1988 90hp yamaha won't go to full power

[<jneb1430@aol.com>]

My 1988 90 hp Yamaha intermittently backs off to about half power. On my last trip, on the way home it stayed on half power. Any theories//
Thanks Jim

[<dsw@by-the-sea.com>]

Tough to tell without more info - but one item to check iswater in the gas...I experienced this problem and it cut the power way back - even needed to choke it a bit to get to half power.

[<Jstenf>]

Had the same problem with a 1989 70hp. The problem was water and dirt in the carbs. If you don't want to rebuild them, which is easy, just take them off and take the bowls off to drain the gung out. You really don't need a gasket set because it's a rubber o-ring around the bowl. After that I installed a Racor fuel/water seperator and no more problems.

[<jeff25@verizon.net>]

I have a 90 HP with the same type of problem.I get the boat up on plane and it goes back down to half throttle.I had taken mine to a repair shop and they took a fuel sample and cleaned the carbs and it still does it.I then brought it back and they said it is probably then the ignition madule getting hot and causing the problem.Maybee this will fix it maybee not but im going to give it a shot.Email me if you try this and i will let you know.Jeff

i have a 1992 25hp and i am having the same problem. i have had the carbs re-built, all the fuel lines and filter have been replaced. i decided to pull the spark plug wires while running the engine. when i pulled the #1 coil the engine continued to run, i then put it back on its spark plug. then i pulled the #2 coil and the engine quit. i repeated this several times and the results where consistant. This led me to believe that possibly the #1 coil pack could be faulty, so i swapped the #1 and #2 coil packs and repeated the same process. mysteriously the engine did not quite with either one of the plugs pulled. i swapped the coil packs back to their original positions and i could not reduplicate the gripe. Am I on to something here??

Hi,
Just had a similar problem with a Yamaha 100. Does the engine pick up if you prime the fuel bulb?
If so try using a remote tank directly to the fuel filter to rule out any problems with the boats fuel system. I was still having problems with the remote tank fitted, so I removed the carbs and each carb had a small filter inside each fuel inlet pipe, some of these were partialy blocked.
Might be worth you checking these first before wasting money paying Yamaha dealer rates for repair.

The engine does not pick up when i prime the bulb. what does it mean when the engine quits running when one of the plugs wire is pulled? thanks.

today i fixed the problem. The faulty carburator had a particle stuck in its main nozzle. after removing it and cleaning out that carburator the engine ran great. The mechs who claimed to have re-built these carbs a few weeks ago should rott in hell!