Bonneville America Forums Forums Technical Forums General Tech carb "backfire"

Yesterday I started getting some backfiring occurring through the carbs. I've up the mains to 145s, pilots to 42s, drilled the slides, airscrews out about 3 turns, pods, and shorty pipes. I haven't yet balanced the carbs and I think I'm still running a little lean. The bike backfires regularly through the pipes on deceleration and occasionally through the carbs when starting out from idle. The majority of my riding is done at 3,500-5,000 ft.

Anyone have any suggestions? Thanks in advance!

I'd check for an exhaust leak. did you use silicone on the muffler to pipe connection?
G

no, I didn't use silicone on the muffler/pipe connection. Never really thought about it but I'll give it a shot. Thanks for the tip Geoff.

I did find out that my head gasket is leaking, so I don't imagine that is helping anything. It's always something but I enjoy working on the bike so I guess it's not all that bad.

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I did find out that my head gasket is leaking,

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Is the head gasket leaking or is the header gasket between the header pipe and head leaking? One is a simple fix and will probably stop your back fire problem and the other is a major repair that needs to be fixed ASAP as well as finding the cause. Make sure the head and top of the cyl. is flat using a special straight edge and feeler gauges. If it is the head it can be made flat again by using a piece of tempered plate glass and very fine emery cloth but this is not for the novice. Same can be done for the top of the jugs but requires removal of the jugs and the flattening again is not for the novice. If they are way out then this method can't be used as everything has to remain square.

The plate glass can also be used to check to see if the edges are flat but not to check the area between cyl.

there is some oil leaking from the back of the cylinder and after riding through some water over the weekend, I noticed some air bubbles coming from the seem between the cylinder and head up front.

I'm hoping that it is something simple, like the head just needs re-torqued or possibly a gasket. I didn't think about anything being out of level or warped. What are the consequences of running it like this, or maybe a better question would be what may I have already damaged?

Chances are you haven't damaged anything. It is possible that it's just a faulty gasket or the head was torqued wrong. Just torquing the head again will probably not solve the problem (although it could be a temporary fix) since the leak you have now probably did some damage to the gasket. I would pull the head and either check for any low spots or take the head and cyl to a machine shop and have them check them for you. If all is flat install the new gasket. You can put the bike in the back of a truck or on a trailer and have the cyl checked without pulling it off the bike. If the shop guy is reasonable the check should cost very little since there isn't much to it. I mean an engine machine shop not sure a regular one would have the straight edge or know how to perform the check properly. Don't use just any straight edge a special one is used that can be purchased just for this job and is machined to very close tolerances and should be kept in a protective tube or case.

Thanks for the heads up dog

I meant you can have the cyl. checked without pulling it off the bike, the head would have to come off.