1988 Yamaha 90 hp Trouble

jodee95

Cadet
Joined
Jul 28, 2010
Messages
23
Hello First off Motor was all rebuilt last year new piston rings carbs redone lower unit seals etc New 24 gallon fuel tank mounted on a BW montauk. I enjoyed a trouble free year last year work was completed by a very good local shop. Only used the boat twice this year in the water did not start for two weeks. Started yesterday ran fine stayed in slip and motor ran rough like on two cylinders?? New plugs were installed this year cleaned off drained down carbs thought I may have had some sediment. Ran fine on all 3 cylinders then at idle ran rough an stalled. I always use startron I believe my fuel is fine. I have read about an issue with the spark plug caps coming loose mine are original could this be the issue? I tried to crimp the ends to tighten but that did not work. It appears on this model I can not buy the whole wire? It's part of the coil. I have to buy the caps ends and splice in. I am trying to make sure I dont over look something small because this motor ran so well after the rebuild. Any thoughts. Thank you very much for your input.
 

old evin

Cadet
Joined
Jul 17, 2014
Messages
21
I had same trouble my plug boots when I pulled them off and look in side were rusty and felt loose when connected to plugs. with motor running if I touched the boots I would get shocked. motor didn't sound like it was running right. my coils are the same I had to cut boots off and re boot.also I went to ngk plugsi it didn't run that great. so I went back to champions. with the plug boots and the proper plugs made a big difference.after I rebooted I could touch boots and not get shocked.
 

robert graham

Admiral
Joined
Apr 16, 2009
Messages
6,908
Maybe check your fuel pump for a cracked diaphragm....remove pump with 2 - 10MM hex screws but leave it hooked up with the fuel hoses....pump primer bulb and check for fuel coming out of port hole on back of pump...should be none. New pump is about $50. May also try removing the 3 idle mixture screws, taking note of each set out from lightly seated....spray carb cleaner into each port and replace jets....could be some trash in those jet areas....
 

old evin

Cadet
Joined
Jul 17, 2014
Messages
21
I had same trouble my plug boots when I pulled them off and look in side were rusty and felt loose when connected to plugs. with motor running if I touched the boots I would get shocked. motor didn't sound like it was running right. my coils are the same I had to cut boots off and re boot.also I went to ngk plugsi it didn't run that great. so I went back to champions. with the plug boots and the proper plugs made a big difference.after I rebooted I could touch boots and not get shocked.
 

jodee95

Cadet
Joined
Jul 28, 2010
Messages
23
I am going to go with new spark plug caps but This happen in the slip not moving When I idle the motor down it runs on two cylinders and coughs and dies. The fuel pump is also new with the rebuild. I am wondering if a coil is going bad they are all original I understand when they are on there was out the work intermittently That would explain it happen at low idle. Does anyone know how to test? They are expensive for guess work Thanks All
 
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