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SuzukiSavage.com
/cgi-bin/YaBB.pl General Category >> Rubber Side Down! >> Transient Enrichment Valve (TEV) /cgi-bin/YaBB.pl?num=1523820886 Message started by DragBikeMike on 04/15/18 at 12:34:45 |
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Title: Transient Enrichment Valve (TEV) Post by DragBikeMike on 04/15/18 at 12:34:45 I did an evaluation and modification of the TEV and I wanted to share the results with the forum. The TEV provides more fuel when manifold vacuum is high, like when you chop the throttle to decelerate. Under a high vacuum condition, our particular motorcycles have a tendency to backfire. I'm sure everyone here is familiar with that little problem. Adding more fuel during the high vacuum condition helps to eliminate or mitigate the backfire condition. The TEV accomplishes this by closing off the #230 pilot airbleed jet located in the dome of the carburetor, just under the diaphragm. During normal idling, cruising and acceleration conditions, the pilot and transition circuits receive air through two jets, the #230 pilot air bleed and the #45 air bleed. Both are located in the dome of the carburetor. Under high vacuum (deceleration) the TEV closes off the #230 pilot air bleed and the only air the low speed circuit receives is through the #45 air bleed. This #45 air bleed is extremely small (only about .016"). I noticed that on older models Here is a picture of the totally sanitary and professional installation of my vacuum gage. BTW, any of you old timers remember Montgomery Ward? |
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Title: Re: Transient Enrichment Valve (TEV) Post by DragBikeMike on 04/15/18 at 12:36:26 Here is a shot of the sophisticated snubber assembly I installed to smooth out gage oscillation. |
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Title: Re: Transient Enrichment Valve (TEV) Post by DragBikeMike on 04/15/18 at 12:49:38 I always try to get some good data before I make any changes, so I wanted to see exactly what sort ov vacuum this big single generated under various conditions. I knew that vacuum would be high at idle, very high under hard deceleration, moderate at cruise, low under acceleration, and very low under WOT. Here are the test numbers: Idle: 6.5"Hg Blipping throttle in neutral: 3" to 8"Hg Moderate acceleration on surface streets: 3"Hg Cruise on surface streets: 5"Hg Moderate acceleration on the freeway: 2"Hg Cruise on freeway: 4"Hg WOT: 0.5 to 1.0"Hg (Petcock opens at 1.25"Hg. Topic for another post) Normal deceleration: 10"Hg Hard deceleration: 15"Hg Now that we know what sort of vacuum numbers we are dealing with, let's take a look at the TEV components and figure out exactly what sort of behavior we can expect based on its dimensions. Here is a picture of the components that make up the valve assembly: |
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Title: Re: Transient Enrichment Valve (TEV) Post by DragBikeMike on 04/15/18 at 13:36:24 To determine expected behavior we need to know diaphragm effective diameter, spring rate, spring force with valve parked (open), spring force with valve shuttled full right (closed). Diaphragm effective diameter: 15/16" Spring rate: 39 oz./inch Spring force valve parked (open): 38.5 oz. (2.41 lbs.) Spring force valve shuttled full right (closed): 43.0 oz (2.69 lbs) Using these numbers I calculated how many inches of mercury vacuum would result in the TEV valve just starting to move and then reaching the closed position. The TEV should start to move at about 7.1"Hg and reach the full closed position about 7.9"Hg. Here is a picture of the spring test. |
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Title: Re: Transient Enrichment Valve (TEV) Post by Tocsik on 04/15/18 at 14:11:46 Very educational reading. And heck yeah I 'member "Monkey Wards"! Anyone remember White Front? Or these, not sure if they were nationwide be we had 'em in San Diego: FedMart Alpha Beta (groceries) Two Guys Walker Scott Pic 'n Save |
