Backfiring

[Take Warning15]

What could cause backfiring out of one exhaust when I close the throttle? If I close it most of the way but leave it cracked it is quiet. I've rea a lot and checked timing carb sync valves cam chain and mixture. Could it be float height? Carbs are from a 79 and tee bike is a 75 with a pamco and mechanical advance

 

[chopit25]

Could it be an exhaust leak?

 

[Take Warning15]

How can I trouble shoot that?

 

[jd750ace]

I'd highly suspect an exhaust flange leak. Torque check the flange nuts. If they are good, you can pull the head pipe and usually see a clean spot in them if they are sucking air, but not necessarily every time. If the head pipe area that sits against the exhaust gasket is crusty, It's tough to get a good seat, even with a new seal.

 

[TwoJugs]

carb sync and exhaust leaks are the most common cause. beyond that you need to look into anything and everything

 

[Maurice]

Nobody mentioned that, you could be running a tad lean on that side. Is it backfiring or popping? On deceleration as well? In any case check the mix screws/o-rings there? You running straight pipes by any chance?

Good luck

 

[Take Warning15]

I'm running reverse megaphones with baffles. I think it's backfiring but could be wrong. It does not do it so bad if I leave the throttle cracked instead of completely closing it. But yes, it only does it on deceleration. The plugs look a decent tan color. If anything, they are a bit too dark.

 

[5twins]

Could be an air leak in that carb mount.

 

[Take Warning15]

So I tried to synch the carbs better and ended up very close to where they were. I also cleaned up the exhaust port in the head, the header, and the gasket. I reset the mixture screws as well. I think it got a bit better but is still not fixed. I noticed that it doesn't get really bad until the engine is very hot. For example, on my way home it sounded great for several blocks. However, after a five block stretch of hard running it began popping.

 

[Take Warning15]

I'll have to check the intake side for leaks tomorrow... thanks

 

[5twins]

Yes, sometimes your air leak will only show up when things get hot and expand.

 

[Screaming Meemie]

Just had the same problem, right-hand side cylinder only on a stock '79 with BS38's & UNI pods.. popping on deceleration. I dont think it was technically backfiring, just popping very loud & annoyingly. Carb sync & tightening up the manifolds (intake & exhaust) cleared it right up. Mine did the same 'gets-bad-when-hot' routine as well. She's happy as a clam now.

 

[Take Warning15]

Thanks, I've got it to where it does it only intermittently. I'll keep tinkering and hopefully get it all sorted to satisfaction.