90 hp yamaha 2 stroke need help with wot!!??

[robert graham]

Re: 90 hp yamaha 2 stroke need help with wot!!??

Any final resolution to the cause of this WOT RPM issue?

 

[THE OPERATOR]

Re: 90 hp yamaha 2 stroke need help with wot!!??

ok I put a new fuel pump in and all new plugs and took the carbs completly apart soaked them and reassembled set them to spec put them back on the motor. when I went to restart the motor it caughed really hard and wouldn't stay running at idle I faught it for a few mins. Then I went back and started checking everything again. Compression test again @ 105 psi on all cylnds, spark test on all three coils with spark tester @ 7/16 gap good blue spark, sync all three carbs and set idle screw to 1 1/2 turns out, set all lengths of linkage to spec. tried starting again same result motor caughed and sneezed real rough. walked away for a little while then came back and tested the brand new spark plugs AND WOW ONE OF THE NEW PLUGS WAS BAD WOULD NOT FIRE AT ALL. went and bought another new one and then tried again. the motor started up and ran alot smoother. set the idle timming to 8 degrees ATDC, then set the WOT

 

[THE OPERATOR]

Re: 90 hp yamaha 2 stroke need help with wot!!??

Set the WOT timming to 22 DEGREES BTDC. Took the boat to the lake and tried again was only able to get 2900 to 3000 rpm and finally got the boat up on plane but still not able to get WOT of 5000 rpm plus. I am thinking that when I was trying to start and run the motor when I had the bad plug and It caughed and sneezed that I may have blown out the diaphram in the new fuel pump and may have to replace the diaphrame in it. if anybody has any other suggestions please let me know as I will not be back home untill thur. night I work out of town during the week. AND A LESSON LEARNED THAT EVERYBODY NEEDS TO KEEP IN THE BACK OF THEIR HEADS IS JUST BECAUSE A PART IS NEW DOSEN'T MEAN IT WILL ALWAYS WORK. ALWAYS CHECK THEM OUT!!!!!!.

 

[jeffersondodson561]

Re: 90 hp yamaha 2 stroke need help with wot!!??

What is the max HP rating on your boat placard?

 

[THE OPERATOR]

Re: 90 hp yamaha 2 stroke need help with wot!!??

I don't have a placard on my boat as it has been modified by the previous owner and I had to replace the subfloor. But I have seen the same boat on the water with 150 hp on them. factory this boat came with a 75 on basic models the original owner purchased it with a 90hp upgrade.

 

[robert graham]

Re: 90 hp yamaha 2 stroke need help with wot!!??

So if you're able to get WOT of 5000RPM's consistently then maybe the rest is just prop and motor set-up. My 90HP Yamaha is on a jon boat and I can trim it up and get maybe 5400RPM's, but the boat's not really designed for speed and it starts to porpoise at 5200+, so maybe you're O.K. Several years ago I bought a Harbor Freight Spark Plug Sandblaster($15) and it's really paid for itself over and over in motor performance and new plugs, outboards, lawnmowers, everything! I like really clean, shiny spark plugs. Even with Ringfree, Stabil, whatever, a 2 stroke motor is going to carbon up a plug to some degree. Good Luck!

 

[jeffersondodson561]

Re: 90 hp yamaha 2 stroke need help with wot!!??

What type of hull: V, flat bottom, displacement...pictures?

 

[jeffersondodson561]

Re: 90 hp yamaha 2 stroke need help with wot!!??

...porpoise at 5200+, so maybe you're O.K.

No way this is OK, you need to be able to achieve towards upper RPM (5800), you may have a rigging problem, is their any obstructions along the keel, like akwardly placed strakes, transducers, etc that could be causing cavitation?

 

[THE OPERATOR]

Re: 90 hp yamaha 2 stroke need help with wot!!??

Does anybody have some advice if I should replace the diaphragm in the fuel pump?

 

[99yam40]

Re: 90 hp yamaha 2 stroke need help with wot!!??

Check it to see if it is still in good shape.

I have heard you can unbolt it from motor but keep lines hooked up, and pump the primer bulb to see if fuel comes out of the pulse port

 

[robert graham]

Re: 90 hp yamaha 2 stroke need help with wot!!??

No way this is OK, you need to be able to achieve towards upper RPM (5800), you may have a rigging problem, is their any obstructions along the keel, like akwardly placed strakes, transducers, etc that could be causing cavitation?

My jon boat would be porpoising, chine-walking, out of control at 5800RPM's...I'm confident I could trim it up to do that, but it wouldn't be safe. His Polar Skiff is flat bottomed and maybe too much drag down there for the higher RPM's. I'm not saying he doesn't have an issue, but it could be related to the boat/prop/set-up more than just motor tune.

 

[jeffersondodson561]

Re: 90 hp yamaha 2 stroke need help with wot!!??

