I looked at a used 1989 150 today and when it ran ok, but the compression checked out to be only 75-80psi in all 6? The guy that has it said that's all it ever had? I am used to seeing about 145 on most OMC motors with this gauge.
Were there any super low compression motors made? He siad he was told that it was because it was a commercial engine? He is selling the engine due to a badly damaged hull, it appears to have been used pretty recently but is out of the water now. The plugs all look good and the motor looks super clean. I didn't remember to get the tag number though.
I've read over 100 is good. My OMC manual says the lowest cylinder should be at least 80% of the highest and the average of the port and starboard side on "v" engines should not vary by more than 15psi.
I agree, I never heard of a 2 stroke that runs with that low of compression. The only thing that gets me is that I heard it from not only the seller but a local marina and boat shop as well. I think the motor is toast and needs a rebuild, even if it does run and can move the boat, it's got to be well worn with that low compression all the way across the board.
What really gets me is that it runs good, it felt fine on the water, no lag, good power and it starts fine cold and hot. If I didn't check the compression myself, and had he not told me about the "lower compression, I wouldn't have ever bothered checking it on the spot. The motor looks fairly well kept and doesn't look abused and there's no sign of any overheating or saltwater damage. The plugs are burning well and the prop looks new.
The price is right and I may grab it just for parts anyhow, but it runs so good, I may hang it and run it locally just to see what it does. The current owner has been running it on fairly long trips, he seems pretty confident in it. He didn't get nervous when I headed offshore with it under full throttle. I wanted to see if he's get nervous or try to limit my driving, but I followed one of his last GPS tracks out about 8 miles and back.
After I came home I even retested a known good motor here to be sure my gauge was ok, and it read 150 on another motor I have here.
Did you take the compression reading with all 6 plugs out of the motor? The older 140 V4 crossflow engines would run in the 145 range. Most V6 egnines are much lower. I would expect to see 95 on that engine, unless it is an "S" model-which could run 10# higher. You can run a can of engine tuner through it and see if the compression comes up any. If not, you have a candidate for an overhaul.
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Did you take the compression reading with all 6 plugs out of the motor? The older 140 V4 crossflow engines would run in the 145 range. Most V6 egnines are much lower. I would expect to see 95 on that engine, unless it is an "S" model-which could run 10# higher. You can run a can of engine tuner through it and see if the compression comes up any. If not, you have a candidate for an overhaul.
Actually I didn't have all out at once, I did a bank at a time, but they were all pretty close. If the norm is 95 than I can believe that a decarb may help. The part that gets me the most is how well it runs and pulls the boat it's on. It sounds nice and crisp and responds well. It starts easy and idles fine and all, if the guy didn't tell me that it's shot, I wouldn't have given it a second thought. The motor is even clean looking, no corrosion or even paint loss anywhere. I am wondering if maybe it's just been sitting and is gummed up or carboned up. After driving the boat it's on for a good long test run, I can't for the life of me figure out why he ever even felt there was a problem. The boat ran well and achieved proper RPM, (top cruising speed was abou 5600-5700 RPM if the tach was right). It pulled out of the hole strong and didn't miss a beat the whole way, and I ran if for a few hours. The tilt and trim all worked great and the prop looked new.
I've had tired outboards, although not a V6, and they feel mushy and a bit noisey on the water, but all of my prior motors have been 3 or 4 cylinders. I have a buddy that has a later V6 that said his checks out around 80-90psi, and hasn't lost any over the years. His runs just as good.
I just find it hard to believe that any motor could run well with such low compression.
Evinrude 150 V6 Compression?
Linear Mode
