When I first got the boat in the water it would barely run. I had a mobile mechanic working on it. He adjusted and cleaned the carb. Set the timing and replaced the fuel pump diaphragm. It seemed to run much better, but all we could get out of it was 7 MPH and it was overheating. I took it out of the water so he could replace the thermostat, and water pump, also had him replace all the seals in the lower unit. Getting the boat to the ramp was not easy because I could not get the engine to run above idol speed. I put a new prop on it, but we haven't found out why the engine is running the way it is all of a sudden since it's not back in the water yet. I really can't afford to have him do too much more work on it because I'm running out of money. I'm wondering if it could be the float and or the needle valve? PS, he wasn't with me to see how the engine was running when I took it out of the water.
yes, the mechanic did test compression. I believe it had 35 lbs in each cylinder. I don't think spark is the problem because the plugs are new also and we have taken it out a few times. The reason I keep thinking it might be the needle is because when he cleaned the carb, he had to keep messing with the needle because it seemed to be hanging up. I'm sure he would have replaced it if he had one on the spot. Since it would run fine one time and then not the next is what brings me back to the needle. Sticking?
Unless you misunderstood your Mech. 35lbs of compression is BAD. They are supposed to be at 120 or above for good compression and they are suppoesed to be within a certian % of each other. As far as spark I have a 1990 50hp and mine ran and idled on 1 cylinder until I realized there was only spark to 1 cyl. yours sound just like the problem I was having. you can get a sprk tester at autozone for a few bucks and you can rent a compression tester from there also. run those tests yourself and SEE the results for yourself.