Blown valve spring?

[Kenny_McCormic]

This thing has got me stumped, briggs 5hp flatty, for the most part runs like a yugo stuck in second, wont rev past maybe 3k. Sometimes for no apparent reason it comes to life and runs GREAT(revs up and takes off like a shot while holding high RPM) for a few seconds.

Only thing I can think of is a valve spring broke causing early float and revving the motor just right stacks the pieces increasing tension.

 

[jr dragster T]

I'd check it all over. Might be a spring or timing...Could be quite a few thing's.

 

[Kenny_McCormic]

Electronic ignition pack, doubt its timing. Problem with checking the springs is the cover is behind the carb, pulling the carb involves pulling the motor out(TAV jackshaft). I know it isnt the carb, played with setting and just recently rebuilt it.

 

[Kenny_McCormic]

Managed to get cover off without pulling the fuel can out, checked with a mirror, they look fine. I would make a vid but its snowing.

 

[jr dragster T]

You never know...It could be timing 100%. One time on my dragster we sheared a timing key and the car would stumble for about 60 feet then run like a champ.

 

[Kenny_McCormic]

Hmm I wonder if it has any timing marks, I have access to a light. Dont wanna pull the flywheel if not necessary. But it isnt consistent like a shifted flywheel would provide. And if the key semi sheared it would advance it a few and this is a stock motor that would gladly take that.