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Title: Re: Transient Enrichment Valve (TEV) Post by DragBikeMike on 04/15/18 at 14:20:10 We can close the TEV at a lower vacuum by shortening the spring. Every 1/8" we remove from the spring free length should decrease the amount of vacuum required to close the TEV by about 0.9"Hg. But if we remove too much, the TEV may close during engine operation at idle or even cruise, which would make the mixture overly rich for the condition. I did not choose to shorten the spring, but if you do, I would not shorten by more than 1/16", which would start the valve moving around 6.7"Hg and shuttle the valve fully closed about The other approach is to try and reduce the size of the #45 air bleed, or possibly close it off all together. I found that a main jet from an old Harley DynoJet kit fit perfectly in the #45 air bleed position. I wanted to see how the engine would run with that particular air bleed closed off so I filled the Harley DynoJet with epoxy and installed it. Here is a picture of the blocked off jet. |
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Title: Re: Transient Enrichment Valve (TEV) Post by DragBikeMike on 04/15/18 at 14:49:22 In the picture of the blocked off jet I am using an old needle jet from some other Mikuni carb as a holder for the jet so I can file out the groove for the screw driver. In actuality, the DynoJet looks pretty much exactly like the stock Mikuni #45 air bleed, except the jet hole was very large. It was a perfect replacement. Now, with the jet hole completely blocked off, the pilot and transition circuits will get ZERO bleed air under high vacuum conditions. How did it work? Great! The engine performance remained the same. Easy start up, good idle, great throttle response, good roll on power, good cruising power, no surging, no afterfire or backfiring while riding the bike under any conditions. There was some very mild afterfire when blipping the throttle in neutral. The test data I took with the vacuum gage explains that. I will elaborate. When blipping the throttle in neutral, the vacuum ranged from 3" to 8"Hg. There isn't much force decelerating the engine, not like you would experience say coasting down a steep hill or downshifting to use engine breaking. You have to really blip it hard even to get the 8"Hg. So you don't really achieve a sufficient amount of vacuum to overcome the TEV spring force and shuttle the spool valve closed. It doesn't close fully until you reach about 7.9"Hg. If afterfire drives you nuts when blipping the throttle, you may want to shorten the TEV spring a bit. Be prudent, don't take a lot off. If you do, let everyone know how much you take off and how well it works. In closing, my bike did not have much of an afterfire issue prior to fiddling around with the TEV. The mods that I described in a prior post (see stock carb slide mods) pretty much had all the issues with this carb taken care of. It wasn't a good test bed to determine correction of an afterfire issue because it didn't have that problem. But the blocked jet mod shows that it can be done with no adverse effect on performance, and I'm certain it will mitigate afterfire. I also learned a lot about the vacuum characteristics on this engine and was able to acquire good data to share with everyone. You should be able to dramatically improve afterfire problems by reducing the size of, or completely plugging, the #45 air bleed. If you want to take it a step further, you can shorten the TEV spring a bit. Batman mentioned in a prior post that he shortened his spring in one-third coil increments, and also commented that if you go too far you can get back some spring pressure by filling in with a washer under the spring. Hope this post is useful. If you try it, let us all know how it goes. |
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Title: Re: Transient Enrichment Valve (TEV) Post by DragBikeMike on 04/15/18 at 20:10:59 DragBikeMike wrote: "I would not shorten by more than 1/16", which would start the valve moving around 6.7"Hg and shuttle the valve fully closed about 7.0"Hg." Oooooops! That's a typo. Should read "I would not shorten by more than 1/16", which would start the valve moving around 6.7"Hg and shuttle the valve fully closed about 7.5"Hg. Sorry for the mixup. |
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Title: Re: Transient Enrichment Valve (TEV) Post by Dave on 04/16/18 at 03:51:24 02040B77757276460 wrote:
You can go back and fix that typo, and make the thread read correctly. Once the discussion is over and folks post their results, this thread can be cleaned up and should be posted in the TECH SECTION (I will do that when the time comes). 1D1B14686A6D69590 wrote:
I really don't see much of a reason to "blip" the throttle on a Savage. The engine has big heavy flywheels, a heavy crank, a heavy rotor....there is a lot of momentum in the engine. Blipping the throttle quickly places the engine in a situation where the fuel/air mixture just isn't good as the engine is slowing down - and there is also a slightly lean condition that occurs in the instant you crack the throttle open. The Savage engine would prefer that you "roll" on the throttle a bit slower. Blipping the throttle and making a lot of noise may feel "bad ass", however a good running engine really doesn't need (or like) to be blipped. |
