12WJ RPM question

[tbcseod]

Hi all, I am hoping someone here might be able to clue me in on a problem I am having.
I recently bought a 21 foot SKV jet boat and have basically had to rebuild it as the guy I bought it from marked me as a n00b to boats (and he was right). Anyway, It has a fresh (rebuilt it myself) Chrysler 400, new Eldebrock 800cfm carb, and converted points to electronic ignition kit - all hooked to a 12WJ that had a "B" impeller. I got and installed a "A" cut and installed it but the boat tops out at 35ish MPH. The problem I am having is that I have been told the RPM is too high by 2 people and had 1 person at the lake tell me it was too low (he was in a jet also)........
Its turning at about 6000 or so at WOT (at 35ish mph) on a flat lake....... it seems to me like that is alot of RPM for that big a motor:sqeyes: , I have searched and searched but all I can find are Berkley RPM/HP charts........ can anyone steer me towards what RPM I SHOULD be seeing with this set up?:confused:
Sorry if this seem s like such a basic question, but I am at a total loss on this, its my 1st boat and I got taken when I bought it (cost wise) and now have twice that in it in parts, last thing I want it to blow the engine because I am over revving it just to scoot accost the lake.
Thanks much in advance for any and all help.
~T
PS - incase this would affect the issue: Also has a SE loader and new place diverter on it all so (Non-energizer)

[hondo454]

Something is way wrong with your pump! Or maybe your tach is bad? But you should be seeing around 4000-4500 I'm guessing, I don't know how much HP your making but it would take over 600HP to spin a "tight" pump 6k. I had a 12wj with a B impeller that i spun 5000 all day. It was thirty years old, very beat. I sucked up some rocks one day and then ran almost 6000! I had rocks stuck in the impeller and broke off vanes in the bowl:(An energizer kit from Tom at jet boat performance put me at 4700 with an A. This is when I discovered that jet boats launch hard! My old pump was junk! How is your boat out of the hole? Does it feel like it has a slipping clutch or does it hook up? First thing to do is pull the clean out cover and look for junk stuck in the impeller. Also inspect the impeller for damage while your in there. Did you replace the wear ring? Come back with any info you may have there are a lot of sharp helpful people lurking here that will have more to add:)

[malcolm]

Did you notice any diffference when you switched impellers? Did it have the black plastic wear ring in the intake housing? I can't imagine getting one to spin 6K even with the B still in it. They run a little bigger than the Berkeleys. A 'B' is closer to an 'A'. I'm only turning 5000 in a heavy boat with a B and doing around 55.

[pw_Tony]

Where did you get the A impeller for the Jacuzzi? Like Malcom said a Jac B is closer to an A Berkeley

[tbcseod]

:)
Ok, see if I can respond in order.
We thought may be the tach was bad also (it did have a internal wiring issue that would cause the needle to "drift" until you thumped it with your hand or hit a hard wave) - so it was replaced a few runs ago - no consistent change noticed (as I noted - the original gauge wasn't reading accurately about 1/4 the time - but even when it wasn't accurate it didn't ever seem to be more than 500-600 high or low, that I was able to notice and verify).
This pump is 72 vintage, the new impeller was a local purchase - in rather nice shape, no nicks and still had 90% of the original greenish paint on it - also it did measure out to 9 9/16 diameter.
Wear ring was replaced before the impeller was changed - and again with a new ring when the "A" when in.
The vain's in the bowl look kind of rough, most of the leading edges were rounded back a bit so I took a dremel and tried to clean them up some but one did have a quarter sized (maybe a bit smaller - its hard to remember exactly) chip taken out of the leading edge. I have agreed to buy the guys bowl that i got the impeller from - its pretty sharp looking inside, not noticeable dings or nicks - I just haven't gone to pick it up yet a I don't really want to tear the bowl off again (this soon- it would be the 5th time in 6 weeks......)
out of the hole - its like a slipping clutch. It gets up on plane fairly quick but it feels sluggish as all get out.
Have checked the grate and inside while at lake. Did find a little log in it the 2nd or 3rd time out at the lake and had hoped that was the problem....... but it wasn't (though it WAS a noticeable difference, witch shocked me that such a little thing could cause so much difference).
Replaced wear ring before and after the impeller swap, both brand new.
when I switched impellers it didn't really seem to change anything. at first I thought it felt like it was getting a better hole shot and faster on plane, but after a GPS check - it wasn't really any different.
I got the "A" impeller at a local (mini) boat grave yard - happened to see a boat that looked like it had a WJ on craigslist being offered for scrap and offered to buy the impeller out of it (if it was in good shape). it was qiute clean shape and so I took it hoping that a "A" might drop the RPM / increase the speed/power.
I haven't checked the front bearing lip seals though, and was wondering last night when I made my origonal post - could air be getting sucked through the bearing when its under load ad be causing cavitation and loss of power? There's no water leaking in from the bearing cap area - but I thought maybe air could suck back through it under load?
I'm still at a loss - but I really appreciate the help so far, and actually feel good again that maybe I am in the right spot to find some good help now - please keep the help coming :D
~T
Edited for about 40 spEEling errors................. :/

