Backfires when starting

[djwilpers]

I used search; but, didn't find what I was looking for. I'm a "newbee" of course and I'm hoping that somebody has already found the solution to this problem.

When I re-start my 2006 K-9 after riding if for awhile, about 80% of the time, it will backfire through the exhaust like a gun going off! Never does it cold!

Doesn't seem to matter if I turn the fuel off or not.

I have Vance and Hines curved pipes and one of my buddies says that they have so little back pressure and are so short, that they promote this kind of backfiring.

Somehow, I think I'm getting some unburned fuel into the exhaust and fresh air is getting up these short pipes to it and the first firing of the engine is lighting it off! I wonder if the compression release is allowing an exhaust valve to hold open to begin with or something?
dale

 

[MARV]

when warm tighten up the exhaust flanges. your probably suckin air.

 

[Eric]

when you go to start do you give it 2 shot of fuel before starting if so try one, exces fuel entenering hot pipe will fire off causing a loud bang, mine does it too, so on first start up 2 shots of fuel, after hot only 1 shot try this it works for me

 

[djwilpers]

I give it 2 shots when she's cold and she never backfires cold! I give her no shots of fuel when she's hot and she backfires almost 80 percent of the time anyway?
dale

 

[Eric]

is bike running rich?? check plugs

 

[djwilpers]

I've pulled the plugs thinking the same thing; but, they are running clean as a whistle! I should also mention that if I shut it off and restart her right away, she won't backfire. But if I stop for gas and restart after filling, that's about how much time it takes her to work up a good backfire! Cold,,,never a backfire.
dale

 

[Eric]

have you got cut down baffles?? mine does it more since i cut baffles in half, it my be a flange leak, but wouldnt think air getting into pipes would cause a backfire, you got a carb right, not injected

 

[djwilpers]

Carb...
dale

 

[Eric]

when did it start, did you change something, are you sure comp release are working properly

 

[seatmaker]

Mine does the same, E carb to the now G carb. Big radius with baffles to the
Martin bros with no baffles, same bang. No gas after she's warmed up either. I'll be watching this thread for help too.

 

[Vegas]

Mine does it too. My guess is fuel percolation due to heat. I've noticed on my Holley on my car that fuel will dribble out of the squirter after it's heated up and sits to cool. I would imagine the super g does the same thing. A small amount of raw fuel gets into the cylinder and is pushed out into the exhaust pipe upon cranking. First time that cylinder fires and fire shoots out the exhaust port it ignites the fuel in the pipe. I'd just ride it.

 

[Raywood]

As MARV already stated......... Tighten up your exhaust flanges or replace the gaskets. You have an exhasut leak! Some pipes cause the flanges to not tighten down hard enough so I use two flat exhaust gaskets to ensure I get a tight seal. Check them weekly.

And keep your throttle closed while starting.

:flag:

 

[BrianLo]

I have Hooker Troublemakers on mine and I get the same exact thing. I've had the exhaust off once and don't remember seeing any gaskets... I'll check it again next week when I bolt on the fourbiddens I just received... mid 80's and sunny, hope to get in about 800 miles this weekend :2thumbs:

 

[IrishGuy]

Did you change your jets when you put your pipes on? My bike would also backfire on warm startup only when I first put my mean mothers on. It made lots of people run for cover. Once I stepped up my jets problem went away

 

[BrianLo]

Now that I think about it, when I replaced my stock air filter and cover I noticed that there was a lot of gas in the carb throat. It was wet... could be that from a cold start enough time has passed for it to evaporate, something else to look at next week.. float height adjustment? The carb was rejetted by the dealer when they installed pipes before delivery.

 

[scubaman15]

My 07 Chop would do this when new !! and I have changed out the pipes and rejetted the G carb and guess what ,it still does it about 60% of the time ...,I have tripple checked the exhaust pipes ..tight no leaks ,my bike does not have any decell pop and run's great ..but for the clutch I have never been happy with it ..and will be getting a Bandit someday ! That aside the one thing that seems to work is holding the throttle closed "NO GAS at warm start up . Its a hoot at the bar late at night ...kinda fun watchin everyone run for cover . So its been a love hate with me ...:lol: I thought the Compression Releases were to blame at one point also but not sure ? The mystery continues but I do know many BDMs have this quirk

 

[07bigdog]

Ive got mean mother pipes and mine backfires on startup also about 80% of the time when it is hot. For some reason only right after i gas up. I've leanred to live with it. It wakes everybody up at the gas pumps.

 

[RCAdd1ct]

I am not a BD owner, but have messed with bikes for a while.

Check the float level on the carb.

Try closing the fuel petcock before you are pulling into the gas station to drop the fuel level in the bowl a bit. After you restart, turn the fuel back on. If it is a carb heat issue this should help.

Don't be a noob and forget to turn the fuel back on. Been there, done that.

 

[T.Byrd]

Brianlo If this is the second set of pipes you have put on you defently need to change gasgets. Look in your exaust holes on your heads they could be there.

 

[djwilpers]

Ok,,one of the suggestions was to tighten the exhaust manifold nuts. I hadn't checked them yet so I did and was able to pull all four of them up about 1/2 turn. So took a little ride and no backfire so far...may be just luck or it may be working? I'll keep you updated.
dale