Power Surge

[2botes]

Any advise on what would cause a power surge or power fall off @ WOT? This 90TLR was rebuilt now about 1.5 yrs ago & has ~ 110 hrs on it & been running like a champ (Tks in part to some of you folks as I limped along the way of the rebuild!) It has been starting to act up when we go tubing w/ the kids, but not for long. Some info:

Use oil mix now; disconnected the oil pump.
New plugs
New water separator filter
clean fuel filter on motor
always fresh fuel!
Motor mounted on a 22' Crest Family pontoon
Have run Seafoam on previous full tank
Idles @ 850RPM
This screwed up a fishing expedition!!

Wondering if an electrical component is on the verge of faulting. Any help here is, as always, more than appreciated.

Tks in advance.

 

[Scott Danforth]

not enough information to even guess. kind of like shooting in the dark while blindfolded

what are the symptoms?

power surge, such as an actual power and RPM surge is most likely fuel related

power falling off at WOT as you are moving along is most likely fuel related, or specifically, running out of fuel to the motor

your issues could be anti-siphon valve, poor fuel quality, crud in the fuel, plugged carbs, air leaking into fuel line, etc.

 

[2botes]

OK, fair enough. Motor runs good under 4K RPM; once up to WOT (~5600 RPM) it looses power...doesn't die, just backs off. Once under 4K RPM again, all is good. Now, as mentioned above, when I rebuilt this, new fuel lines, including primer bulb, were installed including the lines to the carbs from the pump. A water/fuel separator was installed, onboard filter cleaned...the pump was not overhauled, nor was the tank flushed. Since it runs good under the 4K RPM, I'm inclined to look more toward the pump or the anti-siphon valve as Dan suggests. Another factor here, again, is that I mix the oil & fuel & have disabled the oil pump; this was due to the #3 cylinder NOT getting sufficient lubrication causing the rebuild. That said, could the mixture be causing this in some way?

Will look into a new pump / anti-siphon valve this week.

Thoughts?

 

[Scott Danforth]

you may be running out of fuel and running lean which is bad for the motor

you may want to check fuel system restriction. it sounds like you have a series of filters in-line. should only need the fuel-water separator and the inlet fitting screen

 

[99yam40]

what made you think #3 failed due to lack of oil?
gear driven pumps do not normally fail much less cause a problem on only 1 cylinder.
normal failure on one cylinder is running lean on fuel and overheating of that piston

 

[2botes]

The only filters are the onboard aand the separaator.

I also have aa 1987 70ETLH. that had the #3 cylinder failure as this 90; Wdvise from some was to convert to the mix. Recent compression check shows all good. I know other posts read that pumps rarely fail, I just decided to go old school.

Will continue the troubleshooting when i return to the lakehouse this w/e. Tks for the input.

 

[2botes]

Latest on this......looked @ the hose nipple / fuel pick up tube in tank...no anti-siphon valve present..(when did these begin to appear?) Changed out the fuel pump...all is good..in fact it found another 200 RPM!
Had another more knowledgeable than I adjust carbs; motor runs much smoother.

Tks again to all.