90 HP Force w. o. t. 1/2 power

[rlouns]

I have a 1991 90 HP w/Prestolite ign. It started running crazy. After running for a period of time (different each time) it would go to half throttle on its own (with out moving the throttle lever). I changed plugs and it ran OK for a short time. Then it started all over again. I changed plugs again and nothing happened (by changing plugs I mean I installed brand new plugs - I changes from Champion to NGK). It left me stranded (had to be towed in) taht happened to be the bottom carb flooding out. I cleaned all three carbs took it back out and still only half throttle at w.o.t. When it ran OK it ran at 4300 RPM's (23 mph) at w.o.t. At w.o.t. and runnning at half throttle it runs at 3750 RPM's (less than 10 mph).<br /><br /> Can anyone help. Any and all Ideas appreciated.<br /><br />Robert

 

[sony2001]

Re: 90 HP Force w. o. t. 1/2 power

A few remarks on your short description!<br />If your high wot is 4300 rpm I think you are OVERPROPED. Go down 2".<br />You are carboning up, so DECARBONIZE.<br />Go back to CHAMPION plugs.

 

[rlouns]

Re: 90 HP Force w. o. t. 1/2 power

By go down 2" do you mean from 17 to 15?? It currently has the number 17 on it. No other numbers visible.<br /><br />I bought another boat (24' Pontoon) that has a 1997 (I was told but my book only shows to 1996). It got hot seized up on me before I got 300' at wot. At no wake speed it was pumping a stream of water out the bypass. I do not remember looking once I went to wot. Is it worth working on??<br /><br />Thanks <br />Robert

 

[rlouns]

Re: 90 HP Force w. o. t. 1/2 power

I forgot to mention that the 1991 90 HP is on a 21' Deck boat (fiberglass tryhull type pontoon boat).<br /><br />What should the RPM's be on a 1991 90 HP Force.<br /><br />Robert

 

[sony2001]

Re: 90 HP Force w. o. t. 1/2 power

Robert L 17" is way too large for a 90 hp.<br />On a 21' I would TRY a 13" if necessary to get the rpm's to 5000. That engine is best from 4500 to 5500 rpm.<br />The other engine probably seized from a lack of oil. Soak the cylinders with releaseall and try to get the powerhead to turn over.<br />Both engines are much the same.

 

[rlouns]

Re: 90 HP Force w. o. t. 1/2 power

Thanks. The engine did not stay seized. It cranked and blew steam out the exhaust and bypass hose. I cranked it for short bursts and waited, short crank and wait etc. until it fired. I shut it off immediately and waited and fired it again shut it down and waited. Then I started it and when it was pumping water I started to head back in. The hot horn went off and I shut it down and waited (the horn never went off the first time until the engine quit). I started it up and ran short distances and shut it down until I got back to the dock. It sounded like marbles in a tin can. Do you think it will be OK or is there something that I need to do to it??<br /><br />Robert

 

[rlouns]

Re: 90 HP Force w. o. t. 1/2 power

I found my problem (I hope).<br /><br /> I found a wire broken off at the wiring block. It went to the #2 coil. I found it after I found that #2 was not firing. I did a compression check (top 110 - Middle 115 - bottom 115) so I devised a wire that i could check the firing capability and found #2 dead. I reconected the wire and #2 fires wit no problem. I need to take it out and test it out. I will still need to reprop though. Because before the prob it would only do 4300 RPM's and 23 MPH.<br /><br />Thanks for everyones help. It was greatly appreciated.<br /><br /> P.S. I could not find anything to decarbon the cylinders with. Only one place acted like they new what i wanted but he would not sell it to me. He wanted to work on the motor.

 

[sony2001]

Re: 90 HP Force w. o. t. 1/2 power

Quicksilver Power Tune will do it and raise your compression to boot.<br />Don't breathe it and use older plugs.

 

[rlouns]

Re: 90 HP Force w. o. t. 1/2 power

Thanks Sony

 

[rlouns]

Re: 90 HP Force w. o. t. 1/2 power

I took it out for a test run. I ran it for 1/2 hour and no problems. <br /><br />Thanks all

 

[Fouled Plug]

Re: 90 HP Force w. o. t. 1/2 power

You can decarbonize right from the fuel tank with either Seafoam or Yamaha's Ring Free. It's a painless way to get rid of the gunk.