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Title: Re: Transient Enrichment Valve (TEV) Post by DragBikeMike on 04/17/18 at 00:07:19 My post on the TEV was intended to benefit all the members of the forum. While I personally am not a big fan of blipping, I'm pretty sure there are some folks on the forum that actually enjoy blipping the throttle on their Savage. Since I determined that the plugged #45 seemed to completely eliminate afterfire under all conditions with the exception of blipping, I figured I should let the blippers know that they too could take advantage of a mod that possibly would snuff out their blipping afterfire woes. I aim to please, so I shared what I thought was a possible cure to the blip-pop phenomenon. After all, what could be more obnoxious to the average, peace loving citizen than some geek on a savage blipping & popping at the red light. It's gotta be at least 50% better if the pop is gone. |
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Title: Re: Transient Enrichment Valve (TEV) Post by batman on 05/13/19 at 17:06:08 DBM , Wow , some how I missed this post, and as usual you've done a much better job of research . WELL DONE! |
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Title: Re: Transient Enrichment Valve (TEV) Post by Ruttly on 05/15/19 at 13:14:24 Very cool gauge, I have a real old “Sun” Pay attention guys DBM is real smart and a progressive thinker We all should be thankful that he is a member here and shares all his info ! |
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Title: Re: Transient Enrichment Valve (TEV) Post by LiftdT4R on 06/25/19 at 19:17:41 I just did this, I wound up filling my existing 45 jet with solder. I'll post the results but I had very little backfiring to begin with. Only once every so often on upshifts and sometimes a small poof at shutdown. I'm running a 155 main 55 pilot, air screw 1.5 turns out on a RYCA setup. |
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Title: Re: Transient Enrichment Valve (TEV) Post by ThumperPaul on 08/31/22 at 06:00:56 Excellent research, analysis, and write-up! It does raise a few questions though. 1) Any hunch why the engineers went from a single #70 air bleed to a #230 and a #45? If blocking off the #45 only improved things without hindering performance otherwise - why was the carb redesigned? (Trying to lean it out more for EPA, improve fuel economy, reduce emissions??) 2) When you say shorten the TEV spring - does this mean snipping off a tiny bit (1/16”) of the existing spring? The springs are “double wound” at each end. Seems that snipping off one of the double wound ends of the spring would “dramatically” alter the mechanical characteristics of the spring?? (Perhaps this is why DBM opted not to snip the spring??). Thanks in advance. I realize this is an older post and I’m late to the party. |
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Title: Re: Transient Enrichment Valve (TEV) Post by justin_o_guy2 on 08/31/22 at 06:48:33 The drill press and scale spring test setup, obviously also very professional, is seriously clever problem solving. If I still had any, I'd award you a Gold Star. You have an interesting collection of Stuff to fashion necessary solutions to problems. What you're calling a snubbed is that needle valve that you can adjust to very limited flow rates so a prolonged high vacuum will get to the gauge but short spikes will be attenuated? I've been around since 05and seen the various skills of the people here. I'm really surprised at the widely varied experiences and skills I have seen. If a dealership would have a mechanic check this place out they could learn a lot. Right Now we have several relatively new guys who have some real problem solving skills. And then the Old guys who know what to do to get the carb jetted,how to feel for a little drop off on acceleration and how to interpret what it is doing and what to do to fix it. The Tev has been difficult for people. Well, for me. I'm more willing to just accept a bike that has a bit of performance and good manners left on the table. If you're one of today's shining stars and I didn't mention you, mehh, we all know who you are. You guys should have been here when Hutch was pioneering the swap to chain. |
