1983 Johnson 150, do I have a carb or compression problem

[benw88]

83 block and heads, 89ignition, 88 175 exhaust housing because it was originally a 1988 175

Motor runs but is hard to start and has misfire.

Compression numbers:

1: 95
2: 100
3: 100
4: 90
5: 95
6: 100

I had the heads off and the pistons have carbon buildup but the cylinder wall didn’t have any scratches. 1 piston looks different than the others like it has been replaced.

I pulled the plugs after high idle and reving a bit and #6 is dry and black, all the other ones look wet.

Carburetors cleaned meticulously and checked three times. No shared flywheel key. I have 170 V at each power pack orange wire using DVA adapter. New coils. Rebuilt dual fuel pumps. New fuel lines and primer bulb. I drained the tank as much as I could by using a fuel pump and filled with 10gal of premix.

Racerron suggested I look at crankcase compression in a previous post but I am not sure how to do that.

Can’t get too idle or run smooth.

could it be jetted to rich? High speed jet is 56c which is correct for a 150, I could see that the exhaust might have an impact on performance, but not sure that it would cause a cylinder to misfire.

At this point, I also can’t tell if the cylinder is mostly firing and dropping out or mostly missing and firing every once in a while. I am not sure how to test that.

Any help is appreciated. I am willing to pull the powerhead apart if that will solve things. Everyone is telling me to give up and just move on, but I have a hard time with that, it also doesn’t change the fact that these engines ran well at some point so just blaming old technology is sort of wimpy in my opinion.

 

[benw88]

Let’s say that the cylinder walls were damaged, maybe where the piston is covering it up when it’s at the bottom of the stroke. Would the next recommendation be to have the block board out and try to find oversize pistons? Can any Automotive machine shop bore or does that require a specialty shop?

 

[racerone]

Remove bypass cover on #4 , just 6 wee screws.----Have a look at the piston / rings.

 

[faztbullet]

Is the same one you have posted on other site?

 

[benw88]

I started a thread on a different site when i first got the engine to try and help Id the powerhead.

 

[benw88]

Update, because of varying compression numbers and the mix matched parts I looked and bought a 1990 175 Evinrude with controls that is complete and has 120psi across all cylinders and will focus my attention on that engine instead.