hey..my trike is backfiring like a ****....i know the needle jet is worn..could this be causing it to do that or timing...any one know??it only backfires after i let off the throttle...any help would be awesome!!!

 

i forgot to mention that the exhuast has a small leak..but it had one before and it never backfired,,,

 

Well I'd have to hear the problem to see how bad it is however timign will make your bike backfire a lot and will be very well annoying when acceleration. If bad enough you might never get over 20km/h. The exhaust leak depending how bad it is will cause backfiring as well. The needle would only cause sputtering as far as I know, hwoever maybe all of these factors added togeather is the reason why your backfiring.

 

Take the carb off and clean it. It could be from a clouged jet or even an air leak, so also check around the intake boot for cracks..... One way or another its because its sucking to much air or as weapon said bad timing.

 

Its most likely your exhaust leak. Id almost bet on it.

 

mine had the same prob. The timing was a little retarded and I had a tight exhaust valve adjustment.

 

yeah im gonna look into the exhuast a little more next week once all the snow melts again.....9 inches of snow in may....whats up with that??[img]i/expressions/face-icon-small-confused.gif[/img]but i have had trouble doing timing before...iv got a timing light, but its impossible to see the "f" mark when its running..so i put soapstone on it to make it apear better and it seemed to work better but i lost it and now i cant see squat...is there something i can do to make this f appear better..no i dont need glasses lol

 

Most the time when you get backfiring when letting of throttle it's an easy fix, usually it is a lean condition between 0-1/4 throttle and will backfire after letting off from fullthrottle(but there could be other things to factor in) the first thing you should try is to adjust the air jet out a 1/4 turn at a time untill backfiring ceases. This may or may not be your problem but sounds like it very well could be. I learned a long time ago to always look at the simple things first and work your way up from there. Hope this helps . P.S. like Thrash stated it could also be the valves are out of adjustment or they are just to tight. Those would be the first 2 things I would check. Air screw first valves sec.

 

yeah im thinknin that your right about the mixture being off..but i dont understand what you said...i learnt backfiring is caused by a too much fuel or rich mixture and unburned fuel in the exhuast creates the backfire.not tryin to oppose you or anything.im just wondering if you meant rich...if not....ill definately try that and about the valves..how do u adjust them? are there any tools i need?

 

This is from the mikuni website
"
4: Backfires in Exhaust

Note:

It is normal for many high performance exhaust systems to moderately backfire or pop when the throttle is closed from mid-to-high rpm. In fact, one should expect a well-tuned high performance engine to "pop" and "crackle" when the throttle is closed at high rpm.

The popping is a result of the air/fuel mixture becoming very lean when the throttle is closed and the engine is rotating well above idle speed. It is also necessary that the exhaust system have rather open mufflers.

Why This (normally) Happens:

1) When the throttle valve is in the idle position, fuel does not flow out of the main system (needle, needle jet, main jet). Fuel is only delivered to the engine by the pilot (idle) system.
2) The combined effect of the closed throttle and elevated engine rpm is to create a fairly strong vacuum in the intake manifold. This vacuum, in turn, causes a high air flow rate through the small gap formed by the throttle valve and carburetor throat.
3) Under these conditions the pilot (idle) system cannot deliver enough fuel to create a normal, combustible air/fuel ratio. The mixture becomes too lean to burn reliably in the combustion chamber. It gets sent into the exhaust system unburned and collects there.
4) When the odd firing of the lean mixture does occur, it is sent, still burning, into the exhaust system where it sometimes ignites the raw mixture that has collected ---- the exhaust then pops or backfires.
"
So, youre on the right track, adjusting the mxture screw. Have you done any modifacations to the intake?Higher flow filter, air box lid off? The exhaust leak will also cause backfiring, so if adjusting the mixture screw doesnt help, plug the leak.
Get some bright finger nail polish, and put that on the timing mark, ive been doing that for years, and it works good.
heres a link to a site on adjusting the valves, it does a better job of explaining it, than i can . It descibes motorcyle motors....but the info works for atvs also.
You may want to get a service manual, alot of the fixes and adjustments are layed out pretty good in there. Try the local library, in the 629 nonfiction area, Id bet they have one for your trike.

valve adjust