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Title: Re: Transient Enrichment Valve (TEV) Post by DragBikeMike on 09/02/22 at 19:41:23 Paul, I’m glad you brought this up. Forced me to go back and take a look at this old post. I wrote this report in April of 2018. At that time, I did not have the luxury of a factory service manual (FSM). I based my assumption of only one air bleed on the parts fiche. I used Babbitts Suzuki Partshouse online to view their illustrated parts breakdown. The illustrated parts breakdown only shows one #70 pilot jet for model years 1986 through 1995. The factory service manual lists two pilot air jets in the illustration for the early models. It refers to the two jets as: Pilot Air Jet #1: 67.5 Pilot Air Jet #2: 2.0 mm On the early models, 1986 through 1995, Pilot Air Jet #2 is simply a drilled passage. I assume it is a 2 mm drilled hole. So, it’s a fixed jet that can’t be replaced. However, I suspect you could drill it out if you wanted to play around with it (last thing I would do, don’t recommend it, wouldn’t be prudent). On the later models, Pilot Air Jet #2 is removable. It is a standard Mikuni large round jet. The parts fiche identifies it as a #230 jet, which is 2.3 mm. I’m pretty sure the factory made the change to comply with stricter EPA standards. They decreased the size of Pilot Air Jet #1 from #70 to #45, and increased the size of Pilot Air Jet #2 from 2.0 mm to a #230 (2.3 mm). You are absolutely correct; I am not a fan of cutting the spring. It screws up the geometry of the end turn, and the spring no longer sits square with the spring seat. I much prefer fiddling with the jets, which can easily be replaced if things don’t perform as expected. Maybe someday I will fiddle around with the jet combination, try increasing the size of #1 and decreasing the size of #2. Don’t hold your breath for that test, I’m pretty committed to the PWK carb, and the stock carb simply can’t support my engine in its present state of tune. Here is a picture of Furby’s early style carb. Note that the location of Pilot Air Jet #2 is just a drilled passage. There is no provision for a replaceable jet. The hole looks a lot bigger than 2.0 mm, so I suspect that somewhere down that hole there is a smaller drilled passage. |
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Title: Re: Transient Enrichment Valve (TEV) Post by DragBikeMike on 09/02/22 at 19:42:17 Possibly in this location. |
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Title: Re: Transient Enrichment Valve (TEV) Post by DragBikeMike on 09/02/22 at 19:45:28 Justin, I'm glad you were impressed with my gage snubber. As you can see from the photos, I only use the highest quality, most precise, big buck$$$, precision test instruments. I've had that Monkey Wards vacuum gage since I was a teenager. :D |
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Title: Re: Transient Enrichment Valve (TEV) Post by ThumperPaul on 09/03/22 at 06:39:55 Thank you, Mike. I appreciate you responding to me, the newbie. I can tell you have a wealth of knowledge and experience! I need to get a service manual. I’ve been winging it so far and without this forum, I’d be pretty lost and probably dangerous to the bike and myself. I have very little experience with CV carbs. I had one on another bike, but never really fiddled with it. For such a simple bike as the Savage, it seems the Suzuki engineers felt compelled to insert something complex and sophisticated to keep the average Joe grease money entertained and dropping F-bombs. Burying the air/fuel mix screw under a Welch plug as if there is a perfect setting for all environments is just proof they have a warped sense of humor (I digress). But, I’m going to keep dealing with it for now. Having much more experience with round slide carbs, and how I ride, I’m am seriously considering a swap out, but I want to see what I can accomplish with the stock CV carb first. I still don’t have a good overall feel for the performance of this bike - owned it for 5 months now and I’ve mostly been focused overdue maintenance and ‘clean up’. The issue bothering me is afterfire on “harder” deceleration. Bike is stock except for a Jardine Rumbler series exhaust (virtually open pipe with a wrapped core). I’ve rejetted to #150 main and #55 pilot and did a spaced mod to 1/3 thinner spacer (0.11” down to 0.067”). Mid range performance improved and the bike runs very well, but the afterfire is virtually unchanged. I think Versylagen said I’d never get rid of the afterfire