Expert: Jeff Grigg - 1/25/2008

Question
Jeff, I have a 1995 25hp Merc. Serial#0G120315. It runs great and idles great. However, recently I have lost all top end speed. It just doesn't jump up on plain and feels like I'm running at 1/2 throttle all the time. It has a brand new prop, so I know its not slipping. Do you think it is a carb problem and if so why does it still run like a top? On the internet I saw something about a stator or trigger. Please help, where do I start?
PS - I haven't taken the carb off - does this year have two jets or one? And is it a major job I should not attempt myself?

Answer
Your carb has two circuits, idle and high speed. If the engine sat for quite a while it could have become gummed up and in need of a rebuilding.
A cheap simple way for you to diagnose an ignition problem is to run the motor with an inductive timing light hooked to the spark plug wires. Do the top cylinder first then the bottom cylinder. All you are looking for is a consistent flashing from the timing light as you throttle up the engine. Do this in the water under load, never on the hose. If you have good flashed all the time the ignition is OK. If you drop one cylinder then you have an ignition problem. For further diagnosis take the engine to the shop.
The carb rebuild is not beyond the scope of a good amature mechanic. I would not recommend it to someone who has not done any carb rebuilds before. Always use new gaskets and a service manual. For piece of mind the shop is the best place.
Post back if you need further help.
Jeff