Backfires, and how to address them?

[Sojourner]

My 80' GS1100E has it's share of issues, but with a little time and money, most of those have been addressed. So now I'm on to the annoyances...

When warming up my bike backfires occasionally.
When decelerating my bike backfires occasionally.
When I temporarily roll off the throttle my bike backfires occasionally.

When I say occasionally I'd say it's somewhere around a 25% chance of it happening.

Carbs dirty? Exhaust leak? Bad mixture adjustment? Need a good sync? Anyway sure-fire signs to point me in the right direction?

Thanks

 

[tkent02]

The warming up one os probably one of your chokes not working, too lean on that cylinder.

The others could be tuning or exhaust leaks.

 

[Guest]

Backfiring as through the carbs? As far as the decelerating and temporarily roll off the throttle could be misidentified as a back fire. It makes a popping noise when you do that right? If so, you have a cold air leak mixing with the hot exhaust cause the popping. My bike does that and I know exactly what is causing. It is the connection between the collectors and megaphone. Once I tightened up that seam it pretty much stopped. Backfiring through a carb can be dangerous. So yeah like tkent said, check your chokes and the other items.

 

[Sojourner]

I'm fairly certain it's exhaust backfire, and there is an audible pop. One of the areas I'm investigating is where one of the header pipes seats within the head. One of them doesn't go in nearly as far as the other three. I replaced the exhaust gaskets early on when I took the header off to wrap it. I have a small oil leak in that general area anyway (possibly the head gasket ), so I'll take them off again and see if I can bend them ever so slightly to get a better fitment.

A lean cylinder would be hotter than the rest correct? I might pick up one of those laser thermometers to check it out.

 

[terrylee]

Do you have stock exhaust? I have a Mac 4 into 2 and always had exhaust backfiring when letting off throttle. Recently bought a pair of slightly used Harley mufflers at a swap meet, put them on, and haven't had any backfiring since. terrylee

 

[Rick Romero]

Backfiring through a carb can be dangerous........i second that! was working on mine and it backfired thru the carb, didnt know but the petcock was leaking...huge flame, melted a bit a harness

 

[loud et]

Backfiring as through the carbs? As far as the decelerating and temporarily roll off the throttle could be misidentified as a back fire. It makes a popping noise when you do that right? If so, you have a cold air leak mixing with the hot exhaust cause the popping. My bike does that and I know exactly what is causing. It is the connection between the collectors and megaphone. Once I tightened up that seam it pretty much stopped. Backfiring through a carb can be dangerous. So yeah like tkent said, check your chokes and the other items.

On my 1100 I have his same backfiring as you Mr Bill. My collector to megaphone connection was so tight I didnt worry about a clamp. I had to "beat" the megaphone on far enough to get the mounting bracket to line up so I thought it was tight. Guess I will get a clamp and see if it stops some of the popping on deceleration.

 

[Homie]

When warming up my bike backfires occasionally.
When decelerating my bike backfires occasionally.
When I temporarily roll off the throttle my bike backfires occasionally.

These symptoms are usually indicative of a lean mixture. Since it does it when riding with the engine up to its normal operating temp I would say its not a choke issue, but an overall lean mixture. It could be a dirty carb issue with some gunk partially clogging something up, or you may need to rejet to a slightly richer setting.

 

[Guest]

On my 1100 I have his same backfiring as you Mr Bill. My collector to megaphone connection was so tight I didnt worry about a clamp. I had to "beat" the megaphone on far enough to get the mounting bracket to line up so I thought it was tight. Guess I will get a clamp and see if it stops some of the popping on deceleration.

I'm trying one of those exhaust pipe expanders, while my bike is down I inserted in to the collector end and would tighten once a week. When I reinstalled my exhaust system, seemed like the mega phone was fitting a bit tighter. I won't know if it worked until I get the bike out. I was thinking about using some exhaust wrap around the connection, see what it would do.