On a 2 stroke engine any compression reading under 90lbs is usually considered no good. What compression readings do you condem a 4 stroke engine? I have a 5hp briggs with 40 lbs compression, yet it shows no leakage on a leakdown test. Should I consider this engine good or worn out?

Thanks for your thoughts and advise.

Does it run ??

The engine will run on carb cleaner. Its not getting gas up to the carburetor. I just don't want to spend the time removing the carb, cleaning, installing new gaskets, etc. just to find that there is not enough vacume because of low compression to actualy draw the fuel up into the carb.

This is on a briggs with the carb on top of the gas tank.

Thanks

I would say if it runs with a boost, I would invest the $4-5 in a new diaphragm and clean the carb real good and give it a go.
You won't have much time or money invested.
thanks,

Post the engine model, type and code numbers usually found on the engine shroud just above the spark plug, so we know what you have. Have a good one. Geo

In my repair manual,on 2 cycle engines they all say at least 90# or better to run.This is one of the things I do is check the compression on every engine I do before starting to work on them.I just replaced a gas tank on a 6.5HP briggs, and I check the compression and it showed 45# this it a 4 cycle engine,and it runs great.

Jerry

Briggs and Stratton Model 91212 Type 0219-01 Spec 961209EA. I replaced the pump diaphgram and tank gasket. Cleaned the carb good. The engine now runs good. I was looking for a compression reading that people use to know weather a 4 stroke engine is worth fixing or not. Most people use 90lbs for a two stroke, just wondering about a four stroke. I now know that they will run on 40 lbs compression.

Thanks for the replies.

40lbs is quite low. I'd be looking into some new rings and lapped valves some time soon. A rebuilt 5HP should be doing 100lbs+ before break-in.

A model 91212 is a 3.5HP or so IIRC... a 12xxx series is a 5HP :eek: 10xxx is a 4HP, 80xxx is a 3HP, 60xxx is a 2HP.

Keep in mind that most 4 stroke engines utilize some sort of compression release mechanism that may affect compression readings at normal cranking speeds. This is why Briggs does not publish compression readings for their engines. They simply state to crank the engine and then watch it spin down, if the flywheel stops abruptly or bounces back, then the engine has sufficient compression to start and run.

As for 2 strokes, reed valve engines will start and run with lower compression then ported engines, I have had 2 stroke reed valve engines start and run fine with 60 lbs of compression, but ported engines require much higher compression to start and run effectively.

Thanks for the replies.!!!