architorture
Well-known member
I've been dealing with overheat problems on my 84 yamaha 40 hp for a while now. I replaced the water pump and thermostat and after taking it out yesterday the problem seemed better but was still there. Also, ever since I got the boat (2 years ago) the motor would start missing/cutting out at about 2/3 throttle. Yesterday when we were out we tried giving it a little bit of choke when it started missing and that made it stop but I couldn't really rev it much higher. I'm now thinking it's been running lean and that's what's causing it to overheat.
I did a compression test (cold) and got about 60-70 psi on all three cylinders. I poured almost a cap full of oil into each cylinder then got 90, 100, 110 psi from top to bottom cylinder. I'm guessing this means either the rings are shot or the cylinder is scored or both. If the cause of the miss at high revs is from running lean then I'm a bit worried about the cylinders as the PO told me that it had done that for two years and he couldn't figure out what it was.
BTW, when I replaced the thermostat the other day it was the first time those bolts had ever been removed. All the powerhead bolts still have the factory paint on them.
I did a compression test (cold) and got about 60-70 psi on all three cylinders. I poured almost a cap full of oil into each cylinder then got 90, 100, 110 psi from top to bottom cylinder. I'm guessing this means either the rings are shot or the cylinder is scored or both. If the cause of the miss at high revs is from running lean then I'm a bit worried about the cylinders as the PO told me that it had done that for two years and he couldn't figure out what it was.
BTW, when I replaced the thermostat the other day it was the first time those bolts had ever been removed. All the powerhead bolts still have the factory paint on them.
