| Author | Message | ||
     S2forever |
What can make 40 slow jet so rich that even kill switch won't stop dieseling? I double checked idle screw, float check valve and choke. Slider diaphragm slightly burnt but probably OK. What else? | ||
| Upthemaiden |
Have you given your idle screw a good inspection? Any chance maybe the tip of that needle broke off and even with it screwed all the way in, it's still letting fuel shoot past it? | ||
| S2forever |
Tip is fine. | ||
| S2forever |
It is most mysterious thing I ever have on my S2. I m running ~205 (not exactly sure but close) main jet. Ideally it is independent circuit but have slight effect on idle circuit. I will try ~190 and see if it makes any difference. | ||
| 651lance |
It sounds to me like the jet needle isn't seating into the main jet at idle. | ||
| S2forever |
I will check needle jet this weekend. | ||
| S2forever |
It is likely as WOT decelerates even with 205 main jet and stock muffler. How can needle jet be stuck? Is it a common mode of failure? I will let you know this weekend. | ||
| Hootowl |
If you shut off the ignition, something is igniting the mix in the absence of spark. Check for carbon deposits on the intake valves? | ||
| Upthemaiden |
Did you ever shim your needle? I have two thin ones under mine and it's been fine, but I have heard someone on here say that if you shim these needles there's a chance it'll lift the needle up high enough that it will fully lift out of the needle jet and can get stuck when you release the throttle if it doesn't go back into he jet properly. Just a thought. Maybe there's a rip in the diaphragm? I'm not sure if this is a problem that would affect or not. | ||
| S2forever |
Fresh new Thunderstorm heads installed last year. Opened front head for fixing leaking valve stem seal (well, seal wasn't properly installed, it was moving with valve), found just normal carbon build-up. | ||
| S2forever |
I did change needle long time ago, but did not shim it. Anyway needle is suspicious. I will check it this weekend. (Message edited by s2forever on May 01, 2018) | ||
| Ratbuell |
You say thunderstorm heads - presumably you did pistons as well? | ||
| S2forever |
Of course, matching Thunderstorm pistons, 497 cams. (Edited for spelling) (Message edited by s2forever on May 01, 2018) | ||
| Ratbuell |
Strange. My S2, with thunderstorm top end and X1 cams, S1W race ignition, runs like a champ with 45/190. Stock exhaust. | ||
| S2forever |
Yes that is why I post here  | ||
| Williamscottrobertson |
My S1 would run in reverse a few revolutions after killing it. Idled it down and that seemed to fix that idk. | ||
| Hootowl |
1. Check plugs. If they look like they're running hot, they could be glowing enough to cause ignition. Make sure you've got the correct plug. 2. Check for bad intake seals. This will cause a lean condition, which in turn causes condition 1. 3. Use a higher octane fuel. Higher octane fuel is less prone to detonation and running on. 4. Check fuel mixture. Since you've done this, I'd look at 1-3. | ||
| Screamer |
Incorrect ignition timing can contribute to dieseling, also an extremely hot engine can diesel after shutoff. Either is more common than excessive fuel. If you truly believe it's over fueling, something that hasn't been mentioned is a problem with the accelerator pump adding fuel at idle. Sometimes a damaged pump diaphragm, binding linkage causing the rod to depress the diaphragm, or (rare) a rod that is slightly too long which is constantly depressing the diaphragm. | ||
| Buelliedan |
Your jetting sounds totally screwed. A 45 pilot and a 185 or 190 main is usually where you should be. A 40 pilot is WAY TOO LEAN and might be the problem as it might be causing the combustion cmabers in the heads to get way too hot which can cause it to diesel after shutting it off. | ||
| Hootowl |
"What can make 40 slow jet so rich that even kill switch won't stop dieseling?" Dieseling isn't the result of a rich condition, it's the result of a lean condition. Dan's right, I think. You need to swap out that 40 for a 45. | ||
| S2forever |
It seems better with smaller slow jet and mixture screw fully seated. That is why I think rich condition is the reason. I did retard ignition timing one degree or two (I will look up exactly how much) when I installed Thunderstorm heads. I will dial it back and see what gives. Spark plug is Harey 10R12. Intake seal is tight. Premium gas is not always available. I never paid attention to accelerator pump. I will check it. | ||
| S2forever |
If 45/190 had worked good I wouldn't have posted here. Nevertheless I will restart with 45/190, to make absolutely sure... (Message edited by s2forever on May 01, 2018) | ||
| Hootowl |
What do your plugs look like? That will be instructive as to whether you've got a lean or rich condition. | ||
| S2forever |
They looked normal to me. No black, no white. | ||
| S2forever |
One (maybe front) was relatively more white than the other but not much difference. I check plugs whenever I pull them out. I did it for last 10 years but I found nothing unusual. | ||
| Buelliedan |
your pilot jet is not why it is dieseling after shutdown. Now you have to find out what is. | ||
| Ratbuell |
45/190/1.5 turns out has worked on every tuber I've had, just fine. Something else is going on with your engine. Are you still running the stock S2 ignition? That could be your issue right there - the S2 ignition has a much more aggressive timing advance curve than a thunderstorm box does, because of the S2's original lower compression ratio and milder cams. When I swapped the top end in my S2, it ran like CRAP on the stock box. I pulled out several degrees of timing - it quit pinging under load, but it didn't have any balls until the advance kicked in. Swapped to the S1W race box, set timing like it was an S1W, and haven't looked back since. But I concur with Dan above - something besides the jetting is causing your issue. | ||
| S2forever |
No its got Buell ignition module (N0306.9). | ||
| Tootal |
It seems better with smaller slow jet and mixture screw fully seated. Check your slow speed air jet. If it gets clogged up it will screw up the bottom end. There's no way it should idle with a 40 jet and a closed needle. You can remove the needle and slow speed jet. Cover the needle hole and blow compressed air up through the slow speed jet hole. Don't point the slow speed air jet at your face! See if anything fly's out. | ||
| Gmaple |
My recommendation is to rebuild your carb. It is easy and plenty of rebuild kits for the kehin carb. Try to buy a sonic cleaner at harbor freight. I use simple green for the fluid and makes the carb look new.clean and blow the compressed air thru all the jets and the air passages.good luck. |
