YAMAHA 90 loss of power

[gaylejan]

i have a 1998 yamaha 90 hp 3 carb setup. i just bought the boat and it would only get to 4500rpm. i was told that it shuld get close to 5500rpm. i changed from a 19pitch to 17 pitch prop. now it will get 5000rpm and run 36 miles per hour . this is on a 17.2 foot keywest at aprox 1150 pounds i believe it should run faster about 42. my question is with it ideling at 1000rpm i can pull the sparkpulg wires off one at a time and the top and bottom cylender will cause a rough ideal. the center causes almost no change at all. i do have plenty of spark and did change pulg. but it stayed the same. if it had a bad cylender would it achieve 5000 rpm . and i also herd that i may not be able to hear or see a rough ideal with the center plug wire off. have any of you got any ideas for me or does it sound like it is ok. thanks much ..gayle

 

[JB]

Re: YAMAHA 90 loss of power

Hi, Gaylejan.<br /><br />Welcome to the board.<br /><br />While it is possible that your middle cylinder is making power, I doubt that it is making much.<br /><br />You need to do a compression check and confirm that your carbs are synchronized properly.<br /><br />If both check out okay, confirm that the center plug wire will make a 1/2" to 3/4" arc to the block. If that checks okay try spraying a bit of fuel mix into the center carb and see if the idle picks up. If it does, overhaul your center carb.<br /><br />If it comes to that, you might as well do all three.<br /><br />Be sure to get and follow a Repair Manual before you start taking anything apart or synching your carbs.<br /><br />I hope you didn't dispose of the 19" prop. You may need it again.<br /><br />Let us know your results. Good luck.