lost power

[Bogged]

I bought a new prop for my 80hp mercury took it out on the lake today engine ran fine for 20mins or so then i heard it sputter after that it wont build R.P.M.s dont know
a lot about boat engines any suggestions on what could be the problem would be helpful. the motor is an early 70s 2 stroke thunderbolt. it idles and will reach 4000 rpms in nutruel
but wont go more than 3000 in drive. the rpms used to go to 6500 or better.

 

[RaScLeS]

Re: lost power

sweet man you had a early 70';s motor wind out that high without blowing and even in neutral what a tank! hahaha, check spark then clean the carbs after checking compression. THEN make a video of 6500+ rpm what is the pitch and boat size?

 

[achris]

Re: lost power

Was the new prop the same pitch and diameter as the old one? If the new prop was higher in pitch you may have destroyed a piston, hence the loss of power... Tear down and rebuild...

 

[aussieflash]

Re: lost power

Normally I would say check your stator and spark,but after your description I would check your piston isn't hanging out the top of your cowling.

 

[Bogged]

Re: lost power

sweet man you had a early 70';s motor wind out that high without blowing and even in neutral what a tank! hahaha, check spark then clean the carbs after checking compression. THEN make a video of 6500+ rpm what is the pitch and boat size?

Thanks for the info turns out it fouled the plugs engine running fine again and headed back out on the lake since i dont know that much about it maybe you could tell me what would be consitered normal operating rpms for this motor sounds like ive been pushing a bit hard and dont want to destroy it the old prop was a 17 pitch the new prop is a 13-1/2 x 23 is that to much? the boat is a 16' tri-haul 1972 hurricane