1986 Cajun w/ Johnson 150 GT (V6)

[TWO21]

Planning on renting compression testing equipment from an auto store to check that later this week. That maybe should have been one of my first steps but I guess I was too optimistic. Will report back on what I find.

 

[TWO21]

Compression test results, looking from the back of the motor starting at the top left as #1

1: 75 4: 80
2: 70 5: 75
3: 70 6: 80

I don't really trust the gauge I was using because I read several reviews about it only hitting around 80-90 psi and not going any further. Going to try and check the gauge with my air compressor.

Based on those numbers, am I looking at an overhaul to replace gaskets or should I try some engine tuner first?

 

[emdsapmgr]

That engine has low compression "bathtub" heads from the factory. I'd think 90# compression would be about normal. Your readings are over 10% less than normal, which usually indicates a powerhead problem. Good idea to check with another compression gauge... Engine tuner is always a good idea. If your engine has a lot of carbon inside, I'd expect the compression to come up somewhat after doing the cleaning process. Does not hurt to do it a second time, if you see some improvement.

 

[TWO21]

It was definitely a bad gauge. Used a different one today and came up with these results:

1: 90 4: 90
2: 85 5: 95
3: 85 6: 95

Put in "new" plugs, used the old plugs to burn off engine tuner for the de-carb. Ran it several times with an occasional rough idle and got it to throttle halfway in gear! Anything past halfway would make it big down but wouldn't kill it. I'm thinking there's a spark issue but not sure if it's bad plug wires, bad coil(s) or bad power pack. Will try to check those tomorrow. Advice on checking coils and power packs...is there an easy way to use a multimeter (w/o DVA adapter)? Plug wires probably need to be replaced anyways, they're in pretty bad shape.

 

[TWO21]

Update:

I replaced the spark plug wires and put in new thermostats at the end of July. Could hardly get the motor started and once I had it started, would only run for a few seconds before dying. Really not sure where to go from here. Considering taking it to a mechanic who can spend an hour or two looking at it and telling me if it's worth pursuing. My hunch is an electrical ignition problem but think it's worth a couple hundred bucks for a mechanic to take a look.