Thread: ‘95 Mariner 40hp rebuild or scrap

Sounds like a bad stator to me because i had a slow idle & very weak holeshot on my 2003 Johnson 175 & felt like it was dropping a cylinder after getting good & warm on a decent run. I'd get a manual for it if you don't have one so you can do some tests before tearing down & ordering parts. I was told i had a bad power pack so i thought with it being 21 years old i replace power pack, optical sensor, plugs, wires & coils. After all that i still had a slow idle & weak hole shot. I downloaded a pdf manual specifically for my motor & done some test like the book said & turns out my stator is bad & causing all of my problems. If i'd had a service manual before i'd have saved $500.00 & only replacing the stator. I ordered the same exact over 400 bucks cdi brand stator off of amazon for $218.00 & will be here Wednesday & i'll put it back together. Yep i could have been at just over 200 bucks if i'd had the manual & am at a little over 700 now. I will say i wasn't cutting any corners when i tore it down & now have everything but the regulator/ rectifier preplaced for what a local mechanic wanted to just replace the stator so i'm fine with that. The old motors been good to me soi figured why not. If something bad happens to it there will be a new 4 stroke go on in it's place.

OK, you have a better compression test, and you did it properly. The rule of thumb is, compression is good if all the cylinders are within 10% of each other. The truth is, you have to have enough compression to make power and honestly with that motor you don't. What you are describing is symptomatic of a worn engine. You rings are leaking. When on muffs, an engine will run like a top at any RPM because there is no load. Some engines will even rev with no timing advance due to this. On the water under load is a completely different story. Now there is weight and counter-acting forces and the engine just can't overpower that. I stand by my statement that the engine is worth rebuilding as They are very good engines. Here is the caveat to that; It has to be worth it to you. You rebuilding this engine will not make it more valuable for resale, you will simply be returning to a running status which is the bare minimum of a good used motor lol. if it is sentimental and you want to learn the inner workings of a small outboard and you have the disposable cash, then it is a great idea. This is not something a reasonably intelligent person with some basic tools and basic mechanical skills can't do. If you just want your boat to go. put the rebuild money towards another engine. There will be more to do besides the rings, someone mentioned the stator and they are right, it is more than likely struggling. there will be bearings that should be replaced since you have the crank out anyway, you will need the cylinders polished at the very least if one or more are not scored from the bad rings, if that is the case it will need to be honed and sleeved. I am not trying to discourage you, just make you aware of what "could" happen. It can be done in a garage at home, but it will be more than just some rings and bang you done and on the water. Heed what S10chevy said, buy nothing until the engine is apart, that is sage advice and I'm betting it comes from wisdom gained by experience.

I have a shop manual that I believe covers that motor. I’m already late for work but I’ll get with you later today.

Boat has no real sentimental value and I would like to have bigger motor. But at the same time don’t have $$ for motor or boat. So I want to rebuild. And also redo carpet and get gauges all back to working.

I have a manual that covers this engine.


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Update. Replaced stator and trigger but have not ran it on the water yet. Also found the woodruff key sheared on fly wheel when I removed fly wheel. Didn’t catch it right off so I don’t know if it had slipped on shaft and didn’t see any scoring or scratches on shaft like it was slipping a bunch.


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So you have now replaced the stator, trigger, and powerpack? All that's left electronically are the coils and plug leads, and its almost impossible all 4 of those failed all at once. So if you still have issues with the ignition system you can isolate them to rulle out or confirm if they are an issue.

If it were me, before I water tested it, I would do a spark test with an air gap inline tester. Make sure all 4 plug leads are jumping a 3/8" gap with a nice healthy snappy spark. I would also check the idle timing with a timing light and make sure the spark advance linkage is working. The manual should tell you how to do a static check of the fully advanced timing and give the spec. If you dont have a timing light, I think you can rent one from autozone.

If its timed just close to correct and you have good spark on all cylinders (and assuming fuel delivery was not an issues all along) it should get up and go when you give it near WOT....at least initially. If it doesnt then seems fuel related to me. If it works then starts bogging, it could also be fuel, but could also be failing coil once it gets hot.

FWIW, I had the same Harbor Freight compression tester at one point as a spare and it has almost the exact same issue. It will read no higher than 60 psi on an engine but I can push the rubber tip up to an air hose regulated at 90 psi and it will show 90 psi. I have 2 basic Innova ones I got from a big box auto parts store and both work fine and were only like $10 more than the HF one. HF one shows 60 psi and the good ones read true at up to 140 psi on my various outboards. I'm sure the HF one has a use somewhere but its useless for an engine compression test IMO.

Good luck.

That sheared woodruff key is/was the problem. Motor out of time.