no full power without holding primer in

[scottandrea]

I've been working on a 1994 9.9 hp Johnson with electric start. motor has sat for a few years - finally got it running by cleaning carb. and putting new spark plugs. it runs good and has good compression - holds an idle and even planes my 15 ft. boat off. the problem i am having is that after I have reached wot the motor drops a few hundred rpm and the boat slowly drops off plane. If I tap the primer button on the controls a few times, the motor will pick up speed again only to slow down after a few minutes. Could this be the fuel pump??????? Please help.

 

[Barnacle_Bill]

Re: no full power without holding primer in

Yes it could be the fuel pump.
Since it has sat for a few years there are some other things that is recommended to be done. Rebuild the carbs, replace the impeller and change oil in the lower unit. Check the FAQs for "awakening a sleeping motor" lots of good info there.

 

[HighTrim]

Re: no full power without holding primer in

Sounds like your carbs are starved for fuel. I would rebuild the carbs and do a good decarb. I would invest in a can of seafoam, in a portable tank, mix 3/4 gallons of premix gas, an 3/4 can of seafoam, (assuming you don't have the vro connected). Put the remaining seafoam in a spray bottle, run the motor up to temperture, remove the plugs, one at a time, spray some seafoam into each cylinder and replace plug. let sit 15 minutes, remove the air silencer from the carb while waiting, restart motor, and spray seafoam into each carb, until it start to stall. repeat till seafoam is gone. run out the rest of the gas. it is going to smoke like it is on fire, and drip goo on the ground. replace the plugs with new ones, and then do the compression check again. this procedure burns the carbon out of the motor and been known to free up rings, and increase compression.

 

[iwombat]

Re: no full power without holding primer in

If the primer is perking it up, that means there's fuel being delivered. The primer is delivering more fuel, which means the main jets aren't delivering what they should. You need a carb rebuild.