1989 3cyl 90hp merc runs wierd

[bruce7872]

this motor will usually start pretty well but will idle with only 2 or the 3 cylinders running. If I use the fast idle it sounds good and will go all the way up the tach but as soon as it's put into gear it will go back to 2 cylinders and only get up to 2500 rpms WOT. Every once in awhile you can hear the 3rd cylinder trying to fire up. After it gets good and warmed up and you keep hitting the throttle finally it will fire up on all three and run great but for a dead spot when throttling up at the very beginning of the throttle range. I've had all my carbs out and cleaned them, I've went by the manual and seated the air mixture screws and backed them out 1 1/2 turns and then leaned them out but the one thing that seemed to help is to richen them up alittle instead. That helps the dead spot anyway. I'm really hating this motor. I can't get rid of the miss and now today my power trim quite on me with the motor all the was down cause that's the only way it would go.

 

[emckelvy]

Re: 1989 3cyl 90hp merc runs wierd

Is the compression good on that cyl?<br /><br />Tried changing spark plugs?<br /><br />Put an inductive timing lite on the "bad" cyl and see if it's sparking. If so, may you have other internal problems or fuel problems.<br /><br />Check all the elect. ign wiring for loose conn's.<br /><br />Also a very simple thing to troubleshoot would be the coils, if you find it's a spark thing you could swap coils and see if the problem stays on the same cyl, or follows the coil.<br /><br />Not sure if a bad power pack (ign box) could cause lack of spark on one cyl but I suppose it's possible. Usually it doesn't come back, though. If you take the coil off, inspect it carefully for cracks.<br /><br />HTH and let us know if you figure it out........ed

 

[bruce7872]

Re: 1989 3cyl 90hp merc runs wierd

haven't figured it out yet but I did find that I had two cracks in two different oil injector lines. will see if that changes anything after I replace them. sorry its taken so long for me to respond to your suggestions but I have alot of other things to do also and not much money to go around with repairing a house and motorcycle too!

 

[bruce7872]

Re: 1989 3cyl 90hp merc runs wierd

Well, I hope this is not premature but I replaced all the oil injection lines from the tank to the fuel pump. Took the boat out and it started and ran like a new boat right off the bat and not a problem with it all day long! You'd think a lack of oil would just burn the cylinders up but everything seems to be working great.

 

[bruce7872]

Re: 1989 3cyl 90hp merc runs wierd

Well, I'm learning about what everybody has been saying about boating means. It's a big hole in the water to throw your money in! It seems to be alot like biking....if there's something wrong don't waste time with the little inexpensive stuff, just go right to the most expensive fix and that will take care of it. I've been trying to fix a missing cylinder for quite sometime trying all the litttle inexpensive fixes but I finally broke down and replaced my switchbox for $200+ and that was the problem all along. I could have saved probably that much with other parts and my labor if I'd have just got that part right off the bat. For alittle humor...I've also learned to pick up my motor before I pull my trailor up the ramp, put my plug in before I put the boat in and my most recent lesson...take my key with me when I'm planning on shoving my boat off the trailor into the river. That was a wet lesson there!!

 

[ronmold]

Re: 1989 3cyl 90hp merc runs wierd

I've found aftermarket ign. / elect parts from CDI/Rapair work better and are cheaper then merc.