobes having the same lifts and duration, even the Savage as equal valve lift, it's .330/.330 stock . the stock lobe lifts are .254/.244 but the rocker ratios are 1.299 In/ 1.352 Ex Web cam standard for the Savage (the mildest performance cam) has lobe lifts of .256/.256 which gives valve lifts of .332(.5) /.346 . The bias is need to offset our rather poor exhaust passage. So unless you want do vast changes to the motor ,putting on a big honking 40mm carb isn't going to allow the bike to run well. If you can't get all the exhaust gases out then there's little room to get a fresh charge in.Cavi is looking to start at the wrong end of the horse. The Savage isn't along stroke motor ,it's a square motor 94mm x 94mm . Piston speed at 60mph is 4006rpm /2=2003 combustion strokes/60 sec =33.38 times/sec , or as long as it takes you to say,0ne-one thousand. So I don't think piston speed is much of a problem ,even at 1000 rpm idle its firing at 8.3 times per sec. |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by kamelryttarn on 01/28/20 at 07:26:48 Today I received a recommendation for flatslide TM38 or even TM40 over any of the round slide VM-carburetors and they also explained to me that a too small carb could actually cause worse fuel economy than a larger carb which I did not know. Has anyone used a Mikuni TM-series carburetor on their Savage? |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by verslagen1 on 01/28/20 at 07:55:18 The stock carb is a 40mm carb with obstruction... the throttle plate down stream of the slide. If you're looking for similar performance to stock, then a TM38 would be appropriate. |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by srinath on 01/28/20 at 09:33:06 If I want to keep the airbox and paper or foam stock like filter, would any of these carbs 36mm round slides or flat slides do much of anything better than the stocker ? Cool. Srinath. |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by verslagen1 on 01/28/20 at 09:45:45 They would go slow real good... if that's what you want to do. |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by srinath on 01/28/20 at 10:05:30 7E6D7A7B64696F6D6639080 wrote:
LOL, I asked cos I got them lying about somewhere - these things that had an acrylic float bowl. I actually have a few of em things here and there, I think one was a virago 2 into 1 intake idea, ofcourse I sold the virago so that took care of that. Cool. Srinath. |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by verslagen1 on 01/28/20 at 11:48:39 6C6D76717E6B771F0 wrote:
LOL, I asked cos I got them lying about somewhere - these things that had an acrylic float bowl. I actually have a few of em things here and there, I think one was a virago 2 into 1 intake idea, ofcourse I sold the virago so that took care of that. Cool. Srinath.[/quote] Not saying they wouldn't work, just where you would be at 1/4 to half throttle on a stock savage you will be full throttle with those. |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by Psydton3 on 05/13/20 at 01:02:32 So here we go again. Please indulge an Aussie ;) I have a 2016 S40 with the stock BS40 and a dyna muffler. I've changed up the main jet and performed the spacer mod and that has improved things as far as WOT and top speed. I've been thinking about fitting a VM36 or a VM38 after reading all about Lancers kit people have been using with great results. I live in Australia and well to be honest I'm kinda better off buying locally. I've made some enquiries to a well known Mikuni dealer and asked him about fitting a VM and what jets/jet kit may be required along with adapters for the existing airbox and manifold to the engine etc including a cabling solution. The guy does know his stuff. However his recommendation is to use a flat slide TM40-6 pumper as he says that if the savage engine is similar to the DR650 (which i understand it aint!) then this would be a better bolt on option. After reading this thread I my doubts on his recommendations. Not to mention the price difference is significant in the kits on offer. I am after the best bang for buck option which i agree seems to be the VM. My confusion lays with what adapters to use for the carb to the engine and to the standard air box along with the cable and throttle to use. I understand needles and tuning are the most interesting part of any carb mod and i am looking forward to that part I just need a few pointers and I'm hoping that there might even be some Aussies that may have done something similar. Thanks for your time and patience in advance ;D |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by kamelryttarn on 05/13/20 at 01:24:13 I find it interesting that a Swedish dealer and an Australian deealer both recommend the TM40 over the VM carbs. I doubt this is a coincidence and they may have good reason for their recommendations. I often like to try unconventional solutions but in this case I think it is worth to listen to those with more experience. Personally I think I will try a TM-carb when/if I choose to replace the original carb but first I need to get my bike together since it is all over the workshop right now. |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by Psydton3 on 05/13/20 at 02:32:55 He's told me that i would need to find out if the DR650 BST40 stocke needles are all the same as the stock LS650 BS40 carbs needles. He advised that if the same then he would have no issues in putting together a needle kit that would allow me to tune the TM40-6 without issues for the S40... I'm hoping for lots of input. |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by LANCER on 05/13/20 at 03:30:44 If using a new 36mm VM you will need to change the pilot and main jets, a new rubber mounting flange and a custom throttle cable to match your throttle assembly attachment and VM carb attachment. Finding a rubber tube to connect a VM to the stock air box is possible (I found one once in a building supply store/plumbing sect.). That was years ago. This is a minimum just to function. If you would like details on parts send me a PM |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by Psydton3 on 05/13/20 at 03:53:10 Thanks Lancer :) I'll send you a PM very soon. I appreciate it! |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by Dennisgb on 05/13/20 at 04:05:41 7D5E54495942431E2D0 wrote:
