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Thread: too slow and too cold

  1. #1
    Sorry I didn't think of the tach being off, it is the original tach in the boat. And the MPH was from a GPS. So am I to assume that 50 is pretty much normal for my 21'.
    [This message has been edited by oneultrarat (edited March 25, 2002).]

  2. #2
    3000 RPM????????????????????

  3. #3
    flat broke
    50 is probably a fair expectation for a relatively stock 21' jet. But 3000RPM is not consistent with that speed. Was the speed measured off the speedo or GPS? If you're boat really did 50 mph at 3000 RPM, you have one of the most efficient pumps I've ever heard of http://free.*** More likely than not, your tach is not giving you an accurate reading. If you have a diagnostic tach at home, I would bring that along next time out and see what it says in comparison to the tach in the boat. If you truly are turning 3000 RPM, you're probably not going 50. Once you get your tach issue worked out, I think you'll be very pleased with the droop and diverter addition. They will help your speed(when used properly) with no increase in RPM.
    Good luck,
    Chris (

  4. #4
    Sounds to me that the tach is off in the boat, there is no way that it would do 50mph @ 3000rpm..

  5. #5
    spectras only
    Check the backside of the tach.Normally there are 3 positions to set for,4 , 6 , 8 cyl.Either the pointer moved or the contact is bad.3000RPM for jetboats normally yield between 30-40MPH depending on boatsize.

  6. #6
    I would wager as well that the tach is messed up. With a 340hp motor (stock big block), a larger, newer Ultra will run over 55 all day. Bump up to the 390 and you will see around 58-59. The 496 HO gets you a little over 60. With the smaller SS version you have, you should be able to run in the mid fifties for sure if you are tuned right and your pump is solid. Take your time, and find out where the mess up is. Some ignition computers or timing lights also have a tach on them. See if you can borrow one that has it to check yours with.

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