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1974 Evinrude 6 hp Compression / Idle

S

Stripgear

Member
I picked up a '74 6 hp cheap. I got it running but the idle is poor with compression of 75 / 75 psi. I took it apart and both cylinders mic 1.940 / 1.938, so .002 out of round. I have a set of NOS STD piston rings. Would this be a good candidate for a hone and re-ring? What compression could I expect?
 
.012 isn't all that bad .
Your only going too tighten it up about .008.
The ring seal will be the advantage, if there is any .
What does the manual say cranking compression should be ?
 
I believe timing and good clean carb with adjustments dialed in will give you good idle. I have a 75 6hp. With 68 lbs compression that idles and runs strong.
 
Could be fuel pump leaking into its pulse supply port causing that cylinder to run rich. Also o ring gasket at float bowl base.
 
I have 2 other 6 hp’s with compression of 85 and 90 psi. Those two run great. I have another with 55 psi. That one will stall unless I keep it revved up. Then there’s this one at 75 psi that runs “OK” but not as good as the first two. So that’s where I’m coming from. I know the 9.5’s will run good at lower numbers, but I’ve never seen any published numbers for the 6hp’s. If you have one that runs good at 68 psi, I may just give this one a light hone and see what happens.
 
Sounds good. Just bought a 1959 Golden jubilee edition 5.5 last night in mint original shape I'll check the compression on that. I think my gauge might read a little bit low as I have used other gauges on the same motors and they read about 10 lb higher. Typically on the 9.9 and 15s I get about 110.
 
Did you check the timing with an old school timing light? Setting points at .020 doesn’t mean it’s exact. I’ve seen them fire several degrees early, & rough idle. Setting with an ohm meter to be in the middle, of the two hash marks made it smooth idle right down
 
Yes that is the best way to get the points properly timed. Also I have been known to put a ground wire from the stator plate to the powerhead body. It is uncommon but sometimes the physical grounding is unreliable. As these motors wear, the stator pivot gets loose and setting the points with a feeler gauge becomes only ballpark work. As the magnets come around they of course pull the stator and change what you think is the correct gap into an unreliable gap.
 
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