with the Jardine pipe, but I’m stubborn and don’t listen sometimes. The TEV is now in focus after reading your article and research. I’m also considering thinning the spacer some more. I’m also wondering if I have a weak diaphragm under the dome on the slide or a crapped out TEV. The way you researched the vacuum tells me that there is very little margin of error for the TEV to do it’s job properly. Very interested to hear your thoughts. Also, what brand/size of round slide carb might you recommend for a bike with my fairly stock set-up? Thinking about easy of installation with minimal mods. The stock 40mm CV carb seems huge, but maybe that had to do with being a cv carb. Makes me wonder about slow air velocity, but it works and I have to respect whatever the Suzuki engineers were thinking. Thanks for your time! |
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Title: Re: Transient Enrichment Valve (TEV) Post by TheSneeze on 09/03/22 at 08:28:58 PWK 40 carb. You can get them for under $50, but sometimes the cheap knock offs show up, so try and get one from a reputable source. |
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Title: Re: Transient Enrichment Valve (TEV) Post by justin_o_guy2 on 09/03/22 at 08:34:33 5E58572B292E2A1A0 wrote:
I do enjoy being the guy who works out the answer. And when I see it done, I get a kick out of it and try to learn, so if I see a problem one day, the cheap, easy answer is InThere somewhere. So, I'm understanding your setup okay? had that Monkey Wards vacuum gage since I was a teenager. It's a treasure. |
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Title: Re: Transient Enrichment Valve (TEV) Post by ThumperPaul on 09/03/22 at 10:54:40 332C090E040D01120B600 wrote:
Thanks. Very familiar with the cheap Chinese knock offs. Messed with plenty of those on 70cc-150cc junk Chinese dirt bikes. I call 'em throw away carbs. Great for getting a bike running again on a low budget. People let 'em gum up in the winter. Bring the bike to me in the spring and I don't even try to clean or rebuild. Just rip the old one off, throw it in the trash, and slap on a new one. ;) |
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Title: Re: Transient Enrichment Valve (TEV) Post by DragBikeMike on 09/05/22 at 15:28:30 Paul, seems to me you have an excellent opportunity to learn and share. You have an exhaust system that is afterfiring with vigor, and an emission compliant carburetor with an afterfire mitigation device that can be tuned and adjusted. I’ll be the first to admit that I didn’t have this TEV thing figured out completely when I wrote this report back in 2018. At that time, I thought there was only one pilot air jet in the early model carbs. Now I know there are two. After more consideration, I also think there is a good chance that under certain conditions, manifold vacuum works on both sides of the TEV diaphragm. I’m thinkin there’s a lot more to this issue than meets the eye. Food for thought: The idle circuit gets bleed air from three different sources when the throttle is closed, pilot air jet (PAJ) #1, PAJ #2, and the transition port just upstream of the throttle plate. When you crack the throttle, the transition port changes from an “air bleed” to a “fuel supply port”. When PAJ #2 gets closed off by the spool valve, vacuum will develop in the chamber on the left side of the TEV diaphragm too. That vacuum will assist the TEV spring and help offset the manifold vacuum applied to the right side of the TEV diaphragm. That makes analysis very complicated. What the heck is it doing as throttle position changes (idle, cruise, coasting, decel, WOT, etc.)? Not as straight forward as I previously thought. The pilot jet does not utilize emulsification ports in the periphery of the jet. It is simply an orifice. The air bleed is introduced downstream of the pilot jet. How the heck does it ever develop enough vacuum to lift fuel out of the float bowl. The idle fuel port and transition port are at the top of the carb bore, so the vacuum has a long way to lift fuel. With three sources of air bleed (PAJ 1, PAJ 2 & transition port) breaking vacuum, how does it lift the fuel that high? I’ve been able to pretty much eliminate the afterfire by simply installing one-size larger pilot jet and raising the slide needle about .05” to .06”. It still afterfires if I don’t raise the slide needle? Why? The slide needle should be offline when the throttle plate is closed. On 9/3/22 you wrote: “The TEV is now in focus after reading your article and research. I’m also