1988 Force 15HP Loss of Power - Runs ok in the tank

[karvin]

I've been chasing down a loss of power problem at WOT and am still stumped. Symptoms: At WOT on the water under load it seems to be running on 1 cylinder in terms of power. Motor sounds fine but just is bogged down. It seems to run fine at in the test tank in gear WOT.I've checked the fuel pump and it seemed ok and put clear hose from fuel pump to the carb and no air seems to be getting sucked in. I have not put in a new fuel pump diaphragm yet, that is on order even though the old one seems fine. I cleaned out the filter on the fuel pump and thought that was the problem but it wasn't.The top cylinder, it's a two cylinder is running hot according to the plug and bottom one burns ok. This concerns me. Is it a fuel problem of not enough fuel getting to the top cylinder but the bottom one by virtue of gravity gets enough?Carb was suposedly cleaned recently by the mechanic but maybe this is still a problem in fuel delivery.Motor seems to pee ok but I'm checking the water pump tomorrow.Another thing I noticed at WOT under load on the water is the lower exhaust seems to shoot out a lot of air on top of the prop on the lower exhaust seeming like it causes cavitation which I don't recall if it did this before it started having trouble but an underwater stream of shooting bubble seemed a bit extreme.There's the bloody details...I've posted before on this one before and continue to work through the problem hopfully.I do have an electronic conversion ignition kit on order to help eliminate anything there.

[karvin]

Update - I checked the Water pump and it was in good shape. It was missing a gasket betwwen the back plate and lower unit. From what I can tell there used to be one there originally as I saw left overs. The Clymer manual seems to indicate on the reassmebly this may be optional as it mysteriously says "Install the pump back plate gasket (if used)." I'l order a kit anyway to see if it comes with it.Another thing I found is that the plug that was running hot was not gapped correctly and was way under the .030 recommendations. Would this cause it to run hot and lose power? My local mechanic must have forgot to gap it right, boy am I happy. Also he put in NGK B6HS plugs but when I go to the NGK site and use their part finder it recommends a BP7HS plug so know I wonder why he put the other plugs in.Any ideas on this case?

[steelespike]

Karvin,If you are losing 1 cylinder you would be at less than 1/2 power.Probably wouldnt plane.See if it improves if you hit the choke a little. If the choke helps then you are starving for gas. Could be dirty carb If you had a dirty screen dirt could be in the jets still.