How much PSI should a Briggs & Stratton 190cc walk behind lawn mower engine have

[jpilk99]

The machine runs on starter fluid, quite well, but dies immediately once it's gone. I've cleaned the old carb, tried a new one, swapped fuel line, confirmed gas is good... Checked compression and getting just a hair over 60psi after 3 pulls. Is that my issue, poor compression?

Thank you,

Jay

 

[sea2summit]

Sounds low to me. I only know Honda’s and once they get below 90 your shady, below 85 is a rebuild.

 

[jpilk99]

Thank you. And just to confirm, “rebuild” means what to you? Piston, rings, head gasket?

 

[RandyT]

With compression release you cannot get a usable psi that equates to anything important. Did a generator years ago that showed less than 10% of cylinder leakdown test but only showed 5 psi on the compression gauge. Generator ran fine after determing it had a clogged muffler.

So with some engines 60-70 psi are not unusual. @sea2summit Honda list around 70 psi in a lot of their service manuals for minimums.

To the OP what is the full model type of that engine for reference.

 

[Fuddyduddy1952]

This $30 leak down tester is really handy from Amazon if you're going to work on motors. It tells more than compression test.
I assume you installed new spark plug and have good spark?

 

[jpilk99]

Thanks all. Complete B&S engine details are below. Spark plug seemed good (I cleaned it and reinstalled after testing and it showed good spark; can easily get another). Thinking I might check valve lap?

Briggs and Stratton 128T05-5123-B1​

 

[sea2summit]

Thank you. And just to confirm, “rebuild” means what to you? Piston, rings, head gasket?

Probably…

 

[oldnslo]

I would check valve clearances to see if they have tightened up. Not sure what they should be would guess around .008 -.010 for exhaust and .006 - .008 for intake. Also watch as turning engine over on compression stroke to see if one of the valves is bumped open. This is how compression release works on some models.

 

[RandyT]

Mechanical compression release on exhaust valve Looks like .005-.007 for intake and .007-.009 for exhaust.

 

[tomplum]

If there isn't a problem with the intake tube, it's still most likely carb related. Best thing to do is pick one of your carbs, remove the bowl, flip it over and look at the float level. The problem with aftermarket carbs that I've seen, is that they use brass inserts for the float valve seat. And the level is low. In fact, I had bought a couple of OEM carbs on stock up. One of those wouldn't run as the seat wasn't pressed in far enough- thus lowering the float level to something that wouldn't run. If you fix your old carb 398188 is the float valve kit.