Yamaha VX76 250HP Fuel problems

[sdudra]

I hope that RodBolt or someone else might give me an idea of what the issue will be.

Went to take family and friends out on the 4th of July and it just wasn't in the cards for me.

Motor starts fine and idles fine. when I go to give it gas the boat comes up on plane and goes right back down just as fast. The engine never shuts off and it idles. If I get a friend to pump the bulb, with the throttle wide open, it gains speed but of course dies as it is requiring more fuel.

I am guess a fuel pump issue? But I do computers, not 2 stroke engines.

So that is my story. Let me know what you think.

 

[imwright1985]

Re: Yamaha VX76 250HP Fuel problems

i think that motor has 2 pumps, there should also be a check valve (tire inflator looking thing) check the fuel pressure and post that and look for leaks also while hood is off

 

[sdudra]

Re: Yamaha VX76 250HP Fuel problems

I have checked for fuel leaks and even went as far as replacing all of the hose from the tank. In this process, I eliminated the water/fuel seperator and only currently have the bulb in line.

I will look for that check valve. What should the pressure be at idle and am I to check it while running the motor?

 

[imwright1985]

Re: Yamaha VX76 250HP Fuel problems

dont know it depends on the motor and i dont know the specs on that one. Usually you turn key to on so pumps engage to fully prime motor and it will hold pressure since injectors arnt spraying fuel to keep motor running, sometimes you can do a running test but that is usually just to see if the pumps can keep up with the amount the injectors are spraying. Kinda a consult your service manual deal. also if your thinking likely fuel problem run it off a 5 gallon can so you know all the gas is good and no pickup tube blockages

i keep thinking car mechanics so using a newer 4.3l GM motor psi will be about 55-60 primed then when running will hold around 45psi if i recall correctly some efi systems are fine around 30 psi so that gives you an idea of the differences

 

[rodbolt]

Re: Yamaha VX76 250HP Fuel problems

the 250 was made in 3 2 stroke fuel configurations.
we need a model number to identify what we are dissusing.

 

[snowmon]

Re: Yamaha VX76 250HP Fuel problems

assuming this is an ox66 injected engine. is the bulb collapsing? if so you probably have a restriction on the tank side of the bulb because if the bulb is collapsing the engine is trying to pump fuel. if you've recently switched to e10 fuel check at the anti-siphon valve at the feed tube from your tank. e10 kills these. if the bulb isn't collapsing and you're able to pump fuel to the engine check the 3 low pressure pumps. you might have blown diaphragms. lastly check the filter on the high pressure pump in the vst. these clog and will cause problems. better yet check all the potential problems. a bad low pressure pump will dump raw fuel directly onto bearings and poof.

 

[sdudra]

Re: Yamaha VX76 250HP Fuel problems

Rodbolt,

The model is a 1992 L250 TXRQ. The bulb does not collapse while running. As I stated earlier, if I pump the bulb, it actually tried to pick up speed. I am thinking pumps, but of course, I would like professional opinions instead of just guessing.

 

[snowmon]

Re: Yamaha VX76 250HP Fuel problems

you want a pro opinion best to post all of the info needed from the start. like model number and year. good luck.

 

[sdudra]

Re: Yamaha VX76 250HP Fuel problems

Snowmon,

IF you look right above your post, you would see the model number...... Sorry you missed it......

 

[rodbolt]

Re: Yamaha VX76 250HP Fuel problems

Q is indeed a 92 model code, 3.1L carbed. sounds like one of the 3 lift pumps are failing.
by pumping the primer your bypassing the pumps. could also be a bad T-stat.
bad t-stat can tell the ECU the engine is cold and lean out #6 carb bowl.

 

[sdudra]

Re: Yamaha VX76 250HP Fuel problems

Thanks Rod!

I plan on replacing ALL 3 of the lift pumps since they are so cheap. Do you suggest that I also replace the thermostat just in case? I have owned the boat just over a year and I know that it hasnt been replaced by me.

So let me know!

 

[scjmc]

Re: Yamaha VX76 250HP Fuel problems

I replace my T stats every year or so as preventitave maintenance. I have actually had T stat troubles on 2 other Yamahas I have had.

 

[snowmon]

Re: Yamaha VX76 250HP Fuel problems

Snowmon,

IF you look right above your post, you would see the model number...... Sorry you missed it......

actually i didn't miss it. my first post was to your original post which only included v76 250hp ??? even the king (rodbolt) asked you for a model number. i was only trying to help based on my own experience with similar issues. you posted model number after my first post. lp pumps. good luck. you'll need it.

 

[sdudra]

Re: Yamaha VX76 250HP Fuel problems

Snowmon,

It doesn't take luck to change lift pumps or fuel pumps or whatever you want to call it. it seems that your post have a "negative tone" in them. I am no dummy when it comes to mechanical things on boat engines or car engines. However, since it is not my full time job or my full time passion, I do like to do good research before I spend money on things that maybe do not need replaced.

Rodbolt,

As you and everyone else knows, is probably one of the most knowledgable guys and getting his "blessing" on an original assumption, makes things a lot easier for us people that simply try to save some dough by doing our own work.

Rodbolt,

Thanks so much for your confirmation of the issue. I will have them replaced as soon as they come in. I found them for $30.00 each. So 3 LP's and gaskets will be here by mid week.

Thanks again!

Stephen

 

[snowmon]

Re: Yamaha VX76 250HP Fuel problems

you didn't know what the problem was nor were you able to diagnose it on your own. i only tried to help. we all know you'll need "it, or a good mechanic.

 

[sdudra]

Re: Yamaha VX76 250HP Fuel problems

LOL This is actually entertaining............ However......

From the very first post of this thread you will see the following:

"Motor starts fine and idles fine. when I go to give it gas the boat comes up on plane and goes right back down just as fast. The engine never shuts off and it idles. If I get a friend to pump the bulb, with the throttle wide open, it gains speed but of course dies as it is requiring more fuel.

I am guess a fuel pump issue? But I do computers, not 2 stroke engines."

So as you see, I diagnosed what I thought the problem was. Just as MANY others do, we turn to these forums for answers or confirmation or assistance in trying to save a little bit of money or to get an idea on how much a repair would cost to get us back on the water.

Just so you know, I dont think that I will need any luck taking some bolts out that hold the pumps on or cutting off 2 wire ties and replacing the pump, putting 2 bolts back on and 2 wire ties. Pretty simple but thanks for the entertainment value of this post!