What causes engine to backfire?

[Kypper]

I took my 1995 GS500 out after not using it for about a year and a half. I started it up and it ran rough and then I noticed a puddle of gas coming out of the air box. So I took the carbs apart and noticed all of the gaskets were hard and dried out. I then purchased a K&L carburetor rebuild kit and replaced all of the gaskets along with the needle and needle seat. I checked the float height using the tube on the bowl drain and the level is at the gasket or just a hair below. When I try to start the engine with the choke on it now backfires with a small flame out of the exhaust pipe. It doesn't backfire when turning it over without the choke on. The spark plugs are not wet with gas. What causes a backfire. Is it to rich or too lean?

[Nahian]

Usually, it's too lean, but I've never had fire come out lol. After I rejetted and adjusted the air/fuel mixture screw it fixed my back fires. http://classicmotorcycles.about.com/od/serviceandrepair/a/CarburetorProblems.htm

[frylockjim]

if theres fire coming out of the exhaust then that means your exhaust might be producing sparks. Either get a spark arrestor or get a new exhaust. Backfiring is usually a sign of it running lean, but fire shooting out of the tailpipe could be an indicator of it being rich. I dont really know what to say about this one besides holy crap i wish my tailpipe would shoot fire cause that would be cool!!! but its kinda dangerous...and illegal!

[MalcolmA]

Sounds like it might be dropping a cylinder...

[RossLH]

For what it's worth, the K&L rebuild kits have a pretty bad reputation around these parts. Not saying that is necessarily the issue here, but it is something to keep in mind.

[Janx101]

if theres fire coming out of the exhaust then that means your exhaust might be producing sparks. Either get a spark arrestor or get a new exhaust. Backfiring is usually a sign of it running lean, but fire shooting out of the tailpipe could be an indicator of it being rich. I dont really know what to say about this one besides holy crap i wish my tailpipe would shoot fire cause that would be cool!!! but its kinda dangerous...and illegal!

Pffftt! ... Illegal schmelegal! 

This is cool

... And this would be very cool! And quite handy in those peak hour boredom moments! 

[frylockjim]

if theres fire coming out of the exhaust then that means your exhaust might be producing sparks. Either get a spark arrestor or get a new exhaust. Backfiring is usually a sign of it running lean, but fire shooting out of the tailpipe could be an indicator of it being rich. I dont really know what to say about this one besides holy crap i wish my tailpipe would shoot fire cause that would be cool!!! but its kinda dangerous...and illegal!

Pffftt! ... Illegal schmelegal! 

This is cool

Ha kinda makes me wana remove my baffle 

[Kypper]

It ended up being the spark plugs. I put a new set in and it runs perfectly now. I am guessing that when the excess fuel was going to the engine when the gaskets in the carb were not doing their job it fouled the plugs. I had a spark on them just not a strong one.

[fetor56]

If your interested try Iridium....i'v found them to be great.