Carb cough or hiccup on idle

[telkinsjr]

Hello all. First, this is my first post. I picked up a 72 T500 Titan to tide me over while I do my dream build on my CB450. The bike runs great on throttle, but I get an odd Cough or hiccup on idle. It starts first kick most times, but I cannot get rid of hiccup. It's like air/fuel rise to go out the boot rather than into engine. I have a video here on Youtube that shows it twice.

For more info the bike is running pod filters and expansion chamber pipes. I do not know if it has been rejected for either.

Thanks for any help.

https://youtu.be/pj0FucyDnP8

[telkinsjr]

Now it's doing it enough to blow the carb boot off where it connect to engine. If I rev the engine it stops, but at idle it comes back.

Could idle air/fuel setting cause it to basically backfire through the carb, or is back pressure from the engine causing this?

At start and idle, the left carb gurgles. It takes a few pulls of the throttle cable to get the air and fuel to actually go into the chamber.

Any ideas?

[Jimroid]

I am going to take a stab at this. Maybe lean either from dirty or too small pilots, or air leak on motor(seals,gaskets,boots). Weak ignition, poor timing. How low is the idle speed?

[Vintageman]

My stab
1) Are the carbs sync evenly at small throttle
2) Week ignition: Coil, Plug cap, pitted points (if you just changed may still be pitted due to bad loose condenser)
3) Too rich Idle (slightly leaky float valve...)
4) Too lean
5) Ignition timing off

[telkinsjr]

First, there was a pretty big tear in the carb boot on the engine side. I don't, know if this is the main cause but it was a factor I am sure.

Second, I can dial the backfire on command by changing the air/fuel mixture and idle adjustment. I need to really try to dial the idle in after I get a new boot.