Backfire out exhaust when let off???

[Tayorsturf]

Have gotten my trike running pretty good only problem left is when I let off the throttle and the engine RPMS drop I got some minor backfire out the exhaust .

What carb adjustment should I make?
Lower the main needle a clip? or what?

Any suggestions would be greatly appreciated, thanks.

[Russell 350X]

My Big Red does that, might be getting to much fuel, its nothing big it dosent make much different, mine does it going down a hill mostley, I think it sounds kinda cool. Sometimes they just do it, but they run fine.

[Erics350x]

thats caused from to much fuel. loading up.

[Tayorsturf]

thats caused from to much fuel. loading up.
I figured it's running rich on the high end, What's the proper carb adjustment to correct the condition?

Main needle down?
Needle jet down?
Back out Piolet Air screw?
Something else?

[Erics350x]

start simple with the adjustments, see if that helps.

[atctim]

Are you running stock exhaust or aftermarket?

[Tayorsturf]

stock exhaust with a uni filter

[Bryan Raffa]

??? seen it happen with aftermarket pipes, cant recall ever hearing it with a stock tho..

[freewheel3]

Could be an ignition timing issue but I think it is just too much fuel. Either an incorrect adjustment, plugged jet, floats too high or a leaky needle/seat. Also check & make sure that the choke cable tension (freeplay) isn't too tight. If it is even just a little bit tight, it will let extra fuel into the carb causing it to run rich. How's the plug look?

[69HemiGTX]

The thoughts about too much fuel are logical, but it could also be something as simple as a leak in the exhasut system. My buddy's YZ426 started popping once while we were riding, and we found a crack in the muffler's stinger. It pulled air into the exhast when he chopped the throttle, and that was enough to ignite the small amount of unburnt fuel.

[Tayorsturf]

hummmm, good Idead, I'll check the exhaust, it's not bad but the header piped is pretty beat might have a crack, have to check it out. Otherwise I'm still leaning towards carb adjustments. Going to figure it out soon.

Today going on vacation, in 2 hours loading up the ytm225 and atc200m and heading up to the Hardy dam in White cloud michigan to hit up my ladys family cabin of
+200 acres of three wheeler goodness.

:beer :TrikesOwn :beer

[jbobon007]

The thoughts about too much fuel are logical, but it could also be something as simple as a leak in the exhasut system. My buddy's YZ426 started popping once while we were riding, and we found a crack in the muffler's stinger. It pulled air into the exhast when he chopped the throttle, and that was enough to ignite the small amount of unburnt fuel.

My 1985 1/2 Yamaha Tri Moto 225DRS did the same thing for a long time. I went to change the stock exhaust pipe to a DG and found that there were 2 small 1/4 inch hole on the bottom of the pipe. Plus the head pipe gasket ring was not there. Now with the new exhaust and gasket it has never backfired or popped since ?

John:beer

[sako]

my 70 does it with aftermarket pipe, hasn't bothered me too much.

looks good at night!

[GPracer2500]

Popping through the exhaust on closed throttle deceleration is most often caused by a too lean pilot circuit (on a four stroke). If it's mild and unobtrusive popping then it's not a major concern--there's a temporary leaning effect that occurs under that particular running condition (it's just a fundamental deficency in the way carburators work). A "perfectly" tuned pilot circuit will sometimes (often?) cause slight/mild popping on decel. If it's a very loud "machine gun" type of sound then it should be addressed. Try turning the fuel screw out a turn or so. If you get to three turns out with no relief then go up on the pilot jet.

Exhaust leaks can also cause closed throttle deceleration pops.

A too rich pilot circuit can also cause decel popping but the nature of the pop is a little different. Rich popping is "wetter" sounding--more of a blap than a pop. And in my experience, you have to be very rich for this to happen.

[Dirtcrasher]

Popping through the exhaust on closed throttle deceleration is most often caused by a too lean pilot circuit (on a four stroke). If it's mild and unobtrusive popping then it's not a major concern--there's a temporary leaning effect that occurs under that particular running condition (it's just a fundamental deficency in the way carburators work). A "perfectly" tuned pilot circuit will sometimes (often?) cause slight/mild popping on decel. If it's a very loud "machine gun" type of sound then it should be addressed. Try turning the fuel screw out a turn or so. If you get to three turns out with no relief then go up on the pilot jet.

Exhaust leaks can also cause closed throttle deceleration pops.

A too rich pilot circuit can also cause decel popping but the nature of the pop is a little different. Rich popping is "wetter" sounding--more of a blap than a pop. And in my experience, you have to be very rich for this to happen.


Nice post, My SX would pop like crazy until I backed that fuel screw out an additional 1/2 turn. No other adjustments were made.

[mad_max]

.....If it's a very loud "machine gun" type of sound then it should be addressed. Try turning the fuel screw out a turn or so. If you get to three turns out with no relief then go up on the pilot jet.

My SX (w/ aftermarket pipe) does the machine gun sound. if I turn the mixture screw out it will lessen (but not totally eliminate) the problem. The down side to this is that with the mixture screw turned out further my SX does not return to idle as quickly as it does on the stock setting.

Steve ('crasher), do you know if pilot jets are replaceable on the SX carb?

Thanks
Mike

[Dirtcrasher]

My SX (w/ aftermarket pipe) does the machine gun sound. if I turn the mixture screw out it will lessen (but not totally eliminate) the problem. The down side to this is that with the mixture screw turned out further my SX does not return to idle as quickly as it does on the stock setting.

Steve ('crasher), do you know if pilot jets are replaceable on the SX carb?

Thanks
Mike

I beileve thats the jet that is pressed in the carb on an 85. You get a larger one in the hard start kit but other than that you'd have to drill it out and risk shavings lodged inside.

Solutions are - buy an 86/87 SX carb which has threaded jets. Or - buy a 350X carb.