Cavitation???????
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Cavitation???????

  1. #1
    jetboataholic HawaiianJet's Avatar
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    Question Cavitation???????

    Ok first new thread from me in a few months. And here's a real newbie question for y'all. How do you know if the pump is cavitating? I think mine did it once or twice on me last season out of the hole, but im not sure. So here's what it did; i pressed the gas, and the boat went nowhere, waited a few seconds pressed again, still nothing. So i killed the engine, sat there for a few minutes, talked to another boater that recognized my boat from the last time it was on the river before i owned it, then started it back up, pressed the gas and it actually moved this time. Always a good thing when there are other boats around.

    Also, i still have a little bit of popping at the very highest rpm range that my boat turns. I want to think that it's the pump cause im hoping that it's not the engine. Does cavitation do that (popping)? Cause it doesn't do it constantly like i would think it would if it were the engine, only when i give it the final little bit of gas to go full throttle. Full throttle for me is about 4500 rpm, if i remember correctly, been a long cold winter.

    Oh and i know WHAT cavitation is, just not how to tell when the pump is actually cavitating. So please no long definitions of cavitation, that has been covered on more than one occasion on the site, and has pretty much been beat to death.

    Thanks guys.
    HJ

    ***FOR SALE*** 1978 19' Full Stringer Hawaiian Molokai Jet Boat w/ Berkeley 12JC-AB and Chevy 440 Tall Deck ***FOR SALE***

    Quote Originally Posted by mako shark mark View Post
    Oh yeah, Forgot to mention that the hull is a special mixture of speedcote, herculiner and rain-x, all blended together- good for another 8 mph top end.

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  3. #2
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    I knew my boats pump was cavitating when the RPM's went from 5800 to 6200ish.

  4. #3
    Boat Nut sleekcrafter's Avatar
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    Your pump was fouled, or air locked, it happens. Have you ever checked your total timing advance? If not you should check it, you may not be reaching the max advance. Also check the carbon button in your distributor cap, make sure it's not going away on you.

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    About 500' AGL MudPumper's Avatar
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    Quote Originally Posted by HawaiianJet View Post
    Ok first new thread from me in a few months. And here's a real newbie question for y'all. How do you know if the pump is cavitating? I think mine did it once or twice on me last season out of the hole, but im not sure. So here's what it did; i pressed the gas, and the boat went nowhere, waited a few seconds pressed again, still nothing. So i killed the engine, sat there for a few minutes, talked to another boater that recognized my boat from the last time it was on the river before i owned it, then started it back up, pressed the gas and it actually moved this time. Always a good thing when there are other boats around.

    Did it do this just after putting the boat in the water?? If so you had air trapped in the pump.

  7. #5
    jetboataholic HawaiianJet's Avatar
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    Quote Originally Posted by sleekcrafter View Post
    Your pump was fouled, or air locked, it happens. Have you ever checked your total timing advance? If not you should check it, you may not be reaching the max advance. Also check the carbon button in your distributor cap, make sure it's not going away on you.
    Yes i did finally check it, and got everything set right where it should be (using a good timing light that i borrowed from an engine builder), i can't remember where that is anymore, but im sure it's posted somewhere on these forums so i could find it with a bit of research. The dizzy cap and rotor were brand new and clean, no carbon tracks that i saw.

    Quote Originally Posted by MudPumper View Post
    Did it do this just after putting the boat in the water?? If so you had air trapped in the pump.
    No it was after running for about 3 miles, coming down to an idle, turning around and then trying to go back the other way.



    I'm just trying to get some ideas before i put it back in the water in a couple months, so i know if i need to fix anything, or do anything.

    Thanks guys.
    HJ

    ***FOR SALE*** 1978 19' Full Stringer Hawaiian Molokai Jet Boat w/ Berkeley 12JC-AB and Chevy 440 Tall Deck ***FOR SALE***

    Quote Originally Posted by mako shark mark View Post
    Oh yeah, Forgot to mention that the hull is a special mixture of speedcote, herculiner and rain-x, all blended together- good for another 8 mph top end.

  8. #6
    Senior Member ol guy's Avatar
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    I think you saw two different problems at the same time! #1 pump not being loaded and trying to blow air! #2 engine reaching max rpm for its design. If the pump finally loaded and you are seeing 4500 rpm at wot then the pop would be either a timing issue or valve springs with no or little seat pressure left (valve float). Getting a pump fully loaded is a jet boat racers first concern, it will make the difference between a good pass and a bad one! IMLAO M

  9. #7
    Senior Member rorybsst's Avatar
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    if your engine is popping at WOT it cold mean ur engine is running to lean. and that popping that your hearing is a lean pop.

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    E-7 Sheepdog (ret) SmokinLowriderSS's Avatar
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    I'm with ol guy in my suspicion of valve float "at the very highest rpm range that my boat turns".

    What is that RPM and what is the valve-train setup?

    My stock GM/Hardin setup would float @ 6-grand (did it cavitating hard in a turn trying to avoid a damn jet-ski once (ONCE)), current setup, not a chance, going to take a LOT higher.
    "As democracy is perfected, the office of president represents, more and more closely, the inner soul of the people. On some great and glorious day the plain folks of the land will reach their heart's desire at last and the White House will be adorned by a downright moron."
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  11. #9
    jetboataholic HawaiianJet's Avatar
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    Quote Originally Posted by SmokinLowriderSS View Post
    I'm with ol guy in my suspicion of valve float "at the very highest rpm range that my boat turns".

    What is that RPM and what is the valve-train setup?

    My stock GM/Hardin setup would float @ 6-grand (did it cavitating hard in a turn trying to avoid a damn jet-ski once (ONCE)), current setup, not a chance, going to take a LOT higher.
    I've probably been told before but i just don't remember. What is valve float?? And how can it be fixed?? I think it was 4500 rpm, stock valve-train, stock truck heads, stock 427 tall deck.
    HJ

    ***FOR SALE*** 1978 19' Full Stringer Hawaiian Molokai Jet Boat w/ Berkeley 12JC-AB and Chevy 440 Tall Deck ***FOR SALE***

    Quote Originally Posted by mako shark mark View Post
    Oh yeah, Forgot to mention that the hull is a special mixture of speedcote, herculiner and rain-x, all blended together- good for another 8 mph top end.

  12. #10
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    Valve float is when the springs aren't strong enough to close the valves at rpm. With stock springs and if they are old, this could cause valve float and that could be your popping. The fix is new or stronger springs. Moroso makes a tool that you can check the seat presure with the heads on the engine. Years ago I found out what valve float was when my 289 had a miss at 4400. Wasn't pretty after it dropped a valve.

    Tim
    Last edited by River Rat 005; 02-12-2009 at 07:44 AM.

  13. #11
    ... Some Kind Of Monster's Avatar
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    The pump won't cause a popping noise. I agree, valve float or a lean condition.

  14. #12
    Senior Member kdub's Avatar
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    valve float at max rpm wont cause the boat not to move off idle either. If you have a leaky packing or cleanout cover o-ring on the pump it can suck air, also could have picked up some trash in the pump on your three mile run, lodged in a vane on the impeller or bowl.

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