My 1962 18HP Evinrude went into the shop for a tune-up two years ago and has not run properly since. I took it back and the repairman checked it out and said he could not find any problem with it. He has replaced plugs, coil, etc.

It starts easily and smoothly, runs fine in the tank, BUT, when under load pushing my 14 foot Columbia I can only get a top speed of 6 mph instead of the 16-18 it use to get. It runs really rough as if both plugs are not firing and seems to be missing. The engine jerks like it is trying to get more power, and actually does for short spurts.

I have not replaced the plugs since they are new from the tune-up .

I bought a new gas hose, had the prop tuned, used two different gas tanks and the problem still persists.

I plan to take it back to the shop one more time, but if they can't find an answer, hope that someone can refer me to someone else who works on these old motors.

Any help will be appreciated.