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  1. #11
    PWCToday Guru
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    Re: 1996 seadoo 787 buckshot domes????

    Quote Originally Posted by Bill O'Neal View Post
    Pre-mix vs. oil injection really has no bearing on the compression you should choose. If you mean "pre-mix" to refer to mixing premium pump gas with race gas, yes, it's a good idea for any SeaDoo that will have higher compression, an aftermarket pipe, and an aftermarket ignition. The 43cc domes are the safest option for sure. If you're a decent tuner, you could probably use 39cc domes as well but it will be closer to the edge. Keep in mind it'll be a race boat now. NO full throttle passes all the way across the lake anymore. Unless your lake is the size of a pwc closed course and has rough water all the time.

    And yes, we have some 43cc domes in stock. Should have some 39cc domes in soon. Email my shop manager at cdofixr1@live.com if you're interested further.
    No more full throttle for extended periods with the 43cc domes? or the 39cc's?

  2. #12
    Tech Guru PWCToday.com Is My Home Away From Home Watercraft Magic's Avatar
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    Re: 1996 seadoo 787 buckshot domes????

    Quote Originally Posted by Green95LX View Post
    No more full throttle for extended periods with the 43cc domes? or the 39cc's?
    With the Factory Pipe, MSD, and either of those domes, I would say no extended full throttle runs in smooth water. With just the pipe and the 43cc domes, you could get away with long high speed blasts but it's still be smart to blip the throttle every 15 seconds or so just to be safe. If you're drag racing somebody, doing this won't even make a difference, but it can make a big difference on the life of your motor. And of course, doing a high speed plug check is a good idea before wailing on anything you've made mods to. Plug color should be like a brown paper bag (or darker) and the same on all plugs to be safe.
    email Chris at Watercraft Magic cdofixr1@live.com

  3. #13
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    Re: 1996 seadoo 787 buckshot domes????

    Does that also apply to the MSD enhancer ignition? What do you consider "extended" full throttle runs?

  4. #14
    PWCToday.com Is My Home Away From Home Mr. Bill's Avatar
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    Re: 1996 seadoo 787 buckshot domes????

    Yes, an Enhancer is still there for the property if offers you besides just being a rev limiter.

    A long extended run is anytime the motor is pushed full out until the temps in the chambers becomes so hot it starts trasferring the heat to the pistons and clyinders more than "normal". Smooth water never allows the engine to catch a break like it would if the pump were loading and unloading in choppy or rough conditions.

    Would you take your modified car out on a 100 mile stretch of road and flog it full out, petal to the metal without lifting until it blew apart ? Probably not, but unlike a car, a jetpump powered boat is pulling a much heavier load on the engine unless it had an impellor that was too little pitch to take advantage of the modifications that you made to the motor to get a better accellerating and faster top speed. But if you did that, one of two things would happen, either it would max out the rpm until it was hitting the rev limiter, or it would explode from constant over reving the engine because it did not have a properly set rev limiter for the lesser picthed impellor.

    If you have any ideas of running something like even just a Factory Pipe Products exhaust system on the motor, you had better not hold it wide open too long on plain pump gasoline. Add in any amount of extra compression, or even the stock head with less squish clearances and the Factory Pipe Products exhaust system, without some extra octane fuel, you are asking for trouble even without making any changes to the oem spec timing, much less the options allowed by the use of the Enhancer on top of those other mods to the motor.

    A stock Sea Doo motor is a fairly high compression motor when compared to most other motors in pwc's, and quite a bit higher compression than any stock automobile grocery getter motor. Yet both can operate on lower octane pump gasolines, but if you raise the compression ratio higher on either motor, you must also raise the octane rating, and the more that you modify the motor, the higher octanes will be needed to offset the extra heat generated within the combustion chambers.

    My idea of a long distance is about 1/8th mile before changing my throttle position momentarily. This does not mean long enough to slow down the hull, but just enough to let the motor breathe a little so it can stay within the tolerable heat limits on the pistons.

    One thing that makes me cringe at the lake is to watch someome mount a cold motor pwc and nail it and disappear in the distance without ever lifting. Although stock motors are made to take into account that fools ride watercraft that way a large portion of the time, and they can withstand that abuse, that is still no way to treat your watercraft engine if you expect it to live a long and happy life.
    Back in the day that the two stroke Kawasaki Jetski or the first Waverunner 500 cc 6 to 1 CR motors only made between 28 and 40 HP, depending upon which model you had, you could get away with such things as they never came close to having enough power to blow themselves up, but today, we deal with a minimum of about 70 hp all the way up to 135 hp two cycles in stock form, plenty of power to break parts.

    Bill O'Neal
    WCM

  5. #15
    PWCToday Regular Ashr8's Avatar
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    Re: 1996 seadoo 787 buckshot domes????

    Can you run 39.5cc domes on 98 octane as long as you don't full throttle for more 5 seconds at a time?

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