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1984 75 HP strange problem

C

cbrooke

New member
I would like some help with this absolutely strange problem I have with my 75 hp . When I start up and have a load on I can only get about 1100 to 1500 RPM and speed is under 10 MPH. If I advance it she bogs down and stalls out. However if I let her warm up for about a half hour she suddenly comes back to life Im upwards of 4000 RPM and 35 MPH. If I shut down for time enough for her to get cold again, blam same problem, give it about a half hour she warms up and shes good to go again. Carbs are fine good spark changed plugs and filters, new gas. Still same problem. Any ideas out there ??? I was thinking possible coil problem ??? how about thermostats ??? Its the strangest thing please let me know what you think and if you have ever seen or heard of this before, again as soon as she warm its like there is no longer a problem. It takes about 25 mins to get from my launch to the open bay and you have to go low and slow at 5 MPH that's how I found out about this strange issue and the time issue . Thanks
 
Do a spark intensity check.--A good ignition system can jump a gap of 7/16" on all 4 cylinders.----A must do test.--------Check / inspect fuel pump as well.------------You must make sure that there is no blockage in the carburetors as a fuel restriction also means less oil is going into the motor.
 
Ty I saw spark but I will do the test. I didn't see a problem with the fuel pump and when she gets just about warm enough you can feel the surge. If there was a fuel restriction there would be a continuous restriction. This problem seems to have a relation between time and or temp. I had thought possible stator or box problem but again there would be a continuous problem and not this somewhat intermittent problem, that is once its warmed up problem goes away.
 
I had thought possible stator or box problem but again there would be a continuous problem and not this somewhat intermittent problem, that is once its warmed up problem goes away.
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It sounds like there is a hairline crack in either the stator or box where the circuit is open unti heat expands the defective part enough to close the gap. Just a theory.
 
guyjg said:
It sounds like there is a hairline crack in either the stator or box where the circuit is open unti heat expands the defective part enough to close the gap. Just a theory.
Click to expand...
Ok is there any wAy to test out the parts? The box is easy to get to the stator is a pain
 
A visiual inspection of the stator and trigger is done first of all. Attach an ohmmeter to the output leads on the stator then do the trigger and apply heat to the coils w/a heatgun or hairdryer until the ohm reading jumps to infinity or open circuit. Not much testing you can do w/the box.
 
Can this be done with out a load on the engine? When the boat is out of the water there is no problem getting the RPMs. The only time there is a problem is when there is a load on such as the boat is in the water. And thanks to everyone with all the advice :)
 
Before doing all that, back the idle mixture screws out (CCW) about 1/2 turn and see if that cures it.

Jeff
 
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