Yamaha GURUS..... help point me in a direction

[jerseysportfisher]

Hello,

I am new here, i seen some good advice on some other topic and felt i should try here. I have an interesting issue.

first off it a 1991 250 txrp. the cowling says V-x 250. What is happening is I am get popping and misfire at high rpm. It started 2 weekend ago, ran the boat all day perfectly. On the way in I was getting on it and she started to popped at 4500 when up on plane. I figured dirt in the fuel system so i change out the fuel filter. Took it out this weekend and she started popping again. Started to run her through some tests. What i came up with is that if i am at a dead stop and mash the throttle she will run strong while under a load (turning 4000). Once the boat planes the popping starts. So if i gradually increase the throttle and keep a minimum load on the engine the popping starts a 3800. Mid range throttle no problems. If i get her up to popping again and pump the fuel bulb the mottor bogs a little while still popping. I have worked on cars most of my life. To me this looks like a sensor issue. When i get some free time i will pop the TPS of and check with an ohm meter. I also know that yammis have a similar symptom with 02 sensors. Maybe i am not looking in the right place but i couldnt find one. in the secom manual the only wiring diagram that matches is for a 1995. Any ideas is greatly appreciated.

Thanks

 

[rodbolt]

Re: Yamaha GURUS..... help point me in a direction

your way off base, the TPS cannot be reliably tested with an ohm meter but needs to be tested under a load juat like a car, your 91 250 uses 6 carbs and NO o2 sensor, it does have a knock sensor that will retard timing if activated or lock timing to about 7 degrees BTDC if discconected.
I think your fighting fuel isues, minimum fuel system pressure is 3PSI and maximum fuel system vacum is 6 inches Hg on the 250. a quick check with the yamaha diagnostic lamp will reveal any codes or sensor failure detection, lamp is like 70 bucks and priceless if it keeps you from chasing ghosts.
just remember almost any sensor or ing component failure will lock the ign timing at 7 degrees. also make sure the fuel primer pump is operable, the little electric pump between the carbs, also make sure your Tstats are installed and operating coeectly or its possible to drain 6 fuel bowl. also check the spark plug caps for proper resistance.
sounds to me like trash in the carbs,

 

[jerseysportfisher]

Re: Yamaha GURUS..... help point me in a direction

RODBOLT,

Thanks for the info i will teardown the carbs and see if i got a stuck needle valve. I will also check vacuum as per my local dealer said i might have a leak on the crankcase seal. Whats the chances of a head gasket ? Like i stated earlier, in all my time most of theese symptoms should show under a load and not when the load is released.


just an FYI

a TPS sensor is a potentiometer, aka a variable resistor.
The best way to check theese is with an ohm meter. If you have a bad spot on the pot your ohm meter will click off to infinity. The way to set a TPS is with voltage, per the manufactures specs.

 

[rodbolt]

Re: Yamaha GURUS..... help point me in a direction

wrong,
oh well cant help then, I guess yamaha will take away my master tech certs oh bummer.

 

[jerseysportfisher]

Re: Yamaha GURUS..... help point me in a direction

just for info for everyone

unbolted the 2 lower fuel pumps, immediatley when seperated from the block fuel pissed all over the place. The top fuel pump did not. When i split the halves off the top fuel pump it was the only on that had fuel remaining in it. Off i am to get new gaskets and diaphrams.


rodbolt, know that i am not trying to break your balls. I appreciate the help.

 

[nautihabits]

Re: Yamaha GURUS..... help point me in a direction

Can't point you in the right direction if you refuse to read the reply. Rodbolts first reply was "I think your fighting fuel isues, ........." So why are you surprised it was fuel pumps? Really not trying to break your ball though Jersy. Appreciate the comedy.

 

[jerseysportfisher]

Re: Yamaha GURUS..... help point me in a direction

use you knoggin, i wasnt talking about fuel. I was talking about testing electronic components. Something I have been doing for a long time. If you bothered to read i thanked him for pointing me towards fuel.

 

[rodbolt]

Re: Yamaha GURUS..... help point me in a direction

I usually just replace the pumps, its about as cheap as buying kits.
once your done you really need to test the fuel rail pressure at or near WOT to insure no particles have found their way into the VST/fuel rail.
fuel pressure should be 35 psi and not vary more than about 2 psi at all speeds.
the pump runs at 2 speeds. low speed and high speed seperate at about 1900 RPM and is controled by the ECU and the big resistor on top of the throttle body assy.

 

[jerseysportfisher]

Re: Yamaha GURUS..... help point me in a direction

the local guy wants 40 a pump and 15 for the rebuild kit. now did you mean 35psi or 3 to 5 psi ? I deff agree with you on getting the particles out, i think i will take all the lines out and blow'em out with some air. This low/high sperator, is this the actuators on the carbs ?



thanks
Again

 

[rodbolt]

Re: Yamaha GURUS..... help point me in a direction

sorry my bad mixing my carbs with EFI
on the carbed motor minimum out put pressure from the pumps is 3 PSI.
the electric pump supplys about 6 PSI to the injectors.
the injectors not only work at cold start but also at rapid throttle opening or rapid decelleration. they alter the fuel volume by as much as 20% depending on the conditions.
but the supply for the 6 injectors is from #6 fuel bowl and depending on what failed it can drain #6 creating a lean condition.
slap me when I cross up my V76 carb motors with the V76 EFI motors

 

[jerseysportfisher]

Re: Yamaha GURUS..... help point me in a direction

lol, i was gonna say, **** thats alot my racecar runs that much fuel pressure. thoose injectors are located on the carbs right ? if so how reliable are they ?

 

[rodbolt]

Re: Yamaha GURUS..... help point me in a direction

very reliable, the carb motors need a minimum of 3 PSI at the carb inlets, EFI a minimum of 35 PSI on the rail, the HPDI 50 PSI to the high pressure pump, the Z250 and Z300 run a minimum of 1000 PSI on the rail the Z200 and lower run a minimum of about 600 PSI on the rail.