In the morning when I crank up my bike it pops once loud as hell. Like a backfire. Never did it b4 I shimmed needles & exhaust. Im not choking it or giving it gas b4 I go to start it. Just scared It gonna screw something up. Anybody elses do this?
This should only happen if the throttle is opened whilst the bike is not running, or if the bike turns over more than usual before starting. most likely the popping sound is unburnt fuel in the exhaust port being ignited by the hot exhaust gasses. you may have shimmed your needles too much, or maybe the shims didn't seat properly. how does the bike run??
it's the beautiful sounds of a carbed engine! One reason I love my truck so much. Popping madness coming off of WOT.... Can't wait to make my bike sound the same. This is one thing that FI just can't do as easily, which is one reason (of very few) why I prefer carbs over FI...
While I second that opinion of Jester's... Back to the thread at hand.
Bill: My bike does exactly the same thing. It's only done it to me maybe 5 times, but it is a HUGE backfire, much more so than the normal excess fuel pop. I get a 6-8" blue flame out the tail pipe, and it literally sounds like a shotgun.
I'm shimmed and have my exhaust done too... I think it's just because our bikes are a little richer than they need be.
Jet kit or dyno tune should fix it though (I'm going with the latter), but your bike will be fine without it.
I read something about this poping. It only happens on bikes which have had their needles shimmed. The cure for it is to plug up or remove the fat air hose and valve which comes off the top of the airfilterbox. I have not done this and I don't know if it's right. I suppose one could temporarily pinch the hose shut with a little clamp and see what it does. The kleen air system which mixes air into the exaust stream is what is interfering. I hope I got this right.
If you're running a tidbit too rich, and now feeding clean air into the exhaust, you basically have well mixed fuel-air medium, and when it get's lit by the exhaust, the same thing that happens inside your engine with the exhaust valves CLOSED, is now happening in your exhaust system with little to no restriction...
You are running too rich if this is happening and you don't want that. You are wasting gas and making your valves dirty (which can later cause pre-ignition). A properly tuned engine won't backfire. Even if you are running a little rich, you shouldn't have any backfiring and it is better to run a little rich than a little lean, but you still don't want it to backfire.
This happens to me too. I believe what is causing it is after shimming the bike idles richer. When you turn off the engine, you are cutting ignition - and because it is carbed the fuel is still going. Meaning that while the engine turns a few more times with no spark, fuel is still being drawn out of the carbs into the engine, and out the exhaust. So that nice air/fuel mixture sits in the exhaust until next time you fire it up. A hot puff of exhaust comes out and hits that air fuel mixture and BAM!
If you rev the engine a bit before turning it off (letting even more air/fuel into the exhaust) it happens almost everytime you fire it back up...
It's not really hurting anything, so I wouldn't worry about it.