backfire on hot start up

[soggybottom]

every once in a while i'll hit the button on my 02 xl1200c with v&h straight shots and get a loud backfire. the bike starts as advertised but will on occasion back fire scaring the crap out of my self and every one around me.
could It be building a rich fuel mixture in one of the pipes and just waiting for a spark to set it off?

[andyxlh]

Hello mate
Carb I presume?
what is your starting procedure?
what sort of baffling in the pipes?
Jet sizes?
I'd have thought you are right with your idea...

[soggybottom]

stock jet, v&h straight shots with baffles provided with the exhaust system from v&h. hot start with enrichener pushed in. no twisting the throttle. just hit the button and kaboom.

[andyxlh]

Hello mate
I must admit this isn't really my area, but I'd have to say that the stock jet with the VH might make the bike run lean - the stock jetting is for the choked up stock air cleaner and pipes. I have a converted 883 and run, if i remember correctly, a 180 main and a 45 idle. Your stock idle would be a 40 I think, main a 170ish??? not sure, but almost certainly too small. this is probably the issue. Also changing the pipes and air cleaner without adjusting the carb is a risk of running the engine lean on fuel and wrecking the top end. Changing the jets is easy and cheap, do that first, and whilst you are there replace all the inlet seals and carb to manifold seal too - they go hard and leak. There's loads of info out there on changing jets, if you can't find what you need message me and I will have something somewhere.
cheers
Andy

[soggybottom]

guess i'll be bumpin the jet up a size or two and see what happens, thanx for the come back.

[RayRay12]

Hello mate
Carb I presume?
what is your starting procedure?
what sort of baffling in the pipes?
Jet sizes?
I'd have thought you are right with your idea...

Mine was doing the same thing too! I have a 91 1200 sportster. Before I changed the jets in did the same back firing! i put a screamin eagle air filter and cycle shack slip on pipes without jetting the carb. hence the backfiring! Upped the jets and fixed that problem!

[kik]

I'd be checking the carb for leaks before bumping up the jets. If you're back firing through the pipes it usually means that raw fuel has made it's way through. Pull the plugs and see if they are getting wet, this will tell you if it's getting on the pistons and possibly into your oil. Do you have a manual gas valve or a vacuum gas valve? If it's manual do you leave it open and it back fires on start up? If you do try closing the valve when you get done riding then shut the bike off. Then after sitting awhile try restarting the bike with the valve off. If it's vacuum operated valve you may have a pinhole allowing gas to push into the carb. You could have a bad diaphragm in the carb also. As I stated in an earlier post, the wifes Kaw 1500 runs the same CV carb as my bagger, the accelerator diaphragm had a pinhole in it causing the gas to leak past it and into the exhaust causing shotgun effect backfires at hot startups and sitting at stop lights and taking off when they turned green.

[WhipLash96]

check all major gasket area's with an unlit gas engaged propane torch. If you hear the bike surge at a certain point when the propane is near, there is an indication of a leak. I must say that I have many people suggest that it may be some sort of leak but I have yet to hear that one has actually been found. Every once in a while I get a backfire out of 1996 Sporty but I find that it is usually when I shut the bike down without letting it idle down a bit. Is your float sticking a tad? Run some Seafoam through a tank of gas. Hope you find it....