1971 Johnson 100 hp with power problem

My motor starts fine then within 1 minute at full throttle, while underway, it will lose 80-90% of power, as if it is not getting enough fuel. It does not smoke or vibrate. I have replaced the fuel pump, bypassed the fuel tank and supply line, primer bulb with a temporary tank and line. It still does the same thing. Any ideas?

Re: 1971 Johnson 100 hp with power problem

Did it start doing it suddenly? When was the last time it was running well? Have you done any carb service? Have you done any other adjustments?

Re: 1971 Johnson 100 hp with power problem

Does it idle properly when you pull the throttle back? Sounds like the high speed orifices in the carbs are restricted or plugged.
Normal senerio is the engine starts and idles just fine, bogs or stalls at high speed. If you pull the throttle back quickly, it idles just fine.

Re: 1971 Johnson 100 hp with power problem

check vacumn hose from fuel pump to intake manifold.....disconnect from fuel pump and blow air into hose to clear any obstruction

Re: 1971 Johnson 100 hp with power problem

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Re: 1971 Johnson 100 hp with power problem

When your engine loses power, it may by running on only two cylinders. Possible that one of the two points/condensers quits working after the engine warms up to normal operating temperature. You can check for spark with an inductive timing light. If one of the two points sets quits working, you'll only be running on 2 cyls.

Re: 1971 Johnson 100 hp with power problem

The last time it was running well was 3 weeks ago. I have not done any carb work or other adjustments. Last night I tightened some of the full line connectors. Then I took off the cover for the carb to see if the butterflies were working and to see the gas spray.
Butterflies were fine. The gas spray was intermitent. It was not steady in my opinion, while underway, with throttle wide open.

Re: 1971 Johnson 100 hp with power problem

When you use the term "points/condensers" do you mean "sparkplugs"? Should I just replace the sparkplugs? It does not seem like it is the spark plugs. I pulled them out and checked their spark by turning the motor over while they were hooked up. Also, while underway the engine runs pretty smoothly, just at much lower rpms than it should at full throttle. I would think it would "miss" and vibrate if it was only hitting on half the cylinders.
I did take off the cover for the air intake to watch the butterfly valves and gas spray. The butterfly valves were working but the gas spray did not seem even. All four sprays were equal but they varied greatly and were not steady when the throttle was open. I do not know if it is the rpms that creates the uneven flow of gas or is it the uneven flow of gas that creates the uneven rpms? Could it be the vacuum line from the carb to fuel pump? I put on new clamps on several of the internal gas lines that seemed loose. Still the same problem.

Re: 1971 Johnson 100 hp with power problem

It does idle properly after I pull the throttle back. Then after a minute I can give it full throttle and it will run somewhat well for a few seconds then I lose power again. I did run out of gas one day before the problem first appeared. Maybe I got debris from the tank into the carb? How do I clean out the orifices? Can I do that or do I need a mechanic?