How to fix boat throttle?

My 25hp outboard alternates from going full out to about half throttle repeatedly as you drive, why is this?

• I have a 25 hp 1972 evinrude. This motor just came back from the shop and seemed to run great in a tank, but as soon as it goes in gear and full out, it bogs down as if it is only getting half throttle. It was in the shop originally because there was no spark in the engine. The mechanic changed both coils thinking that was the problem, which it could of been half it, but that still didn't fix it. Then he changed the inner coil, adjusted the points and then that's when it seemed to work good. When i got it home and on the boat it seemed to drive fine for about a minute then started to act up. After this i read up about it and thought it was the low and high speed needles needing adjusting. When i adjusted them it seemed to run fine in neutral and at slow speed but didn't want to go full out still. The high speed needle is a fixed one where you cant adjust it so i just took off the carb and cleaned it out along with the high speed needle. After this didn't work i cleaned out the fuel pump/ filter which also did not help. It almost seems as though it is kicking between running on one cylinder and two, because the change in speed is sudden rather than gradual. What im trying to ask here is it anyone knows why it might be doing this, and what i can do to fix it?

• Answer:

  First, you need to fire that parts-changer masquerading as a mechanic. Those components can be tested, so that you only have to replace what's broken, instead of randomly throwing parts at it. Not to mention which if he'd tested in his tank with the proper test wheel he'd have got the same result you did, and fixed it. You said "both coils" -- if you have two ignition coils and a powerpack, then you don't have a 1972 evinrude 25 hp. anyways, I take it you have spark on both cylinders now? then all they need is compression and fuel. Compression should be about the same on both cylinders (within 5 or 7% or so) or else it'll never run right. Compression test is the first thing any decent outboard motor mechanic does -- he should have written your results on your invoice. Does the fuel line hold pressure? Is the fuel tank vent open and clear? Check the tank for water/debris. If all that checks out, rebuild the carb. You can't tell from visual inspection whether its good or not. For a few bucks you can get a carb kit with new gaskets, orings, float valve...get one and install it.