I believe that engine has the compression release lobe on the camshaft. It could be stuck on, and not retracting when running. With the valve covers off, when you rotate the flywheel and observe the exhaust valve, you would see it bump at the end of the compression stroke. If you are sure that you have set the exhaust lash correctly considering the bump (ie I set when at mid compression stroke before the bump), then you may need to look in the sump at the camshaft to check the compression release dog..
Thanks for the comment and advice. I was going on vacation and had to mow the lawn. Putting some load on the engine helped or I just couldn't hear it anymore. Near the end of my yard it is bumpy and downhill. That cured the problem. No more backfiring or surging. I'm guessing it was something in carb that got dislodged with the bouncing. I'm guessing
I believe that engine has the compression release lobe on the camshaft. It could be stuck on, and not retracting when running. With the valve covers off, when you rotate the flywheel and observe the exhaust valve, you would see it bump at the end of the compression stroke. If you are sure that you have set the exhaust lash correctly considering the bump (ie I set when at mid compression stroke before the bump), then you may need to look in the sump at the camshaft to check the compression release dog..
Thanks for the comment and advice. I was going on vacation and had to mow the lawn. Putting some load on the engine helped or I just couldn't hear it anymore. Near the end of my yard it is bumpy and downhill. That cured the problem. No more backfiring or surging. I'm guessing it was something in carb that got dislodged with the bouncing. I'm guessing