working to get a 1980, 35hp going

[relicshunter]

Bought an unproven motor because it was the exact motor I was looking for and hoping it was salvageable. Well I've rebuilt the carb, replaced the water pump, fuel pump tested good, serviced the starter, replaced the solenoid, compression is top 80, bottom 90 and held at that. Just could not get it started. Had a few small backfires, one start attempt. Adjusted the slow speed knob, checked the throttle cam and control rod adjustments. All seemed good.
I stumbled on the only way to get it to start. I have to manually turn the throttle up to the position the cam roller is right at the adjuster marks, then it starts. Back it off just an 1/8 of a inch and it stalls. I have two books and I am just not getting all the pieces together in my mind. So currently I have the idle speed adjustment screw on the throttle linkage adjusted to position the cam roller just right to start it. I don't think this is how I am supposed to do it, but it runs.
Now next question. Now that it is running I found that the telltail isn't right. I have water out the usual places, but just a weak dribble out the TT. I have run 80lb fishing line through it, couldn't get a wire to bend enough. Got no change. Pump was just done.
Thank you for any help you can give.

[relicshunter]

Anyone have any thoughts. I am going to order a thermostat and gasket set. I'll make sure everything in there is good, and see if it helps.

[waterbum]

If this motor has points, time to look at those.

[phillnjack]

well you have a problem straight away as the compression is terrible.
90 is just about as low as you ever want to go,it realy needs to be around 125 or more.
the 80 is way too low for the engine to be any good on power /performance.

you need to see if any of that water is getting to the plug with the 80 reading !!!!!.
it might be bad head gasket !!!!!!

have you tried a drop of seafoam or deep creep in the cylinders incase of sticky rings and bad carbon build up \/
might be worth a try,it just might bring the numbers up to scratch.

if not then a rebuild will be needed as the 80 psi is killing the engine




phill

[relicshunter]

It has a cd ignition system.

I have not soaked the rings yet, one of the next things on the list. I was surprised the book did not list a recommended compression merely that they should be within 15% of each other. I've seen posts of motor at 90 and less running good. Certainly would like it to be stronger, but it will be pushing a light, small boat. Thanks for posting about the compression I have posted in a few places and gotten no comment on the numbers. I have a full gasket set coming so I'll have what's needed. I'll soak the cylinders and retest before going in.
Any other pointers of things to look at.
Thanks

[phillnjack]

These engine when brand new had around 125 to 130 compression.
After a nice running-in period the compression would usually settle to around 130-135, sometimes a touch more.

The figures spread around the internet about 15% is very misleading.
15% would be far to big a difference even if the engine were producing huge numbers.

Its around 5-8% as difference to be of any use, no point in having 1 cylinder producing good power and the other producing low power, would make for bad uneven running on all internals..

OMC were very crafty in lot producing figures for the engine when new.
99% of engines around the world give compression figures, but not omc ????

Its like on some engines they mention high compression heads, well how is someone supposed to know what is a high comp head if the figures are not given in the books.

But if you go to the race type sites on the net its here that figures are given for standard and for the racing engines when tuned to the max.

90psi is definitely way too low, 100psi is what is considered the normal minimum for a internal combustion 2 stroke engine.


are you testing compression with wet or dry cylinders ?
they need to be wet with the carb on full throttle to get correct readings, and idealy a warm engine !!!!!.

could be a worn head gasket or warped head, or large build up of salt or limescale not only blocking water p***ages but also lifting the head gasket.






phill