12 Hp B&S Crafstman won't start.

[mkf350]

My uncle has an 80's 12hp B&S in a crafstman lawn tractor that is in decent shape but the engine will not start. It did run last year but it stopped. He thought it may have been the seat switch. I jumped that out and it will still not start. Removed plug it looked good, was getting spark when I checked. Also was getting fuel. I removed bowl to check and the float was slightly stuck open. I cleaned it and it move freely now. It had tried to fire a couple of times but more like a backfire. Removed top cowl and the plug wire halfway between the plug and coil the insulation was gone. Darn mice. I though that maybe it was arc to the exhaust manifold but held it away and it still would not start. I know I need to replace it but figured since I was getting spark at the plug it would run. I started to see some fuel coming out of the exhaust after long attempted start.
When I had spark plug removed i put my finger over spark plug hole and turned over engine. It did not seem as if it had alot of compression. Does this have compression release? Anything I missed? Not sure if it is something more. Don't know if it need a rebuild. Would it be worth it to rebuild? It has a cast iron sleeve.Or is it better just to replace it?
Thanks

 

[Ifixcars]

You need compression for it to run. You should feel some decent push with your finger when cranking. The finger method works if you have an educated finger. Fuel out the exhaust is not what you want. Maybe your carb's needle valve allowed fuel to flood into the cylinder. Your cylinder walls might be washed down from the fuel. You can try a squirt or two of oil into the spark plug hole to see if you can help the rings seal again. Don't allow any more fuel into the carb till you see if you can bring the compression back up. As for is it worth rebuilding, it depends on what's wrong with it.

 

[elad]

I had one like that. Problem was that a valve was stuck open. Freed up
the valve and it run like always. Might want to change oil to play it safe,
in case gasoline washed into the crankcase. Worked for me. Good Luck
elad

 

[mkf350]

I did not feel to a very good compression. I need to bring it to my house. I do have a compression tester. Any idea the acceptable range is? Guess I need to get a manual also.

 

[Fordlords]

Most engines with compression release (The 12 HP Briggs should have one) will show about 80-90 PSI when cold cranking. I have seen engines still run (usually bad though) with compression as low as 40 PSI, so it's doubtful that is the reason it won't start. Get a can of spray carburetor cleaner at Wal-Mart (about $1.00) and use it to try to start the engine by spraying a little down the intake. This usually will free up a dirty carb or stuck valve after a few attempts. If it totally does not start at all while doing that, check for a sheared flywheel key. If it starts and only runs for a few seconds, clean the float bowl out, then repeat with carb cleaner until it continues to run.

The Briggs Magnetron ignitions of that vintage still had a condenser used with them, check with an ohm meter to be sure it is not shorted, and that you have a nice strong blue spark.

-Fordlords-

 

[mkf350]

Thanks for the advice I will have to give another try with some of the tips offered. Unfortunatley is it 90mi away. I may need to load it up and bring it back to my house.