Welcome to JUST ANSWER small engines, let me try to help you !!
What is the model number of the engine?
The valves may need adjusting or the carburetor may be dirty. The carburetor is the first thing to check. Remove the float bowl and see if it is full of debris or gummed up from old gas. If it is , best to remove it and disassemble and do a through cleaning.
If carburetor is clean, the figure the valves need to be checked. With OHV engine they can be adjusted by removing valve cover. With flat head, the valves can be checked through the engine vent cover, but to adjust, they have to be removed from the block and the ends ground off to add clearance.
How can I tell whether it's a blown valve or just adjustment? The "popping" is fairly severe Ron
You have to check the adjustment , if you have clearance on both valves, then likely the valve is leaking and will need to be repaired. If no clearance on the valves , adjustment might fix it!
What's the standard clearance? Any trick to replacing valve? Also, are they still available? Thanks Ron
Any answer? Or have I used up my questions? Ron
I asked for model number of the engine. If I had to guess, the valve clearance would need to be about .006 inch.
I was out walking my dogs, ask as many questions as you like, there is no limit. All same 17.00 total.
I've been in garage on another project - Mod 42041 - haven't done anything yet - I'm pretty sure ir's bad valve Thanks I'm going with it Ron
OK, let me know the outcome.