| Author | Message | ||
     Blake |
Aaron, Can the leaking accelerator pump problem be fixed on a stock Kehein CV? What causes it, vibration? Is the amount of fuel significant wrt A/F? Wow, this is significant news. It sould explain some of the poor fuel mileage problems I've heard about. I don't want to blow it out of proportion, as you say it is more of a problem on Mikuni flat slides. Still, might be worth investigating next time I have my filter off. | ||
| Edv |
Aaron: Thank you for the reply, I wasn`t aware that this was that common of a problem I guess , I never noticed it before, do you have a clue as to why this occurs? Is there this much vacuum in the venturi or is it a float bowl pressure problem ? Obviously it is a design fault as the pump shouldn`t deliver fuel at steady throttle openings. | ||
| Jeffl |
Alright! I changed the 42 slow jet to a 45. It only took me like 3 hours to do! I don't know how you could do it in 30 minutes. Well, ok, if you've already done all this before, perhaps. (My excuse is I've never torn apart any bike before nor have I ever touched a carburator?!) Anyway, it runs great but I haven't had a chance to ride it yet. I'll let you know...  | ||
| Shotgun |
Good job Jeffl. Wrenching your Buell is a big part of the fun. And if you decide to re-jet, you will see that time drop to say 1 hour the next time, then less and less. I think 15 minutes is achievable after about the 10th try. | ||
| Sparky |
Here's a question for those experienced with the stock CV carb: if I can adjust for a correct idle mixture with a 45 idle jet, would the mixture be otherwise the same through the rev range if I change to a 48 and adjust it for a correct idle too? Sparky 96S1, 98S3 | ||
| Blake |
From the service manual:
A too large slow jet can provide too much fuel, thus causing the engine to run rich. | ||
| Sparky |
"A too large slow jet can provide too much fuel, thus causing the engine to run rich." True, but the idle mixture screw regulates the slow jet and if it can be adjusted for a correct mixture (at idle), then the engine will not be too rich in the range affected by the idle jet, correct? Or are you implying that the fuel through the transfer ports might be too rich even though the idle is correct? Sparky (pondering a change back to 45 on the S3) 96S1, 98S3 | ||
| Blake |
The idle mixture is an air jet with limited adjustment only. If the slow jet is too big/rich there won't be enough adjustment to allow enough air into the mix. I suppose that if the optimum slow jet were (theoretically) a 46.5, then a 45 or a 48 might be made to work equally well. However, also consider that the slow jet stays in play through the low mid range for small throttle openings. A 48 might contriute to an over rich condition. The guidelins I've seen say to find the optimum slow jet so that idle is maximized at no more than 3 turns out on the idle air mixture screw. | ||
| V2win |
Mikuni carb tuning question. Do you start with the main jet selection and then work down to the needle and then idle or start with the idle and work back up to the needle and then main jet? Also, Has anyone here had any experience with tuning the 42 HSR on a BIG (1426) engine. If so where did you end up with your jetting? Yeah, I know they are all different. Just trying to see where the ballpark is before I start playing.  | ||
| V2win |
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| Doncasto |
V2win; This may help you. Mikuni Tuning Manual | ||
| V2win |
Don, Thanks. I have one of those. Came with the carb. It reads like you might start with the idle circuit and then work up from there but its not clear. I would think you should get the main right and work down. Carb came with a 160 main. I am getting detonation in the mid range and upper rpms. I raised the needle one notch amd put a 170 main in. Bike is now pulling good on the top end but the mid feels too fat. Before I go changing needles, I thought I would see if anyone here is running a similar setup and what their jetting is. | ||
| Gcpoland |
Describe your motor, and I will look at my notes and give you a base line. Always start with idle and work your way up, with main being the last. Change only one (1) thing at a time. Gary | ||
| V2win |
Ok, Bore: 3 13/16 Stroke: stock Compression: 10.5 Exhaust: Borla header/muffler Heads: Ported 97 lighting (62cc) Cams: H/D Screaming Eagle II. 536 lift module: Buell race Carb: HSR42 So far I have raised the stock (97) needle 1 notch.(lowered the e-clip 1 notch) The engine still had some detonation at 1/8 to full throttle opening when put under medium to heavy load. I then installed a 165 main. Top end performance was better but it still had slight detonation. I then installed a 170 main. Thats where Im at now. Top end performance is very good with no detonation but my 1/8 to 1/2 opening performance has suffered slightly. If the main has no effect on the 1/8 to 3/4 throttle like Mikuni says, then I was at a lose as to why the 170 main change caused hp lose there. I guess I will need to back up to the 165 jet, get the needle right and then change the main if necessary. If I only had a dyno and sniffer.  Thanks, John | ||
| V2win |
A slight lose meaning that with the 165 main the bike would wheelie in second gear at 3000 rpm with a gentle roll-on of the throtle. With the 170, it does not lift the front until 4000rpm in second. Again, if the main has no effect until 3/4 throttle why would going from a 165 to 170 have this effect since I operating at slightly more than 1/8 throttle opening then. | ||
| Blake |
