Loss of power 35 HP Evinrude

[Deanrt]

Hi everyone, If it's notta one thing it's anotha:shrug:. Bita history; I have a 76' 35 hp Evinrude that came with the boat i bought about a year ago. It has ran fine until a month or so ago when it developed what the shop called a 'mid range miss'. Ran ok the first quarter throttle and the the last quarter throttle. In between was not good. So, i take it to the shop, have em look it over tell me what they come up with. They say, most likely the thermastat is stuck open, engine not coming up to temp not burning off the fuel fouling the plugs. Bla Bla. $250 bucks later i take it out it runs fine but not ******* as much water, and seemed to me to be running hot, and now has somke or steam coming out with the little water. Anyway not wanting do any damage shut it down took it back to the shop they run it with rabbit ears check the temp and tell me is fine, i think the temp got to 168 or so. Alrighty then, i decide its time to take it out and run it longer and see what happens yesterday. Well it seems to run ok, as in taking off but i only can get 12 or 13 mph out of it when i used to get 23 or 24. Again:shrug:. I had a temp stick of 200 degress and it didnt get there. So thats where im at. Can somebody please help, that $85 bucks an hour would kill me if i keep taking it back to them (shop). Any ideas and I mean any will be apprecitated. Thanks, Dean

[Zeke]

OK, if getting the operating temperature corrected didn't cure the problem then it's time to look elsewhere.

What you are describing could be an intake leak or bad reed valves. The reed valve block is the rectangular block located just behind the carburetors. It's got metal reeds in it (like in a goose call) for each cylinder that open on the intake stroke and close on the exhaust stroke. If they are broken or bent or leaking you will get worse symptoms at lower speeds than at higher speeds, and the problem may not be very noticable at idle. One way to check for bad reed valves is to hold your hand or a piece of paper in front of the carburetor intakes with the cowl off and the engine running. If you see or feel fuel mixture being spit back out of the carburetor throats then suspect bad reed valves.

A fairly major intake leak that adds excess air to the fuel mixture will also cause your symptoms. One tell tale for that condition is that the engine will backfire at low or idle speeds.

Without being able to see and hear the engine run it's difficult to get more specific than that, but those are two things I'd check out.

[Dinikin]

I would invest $ 7 in a pint of SEAFOAM.
I know it cured few problems with my motors.

[Deanrt]

Sea Foam? Tell me more.