troubleshooting 30hp 3cyl

[captainbrad]

Original owner 1987 30SH

30HP ob runs well at low speed and throttleup to plane.

At planing speed power is lost off & on from one cylinder. Any faster throttle will cause power to be lost continously.

Compression test, 120 psi on all three cyc.

Carbs have been cleaned in ultra sonic with simple green & dawn soap.
Carbs also soaked in MEK solvent.
Carbs blown out with compressed air.
New carb kit installed.

Gas changed out twice in 6 gal tank.
Gas connections ok.

Need suggestions.

[mitch]

check your fuel pump for hole in diaphragm as it only works on one crankcase

[captainbrad]

Thanks for the input. Inspected fuel pump diaphragm, found stretched, did not see any visible holes or tears. Will replace with new parts anyway.

[captainbrad]

Installed new fuel pump diaphram and gasket.

Still having the same issues with the motor. Fuel bulb is staying primed during operation.

Still troubleshooting and looking for suggestions.

[99yam40]

Are you loosing spark on one or more cylinders?
Check output of the cdi to all 3 coils with the proper peak reading voltmeter or DVA adapter and regular meter to see if they are staying in spec. at problem RPM and then check the inputs to CDI if you see a problem with the outputs
You might try first with a timing light hooked to the different plug wires to see if you are loosing spark to the plugs at problem RPM.
Have you checked or changed the sparkplugs? Have you tested and inspected the coils.

If all cylinders have good compression and good spark at problem RPM, make sure the timing is where it is suppose to be.
You could try spaying some fuel/oil mix into the different carbs while problem is occurring to see if that will bring the dropping cylinder back.
Too much or too little will make a cylinder not fire properly

My C40 had a high RPM cylinder dropping problem when I first got it,and it turned out to be a previous owner drilled out the main jets to get more fuel I guess. Problem went away after I replaced the jets back to factory ones.

[captainbrad]

Thanks for the information 99YAM40.

Will be a couple a few days before I can run some of the tests, will post what I come up with.

[WET-BOX-MARINE]

did you sync the carbs?
did try pumping the fuel bulb when dying
did you use a different gas tank"?

[captainbrad]

Finially fixed the problem. It was a bad coil on the number 2 cylinder. Old coil ran ok at low speed and manfunctioned at mid & high end.

Motor runs like new once coil was replaced.

Thanks for the help.