Bonneville America Forums Forums Technical Forums General Tech Big Backfire on Startup

My '08 America has less than 300 miles. I just installed a set of TORS, and now I get a loud "bang!" nearly every time I start the bike. I've tried starting it with the throttle closed, and also by using the choke, but nothing stops the backfire. It's coming from the exhaust, and I don't hear anything like this at any other time. Deceleration is reasonably peaceful, with mostly light burbling and an occasional low-level pop.

I searched the forums and discovered that this is not an uncommon problem. However, I didn't find a suggested remedy. I did spot several articles regarding idle mixture adjustment, but it's not clear to me whether the screws should be turned in or turned out to make the mixture richer.

I should add that I removed the AI system today, thinking that it might be encouraging a secondary explosion in one of the pipes. It didn't help.

I'm going out to the garage in a few minutes to see if I can locate the mixture screws (it's been a *really* long time since I've worked on CV carbs). Meanwhile, any advice would be very much appreciated.

Jack

you dont touch the throttle when you start it do you? also what are you running for jets

Frank

To be honest I'm not sure what causes the backfire when starting but I still get it myself ocasionally.

As far as your concerned, if you have put the tors on I'd be changing my main jets to 125's or thereabouts and getting the thumb nail screws most of us get so you can simply adjust the air fuel mixture.

Once you've done that, you can look at getting it sorted so the loud bang should disappear.

That's my experience anyway, but hopefully others with your setup may chime in here to add from what I've said cos mine wasn't stock for very long.

are you leaveing the gas on or do you turn it off when it is parked and not running?? i found that for some reason if i dont turn off the fuel supply when parked, i tend to get a gunshot when i start her up(hahahaha people hit the deck)(i wear Scepters) but if i turn fuel off, i dont seem to get that.

when you changed the pipes did you seal them with hi temp silicone or perhaps not push then together enough to cover the slots before you clamped them down. I am guessin you have an a exhaust leak at the joint which is sucking in air.

OK, I think I've got it. I've been paying more attention to my starting technique, and I think I was pulling the throttle back a little just as the motor would catch. I've made sure not to do that now, and I haven't had a backfire in two days. Windrat, thanks for your suggestion. You've reminded me that I need to reseal the pipes. A close examination this evening revealed an audible leak on the left pipe. I don't think it's enought to warp the valves or anything like that, so I'll wait for the weekend to fix it.

Thanks all!

With my setup, I get the backfire if I over richen my mixture screws. I'm running 42 pilots and have my idle screws out 3.25 turns. If I go beyond 3.5, I end up with the backfire on startup.

PS the reason for richening the idle screws beyond what is best is to reduce/eliminate popping on decel.