considering thinning the spacer some more. I’m also wondering if I have a weak diaphragm under the dome on the slide or a crapped out TEV. The way you researched the vacuum tells me that there is very little margin of error for the TEV to do it’s job properly.” Yes, I would reduce the spacer thickness and try it. Use washers so you can restore things if you don’t like the results. I have had good results and it’s a zero risk modification. “Very interested to hear your thoughts. Also, what brand/size of round slide carb might you recommend for a bike with my fairly stock set-up? Thinking about easy of installation with minimal mods. The stock 40mm CV carb seems huge, but maybe that had to do with being a cv carb. Makes me wonder about slow air velocity, but it works and I have to respect whatever the Suzuki engineers were thinking.” The stock carb is actually only 35mm. It has an oval venturi that is nowhere near a 40mm cross section. Lancer’s 38mm VM is foolproof. If you are adventurous and a tightwad, a knock-off 38mm PWK works real good, but it’s a crap shoot. Never know what you’re gonna get. This should help. http://suzukisavage.com/cgi-bin/YaBB.pl?num=1625732492 |
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Title: Re: Transient Enrichment Valve (TEV) Post by DragBikeMike on 09/05/22 at 15:34:23 It would be cool if you could take this opportunity to do some simple tuning tests and share the results with the rest of us. Am I correct in assuming you have a later model carburetor with two removable pilot air jets? Do you have a #45 PAJ 1, and a #230 PAJ 2? If yes, could you do a few simple tests and share the results? I’m sure many of us would appreciate your help. Test 1 Replace the #230 pilot air jet (PAJ 2) with a #100 jet. I know that’s a gross change, but the intent is to see how the engine operation changes when the air jet is reduced in size. You don’t want subtle results; you want it to be evident. Start it up and get the thing fully warmed up. Then adjust the idle mixture. How was the idle mixture affected? Did the mixture screw end up in the same place or did you have to set it to a new position to achieve best idle. Let us know how many turns you started with and how many turns you ended up with. How does the engine run when you ride the motorcycle? Does it seem to run the same as it did, or does it now run differently? Does it stumble, hesitate, misfire, surge, etc. at part throttle? How does it run at WOT? Did your afterfire get worse, better, or stay the same? Test 2 Plug PAJ 2 with modeling clay or plumbers putty (easy to clean out after the test). Same intent, see how the engine operation changes when the air jet is plugged. Start it up and get the thing fully warmed up. Then adjust the idle mixture. How was the idle mixture affected? Did the mixture screw end up in the same place or did you have to set it to a new position to achieve best idle. Let us know how many turns you started with and how many turns you ended up with. How does the engine run when you ride the motorcycle? Does it seem to run the same as it did, or does it now run differently? Does it stumble, hesitate, misfire, surge, etc. at part throttle? How does it run at WOT? Did your afterfire get worse, better, or stay the same? Test 3 Reinstall PAJ 2 (the #230). Leave it open, don’t plug it. Now plug PAJ 1 (the #45). Use plumbers’ putty or modeling clay so you can clean it out easily. Same idea here, you just want to see how the engine operation changes when the jet is reduced in size. Start it up and get the thing fully warmed up. Then adjust the idle mixture. How was the idle mixture affected? Did the mixture screw end up in the same place or did you have to set it to a new position to achieve best idle. Let us know how many turns you started with and how many turns you ended up with. How does the engine run when you ride the motorcycle? Does it seem to run the same as it did, or does it now run differently? Does it stumble, hesitate, misfire, surge, etc. at part throttle? How does it run at WOT? Did your afterfire get worse, better, or stay the same? |