My jon boat would be porpoising, chine-walking, out of control at 5800RPM's...

Maybe your boat has a hook or rocker along the keel...

http://www.riverracer.net/forums/showthread.php?65870-Rocker-and-Hook

I agree, I think he has a rigging problem, 19' with a 90hp, to me seems a little on the underpowered side. Especially with a flat bottom...

 

[robert graham]

Re: 90 hp yamaha 2 stroke need help with wot!!??

It's an 1870 MV 6 degree deadrise aluminum jon boat and it's never seemed real happy trimmed up for maximum RPM's/speed, The flat bottom has a lot of drag. High speed is an expensive(fuel-wise) thing for them. And mine is painted flat OD green, not a very slick finish.

 

[THE OPERATOR]

Re: 90 hp yamaha 2 stroke need help with wot!!??

Ok To everyone who has helped with all the different ideas and advice THANK YOU !!!. I finally think I am on the right track I disassembled the carbs again and soaked them in new cleaner overnight and WOW what a difference put the boat back on the water was able to get up on plane and the tach read 4000. I know that is still less than the 5500 capable of the motor but I think now I am going to take off the SS prop and replace it with an alum 13 pitch and see if I can get a better hole shot. need it for the shallows. and achieve the higher RPM. If their arwe any more ideas please post them.

 

[99yam40]

Re: 90 hp yamaha 2 stroke need help with wot!!??

It would be best to have the motor run with the Yamaha test prop to see if the motor is putting out the proper RPM and HP. That can be done on the trailer in the water. If it will not then you have a motor problem, and if it will then you have a boat or set up problem.

Still think this is a good idea, if you have carb/motor problems and keep running it it can and will cause more expensive problems

 

[1998Cobia]

Re: 90 hp yamaha 2 stroke need help with wot!!??

I have the same problem with my 90 Yamaha. I brought it in to have checked out. There is a box next to the carbs that will bring down the RPM's if the spark is too hot. The engine should run at 5500 rpm's WOT. Mine is cut down to 4800-4900rpm's. It should be around 2-3 hundred to change out. I am waiting a little while to change per the mechanic said it will not hurt the motor. Hope this helps.

 

[THE OPERATOR]

Re: 90 hp yamaha 2 stroke need help with wot!!??

Ok hi turn everyone. I rebuilt the carbs and the motor is speced out timming,carbs,cdi etc. I tested the boat on the water and it bogged down when I drop the hammer tach says about 2800 the motor runs like that for 5 mins or so then the motor seems to get up a little bit to 3700 rpm and the boat will get up on plane. The best I can get is 38 to 40 on the tach. All fuel system parts are new tank,lines,fittings, bulb, pump,and fuel. When I rebuilt this motor I reused some of the gaskets and had to make a few could this b my problem??? Is it possible that I am getting water in one or more of the cylinders because of the gaskets? ? I am still getting good compression 100 to 105 on all three and good spark during the spark test. Need good advice please ..

 

[robert graham]

Re: 90 hp yamaha 2 stroke need help with wot!!??

Ok hi turn everyone. I rebuilt the carbs and the motor is speced out timming,carbs,cdi etc. I tested the boat on the water and it bogged down when I drop the hammer tach says about 2800 the motor runs like that for 5 mins or so then the motor seems to get up a little bit to 3700 rpm and the boat will get up on plane. The best I can get is 38 to 40 on the tach. All fuel system parts are new tank,lines,fittings, bulb, pump,and fuel. When I rebuilt this motor I reused some of the gaskets and had to make a few could this b my problem??? Is it possible that I am getting water in one or more of the cylinders because of the gaskets? ? I am still getting good compression 100 to 105 on all three and good spark during the spark test. Need good advice please ..

I remain very curious about what is the problem, since it seems you've done about everything, and this motor is among the simpler designs(compared to later models). Maybe put new plugs in, run the motor on the water for a while, turn it off, remove and "read" the plugs. They can give an indication of rich/lean/other problems. Good Luck and keep us posted!

 

[THE OPERATOR]

Re: 90 hp yamaha 2 stroke need help with wot!!??

I have done just that I purchased net plugs and ran the motor for a while on the water pulled the plugs on all three. The electrodes. On two of them were a brownish color and one was a lighter tan color. All three the grounds were black and their was oil on all of them what does this mean?? And what about the gaskets should I replace them??

 

[robert graham]

Re: 90 hp yamaha 2 stroke need help with wot!!??

I have done just that I purchased net plugs and ran the motor for a while on the water pulled the plugs on all three. The electrodes. On two of them were a brownish color and one was a lighter tan color. All three the grounds were black and their was oil on all of them what does this mean?? And what about the gaskets should I replace them??

Tan or brown with a bit of oil sounds about right, at least that's how mine look after running a while. I guess you synchronized the carbs after removal and cleaning? About to run out of ideas here. Good Luck and keep us posted!