Jet question
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Jet question

  1. #1
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    Default Jet question

    I took my boat out for its first run this weekend and it was a blast. First Jet boat!!!!! Plus I did the restore myself. Anyway
    How can I tell if the jet is getting fully loaded with water at faster speeds.
    It feels like it loses water when I get on it from a standstill. I can feel a little pause but how can I check it a crusing speeds? Any help would be great Thanks


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  3. #2
    Screamin SeaMonkees Schi-502's Avatar
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    It's fully loaded. But it doesn't mean you're not gulping air. "V" bottom? Delta Pad? Rounded keel? Rock grate? Loader?
    Loose, the Dogs of War!

  4. #3
    Senior Member jetboatperformance's Avatar
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    Honest horse power estimate (or engine build description) , an accurate Tach reading at WOT (true WOT vs Speed) and if know what impeller cut (if known) will devulge alot , if your inclined post up some pics of the jet and especially the Jet intake area Tom

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    congrats on your first jet boat follow toms advice

  7. #5
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    If the pump is unloading at speed, the RPM will fluctuate up and down, especially in rougher water. If you have an abundance of Horsepower, or a worn pump, the pump will seem to slip and the rpm will climb without any additional thrust on takeoff or sudden throttle application. We can freshen your pump, or machine and install a billet pre-inducer impeller to take care of the launch with HP problem. Also if a pump/loader is set up "old style", an inefficient launch will result.Many current boats were set-up 20 years ago when there wasn't the amount of knowlege as exists today. A loader grate or clearance change can help or cure the launch condition. There are as many ways to set up a pump as there are pump builders. Call me with any questions during business hrs. 623-877-8553 TIMINATOR
    MODESTY IS A CRUTCH FOR THE INCOMPETENT!

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    It is a 79 cobra jet V style hull. I believe it has a rock grate (about 4 or 5 1 inch tall and 1/4 inch thick bars). No loader Berkeley JE pump completely rebuilt. A2 aluminum impeller. We estimate the horse power to be 450 to 500. I will be out this weekend and I will get a WOT tach reading and GPS speed reading. It topped out in semi rough water with the diverter up at 60 mph (GPS reading) I will take some pictures of the intake area, also. I have done nothing to the intake area so I am willing to bet that is going to be the first place I will need to do work this winter!

    These are pics I already had don't know if they will help but I will get those other ones taken and up ASAP!!!

    Thanks for everyone help!!!!!






  9. #7
    Senior Member CK7684's Avatar
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    Hey there!! Mine's a 1979 CobraJet also!! How long is yours?? I notice yours has a different shape in the rear by the angled part of the transom...

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    Quote Originally Posted by CK7684 View Post
    Hey there!! Mine's a 1979 CobraJet also!! How long is yours?? I notice yours has a different shape in the rear by the angled part of the transom...
    Mine is 16'

    Maybe so someone can answer this question for me.

    If I nail the throttle from ideal the boat starts to take off engine rpm's go way up and it takes about 4 to 5 seconds then it seems like the jet fills with water again and pulls the engine rpms back down and I really take off. How can I keep it from cavitating during take off. I'm assuming that is the problem. Its a JE berkeley pump and has just been completely rebuilt. The pics of the intake area will be up tonight.

  11. #9
    Senior Member H20MOFO's Avatar
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    Sounds like you are cavatating(sp?) I can't stand on mine out of the hole right now either. I'm about to tighten things up in my pump, hopefully that will cure me.
    Among other things the tolerance between the ring(that gets installed in the pump) and the part of the impeller it rides on gets sloppy in time. From normal wear and sand and dry startings ect.
    Last edited by H20MOFO; 09-13-2009 at 01:11 PM.
    Another Hot Boat refugee

  12. #10
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    Quote Originally Posted by H20MOFO View Post
    Sounds like you are cavatating(sp?) I can't stand on mine out of the hole right now either. I'm about to tighten things up in my pump, hopefully that will cure me.
    Among other things the tolerance between the ring(that gets installed in the pump) and the part of the impeller it rides on gets sloppy in time. From normal wear and sand and dry startings ect.
    I just when through mine new A2 alumnium impeller, wear ring and seals.

  13. #11
    Senior Member H20MOFO's Avatar
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    [QUOTE=Problem Child;827531]I just when through mine new A2 alumnium impeller, wear ring and seals.[/QUOT
    I'm stumped then... it kinda sounded like you were describing a wore out pump. Sorry if this is a dumb question, but did you or your pump builder check the wear ring clearance. I'm just a rookie....maybe some of the more experienced guys will be more help.
    Another Hot Boat refugee

  14. #12
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    Reread my earlier post about slipping on the launch, TIMINATOR
    MODESTY IS A CRUTCH FOR THE INCOMPETENT!

  15. #13
    Senior Member CK7684's Avatar
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    During the build of mine, I was getting some cavitation during launch, but it went away when I installed an SS loader. However, my engine is making better power now and I am once again getting cavitation, just at higher RPMs. I never get it at speed though (unless hitting rough water, which there isnt much you can do anything about except slow down).
    Mine is a fresh rebuild with an Ultimate Wear Ring, "F" pump and "A" impeller. I did re-use my original impeller which may get changed to a bronze soon...

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