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SuzukiSavage.com
/cgi-bin/YaBB.pl General Category >> Rubber Side Down! >> Mikuni Carburetors /cgi-bin/YaBB.pl?num=1320162143 Message started by spacepirates on 11/01/11 at 08:42:23 |
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Title: Mikuni Carburetors Post by spacepirates on 11/01/11 at 08:42:23 Bad news first: i was adjusting the brass idle mixture screw last night when i stripped the head pretty much flat. I was drilling a hole in it for a screw extractor when I snapped the drill bit off in the screw. well, that didn't go so well. But wait! it was a stock carb anyways! perfect opportunity to upgrade! right? so in my anger and desperation, i turned to ebay, mighty king of cheap used parts. I ask-eth and it giveth: http://www.ebay.com/itm/150684423652?item=150684423652&viewitem=&sspagename=ADME:B:EOIBSA:MOTORS:1123&vxp=mtr is this even remotely close to what I need? It looks similar to a mikuni VM 38 (which is used not infrequently as an upgrade carb here on the forums) but i'm not positive that is what it is. Pricing the replacement jets/slides/whatnot as per Lancer's tuning guidelines (found via the tech section) put it at around $110 just for the internal little brass bits :'( but all in all, $130 for a better carb isn't that much. so... was this carb buy a good idea? or did I just buy a worthless piece of aluminum? AND, even if it IS something I could use, what am I getting myself into? also, sidenote: assuming this replacement carb works out, if there is anyone out there that wants a stock carb (and a few extra jets!) and doesn't mind having to clean up my mess, let me know. |
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Title: Re: Mikuni Carburetors Post by Serowbot on 11/01/11 at 09:34:42 Quote:
If you have to ask,... you're in way too deep... Now,.. instead of just jetting,.. you're into fitment, cabling, etc... PS,.. that looks like a mechanical slide... no room for routing that top mount cable... I'd resell it, if you already bought it... and find a used BS40 replacement... PS... if you can identify the carb and what it came off of,.. you'll get more for it... |
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Title: Re: Mikuni Carburetors Post by Grand Strand on 11/01/11 at 18:35:08 PM sent and not sure if it went through. More Error messages :'( |
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Title: Re: Mikuni Carburetors Post by LANCER on 11/02/11 at 22:23:42 A lot of the used Mikuni round slides on bay are O L D. units left over from dirt racers 20-30 years back and are in pitiful shape. I have bought them in the past and ended up scraping about 8 out of 10 of them because they were not usable. 36 & 38mm new units retail in the $130-150 range. They do require a new rubber mounting flange to bolt up to the head and a custom made throttle cable is needed if you want a trouble free throttle hookup. You will also need an assortment of jets for tuning the new carb to your engine and exhaust setup, and a Mikuni VM carb manual is really freaking handy unless you already know all about the round slides. I've spent a few years doing this and know what is required. |
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Title: Re: Mikuni Carburetors Post by spacepirates on 11/03/11 at 10:16:30 474A45484E59191C2B0 wrote:
Yeah, I'm not deluding myself into thinking this carb is going to be in spectacular shape, but i'm just hoping it'll work given a little time and effort. I've read your carb tuning tips in the tech section (fantastic write up, by the way!) on starting points with vm36 and 38 carbs. I figured that if I'm going to have to buy a new carb anyways, might as well upgrade while I'm "forced" to get a new carb so that i can get some benefit out of the whole predicament. Nichcycle.com is where i've been looking at for carb parts (mounting flange, jets, and all the rest, right there!) . The throttle cable I'm not sure about, but initially i'll be happy for a "just works" kind of set up. over the winter I can tinker and source where to get the finishing touch parts. |
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Title: Re: Mikuni Carburetors Post by LANCER on 11/03/11 at 13:35:21 I've got the parts; flange, jets and custom cables, but won't be back home till mid Dec. Suzuki has used 3 different types of throttle cable hookups on the LS650. One for the 80's models, one for the 95-04 models and one for the 05-present models. I had all 3 worked up under special part numbers with my supplier. I'm traveling and won't be back home till mid Dec though. If you get it worked out before then, great, but if not then catch me then and I will take care of it. |
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Title: Re: Mikuni Carburetors Post by spacepirates on 11/03/11 at 20:47:13 3538373A3C2B6B6E590 wrote:
