99 250 ox66 unstable rpm's high speed cutout

[hank250]

1999 Yam 250 ox66 fuel injected is varying 300 rpms when cruising, 200 rpm's when idling, also cut out on top end 5500 rpm's but restarted normally. Checked compresson 110 to 120 on all cylinders. changed plugs and fuel filter. What next?

Thanks Hank250

 

[yamamarinetech40]

Re: 99 250 ox66 unstable rpm's high speed cutout

You say fuel filter...you have three you need to change....but apart from that, sounds like two different problems....you should have the oxygen sensor cleaned or replaced(depending), and you should hook up a vacuum gauge to fuel line just ahead of primary filter on engine....vacuum should be about 2 inches or so @ idle...never more than 5 inches @ WOT.....did the engine die completely from 5500 rpm? Did this happen once or what?

 

[hank250]

Re: 99 250 ox66 unstable rpm's high speed cutout

It only has cut out once because I havent taken it back up to see if it will do it again. What happened It started to lose power and when I backed off the throttle it died. I will check vacuum tonight. I put the motor on a 6 gallon tank yesterday with fresh gas and ring free. Ran about 3 gal. through.

 

[yamamarinetech40]

Re: 99 250 ox66 unstable rpm's high speed cutout

Wait, are you saying that this happened yesterday AFTER you ran the ringfree gas thru? How much ringfree did you use? If you dosed it right, with at the very least 2 oz./gal.(I would use more)...then you may have just carbon bridged(fouled) a sparkplug....which you state you have changed now...so maybe vacuum check not quite necessary YET...would worry more about the oxygen sensor, can really cause a lot of different runability problems...ever cleaned? What about the other fuel filters?

 

[hank250]

Re: 99 250 ox66 unstable rpm's high speed cutout

No this happened before I ran the ring free (2 oz per gallon). The o2 sensor has never been cleaned. I have only two fuel filters that I know of one on the boat and one on the engine. cleaned the one on the boat and the motor filter was changed last fall. I would like to clean the the o2 sensor, anything to watch out for? The procedeue i have suggests soaking tip of the o2 sensor in ring free and washing off with contact cleaner.

 

[yamamarinetech40]

Re: 99 250 ox66 unstable rpm's high speed cutout

ok, let's back up....if you go to yamaha's site and go to service you can look at very detailed drawings of every part of your engine for free, with numbered parts and a corresponding list to tell you what each numbered part is...it'll show you the filters...it really helps if you know at least the very basic things like the filter in the vst tank, that is called for replacement every 100 hrs...please look at the yamaha site, it's free....now, the way I clean the o2 sensor and the way it's taught at Yamaha school is with a torch, but you have to be careful....just heat the 'can' until it's a nice cherry red to burn off all the carbon/crap, you may spray it with electrical cleaner when it cools, DON'T get any fingerprints on it or ANYTHING else....again back to drawings...there is a tube that you'll see the end of coming from engine into sensor location, this feeds the sensor w/ exhaust to read...pull it out towards you and clean it out (drill bit(careful), cleaner, soak...it'll be clogged off completely I think..get it clean...you'll need to order a gasket kit for re-isntall....let us know how it goes....

 

[hank250]

Re: 99 250 ox66 unstable rpm's high speed cutout

Ordered o2 sensor gasket yesterday wont see it until next weekend.Will let you Know what i find.

 

[hank250]

Re: 99 250 ox66 unstable rpm's high speed cutout

One other thing that didnt look right. Where should the fuel level be on the fuel filter on the engine. The level I have is only about a 1/4 up on the filter element. If I disconnect the fuel line at the check valve the level goes up above the filter element but when I start the engine it goes right back down.
Seems strange but I have never paid attention to it before. Is this normal?

 

[yamamarinetech40]

Re: 99 250 ox66 unstable rpm's high speed cutout

Yep, sounds right...a 15 dollar vacuum gauge mentioned above and you wouldn't have to worry about that end of it anymore....