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Twin 250OX66 Salt Water - port starving after 3000 rpm

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  • Twin 250OX66 Salt Water - port starving after 3000 rpm

    2001 Grady White 30' with Twin 250 - OX66 Salt Water Series II.

    Just located from Florida to Mazatlan Mexico... NO YAMAHA Service available.

    Last three runs 25 miles out, trolling and 25 back, have been excellent.

    Last run we didn't get far; just past the break water. About one minute after I pushed rpm's to 3600 the port engine died off. RPM's went down to less than 800 and bounced around. Shut-down and re-starts were fine, but same result every time I tried to cruise above 3000. Runs OK at lower RPM's and starts fine.

    Examined in-line water separator; brand new and super clean.

    Examined in-line filter in port engine; seems to be OK, but there was a mirco-spec of gas varnish. Cleaned and re-installed. Same problem.

    Switched from main to aux tank; same problems.

    Switched gas lines at the motors; starboard runs perfect and port continues with same problem.

    I by passed the filter in the motor, and the 'check-valve' and everything seemed to run perfectly. Ran for about 30 minutes without a hic-up. Just as I was coming back in, the same problem occurred... it just died off at about 3600; dropped to 1500; jumped back to 3600; dropped to 1500; back to 3600. I wouldn't call it surging, but maybe long-surging.

    It seems like it is starving for gas at cruise speed. Ran all the way back in at 900 to 1200 rpm's and not a problem.

    Lot's of advise: one guy thinks I have water in my gas; another guy says I'm getting air in my lines.

    I'm getting new filters sent down from lower 48 but that will/could take ?? weeks ??

    Is there anything else I can look at?

    I put a quart of conditioner in each tank (156 gal and 150 gal).

    Tanks are super clean. Always put away properly.

    thanks in advance

    PS: I just retired and want to do a little playing; I don't want to take work away from any good Yamaha mechanics. If anybody knows a good Yamaha guy in Mazatlan, please let me know!

  • #2
    your describing a typical VST filter clog.
    need to clean/replace it and test fuel rail pressures.


    • #3
      Thank you. That's good news, I thick.

      I've located an Evinrude mechanic with tools but he doesn't usually work on Yamaha. Oh well, I guess he'll have to learn.

      Which filter is the "VST Filter" ?


      • #4
        the one inside the VST attached to the fuel pump intake.


        • #5
          I'm back in from sea-trial.

          We pulled the VST filter and it was definitely dirty. I cleaned as best as I could and then re-installed. (I'm trying to find a way to get VST filter, in-line water-separator filters and water-separator canisters sent down to Mazatlan, that doesn't take 3 weeks to clear customs). Old VST filter after I cleaned it: holding it up to the sun you can see it is still clogged; blowing through it takes medium effort. I think it's still too dirty.

          Anyway, we idled all the way out to the breakwater below 2000 and had no problem. Pushed speed to 3500 and within 60 seconds it died. Re-starts fine, but dies soon after crossing 3000. Tried variations of cutting the throttle as soon as it starts to die off: the engine will recover to idle without dying. Tried throttling in neutral to bypass problem... no noticeable success. The problem is still there. Simply dies under power. Sometimes it surges back, but ultimately, it dies.

          Assuming the VST isn't the problem, what would be your next step?

          Thank you...


          • #6
            I completely disassembled the VST, off the engine. I found a lot of 'dirt' clogging the top piping coming into the tank... cleaned and re-assembled.

            Ran out to the break water, 10 minutes, under 1500 rpm; no problems.

            Sea trialled: average 4000 rpm for 30 minutes and not a hic-cup. Runs better then it ever has since I've owned it.

            I still can't locate parts down here in Mazatlan. I've got a buddy bringing-down new VST, water separator and canister filters for both engines, on a flight next weekend.

            Thanks for the help.

            Time to celebrate with a tequila!