Ha, till then I've got a 1978 XS750 to tune and get ready for inspection and I just picked up a 1985 Honda Sabre to get road worthy again. I think i'll be able to wait if it means getting good parts. |
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Title: Re: Mikuni Carburetors Post by SuperSavage on 11/03/11 at 23:11:24 Why don't you just let Lancer build one for you and be done with it? |
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Title: Re: Mikuni Carburetors Post by spacepirates on 11/04/11 at 06:41:02 7A5F585E5E4953514402000101300 wrote:
1) money 2) pride :-[ |
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Title: Re: Mikuni Carburetors Post by Grand Strand on 11/04/11 at 16:30:12 6A69787A7C69706B786D7C6A190 wrote:
1) money 2) pride :-[/quote] 1) +1 :) 2) +1 er +2 oh well yeah me too! ;D |
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Title: Re: Mikuni Carburetors Post by LANCER on 11/04/11 at 17:02:30 New rubber flange for a 36/38 VM carb and custom cable +shp is $90 Pilot and main jets are $4 each; 2 pilots and about 4 main jets would be the minimum to cover variations in intake/exhaust/location. |
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Title: Re: Mikuni Carburetors Post by spacepirates on 11/05/11 at 11:26:15 got the carb in the mail today, looks to be in pretty good shape though it is missing the needle (and retaining plate). It also has a different throttle cable "mount" that has got me confused as all get out. going back to that single ebay pic, you can just barely make out a small piece of angled metal tubing out the top of the carb. Now, I don't have a needle or any of the parts that go in the slide/piston valve, but i'm guessing the throttle cable attaches to something inside that slide through that top tube? Most vm38s I've seen have a different top cable mount. Also found this cable on amazon: http://www.amazon.com/Parts-Unlimited-Universal-Throttle-Cable/dp/B0022ZZF60/ref=sr_1_9?ie=UTF8&qid=1320516935&sr=8-9 Might be able to rig it up to work with the savage's controls And this flange (also on amazon, but nichecycles has one too): http://www.amazon.com/Mikuni-Rubber-Flange-Typical-I-VM38-200/dp/B000GZK76Q/ref=sr_1_1?ie=UTF8&qid=1320517189&sr=8-1 I haven't measured the stock flange's distance stud to stud. Hope they are similar... So, yeah. While LANCER could supply everything I need, it looks to be a touch more expensive, assuming these parts work which certainly isn't guaranteed. More research and perhaps some "leap of faith" purchases are in the future.... |
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Title: Re: Mikuni Carburetors Post by spacepirates on 11/05/11 at 11:29:02 787D2A282E2121190 wrote:
Yeah, I know buying guaranteed to fit/work parts is easier and probably the way to go here, but it is a lot more satisfying (and cheaper if you don't screw things up) to do it on my own. I learn a lot more that way too. by the way, found a vm "super tuning manual": http://www.mikuni.com/pdf/vmmanual.pdf |
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Title: Re: Mikuni Carburetors Post by LANCER on 11/06/11 at 19:57:25 That carb manual has good info in it and it's been all over the net for years. It's not extensive as the Mikuni Manual but it's still good to have. I've had a copy for a long time Good luck with the carb work. It's been a while since I had to order a needle but I think they were around $22 (wild guess) |
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Title: Re: Mikuni Carburetors Post by spacepirates on 11/07/11 at 08:21:02 Close, $17 before shipping here: http://www.motorcyclecarbs.com/_C62.cfm (by the way, this site has a nice break down by manufacturer part numbers which makes it super easy to get exactly what you want) but only $6 before shipping here: http://www.nichecycle.com/ProductDesc.aspx?code=6DP01&type=0&eq=&desc=JET-NEEDLE-6DP01&key=it With all the parts and some spare jets the total adds up quickly. I'll put the order in later today and hopefully by early next week I'll have a nice little project to work on. |
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Title: Re: Mikuni Carburetors Post by spacepirates on 11/07/11 at 10:12:30 I don't suppose anyone wants to save me the trouble of waiting till i get home to measure the bolt spacing on the carb flange? After looking I see there are two options: 70 and 75 mm for the VM38 flange. hopefully one of those fits the savage.... |
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Title: Re: Mikuni Carburetors Post by spacepirates on 11/08/11 at 05:46:20 Hm, measuring center to center, the holes are around 72mm apart. weird. Put in an order at amazon for the flange (i just guessed which one) and the throttle cable, as well as an order at nichecycle for the guts of the carb. few more days... |
