intermittent power 70hp 1976

[Josedcr]

I cant figure this one out. At WOT the motor bogs down. A few months ago the motor was running fine. Then it started to sputter here and there and then it started to drop rpm. Now it starts and does not go past half power, it runs like that for a while and then it jumps back up to full for a few seconds and back down.

It runs great on the hose or dunked. It only does it in the water.

I replaced a coil that was arching. All sparks are good. Compression is 125 psi on all 3 cylinders. Carbs are clean. I ran the motor on the hose at high power and sprayed Sea Foam one carb at a time, the rpm lowered every time (figured they are working). It starts right up and idles great, goes to half power fine.

Any suggestions? Thanks

 

[Gazza 2]

Re: intermittent power 70hp 1976

Jose,I have exactly the same engine,they seem to be fairly bulletproof!I have a similar situation,I give it WOT but seems to lag for a second or two .My motor has two filters,one is a wire mesh screen in the fuel pump itself and the other is a small plastic screw apart type which I dont think is original equipment,anyway it was the small plastic one that was partially clogged allowing enough fuel for muff running or limited throttle running in the water.If not this then check your timing and synch.
Cheers Gazza

 

[SparkieBoat]

Re: intermittent power 70hp 1976

sounds like fuel pump or fuel hose/connector letting in air. try pumping the bulb and see if it gets better.

 

[Josedcr]

Re: intermittent power 70hp 1976

Thanks for the info, Sparkie and Gazza. I have never checked the fuel hose, I'll do that next. Also, is the bulb supposed to stay hard? I remember when I first got the boat, I would pump the bulb a few times and it would get hard, then I would start the motor. Now I squeeze it several times and it stays soft, the motor still starts right away. Is it supposed to stay hard through motor operation? When it comes to timing, I adjusted it a while ago (has not changed) and the motor ran great for a long time. This lack of power issue came out of nowhere, while running full power.

 

[SparkieBoat]

Re: intermittent power 70hp 1976

bulb may be bad, it should not stay hard during operation but should pump up hard before start... just buy a whole new fuel line and fittings, they are known to go bad after a few years and have to be replaced regularly. I have also seen the fitting on the tank go bad also and need to be replaced.