Gl1200 deceleration backfire

[docfishr]

I recently purchased a beautiful GL1200 STD. The bike starts instantly and idles smoothly. There is a slight hesitation on acceleration but still pulls strong; and a spitting, popping backfire on downhill deceleration. Previous owner said the carbs were rebuilt by a retired Honda Mech. These are CA carbs but the Canister and whatever has been removed. I synced the carbs and that helped a little. Checked for exhaust leaks, none. So I'm thinking vacuum leak or the anti-afterburn valve? Or could it just be that when the PO took off the CA smog stuff things got FUBAR?
Any specific ideas? Especially things to check before pulling the carbs.

[starfleetengineer]

So I'm thinking vacuum leak or the anti-afterburn valve? Or could it just be that when the PO took off the CA smog stuff things got FUBAR?
Any specific ideas? Especially things to check before pulling the carbs.

It sounds like the Anti- Afterburn valve has gone bad. About the only differance I see in the book for what he would have taken off the carbs is the pcv system. That is just to help with the pollution. Go with the afterburn valve. It sounds like the ticket to me.

[docfishr]

Thanks for the reply. I suspect you are right but this appears to be a quandry. I purchased the Randakk rebuild kit with Howard's repair guide. The kit comes with a new o-ring that fits between the anti-afterburn valve and the plenum. But the repair guide says "Do not try to remove the screws or anti -afterburn valve cover. Do not try to service or repair the anti-afterburn valve."
Also I understand the valves are no longer available. So where does that leave me?
A used set of carbs from ebay may or may not have a working valve. Got to be a solution to this problem.

[starfleetengineer]

The other option is the slow air cut off. It will also cause backfires. 2 screws a spring diafram and your done. I just looked in the book at the anti burn valve. it is 2 screws, take off the top remove and replace valve install the cap and 2 screws and your done.

[docfishr]

Thank you. That sounds very doable if the replacement valve is available.

[starfleetengineer]

You can get the slow air cutoff just about anywhere..

[docfishr]

Yes. One is included in the kit I got from Randakk. It's the Anti-afterburn valve that may not be getable. Any one here ever fixed one? How do you even test it to see if it works?

[Danman132]

I was told by a 75 yo Honda professional mechanic that the anti backfire valve is obsolete now. Randakks doesn’t offer one either. The mechanic said to try disconnecting the vacuum line to the ABV and plug it and hope for the best. There is nothing you can do to repair it. I don’t understand why they still make replacement air cutoff valves but not the ABV valve; why one and not the other? Makes no sense to me. But if the ABV diaphragm is cracked( as mine is, and still backfires after a complete rebuild, plugging off the vac line to the ABV is the only option left. Like you say, mine runs great except for the backfire on decel also. Going to try disconnecting it this weekend and pray I can get to the vac line without having to remove the whole manifold again. I’ll repost the results when I get it done

[docfishr]

Did you manage to get the ABV line disconnected and plugged? What was the result?

[Rambozo]

Plenty of cars had ABV systems, I'm sure something could be adapted.