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Title: Re: Mikuni Carburetors Post by spacepirates on 01/16/12 at 11:02:00 Finally got all the parts together for this. I put in a call to barnett-clutches and they custom-made me a throttle cable to perfectly fit a vm38 to a 2002 savage. cost was around $50 for the cable. I bought a new VM38 off of amazon for around $95, $20 in jets (might go up, haven't thoroughly tuned it yet), $15 or so for the flange, and $50 for the cable. so roughly $180 give or take a bit, if you ignore all the errors I went through. The bike runs well enough for now, but there is a lot of tuning to be done. Weather this morning was 16 and clear, so I took her to work, though the combined cold and new carb made me hesitant to do anything above 1/2 throttle. the important part is that she lives! though i will have to do something about the choke lever. it is hard to get to with gloves on... if i remember, i'll try to update once i get the jetting right (running a cone with a jardine on a stock engine) and after a few tanks of gas for the mileage. of course, now that we're getting into the snowy season rides may be few and far between :'( |
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Title: Re: Mikuni Carburetors Post by LANCER on 01/17/12 at 02:55:07 Which needle jet, jet needle, main jet and pilot jet are you running ? |
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Title: Re: Mikuni Carburetors Post by spacepirates on 01/17/12 at 07:27:47 right now I'm running exactly what you recommended in this thread: http://suzukisavage.com/cgi-bin/YaBB.pl?num=1262724030 needle jet: 166 q-2 jet needle: 6dp1 main: 185 pilot: 20 idle/low end seems good right now. she starts up just fine and idles decently enough, though the air screw is turned all the way in. midrange is ok so far too, maybe just a touch of surging. no chance to test WOT yet. the only "rides" i've been on were a two mile initial assessment right after i got the carb on in 26 degree weather with snow, and to/from work for 6 miles each on busy roads, morning at 16 degrees and dry and evening at 40(ish) and light rain. not the greatest conditions to be testing acceleration in :-/ looks like rain and snow until Sunday, so it might be a while yet before i get to tune her again. i might bump the pilot up (down? i don't know off the top of my head) one size to see if I can avoid having the mixture screw turned in the whole way. |
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Title: Re: Mikuni Carburetors Post by spacepirates on 02/01/12 at 06:59:26 backed the air screw out two and a half turns, seems to idle better now (definitely higher rpm and smoother) but pops on decel and surges a bit at low throttle. beginning to think an overly rich air screw was covering up a lean pilot. choke use on the BS40 usually was a full minute, now it is down to 15 seconds or so after which the bike bogs down. midrange still seems ok, no surging or hesitation. top end/WOT still good. doesn't bog down or hesitate, no real noticeable speed increase when backing off from WOT. Before turning the air screw out i had the bike randomly die on me a few times while sitting idle at a stop light. no warning, no bogging down, just idling away and then out like a light. one time was because i was out of gas. sure wasn't used to it dying so fast, the old BS40 sputtered for a good 10-15 seconds before it finally kicked the bucket. this roundslide just chugs along happy as can be until it up and decides it won't have no more and quits. kind of nerve wracking, but once i go through a few tanks and get the miles-per-tank sorted out it won't be so bad. i'm hoping that upping the pilot jet will help, because I really don't want to adjust the jet needle or needle jet, as that involves taking out the slide, removing the throttle cable and spring, and then putting all those things back together. kind of a pain in the rear. I've only pulled the plug once, after six miles or so of city riding (so sitting idle, then up to 1/2 throttle, then idle again) and it was a light brown, which is encouraging compared to white or solid black. |
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Title: Re: Mikuni Carburetors Post by LANCER on 02/01/12 at 11:34:40 3437262422372E3526332234470 wrote:
