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compression for pull start '1975 15 hp

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dawnfogg

Contributing Member
Rebuilding '75 Johnson 15hp pull start that I have never seen run. Rebuilt ignition and got good spark and decided to check compression before putting everything back together. only got 40 psi on both cylinders. Heard should be around 90-100. Is there any difference between the compression reading for a manual start vice what you can get with an electric start (no comments about wimpy arms, please.) Haven't tried to start it yet because of crack in the fuel filter.
 
Re: compression for pull start '75 15 hp

seeing as they are both the same it might be how you are doing the test.
how many times did you pull it over?

and depending how quick you pulled it over not saying ur weak or what ever but that is what might be affecting your results
 
Re: compression for pull start '75 15 hp

i pulled it over about 6-8 times on each cylinder. Did not have a plug in the other cylinder. Didn't think that mattered. Will the engine even start if the compression is really that low?
 
Re: compression for pull start '75 15 hp

if i were you since they are reading the same psi i would either try out a different compression tester
usually if there is problems with compression the cylinders would read different compressions
if it was me i would just run it i think it will be fine
 
Re: compression for pull start '75 15 hp

Yah, it won't run on 40psi compression - hopefully the gauge is off. Good sign they are even.

If you put your finger over the plug hole (both plugs out) and give a tug - I know awkward - it should pop your finger off.

If indeed it's only 40psi, the head gasket may be blown. If you pull the head and find that to be the problem, pull the thermostat cover as well. Clean out the crud and replace the thermostat.

If you squirt some fuel into the carb(open throttle), it should pop off with a couple of pulls. Ideally, it's best to do it in a barrel.

If you have the motor side connector off, plug it into your hose. The connector will act a a squirting device when you squeeze the bulb.
 
Re: compression for pull start '75 15 hp

Got fuel pump cover replaced and started it yesterday. Does run but not real well. Need to clean and rebuild carb next.
 
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