V2win, Let me get this straight, you are lifting the front wheel with just over 1/8th throttle?! Start with the slow jet, then dial in the needle and main. Follow the directions in the Mikuni tuners guide. | ||
| Sarodude |
I don't mean to muddy the waters, but we always used to tune like this: * Pilot circuit - just so it runs * Main Jet for best top end * Needle for mid range / part throttle (depending on carb type) * Re-vist Pilot circuit and adjust if necessary Just my own experience - mostly with racing machines. -Saro | ||
| Aaron |
I'm with Saro ... the main will affect the mid-range (or part throttle with a flat slide) much more than the needle affects the top-end (or WOT). Therfore you do the main first. | ||
| Gcpoland |
Couldn't disagree more. Dial in your needle jet and jet needle before fooling around with the main jet. If your main jet is having a large effect on 1/2 throttle performance, you have a very rich needle jet. The y-6 needle jet flows a lot of fuel but shouldn't be influenced that severly. I would put in the next size leaner needle jet and go from there. Don't bother moving the clip on the jet needle right now, as that is an extreme fine tune. If you go here Head Quarters They have the needle jet and leaner accel nozzle I like to use. The more people you ask, the more opinions you will get. Gary | ||
| Jima4media |
Techlusion ECM - Anybody ever heard of this little item or maybe purchased one for your Firebolt? http://www.techlusion.com Mark Dobeck was the founder of Dynojet Techlusion Performance Group, Inc. 668 Middlegate Road Henderson, NV 89015 Phone: 702-558-5142 or 877-764-3337 Sounds interesting. I saw it referenced in the Canadian Thunder reference listed on the GDB. Jim X-2.5 | ||
| V2win |
Blake, 3000 rpm is a bit more than 1/8 throttle. 4000 is 1/4 throttle in 2nd gear. And yes, I am. Either wheelie or wheel spin, depending on road conditions. I put about 300 miles on the engine yesterday. I should be able to put another 400 or so on it in the next couple of days. I would like to get it on a dyno asap to sort out the jetting/ingition situation. Kevin at Widmans wanted my to get some time on the engine before doing so. I will play with the carb adjustments some more until we can do a dyno tune. Thanks guys for the advice. I will ponder your suggestions today. ps I have found the following statment from MIKUNI to be very misleading: The main jet does not control fuel flow until the orifice formed by the needle & needle jet become larger in area than the main jet. You could remove the main jet and never miss it as long as you stay below ¾ throttle or so. It's the "until" part that you have to watch out for. | ||
| Coop |
I've been having a little problem lately with my bike, every once in a while when I crack the throttle from about 3000 rpm's the bike breaks up, most of the time it dont do this, the exhaust smells rich at traffic lights, I pulled the plugs thinking they might be wet, but they were dry and black with a sooty coating on them, any suggestions, I have ddfi with race ecm, k&n and d&d slip on. | ||
| Coop |
I also forgot to mention about a week ago I rerouted my breather lines out of the airbox, but before I did this the dealer overfilled the oil and a lot came out the breather lines into the airbox, could this be the reason the plugs are black and sooty, would this cause the break up, monday I will get new plugs, should I stay with the 10r12's. | ||
| Rick_A |
I have a slight issue at hand. My enrichener on my CV refuses to stay in the full out position. It has been getting progressively worse. I don't like sitting there and holding it while the bike warms up. | ||
| Doncasto |
Rick: The enrichner knob should have a nut on the inboard side of the bracket and a plastic knurled knob on the outside. If you tighten the knurled knob it should allow you to do something else with your hands during warmup. Hope this helps, Don | ||
| Rick_A |
Yeah Don...thanks. I got it | ||
| Blake |
Coop, Yes, oil gunked plugs will turn sooty looking and can cause problems. Let us know if new plugs do or don't cure the problem. If they don't, I'd suggest a DDFI diagnostic and TPS calibration verification. | ||
| Coop |
blake, I changed the plugs today and went for a ride, there is no difference, still breaking up when cracking the throttle, not all the time but more than I would like, I also forgot to mention that I have a low rpm stutter and light popping when engine breaking, here is what I checked, when engine was cold I checked for exhaust leaks, with a spray bottle and soapy water, no exhaust leaks anywhere, when engine was warm I sprayed wd40 at the 3 intake seals and the fuel injectors while at about 2000 rpm, there was no drop in rpm's, I did this test twice just to make sure, I just took the bike back to the dealer about 3 weeks ago and he set the tps and checked timing and said everything was where it was supposed to be, even before I did the mods and the bike was stock it did the break up thing every once in a while when cracking the throttle at about 3000 rpm's, I dont know what to do, I was thinking try another dealer to check tps and timing. | ||
| Sarodude |
Coop- Just an idea, but if your plugs looked that bad, think about how bad your O2 sensor could look... -Saro | ||
| Blake |
Yes, I agree with Saro. Next thing to check would be the oxygen sensor. A good dealer's service department should be able to easily/quickly diagnose the DDFI. Popping on decceleration would indicate an exhaust header leak. Not sure it would be detectable with soapy water. |
