89' Yamaha ProV 150 issues: loss of power/speed

BuckTroop

Cadet
Joined
Jul 27, 2009
Messages
12
Hey guys 1st post. I've had this motor/boat for 2 seasons now and it has run great. That is until the last time out. I was out for my Tuesday evening bass league and went to take off for my first fishing spot and the holeshot was not there followed by an extreme lack of speed. Normally runs around 55-60 mph @ 5000 rpms maybe more and this time I could only manage around 35-40mph @ 4300 rpms. It didnt even sound right. I could here a humming noise like a piston wasn't firing. Finished the night with 4 fish and 3rd place finish. Problem is I checked spark plugs and 5 of the six seemed normal maybe a little oily with one that had almost no oil on it and what looked like little peices (small round bits) of metal around the inside of the spark plug. I am suspecting that the oil injector quit on me in that particular cylinder. On top of that i looked for other causes that may have caused a slower speed like a lower unit malfunction. Drained the lower unit oil and it was the dreaded milky color. Hoping that i didn't neglect it for too long and caused it to semi-cease. Anyways i changed the lower unit oil and replaced the bad plug(only thing i could think to do with resources and time i had before my next tournament) and nothing has changed. Still slow and now power. Can only reach 4300 rpms when normal is 5000. I realize running it like that was stupid but it was our league championship. So all that for 3 questions.
1. If indeed the piston and rings in that 1 cylinder did go kaput am I at a total loss or can the rings/piston be replaced in just that cylinder?
2. If water was leaking into the lower unit (couldnt have been for long i checked it recently) could it have made the motor work harder thus leading to slower speeds?
3. Should i be able to turn the prop in gear with the motor off and forward engaged because i cannot?

Sorry guys. I know this long. Any feedback would be greatly appreciated. Love fishing and not real wealthy so this sets me back big time. Got all winter now so hopefully it doesn't cost me an arm and a leg but fearing it will.
 
Joined
Nov 7, 2010
Messages
56
Re: 89' Yamaha ProV 150 issues: loss of power/speed

looking from the back was it the bootom left?? the dry one. yes you can replace one. unless the bottom is seriously corrup it shouldnt slow things. should not be able to turn it in gear.
 

99yam40

Fleet Admiral
Joined
Sep 7, 2008
Messages
9,195
Re: 89' Yamaha ProV 150 issues: loss of power/speed

test compression, my guess is you have messed up a piston and cylinder. How bad who knows until it is taken apart to see what has happened. Probably lean on fuel not oil as oil problems usually get bearings and crank first
 
Joined
Nov 7, 2010
Messages
56
Re: 89' Yamaha ProV 150 issues: loss of power/speed

i dont like the humming noise. i hope it is the piston, not the rod bearing. crank if you can find one i 15-2500$. if that lower left is dry, sounds like arod bearing to me. i hope i'm wrong.
 

BuckTroop

Cadet
Joined
Jul 27, 2009
Messages
12
Re: 89' Yamaha ProV 150 issues: loss of power/speed

Hey guys thanks for the replies. It is not the bottom left one looking from behind the outboard. It happens to be the top left one. I will try a compression check. I didnt think that i should be able to turn the prop in gear. It didnt make any sense to me but outboards are new to me and some older fella told me that it should spin. On the compression check, just pull one plug out insert the compression gauge and crank a couple times?
 

99yam40

Fleet Admiral
Joined
Sep 7, 2008
Messages
9,195
Re: 89' Yamaha ProV 150 issues: loss of power/speed

Pull the kill lanyard to keep things from sparking, pull all plugs, open throttle plate so it can get some air, insert compression gauge into one at a time and spin over till gauge will not go higher( few seconds).

Metal on the plug does not sound good
 
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