Poping engine

[oehlin]

I am in the process of restoring a 1981 XS650 Special to original condition.
The carburetors have been cleaned with ultracleaner and given new set of jets.
New contact breakers and the timing set with strobe according to the service manual.
Starts easily and responds to throttle well but the left side "pops" and is much cooler than the right side.
Any troubleshooting tips please.
/ Göran Sweden

 

[Kevin Werner]

I would think the sync is off. Bench syncing is fine but these carbs a 40 + years old with uneven wear. Try to do a vacuum sync to insure that both cylinders are working evenly.

 

[gggGary]

 

[Bruno_c]

First, check left side ignition : coils, HT lead, cap and plug.
Then the carb.

 

[oehlin]

I would think the sync is off. Bench syncing is fine but these carbs a 40 + years old with uneven wear. Try to do a vacuum sync to insure that both cylinders are working evenly.

Thanks.
Now ordered an set of vacuum sync clocks so I can see the status of the carburators.

 

[Raymond]

Could start with looking at ignition - there are some quick checks and quick fixes. Take the plug out and check spark. Swap the plug leads and see if the right plays up? I agree with @Bruno_c.