When you say low throttle, how much have you turned it ? Keep in mind that when trying to determine what size pilot jet is needed, you are working with idle to 1/4 throttle. With the engine off, mark the idle position with a pencil/marker/whatever on the side of the switch housing and the edge of the throttle grip. Then turn the throttle all the way to full throttle and mark that spot on the grip using the mark on the housing as a reference point. Then mark half way between the two marks for half throttle, and do the same for 1/4 and 3/4 throttle. Now you know with some degree of certainty when you are at or below 1/4 throttle and can use this to see how the pilot system is working. Also keep in mind that on the Mikuni VM carb, turning the pilot screw OUT is "Leaning the mix" & turning it in is "richening the mix". If the low range performance improved when turning out 2.5 turns, then you are almost to the point of going down one size on the pilot jet...not up in size. As always, whether on the VM carb or the stock carb, 3 turns out on the pilot screw is the max safe point. Once at that point it is time to change the pilot jet and start over adjusting the pilot screw. On the VM carb, if the rpm continues to increase as you turn the screw out and you get to or near 3 turns then its time for a smaller pilot jet. You are leaning out the fuel/air mix in the low throttle range and if the engine likes it then give it more of what it wants...less fuel/unit of air. It will run more efficiently; more power; smoother running; better mpg. If it's happy, you will be happy. ;) Review the symptoms for RICH & LEAN conditions in the 3 general throttle ranges and always recheck for exhaust air leaks which can really spoil your efforts to tune the carb...especially where backfiring is concerned. And check the plug after every jet change & and adjustment you make. If checking the low range then never exceed 1/4 throttle when doing a test run. For a midrange check stay within 1/4 & 3/4.....high range, stay above 3/4 but preferably at wide open until you hit redline and then cut it off, stop and when possible pull the plug and check it. It can be a real pain and time consuming but its either that or pay for a dyno that can put it under load for a full range test. Have fun dude ! The info on symptoms, tuning & more should be in the tech section. If you have difficulty finding them you can go to www.mikuni.com and go to the bike section where they have excellent info and "how to". |
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Title: Re: Mikuni Carburetors Post by spacepirates on 02/01/12 at 12:25:30 I haven't marked my throttle, but i'm talking just over light pressure on the throttle is where i get some issues. 1/4 throttle max. right at idle it seems about spot on, and at about half it seems good. I was operating under the impression that while there is some overlap, that the air screw and pilot jet were still separate circuits. the mikuni tuning manual has them as the same though, operating up until 1/4 throttle at which point the throttle valve takes over. Some trial and error will have to happen with the jets to determine what works best. The tuning manual has the air screw and the pilot together when showing what circuits are working based on the throttle opening, but the section on tuning the two makes them seem rather separate. I'll try a bigger/richer pilot first and see what difference that makes. the risks for going rich are much less than going lean. of course, if the air screw and pilot really are very closely related this might be the opposite move i want to make (based on the engine running better with the air screw farther out -- leaner). |
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Title: Re: Mikuni Carburetors Post by LANCER on 02/01/12 at 15:31:55 2A29383A3C29302B382D3C2A590 wrote:
The pilot screw enables you to make some adjustment to the pilot circuit, based upon the pilot jet you have installed. IF you need more than that small adjustment then you go up or down on the jet size. |
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Title: Re: Mikuni Carburetors Post by spacepirates on 02/06/12 at 08:26:46 Went up a size in pilot jet, made the bike next to unrideable. Of course, me being me, I had to take off down the road before the bike warmed up with the starter circuit still on so a few blocks later when I switched it off I was greeted with a lot of surging and an bike that could only idle for a second or two before it died. Got back home, put back in the #20 pilot jet, re-adjusted the idle speed screw and air screw and am fairly happy so far. I've ordered a #17.5 pilot jet so I can try that out whenever it arrives. Jetting is a funny thing; earlier I could have sworn the bike ran like garbage on a #20 and idled like a dream on the #22.5, and yet a short ride later the #20 is almost perfect and the #22.5 was horrible. midrange and WOT still seem good, though now I'm really waiting to judge them until I get low speed and idle finalized (after trying the #17.5 jet in the near future) before I start tweaking there. I plan on jetting the idle/slow based on the feel of the bike and the sound of the idle speed, but for mid and WOT i'll probably pull the plug a bunch of times after riding at mid/WOT for a few minutes to see what is really going on. |