Comparing DR650 to LS650 is where the problem comes in. The DR650 cam and head is completely different. I would be careful listening to recommendations from someone who doesn’t know the difference. |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by Psydton3 on 05/13/20 at 04:59:05 "Comparing DR650 to LS650 is where the problem comes in. The DR650 cam and head is completely different. I would be careful listening to recommendations from someone who doesn’t know the difference." Thanks for good advice mate. He was more about matching (in his opinion) a more "modern" performance carburetor than a VM. He just wasn't sure what needles were going to be needed for the flat slide in this application, but he said he's done a lot of DR650's and they tend to run leaner. SO if the two carby's and engines were similar then he'd know what to look at supplying. Honeslty though his solution is pretty cost prohibitive, so a VM definitely looks like a better solution...i'll get there |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by Dennisgb on 05/13/20 at 08:59:10 0E2D273A2A31306D5E0 wrote:
But they are similar in displacement only. The DR650 is 48 HP while the SL650 is a mere 30HP. The DR650 gains much of this extra HP because it breathes better. The SL650 is very restricted in breathing particularly due to restrictions in the exhaust port. Other here can give you more info than I can but if your restricted a larger carb will do nothing but cause you problems. That is why many of the forum members try to do everything they can to improve flow because there is a lot of untapped HP but to get to it you need more than a bigger carb. |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by DragBikeMike on 05/13/20 at 16:08:03 Psydton, I think the 40mm carb will work fine and allow potential for more improvements in the future. But if you want a quick and easy route to improved carburetion, you will be hard pressed to beat the Mikuni VM. I personally think the VM38 is ideal. The VM36 might work just a tad better on a stock engine, but the VM38 will work great too and it will also support most any mods you perform in the future. This post will give you a good idea how the VM38 stacks up, and also give you a good idea where your jetting will end up. http://suzukisavage.com/cgi-bin/YaBB.pl?num=1585461605 |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by DragBikeMike on 05/13/20 at 16:10:57 If you choose the VM, the jetting data in that post should be all you need to get it very close. Most likely, you will only need to groom the main jet for your application. The boot to connect the carb to the airbox is simply a 2" rubber coupling. This one is perfect. |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by DragBikeMike on 05/13/20 at 16:12:02 This picture provides additional markings on the rubber coupling. You should be able to find the couplings at any decent hardware store. |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by DragBikeMike on 05/13/20 at 16:15:35 If you want to set up a good air filter to support the additional flow, there is info in this old post that shows how to set up a 3.5" x 5" K&N filter in the stock air box. It allows retention of the stock side covers and igniter mounts. http://suzukisavage.com/cgi-bin/YaBB.pl?num=1583103640/0#12 |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by DragBikeMike on 05/13/20 at 16:18:25 The only additional materials you need to set up that K&N cylindrical filter are the rubber coupling and a 2" ABS street elbow. It should be a "street" elbow (male to female). Of course you have to cut up the airbox a bit. |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by DragBikeMike on 05/13/20 at 16:19:23 This shows the SKU for the elbow. |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by Psydton3 on 05/14/20 at 00:20:31 Thanks for the excellent info DragBikeMike. Those pics ill help a hell of a lot :) I've also sent Lancer a PM also and see what advice he has too! |
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Title: Re: Why get a 36mm carb instead of a 40mm? Post by DragBikeMike on 05/14/20 at 15:19:42 That kit Lancer sells is complete. It definitely has all the stuff you need except the rubber coupling and the street elbow. The UNI-Filter he includes will fit right up to the 2" elbow. The kit really takes all the hassle out of rounding up all the parts. The VM38 isn't going to flow as well as the TM40, but I honestly think you will never be able to take complete advantage of the VM38 flow potential. At least not with the currently available performance parts. Stay tuned to this forum. There's always a new trick or two. Good luck, Mike |
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