1988 yamaha 225 cutting out after 4000 rpm

[wwb1969]

i have a 1988 yamaha 225 excel in a 22 foot boston whaler revenge the boat gets right up on plane and then at around 4000-4200 rpms begins to surge.What is happening is that i am getting aeration in the fuel system When this occurs the fuel filter on the motor Starts to aerate with bubbles if i pump the primer bulb manually it gets enough fuel back into the carbs and the boat runs back up to 5200 rpms.I beleive that there is a small leak somewere in a line or fitting from the tank to the motor even though i have no evident fuel leak any ideas on this would be greatly appreciated thanks.

 

[rodbolt]

Re: 1988 yamaha 225 cutting out after 4000 rpm

you either have an air leak, a bad fuel pump or a fuel restriction.
as fuel line vacum increases gasoline can boil at 50*F. use a vacum guage to crefully track back down the system until you either find the leak(0) vacum or the restriction.
any vacum higher than 4"Hg is not acceptable.
Yamaha dealers have a nifty tool called a boat in a box that we can perform all fuel system tests while its on the trailer with the engine off, lessens the risk of lean piston burn.

 

[wwb1969]

Re: 1988 yamaha 225 cutting out after 4000 rpm

thanks for the info i will verify the system vaccum tommorow morning and back track from there the fuel pumps are both new had been running fuel last year with 10% alchohol in it and wasnt aware of the concentration of the gas until i took a fuel sample of it the diaphrams on 20 year old pumps did not like it at all i wouldnt be surprised if it didnt do additional damage on the other lines as they are original.thank you.

 

[Eggo]

Re: 1988 yamaha 225 cutting out after 4000 rpm

Sorry guys I do not wish to hijack this thread, however I am new to message boards and do not know how to start a new one. Would welcome feedback on how to do this.
The reason for my responding to this thread is that I too have a similar problem with a 1988 150 Yamaha. Picked it up from the repairer yesterday fitted with two new fuel pumps, mechanic also fitted an auxilary tank post engine filter (Approx 50mm hose to the tee piece that feeds both pumps. While testing the front carb shroud was removed and six healthy sprays to the carbs at >5000 rpm then the sprays decayed consequently rpm drops. Mechanic removed fuel pump from crankcase while at idle and commented on low crankcase pressure and that this may not be enough to operate the diaphram sufficiently at high demand. Is now suggesting problem may be crankcase sealing rings between 4 & 6 as these are the two cylinders that operate the diaphram pumps (Not sure on the cylinder #'s).
Welcome thoughts comments on both problems.

 

[wwb1969]

Re: 1988 yamaha 225 cutting out after 4000 rpm

its fixed found two problems 1 the vaccum at wot went through the roof removed floor on boat found were the fuel line is routed through a 90 degree conduit that it was collapsing.i smoke tested the remainder of the fuel system up to the carbs and found a small leak at the engine side of the fuel connector.ran back up to 5100 rpms perfect i think that the restriction in the fuel system is was took out the fuel pumps not the alcohol in the fuel as i originally thought.Thanks again for the great advise i tottaly forgot that vaccum and pressure alter the boiling point of fluids wayne.

 

[wwb1969]

Re: 1988 yamaha 225 cutting out after 4000 rpm

heloo there i am by no means an outboard expert but on my snowmobiles if a crank seal is going bad you would nec=ver evn see 3000 rpms much less 5000

Sorry guys I do not wish to hijack this thread, however I am new to message boards and do not know how to start a new one. Would welcome feedback on how to do this.
The reason for my responding to this thread is that I too have a similar problem with a 1988 150 Yamaha. Picked it up from the repairer yesterday fitted with two new fuel pumps, mechanic also fitted an auxilary tank post engine filter (Approx 50mm hose to the tee piece that feeds both pumps. While testing the front carb shroud was removed and six healthy sprays to the carbs at >5000 rpm then the sprays decayed consequently rpm drops. Mechanic removed fuel pump from crankcase while at idle and commented on low crankcase pressure and that this may not be enough to operate the diaphram sufficiently at high demand. Is now suggesting problem may be crankcase sealing rings between 4 & 6 as these are the two cylinders that operate the diaphram pumps (Not sure on the cylinder #'s).
Welcome thoughts comments on both problems.