B&S Keeps Stalling Out

Hi guys.

I've got a late 80's Briggs&Stratton 12hp that keeps stalling at regular intervals. What I do is crank it, it starts to catch, so I stop cranking and itslowly speeds up and sputters, but eventually starts. So after I get it started, it runs really good, then sputters a minute, then runs well, then sputters again. (but not quite a typical surgeing scenario) So I can run it like this for maybe 15 minutes, then It sputters and stalls out. I can run it for another 20 seconds on full choke, but after that it will absoluteley won't restart. So I can let it sit, or empty the carb bowl, the start it and run it again for a short while.

I have checked the sompression hot and cold,(is it supposed to be 85?) checked spark hot and cold, rebuild the carburator and cleaned fuel system. This problem started once I used a little carb cleaner.

Any ideas?

Thanks all!

For compression a minimum of 60 for an engine to function, it's good to see at least 120. Less than 90, time for a rebuild. Less than 90 will mean that after you get it started, it will have a hard time coming off idle because of low vacuum. Whatever is causing low compression, may also cause low vacuum (bad exhaust valve, scored cylinder wall, worn or broken piston rings, etc.) Right off of idle is when an engine needs and builds the most vacuum. Off idle is when the carburetor's is making the transition from the Idle Circuit to the Run Circuit. The carb needs the vacuum to start drawing the fuel from the main jet. After RPM's increase, the increased airflow takes over and not only draws the fuel through the jet, but forces air into the carburetor fuel bowl, slightly pressurizing it to force fuel through the main jet.

Also, try your compression test once more but turn the motor backwards to the way it runs so the compression release doesn't mess with results.

Ahh good to know, thanks. So you think all my symptoms are the result of low compression?

Most likely but if the second compression test gives better results it's carb issues.

I would check the needle settings, sounds like its not getting enough fuel. So high speed needle / jet or similar something with the fuel delivery.

When you say carb re-build: what do you do exactly?

Take everything apart and replace gaskets and jets? Or just clean it?

If you have a fuel shut off soloniod, check that. Take fuel hose off at carb, make sure you have plenty of fuel flowing.

Ya I just took apart and cleand the carb. The needles don't seem to do antthing, nor does the throttle much.