1996 VX 250 fuel starvation??

[fultsie]

WOW, what a great site!
Just bought a 1996 VX 250 that runs great EXCEPT at WOT. After idleing out of the channel and applying full power, she runs strong for 15 seconds or so and then losses power, surging on the way back to about 4,600-4,800 rpm. Reduce power to 4,600 and she runs all day without missing a beat. Obviously a fuel issue. My question is where best to start and are there any common VX 250 issues to focus on? Thought I'd put a tee between the fuel bulb and engine to provide unrestricted fuel to determine if there might be a restriction in the supply side. ANY suggestions would be greatly appreciated. Thanks in advance....Steve

[Ken]

Steve,
Does sound like fuel starvation. When this happens, check the primer bulb - if it has collapsed, then there is a restriction from there on back to the fuel tank. If there is a fuel filter between the bulb and tank, check it.
If the fuel line coming out of the tank has an anti-siphon valve on it, that could be your problem. They are notorious for sticking and not opening all the way when fuel is demanded - check it.
Also, the fuel tank may not be venting properly and forming a vacuum - check the vent hose to make sure it does not have a kink in it.
If the primer bulb has not collapsed when the motor starts surging, then try squeezing the bulb several times to see if the surging stops and motor regains rpm (obviously gonna take two persons). If so, then could be clogged fuel filter on the motor, or faulty fuel pump.
If that fuel pump is at least five years old, might wanna replace it - some owners do this as routine maintenance.
Hope this helps [img]smile.gif[/img] ,
Ken K

[fultsie]

Thanks Ken, much easier than my tee idea. One more thing that might help diagnose is that I noticed the filter/seperator on the engine has about 1/2 of air at the top. If I squeeze the bulb and fill it, it will drop back down to the 1/2 after about 5 minutes. Also if I squeeze the bulb hard many times, fuel runs out the bottom of the intake. Is this normal?

[fultsie]

Relplaced the anti-siphon valve, checked for other supply restrictions and there are none. Cleaned the check valve just after the water seperator/filter and the bowl now stays full. If I disconnect the fuel line at the regulator, the fuel pump will output just over 1.5 oz. in 5 seconds, but then the flow will stop shortly after 5 seconds. Does the electric fuel pump supply only cold start fuel (choke) or does it also add fuel at WOT and/or high power demand? Should fuel continue to flow indefinitely? Also, I can now squeeze the primer bulb many times without fuel overflow. After all of this, still has the same symptoms. Any more suggestions please? Thanks much...Steve

[Ken]

Steve,
I just reviewed the diagram for your fuel system in the online catalog (above). Wow, you have three mechanical fuel pumps, one electric pump and a fuel regulator. I'm gonna have to be honest and tell you I am not familiar with this system - wish I could help you further - hopefully, someone who has worked on this system will chime in and offer some more help.
I feel pretty confident that the Yamhaha shop manual has some kind of test procedure for the above components. If I had to guess at this point, I would say that it is gonna be a component that is common to all three carbs - and most likely the electric fuel pump.
Good luck [img]smile.gif[/img] ,
Ken K

[Ken]

Steve,
I just reviewed back over your posts, and two things stick out. One, your motor runs fine for about 15 seconds and then starts cutting out, and, two, when you kept pumping up the bulb that one time, fuel ran out the bottom of the intake.
Both of these symptoms point to sticky carb float valve(s).
If that motor has been allowed to set up for at least two months w/o being run, then you could have gum/varnish in them. You could try a shock treatment with RingFree or Seafoam - if that doesn't help, then you would need to tear down the carbs, clean, and install a carb kit, and, of course, pay special attention to the float valves and float adjustment.
Good luck and let us know how you come out [img]smile.gif[/img] .
Ken K

[boats.net]

I agree with Ken you stated you had a 1996 VX250 which the VX is a fuel injected engine and they didn't make the 250 fuel injected in 1996 so you must have a carb. engine and what you are describing is a carb problem, need to clean carbs.

[jb123]

i would have suggested to clean carbs also but the motor will get up to proper rpm then cut out which to me sounds like delivery...always a good idea to have clean carbs tho. i would suggest replacing all fuel lines,checking each fitting and minimalize fittings in liew of a possible air leak.for the carbs, remove the breather cover to expose the carb throats, block the openings with your finger or spray gas into each throat, to choke individually, and listen for a change in rpm.

[fultsie]

Thanks for all the input. This engine has carbs AND electric fuel enrichment. If it is a fuel supply problem (which I believe) do I first replace the 3 pulse pumps or the electric pump? Does the electric enrichment work for cold start only or is it used at WOT too? The electric pump is fed from the #6 carb bowl which leads me to believe that it is cold start only, otherwise it would seem to run the #6 carb dry if used for long periods. Anyway, I ordered 3 pulse pumps and will install then report back. Again thanks to all.....Steve