Hi everyone. You have a really informative BB<br />here. I inherited a 1967 18' Larson with a 1966 100 HP Johnson on it recently from my father. The boat and motor have been in the family since they were new and have been kept in a garage, so both are in good shape on the exterior. The motor hadn't been run in two years, but cranked up first time I turned it over. It had been 15 years since I had driven in the boat, but it seemed to me that the the RPM's were a little low at WOT and the boat was a little sluggish. I took it to a local shop for a compression check and a tune up. The mechanic said the compression check registered 1)115, 2)115, <br />3)90, and 4)110. He did not do any other work to it because he felt with the one cylinder down that any tune-up would be wasted and no difference would be noticed. He has suggested either a rebuild or a new motor. The motor is turning about 4700 with a 12.5 x 16 prop at this time. The suggested range is 4500-5500. Someone suggested Engine Tuner to see if the ring on the #3 cylinder is stuck, but with a motor this old I am hesitant to try it and maybe loosen up all the cylinders. I am also worried about the availability of parts for this motor. I was told there are essentially no parts to be had for the lower unit and that new pistons, if necessary, could be very expensive. If I choose a new engine, I would like to have at least as much power that it had originally. I was first looking at 115's, but was told to be careful of the weight and torque on the transom. There are no new 100's on the market, but I was told the new 90's will deliver more torque and power to the prop than the 100 that's on the boat would have new. The boat weighs 900 lbs. and the plate on the transom designates a 115 max for the boat. Thoughts and opinions? All help will be appreciated.
