1987 Evinrude 70hp, can't hold idle

[fireman57]

Going by his numbers were within 10% of each other. I have seen a lot of engines run fine on 90 compression. Depends how they were taken care of. My '76 75rude numbers are between 110 and 115 and it runs fine.

 

[Tim Kane]

in the casket clean the top hole i drilled the hole in gasket to 3mm i had your problems & this solved mine

I looked at the way the gasket was formed and sure enough, it is partially blocking the idle jet. I cut away the gasket area circled in red as shown in the picture. I did this for all three carbs. Installed it back in and just like that, I have idle!! Thank you durban, you were right. The gasket must be an aftermarket gasket that the previous owner put on, or maybe a design flaw? I still may drill out a small hole through the plastic housing too. Thanks again to all that gave me feedback. I really appreciate it.

 

[fireman57]

Great job durban!

 

[phillnjack2]

Just read this post, whoever says 100psi compression is ok for a johnson or evinrude 70hp is dreaming.
100 is terrible and needs to be rectified.
the v6 engines can run at around 90 to 100 all day long and be fine, they were not high compression engines.
the 3 cylinder 2 strokes from omc are all pretty similar as for compression, the higher the better they run.
A decent running engine needs to be atleast 125 psi and most good runners will be between 130 and 150psi.
my 70hp is 1995, never been re-built and shows 149-147-149. that is cold engine not warmed up with no extra fuel added to
bring compression up.and that even has idle relief holes in the bores to lower compression at idle revs. !!
the 1970's models 75hp were around 145 psi too.
if getting low numbers try some powertune in the cylinders to help free up the rings and get out some carbon at same time.
a brand new un-run engine will only be around 125 psi until its been broken in, then the numbers will soon come upto 145 plus.

 

[flyingscott]

A lot of those motors running with 100 psi not ideal but will run. Also a rental compression tester those are suspect especially if the o ring is bad or it was over tightened. What number is on the low speed orifice. These have a tendency to run lean at an idle omc was good for getting around the epa regs doing that. Also What number is on the high speed jet I believe the 87 used a 33 for the low speed and a 64d for the high speed. One other thing that can cause that problem is the lower unit. A bad bearing in the lower can cause the problems you are having especially if it had water in it at any time.