Low compression

[Dster]

Just for fun, I rebuilt a 76 9.9 (10R76R) that was frozen. I got a used power head, cleaned it all up, and put in all new gaskets, seals, including lower end, new rings, new gas lines, bulb, and fuel pump, carburetor kit, and plugs. It started on the third pull and ran for an hour at mid/low speed, with some water spraying out the blubber hole. The next day and beyond it simply will not start. I even used a drill to really crank it over many times! First compression test at this time was 40/40 cold drill-cranked. It will pop every now and then. My first question is will 40/40 prevent starting? I tore it all down again and the cylinders, pistons and rings all look good. The head gasket also looks good although I don't really know what to look for in a blown gasket. So again the question: is low compression enough to keep it from starting? Thanks!

 

[oldboat1]

Yes. Torque the head bolts again to specs (in and out, circular pattern) and see if compression improves.

 

[F_R]

40 psi with a drill is way, way too low. Not meaning to insult, but did you have the correct fuel/oil mix in it when you ran it?

 

[Dster]

On the fuel mix- I was running it a bit heavy, more like 40:1. Does anyone know if you can oversized rings to improve compression?

 

[Crosbyman]

I guess low comp could also mean low crankcase vacum to pull in fresh gas...what happens if you try to mist some fuel in the crab while cranking it ..

how are the sparks ....hot ? weak.. non existent

my 9.5 hp has comp in the 60'S and works perfectly

 

[Dster]

Misting fuel in the carburetor doesn’t help. I’ve also tried squeezing the bulb and fueling the carb externally. I’ve taken out the carb twice and everything looks normal including the float position and function of the pin valve. The sparks are both present but I don’t know how to test the spark strength. When I broke it all down I did see that I mistakenly greased the 5” fiber ring on the ignition timing setup under the magneto.

 

[racerone]

You are supposed to grease that ring !------Make something up with some wires / glue / carboard / clips .-----You just need a gap of 5/16" between wires to see if spark will be strong enuff to jump it.----Also test with another compression gauge.

 

[Dster]

I just tore the whole thing apart an am putting it back together. I’m going to try measuring the compression as soon as get it all sealed up but not wait to put it back into the mount. I’ll order a spark tester. “Ramblings” says definitely don’t grease the fiber ring that it needs friction to work right. Hmmm

 

[Crosbyman]

misting fuel in the carb should have produced some explosions unless the fumes did not reach the cyl or the ignition is not doing much for you …

can you at least feel some suction on the carb face

 

[tomhath]

Can you get hold of another pressure gauge? That might be all there is to the low readings.

Double check that the points are making perfect contact and are gapped exactly correct, that motor is notorious for having fussy ignition.

 

[Dster]

I just got another power head, owner said it had compression of 115,110 last Sept in a barrel. My tester read 40. I’ll get another tester!

 

[Dster]

Different tester now reads 90 in the newer head tested on my bench top. My original head reads 70/70. Now I’ve stripped a couple head boat holes by tightening too much. I’ll tap them out to 3/8-16 and put it all together again, test the compression after running it in a barrel.

 

[Dster]

On the electric side, I bought a spark tester with adjustable distance and I’ll see what that shows. I also realize now that I had the ignition ring offset by about 70 degr! Yikes what a hobby!!

 

[scatgo]

How did it all work out?