Straight Pipe Backfire

[aj_berg]

Hey all,

I am running straight pipes on my '77 GL1000. I got the bike to run great with stock exhaust, and stock intake unit (new filter). Took the mufflers off as I have seen many do. I am wondering if anyone else who has done this has encountered heavy backfire, and popping once letting off the throttle? I am thinking so, due to the loss of all the internals, but I am looking for a good way to combat this and simply ask what others in my position have done, in general? Baffle installation, mufflers, etc.?

Note: the GL still has the post-idle glitch, which is next on my list of to-dos.

Thanks!

[pidjones]

My '78 rescue with Jardine "boom tubes" gets a lot of backfire on decel or slow cruise. Not loud, but disturbing nonetheless. Honda's solution was to enrich the mixture on decel with the Aircut valve. I know of no way to amplify its performance. Cold fresh air is being sucked in and burning unburned exhaust is what I've read. I do know that if the pipes are so short that the cold air gets sucked back to the heads, warped valves is a risk. The old dirt track "claim car" racers often ran without even headers, and they usually lasted one night. Dragsters with short pipes didn't worry because they ran so rich that raw fuel spewed out with the exhaust.

[ericheath]

You can reduce the size of the opening in the air cutoff valve.

Here are two cutoff valves from a 77. The one on the left was filled with JB weld and drilled to a much smaller hole.

B425185C-14FE-42C5-83DE-616331F2B8C5.jpeg

When the air cutoff valve is pulled by high vacuum, the only air to the slow air jets and slow fuel jets goes through this hole, which is considerably smaller thereby allowing a stronger fuel charge.

There’s an inexpensive try for you. If it doesn’t work, drill it out.

If you reduce it more, it is richer still.

[ericheath]

I should have added I did this on the 77 carbs on a 1200. It worked.

[aj_berg]

Thanks for the feedback, gents.

pidjones - I have also heard of the warped heads. I am really just running the stock headers on the bike, with the removed stock exhaust. Have you heard of this damaging heads on a GL?

ericheath - great info. I may have to try this out after fixing the off idle glitch. Makes sense.

[gltriker]

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