TOPIC: Please Diagnose This

1975 70 HP Johnson

I started having some power issues with the motor randomly losing power. I drained the gas, rebuilt the carbs, replaced the gaskets, and replaced the spark plugs. I also filled it up with high octane fuel and added a fuel system cleaner. I took it out for the first time since the work and it did well on the long run to the cove save on moment where the motor lost power but recovered. After several hours of floating we headed back. The motor started fine but lost power at full throttle. At 75% throttle it could get on plane but barely and at 50% max speed. I would like to rectify the problem myself, but at this point I am at a loss as to what else could be wrong. Any suggestions?

It isn't running on all three cylinders. If you did the carburetors correctly, it is one (or more) of the following:
Ignition system
Spark plug (s)
Water getting into cylinder (s)

I may have fixed it. I had to replace the middle carb fuel line that comes off a T. I think I cut it a little too long and it had a kink. If I understand this motors carb set up correctly that would explain why it functioned fine at low speed and failed when the upper carbs came into play. I will find out tomorrow.

Each carburetor feeds one cylinder directly behind it !!---Air that goes into the bottom carburetor does not get anywhere near the top cylinder.

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A restriction in fuel supply to one carburetor means that it would starve one cylinder at full throttle.---That is a bad thing as no fuel also means LITTLE OR NO OIL as well.

"Have you checked the tires for the proper inflation? Might be the wheelbase." - W. C. Fields