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Title: Re: Mikuni Carburetors Post by spacepirates on 03/22/12 at 08:34:10 Think I've all but settled on the #17.5 pilot. The air screw is turned out about one turn and it seems to be idling well for now. I've also put in a leaner #180 main but I haven't tested it out yet; I've just been going to/from work and the traffic here doesn't really allow for a WOT test just yet. I have to add a comment about the two annoyances this carb is giving me so far: 1) the throttle cable is a PITA to take in and out, so i just leave it in meaning I have to work on the carb on the bike 2) the starter system instead of a choke means that the bike starts up right quick, but gets to the point where it stumbles before the engine is warm enough to be taken off the starter circuit. I have to ride it with the starter system on for a few minutes before it'll idle without the starter circuit and if i let it idle with the circuit engaged, the bike dies anyways! |
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Title: Re: Mikuni Carburetors Post by LANCER on 03/24/12 at 17:16:22 7477666462776E7566736274070 wrote:
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Title: Re: Mikuni Carburetors Post by spacepirates on 04/16/12 at 07:32:41 my continuing adventure with jetting.... pilot jet is #17.5, idle screw maybe half a turn out (don't quote me on that) I dropped the clip on the needle to the middle setting and that made the bike buck like a bull. back up the second clip from the top it goes (the lower the clip, the richer the setting) Main jet is back up to a #185, but I can't really say about how that turned out. I gunned it once or twice to see if I could get past the needle jet range but I didn't have much road to work with, nor did I want to get bucked off my bike at higher speeds. I did these tweaks last night and tried to get to work on the savage. I could ride at just above idle or at WOT, ha ha. Turned around to go back home after a mile and switched bikes. by the way, who the heck designed these needles? annoying as all get out to freaking change, the way you have to compress the spring and pull the throttle cable through the spring which is pushing on the plate that holds down the other end of the cable and the slide. I ended up taking the throttle grip apart to get more slack. once I did that it was easier, but still not something that was pleasant. Also, my VM38 came with a part that attaches to the bottom of the needle jet called a main jet extender. It is what the name implies, it is a larger nut that extends the main jet down further in the bowl by half an inch or so. I broke this part without trying at all. luckily it wasn't hard to get back out, but the part is $8 and now I feel all crappy about it :'( |
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Title: Re: Mikuni Carburetors Post by LANCER on 04/16/12 at 15:28:46 It should run fine without the main jet extender. Just screw the main jet into the needle jet directly |
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Title: Re: Mikuni Carburetors Post by spacepirates on 04/16/12 at 19:49:18 222F202D2B3C7C794E0 wrote:
That's how it is now, I kind of figured I'd be ok with it for a spell but I did order a replacement piece off of nichecycle because sometimes carbs have little bits of black magic that i'd rather not mess with. |
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Title: Re: Mikuni Carburetors Post by spacepirates on 04/17/12 at 05:44:26 I moved the clip back, but I still have the surging problem. Guessing at the exact throttle ranges, I'd say up to 1/8th throttle works just fine, then massive amounts of surging until you get to 3/4 throttle which is again, just fine. I had hoped the issue would subside after the bike got warm (I had just woken up, cut me some slack on that gem of bad logic) but it didn't. kind of hard to drive to work in rush hour traffic using only barely open and WOT, ha ha. Any idea what this could be? Day one, I changed out the main jet (broke the main jet extender) and moved the clip down one position. Day two, I moved the clip back up. Could I have screwed something else up here? could it be just low gas level, I'm just about ready to hit reserve in the next few miles? Unfortunately I've got to go somewhere immediately after work on the bike and then get it home. lovely times will ensue, I'm sure. |
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Title: Re: Mikuni Carburetors Post by spacepirates on 04/17/12 at 10:10:04 http://www.sudco.com/Diagrams123/expvm.gif Might have had a brain fart last night. I put the needle through the metal plate that holds the cable in place instead of under it (so from the bottom up the order of parts is: throttle body, retention plate, needle clip, spring...). that would make the midrange super rich. hopefully a few minutes in the parking lot will help me correct this. Do'h! |
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Title: Re: Mikuni Carburetors Post by Celeste on 05/04/23 at 14:08:09 Is it possible to need a 15 on a stock motor? |
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