GL1200A - Mild backfiring during deceleration

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Write2Paul90277

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Hi guys,

Mini backfires! Now that I have the GL1200 I bought last year running, I'm getting a popping sound upon closed throttle deceleration.

Other than that, the engine runs beautifully -- carbs are freshly rebuilt and synchronized, and the compression is about 175-180psi all around.

What might be causing that?

Thanks,

Paul
 

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Hey mcgovern61,

Yep. I put new O rings on the intake manifold -- even used a light coat of silicone seal for good measure.

I did not, however, put new O rings on the secondary air supply tube fittings (the ones that plug into the cylinder heads right next to the intake manifolds). Maybe I'd better check those.

Also, does anyone have experience with the anti-afterburn valve on the underside of the plenum chamber? Is it prone to failure / air leaks?

Any and all suggestions welcome.

Thanks,

Paul
 

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Hi aussiegold and K7TKA,

Wow, I learned a lot from your posts.

I'll try the easiest fix first -- checking for exhaust leaks at the headers (and, while I'm at it, at the header/muffler connections). If there's no problem to be found there, I'll examine the anti-afterburn valve. I anticipate that'll be a pain in the ass, since it's hidden on the underside of the plenum chamber (carb removal time again!).

I'll get back with results by the end of next weekend.

Thanks!

Paul
 
spray some WD40 or other combustible around the intakes, the rubber boots and manifold o'rings then I would move on to the harder stuff. What happens with backfire pops on decel is the butterflies close and the vacuum from the engine pulls harder and will draw air from any leaks, give it a rev them while it is coming down spray and see if you get a rise in idle.
 
Had to replace the air cut off valve on one of my 1200's, not hard at all, but after you replace it if necessary, block off the source of vaccum & richen up the carb.The Motorcycle Project is a good source of info on this & many other subjects.
 
Thanks denver.

So you're saying replace the air cutoff valve AND block off the vacuum source(s)? What do you think of bronko37's idea about making a block off plate for the anti afterburn valve and eliminating it?

Thx

Paul
 
Personally I like the little backfiring on decel. As long as it's out the exhaust I think it causes no harm at all.
 
Read the previous mentioned Mike Nixon motorcycle project write ups about this, & other stuff, :read: DON"T take my guess. :Doh2: He knows HOW WHY, & what will happen, explains, & illustrates so even i can grasp enough to see whats going on. :hihihi:Keihin carb idle circut white paper
 
Good advice, Denver.

I met Mike a few years ago when he was helping me sort out the (very temperamental) carbs on my CBX six. I will dig through his Motorcycle Project site. Maybe the answer's already lurking there. If not, I'm sure a quick call or email will prove enlightening.
 

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