johnson 1975 85 hp compression

so i checked the compression like everyone said on here and it was at 45 on all the cylinders. i put the boat in the water for the first time today after replacing fuel, coils, sparkplugs and fixed the electric choke, so now she starts like dream runs awesome with the muffs, kinda misses out like a little backfireing though but when i put it in the water it wouldnt throttle up and it dies when you try to take off in it. what do i do now?

Re: johnson 1975 85 hp compression

I was having the same problems with my 76 85 hp evinrude. Turned out to be the powerpack that went bad. My motor would run all day long on the muffs. It would stall in the water when submerged everytime i put it into gear. Try disconnecting a a spark plug boot 1 at a time while it is running with the muffs. I could disconnect 3 boots and the motor was running still on 1 cylinder. It was firing on cylinder #2. I was not getting any fire on the other three. I tried rearranging the coils and they would all fire on on cylinder 2 but not the others. I had the motor checked out and it turned out that my powerpack was bad. I replaced it this weekend and now it runs like a champ. By the way your compression appears to be low or was it reading 145.

Re: johnson 1975 85 hp compression

Thank you for checking the compression.

45LBS?

Look for 100lbs each cylinder and only a 10% variance between the cylinders.

What to do now?

If the compression readings are correct. With a known good compression gauge.

I would sit down, have a cig if you smoke, and a cold beer if you drink.

Pull the heads and inspect for a warped head or a blown head gasket.

Put your heads on a flat surface, preferably a piece of glass and look for warpage. Usually bowed in the middle between the cylinders.

If gaskets are good, and no warped head. It is rebuild time or replace power head.

45lbs is not enough compression to carry any load or produce torque.

I am no expert by far and hopefuly some of the experts will reply but that has just been my experience with the V-4's.

Re: johnson 1975 85 hp compression

That compression is low, I would check it once again, make sure you have all the plugs out. Seems like if it really did have that low of compression it wouldn't start all that easily, it would take a little more to make it run.

I have a 78 85hp evinrude, I did a compression check on each cylinder and it was 105 across the board, I did my check by taking one plug out at a time though , so it should actually read higher when having all the plugs out.

Ditto on what wavrider said.

Re: johnson 1975 85 hp compression

I think you made a mistake on that compression. I did not know they would even start if it was that low.

Re: johnson 1975 85 hp compression

I got 125# on all 4 holes when my 1979 85 hp was overhauled. With the compression that low, it won't suck enough fuel through the carbs to make any hp.

Re: johnson 1975 85 hp compression

I ran my '77 85hp ('75-'77 are the same series) all the way down to 78psi and it still ran great. Top end began to suffer, so I swapped powerheads. That said 45 is way too low to be running good at all. Maybe you could explain how you did the compression check. Probably your testing procedure is somewhat off. The good news is that they were all even.

For that series of motor with a little wear I'd be looking for compression in the 90-110 range.

Re: johnson 1975 85 hp compression

well i let it idle with muffs for a minute then i then i put it gear and run it for a minute, like i said it sounds like it runs great with the muffs, full throttle, in gear wide open...so anyway i took out the spark plugs, then screwed in the compression guage and turned the key for about 3 or 4 seconds... i repeated the process on all the cylinders, they all went to exactly 45... one more thing the same 2 spark plugs have fouled in the past 3 or 4 weeks during all this repair does that mean anything

Re: johnson 1975 85 hp compression

is never run one over 1500 rpms on muffs. easy way to have a runaway motor you can turn off. try it with another guage, see if there is a difference. 45 PSI is way too low.

Re: johnson 1975 85 hp compression

WOT on the muffs should have been a shoo-in for a runaway. Low compression probably stopped that from happening.

I doubt this motor is going to idle and run well in the water with some back-pressure.