250 ox66 dying over 4000 rpm

[rocktmnoo]

i have twin 250 ox66 on a grady they both run fine until i reach 4000 rpm then the same one is quitting on me. it will fire back up fine if i hit the primer. i swapped fuel pumps that wasnt it. i noticed on fuel manager that just before it dies it quits pulling fuel . it goes from @1.1 mpg to like 1.5 and then it dies...any suggestions would be appreciated.

[Ken]

rock,
I believe your model Yammie has two fuel pumps - if so, then both need to be checked.
Also, check fuel filters - both local and remote.
Also, if you are using separate fuel tanks, check the anti-siphon valve if your tanks are so equipped.
Good luck [img]smile.gif[/img] ,
Ken K

[jb123]

besides fuel, check your o2 sensors.

[rocktmnoo]

ANY SUGGESTIONS ON CHECKING O2 SENSOR...I HAVE TWINS WOULD IT BE ADVISABLE TO SWITCH THEM?..THAT IS WHAT I DID WITH THE ELEC FUEL PUMP ASSEMBLY TO RULE OUT THAT PROB...WHAT ABOUT COMPUTER?

[jb123]

they are testable on a meter i think the variance should be from 3 to 8 OHMS? my mech heated with a torch, LIGHTLY, to show to high to low and if they do not have enuf change theyre useless. i would suggest getting yourself a manual and it should have the correct test there.

have you ever even looked at them, cleaned them or ran ring-free?

[rocktmnoo]

i appreciate all the info....but it seems like it may be the computer..im gonna try switching the two around and see what happens...

[hotrod]

it could be a filter on the bottom of the elect. fuel pump located in the the float chamber . the same thing happened to my ox66 225hp. when 4000 rpm is obtained fuel consumption is drastically increased, thus any restriction to the pumps can cause stall or cutback in rpm. this filter is located at the bottom of the electric fuel pump which supplies the other three diaphram pumps. it is a very fine micron filter . be very careful when removing as retail price is $80. the screen on the bottom can be pried apart and blown out.

[rocktmnoo]

i already swapped the complete pump assemblies on the two motors and it still did it to the same motor....i swapped fuel lines too...even watched the bowl in the separator and it still has fuel in it

[jb123]

what i remember about he faulty o2 sensor was that i couldnt get the rpms out of the motor, i think it was about max 4800 and there ws a recent post that an owner had a loose sensor with similiar issues. good luck and please post your fix.

[IFish4Tuna]

Yes similar problem but not exact to mine.
My engine never died at 4K, just started to bog.
I did the seafoam dcarb treatment both engines(see their website for how to) and had a loose o2 sensor, cleaned the o2 sensor (both engines using ring free) and I changed my plugs (both engines). All this on a pair of engines w/ 125 hours on them. THe fuel econonmy going shithouse is very similar though to my problem. I also bought $300 in tools and service manual which I have not yet needed to use yet. I DID buy the test light harness which I'm CERTAIN I will need to use at somepoint down the road.

Ed

[rocktmnoo]

WELL EVERYONE..PROB FIXED.....IT WAS A BUSTED DIAPHRAM ON 2 OF THE SECONDARY FUEL PUMPS..YAMAHA PUTS A FLIMSY THIN PIECE ON THERE AND THEY DO NOT HOLD UP VERY GOOD.. REPLACEMENT... WONDERFUL FIT.CHANGED ALL ON BOTH MOTORS. THANKS FOR EVERYONE'S HELP...GOOD FISHING TO ALL