Engine Surges...?

kjprag01

Seaman Apprentice
Joined
Jun 26, 2017
Messages
31
The engine is a 92-94 Force 40 2stroke single carb, the model and serial numbers are missing. Im working on the idle speed and have come across an issue that im sure has been discussed but I don't think im using the right search vocabulary. When the engine is in neutral, jumping between 750-1000rpms, and i shift it into forward gear or reverse gear the engine will remain in the idle speed range, (there is a miss fire or pre detonation which i am chasing down) but when i shift back into neutral the engine roars upto 2500-3000+ rpms with no signs its going to drop down. Also when in idle the engine will randomly surge to a pretty high rpm. What could possibly be causing that issue? I figure before i dig to deep into the misfire or pre det. I should figure that out. My service manual reading is leading me to think its the carburetor, but if thats not broken i don't want to fix it.
 

foodfisher

Captain
Joined
Feb 18, 2009
Messages
3,756
Avoiding the carb- Timing, sheared flywheel key/loose locknut on tower/broken linkage. Fuel, fuel pump diaphram damaged. ??
 

kjprag01

Seaman Apprentice
Joined
Jun 26, 2017
Messages
31
alright i will avoid the carb, the fuel did have ethanol (E10). Its what I could find where i was at, I flushed that sludge out and got some pure gas at my usual place. I did replace the flywheel key recently, and I double checked the torque this evening. It's solid. It is a rebuild project and will check the timing tomorrow. It will be a static timing procedure. But Im pretty sure the voltage regulator is shot(no bid deal). Im almost possitve the time is off slightly. Thank you for the other ideas and the nudge in a different direction.
 

jerryjerry05

Supreme Mariner
Joined
May 7, 2008
Messages
17,923
The timing being off shouldn't cause it to surge.
​That sounds like it's sucking air somewhere??
​Or the fuel system needs work.
​Float set right,, air screw, diaphragm.

​Start the motor, spray starting fluid around the bae of the intake and the rest of the motor.
​If it makes any difference?? then fix the leak.

The throttle cable? when attached to the block, it should have a bit of tension when the connector is slipped over the ball.
 

kjprag01

Seaman Apprentice
Joined
Jun 26, 2017
Messages
31
Thank you Jerry Jerry and food fisher, Fuel system will be tomorrow, I will report back with my findings. . . I don't have enough beer to fiddle this evening. . . Also on a personal note. The timing situation, The set up is: engine on land in a trash can, filled with water, prop is on, using the starting motor to crank the engine over, full battery, I also have 2 other batteries that I swaped around for the test. . . (so full battery was guaranteed), Plugs removed, and plug wires grounded out. The Timing light is set on 0. My timing reads 0 in neutral with the carb Closed and 28 at WOT(still not in gear). Those readings are at the Zero line on the timing sticker. and I did notice a brown sludge like substance running down the mid section of the motor from under the lower cowl section. . . Im almost to my wits end and see a real marine mechanic in my future and that wallet imploding.
 
Top