I'm having this backfire on the right hand side and I have no idea what is causing it.
The head on that side was done by someone else and it was running fine when I had longer mufflers and then when I replaced the mufflers with some shorter ones it started to backfire at 4000 rpm. I took the head off and lapped the valves and it was ok for about 2 days on few short runs and then the started again. I noticed that whoever did the valve job replaced some valves and one of them was sort of small for the opening, it fell further into the seat but after lapping it it gave me a decent contact surface.
All this time I was thinking that it had to do something with back pressure since the smaller exhaust was installed so today I replaced the head with a one I had on the shelf that has original valves in it and that I lapped before storing it. Now it's backfiring even more trough the muffler. I did check for air leaks on the carbs on that side with propane and there are none. I did leave the old exhaust gaskets on there and added another set of copper washers that I made and I don't know if that is causing the problem or is it something else. The exhaust gasket setup seem to be working fine on the other side. It's not backfiring on the down side and even when it idles it sounds that the right side is not running smooth, it pops a little but not like backfire.
The head on that side was done by someone else and it was running fine when I had longer mufflers and then when I replaced the mufflers with some shorter ones it started to backfire at 4000 rpm. I took the head off and lapped the valves and it was ok for about 2 days on few short runs and then the started again. I noticed that whoever did the valve job replaced some valves and one of them was sort of small for the opening, it fell further into the seat but after lapping it it gave me a decent contact surface.
All this time I was thinking that it had to do something with back pressure since the smaller exhaust was installed so today I replaced the head with a one I had on the shelf that has original valves in it and that I lapped before storing it. Now it's backfiring even more trough the muffler. I did check for air leaks on the carbs on that side with propane and there are none. I did leave the old exhaust gaskets on there and added another set of copper washers that I made and I don't know if that is causing the problem or is it something else. The exhaust gasket setup seem to be working fine on the other side. It's not backfiring on the down side and even when it idles it sounds that the right side is not running smooth, it pops a little but not like backfire.