1980 70hp Evinrude Rough Idle

Compression checks normal and

Compression checks normal and the carbs have been gone through by two dealers and an individual. Jets have been replaced to factory specs and are new. The engine still runs rough in idle.It is fine at higher speeds. It does take awhile to get to full power but I have a heavy boat. It is stronger at idle in the shop when hooked up to a hose than it is in the water. It does not stall out. Could you help?

"Gil.... The power out of the

"Gil.... The power out of the hole could be helped by using a propeller that has a lower pitch which will increase thrust.

Assuming that the compression, spark, carburetors are as they should be.... possibly the linkages between the carbs are slightly off, holding one throttle plate slightly open? Check to see that they open and close, and hit full throttle (throttle plate horizontal) at exactly the same time.

Another possibility is that the idle rpm is too low. A 20" shaft engine, on a hose (flushette) should idle at 1000 rpm, a 25" shaft engine should idle at 1200 rpm.

S/plugs should be Champion QL77JC4 plugs, gap set at .040 .

Joe "

" The first thing that people

" The first thing that people look at is "it must be the carburetors". Check compression, check the spark and see that each cylinder will jump a gap of 7/16". Crankcase compression is a different matter and requires a healthy dose of experience to diagnose. Bad bearings will tend to wipe out the " labyrinth " seals on the block resulting in a loss of compression and poor idling.Check the fuel pump diaphragm for a leak.Inspect reed valves for dirt (leaves , small screws ) that might be holding one open. "

" Forgot to mention a thermost

" Forgot to mention a thermostat and poppit valves at the top of the cylinder head. Are these parts there and in good working order, to allow the motor to run at the correct temperature. "

Thanks again to you both.

Thanks again to you both.