1971 Johson 100 hp loses power

[keith brown]

My 100 hp 1971 starts and then has great power for about one minute. It then loses 80% of power, it does not smoke, or vibrate, just acts like the throttle was backed down. I have changed the fuel pump, primer bulb, put a temporary fuel tank and gas line to motor and it still does the same thing. Any thoughts?

[lk2ds0n]

At this point I'd probably replace the fuel filter for no other reason that to say I tried it.

[beachmech]

same problem with 1976 70hp johnson

My 100 hp 1971 starts and then has great power for about one minute. It then loses 80% of power, it does not smoke, or vibrate, just acts like the throttle was backed down. I have changed the fuel pump, primer bulb, put a temporary fuel tank and gas line to motor and it still does the same thing. Any thoughts?

I have the same problem with my 1976 johnson 70 hp runs at wide open for a minute then its like somebody yanked off the fuel line. I replaced all lines rebuilt carbs new fuel tank, new fuel lines, new fuel filter. I ordered a new fuel pump. Also if anybody knows how that crankcase recirculation system works on those would be great. I have one hose that goes from the bottom of the silencer cover to the the motor. Is this an oil drain back to crancase? Is there suppose to be a checkvalve in there somewhere cause i can blow through both ways but on the parts diagram doesn't show one. When my engine stalls theres a little bit of oil under carbs could this be coming from the crankcase and choking the engine because the checkvalve doesn't work? Or if its suppose to be in the hose I changed it awhile back cause it was cracked and i didn't check to see if it had a one way check valve in it.