While the bike is running, cap off the end of the exhaust and hold a lit candle (or something that is smoking) near each joint. You'll be able to see it blown around by the leaking gas as it spews out the crack(s).

HOWEVER, gas leaking INTO the pipe on decel is the problem...so, you CAN find gas leaking OUT of the pipe when the cap is covered, and this gas leaking OUT may not be part of the problem at all. Make sense?

 

If the popping was the ONLY symptom, then I'd say it's worth checking the leaking exhaust... but it's not the only symptom, so this is really not worth pursueing. The fact that the engine is not running, or struggling to run, at idle is the key symptom IMO.

The suggestion to check the idle is set properly could compensate for the wrong pilot jet. But what you'll find if the pilot is too small is that the idle setting when the bike is hot will cause the idle to be way too high when the engine is cold. Been there, done that.

 

Good to know...you're obviously more familiar with the finer nuances of this than I am!

 

LOL. Sadly I learned a lot of this the hard way when trying to get my FCR35 carb jetted right on my bike. I guess everyones experiences will vary when it comes to jetting, and there are some very knowledgeable people in this forum that helped me in my learning journey too.

If you haven't had to learn these things the hard way, I would say that makes you smarter than me I'm just a stbborn and slow learner

 

If you cover the exhaust and the bike does not stall, you have a leak.

David

 

I ordered the #38 pilot jet. Should come in Friday or Monday.

Went online to Carl's and ordered the Kouba Air/Fuel Screw since I do not want to have to keep takinf off the carb or twisting it all around to adjust it to do fine tuning.

I figure with the #38 and 2-1.2 turns out on the Kouba I should be better.

Fingers crossed this solves the issue...


I agree that I may have leak somewhere since bike runs and revs (very quietly like stock exhaust back on) with t-shirt stuffed in the FMF Power Core. If it still pops and shoots flames after that carb work (can't see going any larger than #38 pilot with my #128 main and 2.5 turns on the Kouba), I will work diligently to figure out where this possible vac or exhaust leak is, but I still am clueless on that since I can not find such a leak.

Might just remove the head pipe and figure out a better way to seal where the head joins the cylinder since that's the only place I can even remotely guess such a leak is. The fit seems fine, but maybe there is a better way to seal that part off?

I figure there really must be a leak since I can actually rev the bike with a t-shirt stuffed in the FMF power core like I mentioned. Unless maybe the t-shirt still allows exhaust to pass through it which may be posible since there is a nice exhaust pressure back there.

Any other ideas on how to plug such a large exhaust hole to be sure no exhaust escapes? Or should stuffing the tee shirt in there be enough to make the bike staff? I burned up my t-shirt...lol. Also, any ideas on how to seal off the head pipe if I remove it and re-install the Power Bomb header?

I want to stop working on the bike and start playing now


Thanks, ya'll are great!!!

 

Mate, do yourself a favour and stop chasing this red herring. Change the pilot, get the a/f screw right per the instructions below (i.e. set it when the engine is warm) and see if you still have the problem. If you do still have the problem, then look for the leak. The leak will either be where the header pipe bolts onto the cylinder (fix by replacing gasket) or more likely where the slip-on joins the header pipe (fix by getting some muffler join tape or something similar from your nearest auto store).

My join between slip-on and header has a small leak as evidenced by a bit of soot, but it makes no difference really. Only ever get decel-pop when it is a very heavy decel from wide open throttle to shut when going down a steep hill - hardly worth worrying about.

http://www.dirtbikeworld.net/forum/s...42&postcount=4

 

Tighten the exhaust header screws... takes but a minute!!!

 

The Kouba is 2 turns out. The pilot is now a #38.

I spend more time trying to get the airbox boot back on the carb than anything else! Anyone have a pointer on an easy way to get that back on quickly?

Bottom line, problem solved. She still pops a bit but no more flames and it no longer sounds like a shot gun! Just pops a bit like any single does on decel after long periods of wide open throttle.

The weird part. I can still cover the exhaust up and the bike will run very quiet. Even when I rev it. Have no darn clue where that leak in the system may be. But I am done. Just time to ride and smile now!

PS - I can't get in to tighten the head bolts and really would love to. But those bolts are blocked by the frame and other misc. parts. Seems like a real pain to mess with so I will not mess with it unless someone has a pointer on how to get in there. I can't use open end wrench (not enough room to turn it) or a ratchet (won't work due to angle of bolt and frame)...

 

Glad it's sorted mate