78 9.9 hp. cold compression?

[tidechaser 1]

i am still trying to get this puppy to keep running..got a carb coming from e bay.
i was wondering..i did a cold compression check and both cylinders were the same (whew) at about 88 lbs.
i think i am ok with that right?
i was thinking of seeing if i can get rid of the carbon in the motor..i think i remember people using sea foam..but i cant remember the technique..anybody got a tried and true method they want to share?
thanks.
by the way..i got the carb for 32 plus shipping..they say it was from a working motor..i plan on taking it apart and cleaning it and giving it a try..hope this solves my issue...i saw one for 199 on e bay..gimme a break!
thanks guys for all the useful info..what a great resource for all of us weekend wrenchers

 

[Rick.]

Re: 78 9.9 hp. cold compression?

Your compression is excellent. Should be no problems there. Look at the Top Secret File at the beginning of this forum for decarb (and other good stuff). You will need to get it running for the decarb. Best of luck. Rick.

 

[2manband]

Re: 78 9.9 hp. cold compression?

Yep 88 lbs is fine. My 1976 9.9 has right about the same number and it runs like a champ.

You don't get very high compression ratings on these motors because the starter is kind of "geared down" and doesn't turn the flywheel at a very high RPM.

 

[Bubbles Up]

Re: 78 9.9 hp. cold compression?

I have a '74 9.9 and am at 76 Per jug. It runs like a champ until, (I think) the one coil gets hot and drops a cyl.

 

[OptsyEagle]

Re: 78 9.9 hp. cold compression?

I doubt the carbon is what is keeping the motor from running but to do a decarb., my favorite method is to get the seafoam in the arosol can. Start up the motor and get it warm. Put it on a high idle and start spraying the seafoam through the carb throat, in large quantities. Spray until the motor just starts to chug and then when it revives, do it again. Do this for about 9 or 10 sprays. Now spray it continuously until the motor dies. Now remove the spark plugs, tilt the motor up and spray a good quantity into the cylinders while manually turning the flywheel. Loosely put the plugs back in and let it sit for 1 hour (never tighten the plugs into a hot motor if you can avoid it).

After 1 hour, untilt the motor and tighten the spark plugs snuggly. Fire up the motor and spray some more through the carb throat. Do this 3 or 4 more time. Now, take the motor out on the lake and run it hard (WOT) for about 20 minutes to blow out all the seafoam and carbon that was in there.

I prefer this method then the one where you put large quantities into the gas. Sometimes the seafoam dislodges crud in the fuel lines and carb and this creates a whole new problem. Probably a problem that was going to happen anyways, but a problem tomorrow is usually better then a problem today, so I prefer to avoid it, if I can.

 

[raczekp1]

Re: 78 9.9 hp. cold compression?

last week i rebuilt 9.9 Evinrude 78' powerhead for my friend.
with new rings , seals and gaskets i got 120 psi with rope starter

he had good cylinder set, but i did the same work in my 78' johnson but cylinders are "used" to much, and even with new rings with gap 0,15 mm still i got only 90 psi, motor start with choke on with 3 puls, but when he colds down after while needs choke .
in my opinion 90 psi is low