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I have a 1976 Apollo, a 12S Dominator Pump with an A impeller and a wedge pointing nozzle down; a 454 drives the rig. I am new to jet boats and took this one out for the first time last Saturday. When the boat comes out of the hole it acts like it's spinning its "tires" if you give it full throttle. You have to ease into it and then you can nail it in order to not have the thing spin out. Is that a cavitation problem or is it considered blowout? What could be done to the boat in order to make the boat "hook" coming out of the hole. The motor is fairly strong and turns the pump 5600 rpm at full throttle. The boat also has a tendency to slightly change directions if you nail the throttle when doing around 40 mph. Is this normal or are there any fixes for that situation? Other than the two forementioned problems the boat runs great. There is no porposing or anything of that nature. The hull rides very level and seems to be doing everything it's supposed to do. Thanks a lot for any help or suggestions that are given.
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A loader impeller should take care of it. Contact your nearest jet guru or Dons Pump Service (not sure what his web address is). He invented it for the reasons you just mentioned.
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sounds like you might be in need of a pump rebuild.your clearances sound loose.5600 with an a impeller would take alot of hp.
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Originally posted by 77charger:
sounds like you might be in need of a pump rebuild.your clearances sound loose.5600 with an a impeller would take alot of hp.
i just started having the same problem, but my pump just got rebuilt. it takes for ever off the line like the impeller is just spinning and not pushing. it just all of a sudden started doing this. please help!thanx
mach1 454
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Mach 1, it sounds strange that you had developed your problem in such short time since your rebuild! Start with looking at your packing gland.If you see water coming in faster than only a few drips per minute ,you're sucking air through the packing.I assume the key was put in the pumpshaft and the impeller nut tightened. 76 Apollo ,It would take around 500HP to turn an "A" imp at 5600 RPM,give or take a few horses.Either you have a very healthy engine ,or you need a pump rebuild.You didn't state your speed at WOT .Your Apollo has a bit of hook what explains that you have no porpoising problem.I've worked on a similar setup as yours in the past.
[This message has been edited by spectras only (edited April 12, 2002).]
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This boat has been clocked in the mid 80s on GPS so it is a fairly healthy 454. It doesn't do what Mach1 described. You have to really get after the thing to get it to spin out of the hole, but it will do it. It's not like it just spins and spins normally and never goes anywhere. If you nail the throttle and then let off it a little (maybe mid throttle) and then ease back into it the thing will come out of the hole pretty stinking hard. The boat just won't take full throttle coming out of the hole without breaking loose. I really doubt the pump is worn out with the thing turning that kind of mph. Not sure if some of you guys are selling pump rebuilds?
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Apollo, almost all jetboats will cavitate to some point nailing the throttle from dead stop ,but excessive cavitaton is a definite sign of large impeller clearance.I'm not doubting your engine's output,but the topspeed you stated and "it s like spinning it's tires" don't add up !? Yes you can get rebuild kits from lot of places ,including california marine [that's us Dave/Attila]604-278 1880 , or anybody else listed in ***boat http://free.***boat.net/ubb/biggrin.gif Feel free to call Dave between tuesday-saturday 9.30 am to 4.00 pm
