Evinrude 140 hp Year 1990 will not run properly between 3100 and 3500 rpm?

Question

The motor runs fine upto 3100 revs and from 3500 onwards, but trying to cruise in between was not possible. Took it to a OMC mechanic as I thought it was a carburettor/fuel problem. Carbies and timing checked then took boat for a test run with Mechanic on board. He was able to get the revs to sit within the range but the motor started to run on 3 cylinders therefore he said it was an electrical problem which would be hard to diagnose other than trial and error with replacing electrical parts. He also noticed that after starting from cold the motor went into fast start mode after a couple of minutes then back to normal after a minute. I hope some one may have an answer as my son skis at 3300 rpm. Thanks

Answer 1

trial and error repairing means I dont have a clue dont do this. you can easily check if it is spark or fuel. run the motor where the problem occurs and then push in on the primer(choke) and see if the motor picks up or smoothes out. if it does you have a fuel problem(this can be a gasket leak also) to check the ign place a inductive pickup timeing light on one of the spark plug wires and run until the problem occurs shine the light at your face and watch the light(ign flashes) if it is flashing steadily and not intermitent then that cyl is running finr(ign wise that is) do this for the rest of the cyls and you will see if any ign misses are hapening. I would guess(I am not looking at engine) that it is fuel related. it sounds like you have an intermediate jet and or high speed jet partially plugged. you should also look at the gaskets on the carbs especially where they cover the fuel passages and make sure they are not swelled from alcohol from gas. there was a service bulliten talking about this problem as the gaskets would swell in alc. fuel and partially obscure the passages. it is also very very important on those minlon carbs that proper torque be applied to the screws as dammage may result. the float level is also critical on that engine. as far as quick start is concerned it is a function of time and temp. if your engine is cold it will stay iin quick start until the temp sensor tells the pwr pack to go to normal ign timeing. when the engine is warm and you start the engine it will still go into quick start for approx 15-25 seconds. if the thermostat is sticky or faulty you can see how it will affect quick start. ps the synchronization and linkage adjustments MUST be performed correctly to get the proper operation this is the most overlooked things even seasoned mechanics forget about

Answer 2

is it the bottom cylinder not running right,if so it's probably the crankshaft oil seal.

Answer 3

have another mech. check out the carbs, i have had a similar problem w/ my 140, after the second mech. rebuilt and sync. the carbs all was fine. check yourself for elect. problems(old wires, cracked coils, etc.) it can get real expensive having them trial and error.