Exhaust Backfire, starting problems since new

[tommyboy]

2004 Busa, 12,000 miles, had it since new. Only mods are punching some holes in stock exhaust baffles and a larger rear sprocket. For the last year when slowing down for a stop, I occasionally get a very loud exhaust backfire. Once in a while the bike stalls. I'm wondering what could cause this. Leaking injector?

I have a number of other bikes but the Busa always seems to be the PITA. I have had starting problems with the bike since new. In hot weather, if I stop after a ride and then try to start the bike after a short wait the engine "kicks" back and stalls the starter. I've lost track of the number of new batteries I've put in the bike. I always buy a battery with higher CCA than stock. I think when I perforated the exhaust baflles the starting problems got worse. It can now take multiple cranks to get the engine to light off.

[sixpack577]

Search for Pair valve mod, that will eliminate any popping on deceleration. The pair valve pumps air into the exhaust for emissions. The mod stops that, so the popping goes away.
The popping happens when you change exhaust or modify the stock ones. That will fix part of your problem.

[tommyboy]

I don't want to mask a real issue by doing the pair valve mod. I have not modded the bike for a very long time. The backfiring is a recent issue. I don't get to put many miles on the Busa anymore. About a year ago I did a throttle body sync. I'm wondering what is causing a random backfire when stopping. Could an injector be leaking fuel that is dumping into the exhaust? Is there a chance I did something wrong during the throttle body sync?

[Nicholas]

I don't want to mask a real issue by doing the pair valve mod. I have not modded the bike for a very long time. The backfiring is a recent issue. I don't get to put many miles on the Busa anymore. About a year ago I did a throttle body sync. I'm wondering what is causing a random backfire when stopping. Could an injector be leaking fuel that is dumping into the exhaust? Is there a chance I did something wrong during the throttle body sync?

back fire is just a fuel/air mixture being to rich in the exhaust and it ignites and thats the flame and loud pop

[Mikael H]

so back fire is not bad for the engine?

[tommyboy]

back fire is just a fuel/air mixture being to rich in the exhaust and it ignites and thats the flame and loud pop

I have owned the bike since new, seven years total. It has never had a backfire problem until recently. I am wondering if a leaking injector or some problem due to not being able to ride the bike as much could be causing the problem.

[H2447INTX]

the fact that you punched out the baffles is why its doing it you just changed the flow or back presure on the exhaust,, the pair val mod is nothing to worry about all you have to do is put a marble in the tube that runs from the vent to the air box ,, that will stop the poping

not to be a prick but if you would do things correctly you would have put slip ons or full exhaust and had it tuned ,, you may still get the pop

just block the the hose

[sixpack577]

I have owned the bike since new, seven years total. It has never had a backfire problem until recently. I am wondering if a leaking injector or some problem due to not being able to ride the bike as much could be causing the problem.

If you think so it's very easy to acess the injectors, as well as pull the sparkplugs and see what they look like. The service manual is also a free download from this site.

[tommyboy]

Backfiring is a recent problem. The exhaust has been modded for a very long time too. Plugs were replaced a few thousand miles before the backfiring problem popped up. I don't like the thought that so much fuel is getting into the pipes. It may only be one cylinder doing it.

[delbert]

you say its a recent problem after a throttle body sync , is it possible you may have left a hose off or simular ,i done it myself once

[tommyboy]

you say its a recent problem after a throttle body sync , is it possible you may have left a hose off or simular ,i done it myself once

The exhaust can mods were done a very long time ago. Never had a backfire problem until late last year. I guess it is possible I have some type of vacuum leak from doing the sync. I would have though it would run like crap and not idle if I left a hose off. The bike runs fine 99.99% of the time and idles OK. It just randomly backfires a few times a day when stopping at a light. I don't mean a pop. I mean a gunshot loud bang.


The only reason I synced the TBs was because I was having trouble with engine revs not dropping between shifts until the bike fully warmed up. I figured it was either linkage or sync issue. Borrowed a Carbtune from a Buddy and did my best. It is the type with glass tubes and aluminum rods. Unfortunately it worked like crap so I could not do a good as job as I wanted. I had to keep switching lines since the four gauges did not read identically or have the same response time. The bike linkage is not the easiest to adjust either. Too much slop and lash.

[delbert]

my advice would to be to get some decent gauges and re do the sync , from what you say it sounds like it may have gone pair shape

[rusheriv]

Satellite Beach is a bit of a haul.

I was gonna say you could use my mercury sync tool.
Not something I'd want to ship due to the merc and fear of damage.
When I got it new, the box was busted open by USPS.
Luckily the tool wasn't assembled and the merc was in a bottle.

If you make it to the bash, they usually have the Busa Hospital there and do TB syncing.

[tommyboy]

I was thinking of buying one of the Bourbon tube style gauge sets on ebay. Not sure they are as good as a mercury manometer

Precision Carb Sync Gauges | eBay

[spikyboo]

I get backfire when I put 91 octane or more. Switch to 87 octane, no more backfire on deceleration.

[Supersmoker!!!]

Wtf!!!