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Title: Re: Transient Enrichment Valve (TEV) Post by ThumperPaul on 09/06/22 at 06:01:12 Thanks Mike. I really hope I can contribute something of value to the group one day. Right now, I’m just trying to be a good sponge and absorb as much as I can. 1) Thanks for setting me straight on the carb being 35mm! The 40mm seemed huge and I was thinking 32-36mm would be more appropriate. I bought a cheap project bike yesterday to use as a Guinea pig as I learn these bikes. It’s completely missing the carb, so it will be getting a cheap aftermarket carb for starters. I saw Lancer’s kit. Can’t say I want to pay that kind of money. I would like a clue though of how much exposed throttle cable would get me close for set-up. For the carb, not to get into exact knock-off brand names, but what size might afford the easiest set-up that’ll feed the bike (36mm, 38mm, other)? I really want to try this route on the project bike #2. 2) The bike #1 that we’ve been talking about is a 2004 Savage. I think it has the newer carb jetting, but I haven’t been paying enough attention when I’ve gone under the dome. I need to check and I start taking pictures. Assuming it is, I’ll probably move forward with the experiment you outlined. Before I go there though, I’m going to try raising the needle some more. This time I’m going to try a single thin stainless steel washer. Haven’t measured but it’s about 1/3 the thickness of the stock spacer (0.11”). So roughly, the new spacer will be about 0.035”. 3) The TEV makes me think about the human epiglottis. Doesn’t seem like a big deal, but fills a very important role. FYI - I ordered a service manual yesterday. Won’t help me much with the carb, but will spare the group some of my more novice posts. Thanks again! Very appreciative of your time and expertise! |
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Title: Re: Transient Enrichment Valve (TEV) Post by ThumperPaul on 12/28/23 at 07:25:38 Hi Mike. There is so much information (or misinformation) on the internet about these rascals. I'm coming to you as the source of trustworthy and accurate information and knowledge. First, it seems these TEVs (Transient Enrichment Valves) have alias names like Air Cutoff Valve, Accelerator Pump, Accelerator Enrichment Valve, Throttle Pump, Transient Throttle Enrichment. Do I have this correct? I also want to confirm that these rascals do more than just address afterburn on deceleration. This seems to be a common misconception going around on the internet. Note: My question isn't Savage related. I'm going to talk Honda, but I think this cross applies to all CV carbs with a TEV. My Honda Shadow 750 Spirit with a pair of Keihin 34mm CV carbs has this "dead spot" right at the point of cracking open the throttle up to about 1/8th throttle. It's extremely annoying, unnerving, and unsafe particularly coming out of corners at low speed. Past this throttle position and otherwise, the engine revs and runs beautifully. There is only occasional mild afterburn on deceleration (which probably shouldn't be happening on this v-twin). Idles great, runs great on choke... If I was a throttle blipper, I can't be a throttle blipper with the state the carbs are in. I can blip with the choke on and the bike sounds terrific. But you can't run around with your choke on, and I want to get this corrected. I've tried synchronizing the carbs, but my vacuum gauge even with reducers employed wasn't having a great day (or maybe it was me). I think I basically ended up in the same place after my attempted sych adjustment. I've also tinkered with and turned the A/F mix screws about 1/4 turn more to the rich side. This initially helped a little, but the problem is coming back more noticeably. My thought/question - Are the TEV diaphragms becoming progressively more worn out/decayed/damaged? I've ordered a pair of Air Cutoff Valves (Honda language) anticipating they are the culprit. I haven't inspected the current TEVs and just bought new ones anticipating they need replacement. There are a couple discussions on the Honda Shadow forum that the air cutoff valves could be the source of the problem. Speaking with a master technician at the local Honda dealership, he actually mentioned the air cutoff valves as possibly being the problem without me suggesting it. They want $450 plus any extra parts (beyond normal) to clean, synch, and tune the carbs. I'm not ready to spend that kind of money yet and I want to learn and deal with this 'myself' (read - your help). It's like the bike has this super lean dead spot upon initial opening of the throttle - like it's getting a big gulp of air without any accompanying fuel to go with it. The bike is a 2006, only had 2600 miles when I got it in July, and I'm up to about 4200 miles now. There is some evidence the carbs have been removed (probably cleaned) in the past. I addressed a small air leak at one of the carb/manifold boots (front cylinder carb). My hunch is that the carbs were cleaned perhaps without removing the TEVs and carb cleaner ate up the diaphragms. Just my uneducated and uninformed guess. Thanks in advance for reading and your thoughts!! |
