Yamaha 90ph max out at 4500 rpm

[Joeyjoe]

I have a 2002 yamaha 90hp. It is on a 17' sylvan boat.
I can only get the rpms up to max 4500. BUT if i spray in some carb cleaner i can get it up to about 5100 rpm for the durration of my trip, on shutdown/restart im back to 4500 max.

I have tried new plugs with the same results. I do wounder about the prop, but I am unable to find a site that will tell me what the orginal one is suppose to be.

I also have some slight surging when im slowing down. Someone say it might be the floater, but I have yet to purchase a repair manual to figure this out.

Any suggestions would be great.

Thanks
Joe

 

[Ray Neudecker]

Re: Yamaha 90ph max out at 4500 rpm

Definitely have the signs of a fuel retriction. Carbs and fuel pumps are logical sources of the problem.

 

[Redneck Yacht Club]

Re: Yamaha 90ph max out at 4500 rpm

WOT specs=4500-5500 rpms
Ok, what rpm did it run at before problem?
Is the the fuel old?
Did ya drain the float bowls, any signs of water?
Did ya try pulling spark plugs wires off went it was running?
Did ya check compression?
What do the plugs look like?

 

[Joeyjoe]

Re: Yamaha 90ph max out at 4500 rpm

WOT specs=4500-5500 rpms
Ok, what rpm did it run at before problem?
picked up the boat used. 4500 was all i was getting before

Is the the fuel old?
nope, drained the tank before winter and have been using fuel stablizer

Did ya drain the float bowls, any signs of water?
for thte carbs? sorry this is my first boat. Stil waiting on the manual to come in. I drained the resivor under each carb and no sign of water there.


Did ya try pulling spark plugs wires off went it was running?
Nope didnt try that yet. I will check for a good spark at night when im back at the cottage this weekend.

Did ya check compression?
Dont have the specs on what the compression is to be. But i can check to see if they are at least close to the same.


What do the plugs look like?

New plugs gapped at .039 thou. They are NKGs, but i think i should try the champions to see if the problem happens

Thanks for the tips.
Anyone know what the coil packs resistance should be?? i can check those as well.

Joe

 

[Joeyjoe]

Re: Yamaha 90ph max out at 4500 rpm

Definitely have the signs of a fuel retriction. Carbs and fuel pumps are logical sources of the problem.

The fuel filter looked clean, but i get a new one. As for the pump, ill have to find out what the OEM one is rated for. I have to get a guage to put in line to check it.

thks

Joe

 

[Redneck Yacht Club]

Re: Yamaha 90ph max out at 4500 rpm

coils= 4.1 ohms
CDI output= 130 volts loaded=peak at 155@1500rpms
Try the primer bulb when running, see if it picks up rpms.
Compression is anything over 100 psi should be good.
Any fuel spiting out of the carbs when running?
Spark plug types are NGK B8Hs-10 and the Champs are L78C
They work better on the NGK's,in my opinnion
It might be proped wrong too, if all cyclinders are working good.

 

[Joeyjoe]

Re: Yamaha 90ph max out at 4500 rpm

Update.

I added seafom to the gas tank and ran a ful tank, re-cleaned out the carbs with deep-creap (seafoam). Use fuel stablizer now all the time. Fast out of the hole and gps mph is around 32-34.

I get a constant 5100 rpm now. Compression is 115 across the board. Solid spark (check at night time). Nice clean blue color.

Ball keeps hard during operation. Current prop is 13.5 x 15. Recommended is a 17" pitch, but I am unable to find a 13.5" dia (only 13" and 13 7/8 available). I might be able to fit a 13 7/8, but it will be close. But since I am only getting 5100rpm, if i got to a 17" pitch i will be dropping RPM.

I have been trying to find a service manual, but there is so many out there I am not sure which one to get. I will visit my local yammy dealer this week to see what they recommend.

One question. There are 2 adjustment screws on the engine throttle arms. In the netural position the throttle rests on one and when i enguage the motor in the forward position it hits the second screw about a 1/4-1/2 of the throttle position, then from there (fully depressing the throttle arm) will only open the carb butterflys to max. So what are these adjustment screws used for? I also noticed that my RPM at idle will not go under 1000rpm (even after warmup). Adjusting the carbs does not do anything.

Thanks

Joe

 

[Ray Neudecker]

Re: Yamaha 90ph max out at 4500 rpm

Those are the timing stops. About 1000 rpms is right for out of gear idle on those models. Adjustment of the stop at idle can be used to lower the idle by reducing the timing. Investment in a Factory service manual would be a good idea before adjusting the timing.