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Title: Re: Transient Enrichment Valve (TEV) Post by DragBikeMike on 12/28/23 at 09:47:12 Although your questions pertain to a Honda, they are directly applicable to the CV carb and TEV, which should help all of us Savage fanatics better understand our carburetors. The moderators will decide whether or not this belongs in Rubber Side Down. The approach you take will probably depend on how difficult it is to access the carbs on the Shadow. When faced with a problem like this, I like to make large changes that are easily reversed. You always must start from a point of knowledge, that's why the access is important. Can you remove the TEV diaphragms without taking the carbs off the engine? Can you remove the float bowls without taking the carbs off the engine? Can you remove the slides without taking the carbs off the engine? Is it easy to take the carbs off the engine? You want to know if the TEV diaphragms are brittle cracked, torn, or pin-holed. You want to know if the float bowls are clean and what size main jet & pilot jet are installed. You want to know the air bleed jet configuration and sizes. Those jets should be located underneath the slide diaphragm. You want to know if the slide needle is the same design configuration as our LS. Can it be raised by changing the thickness of a spacer? Once you have the answers to those questions, you can make some fairly big changes to help diagnose your problem. But you want those changes to be easily reversed so you can put the carbs back exactly as you found them, and you want to make only one change at a time. You want the changes to be significant so that the outcome will be evident. You say the hesitation is gone when you run with the enricher on, so you already know you are lean just off idle. So, open your idle mixture screws about one-turn and see if the hesitation goes away or is significantly improved. See what you learn. Don't worry if it idles lousy, just ride it and see if the hesitation goes away. If the hesitation goes away, you might be able to correct the condition by installing larger pilot jets and readjusting the idle speed and mixture screws. If increasing the pilot jet and adjusting the mixture screws doesn't work, put them back where they were. The Honda specialist seemed to zero right in on the TEV diaphragms, so if they are the least bit questionable, change them. Raise your slide needles. Don't be shy, raise them up a good amount (like 1.0 to 1.5 mm). Use washers so that whatever is in there now (plastic spacer, washer, etc.) can be put back in. You want to be able to return it to the original condition if your troubleshooting adjustment doesn't work. See if the hesitation goes away. Don't worry if it runs a little rich, you are just trying to find out if the hesitation can be eliminated by adjusting the slide needle. Install smaller pilot air bleed jets. They are air jets so don't fiddle around with a one-size change. It's controlling air which has almost no viscosity, make big changes. For instance, if the larger jet is a #200, put in a #100 and see what happens. Same guidance for the smaller jet. If the smaller jet is a #100, put in a #50 and see what happens. Only change one jet at a time. See what happens, then put it back the way it was and try the other jet. You are not dialing in the system; you are trying to learn how each jet impacts operation. You can fine tune later. Tell us what you learn. But hey, let's finish Woody first. |
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Title: Re: Transient Enrichment Valve (TEV) Post by ThumperPaul on 12/28/23 at 15:20:26 Thanks Mike. The carbs are difficult to access and remove - they are wedged in the "V". I can access the TEVs as they face the outsides of the bike on the carb body. I am hopeful that changing the TEVs does the trick because getting the carbs out is a pain. I've enriched the A/F and had some limited short term success. So, I'm looking now at the TEVs. Woody is priority, but I want my main ride running right! Woody also gets priority because I'm still waiting for TEVs to arrive. ;D If I end up opening up the carbs, I already know the jet sizes I want to install for a little extra boost. But I can live without the boost if installing new TEVs cures my hesitation/bog. |
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