[tbcseod]

http://media.putfile.com/Stop-to-full
If I did that right, that should be a link to a video I shot yesterday, this is from stopped to full WOT - top speed was 33-34mph and RPM was 6000+
thought maybe this might help "see" what was happening.
~T

[McIntyrelocal]

it sure doesnt sound like your reving to 6000 i wonder if you have your tack on the right setting most tacs have a little dile on the back for different cylinder engines you might want to check that but i could be wrong.

[napabob]

T,
I have a Jacuzzi 12WJ/B on a 454. The boat was/is equipped with a Steward Warner gas/ignition tachometer for 0-8000 RPM, it is recommended for 4, 8, and 12 cylinder engines. The 0-6000 RPM tachometer is recommended for 4, 6, and 8 cylinders and both run off the ignition. The marine engine manufacturer recommends not turning my engine above 4800 RPM, but I have had it at 5100 for short periods of time with GPS speeds in the mid 40's. I have not rebuilt the Jacuzzi and it has about 400 hours on it as far as I can tell.
Some tachometers have sending units, but they are mostly for diesel engines.
Also, do you have a diverter installed (Oops yes you do)? The reverse bucket might not be clearing the nozzle causing some loss of thrust.

[oldbuck40]

it sure doesnt sound like your reving to 6000 i wonder if you have your tack on the right setting most tacs have a little dile on the back for different cylinder engines you might want to check that but i could be wrong. i would agree it doesnt sound like 6k.
i run a wj with an A and believe me at 6k you are haulin the mail!:D

[napabob]

ob40,
Aren't the A impellers hard to find, looks like a propeller and is made out of stainless steel and are expensive?

[napabob]

ob40,
I looked on the North American Marine Jet, Inc, web site and the 12YJ has the propeller looking impeller.
http://www.marinejet.com/view.php/id/31

[Devilman]

i would agree it doesnt sound like 6k.
i run a wj with an A and believe me at 6k you are haulin the mail!:D
http://www.hotboatpics.com/pics/data/500/10158rolleyes.gif

[bulldawg art]

i would agree it doesnt sound like 6k.
i run a wj with an A and believe me at 6k you are haulin the mail!:D
What kind of HP are we talikng to turn a jacuzzi A to 6k?

[jetboatperformance]

Terry i agree with the guys the motor doesn't sound like 6k but it does sound like its runnning fairly well . Were you ever actually able to get a OD measurment on the Impeller skirt and contrast that to the wear ring ? The OE nominal measurement on the Impeller (new) is 7.373 to 7.375 max The new plastic wear rings are 7.396 to 7.398 this allows for .023 to .025 clearance (WR to wear skirt) Much beyond that can produce high RPMs vs speed such as you descibe in your post . By my estimation (former 70's mopar tech) the Chrysler 400 probaly made about 300 hp in stock form this should turn your Jac "b" around 4400 and their "a" a little a less maybe 4200 From what i can gather you still have low end "tire spin"? Call if we can help you as well... Tom

[tbcseod]

Terry i agree with the guys the motor doesn't sound like 6k but it does sound like its runnning fairly well . Were you ever actually able to get a OD measurment on the Impeller skirt and contrast that to the wear ring ? The OE nominal measurement on the Impeller (new) is 7.373 to 7.375 max The new plastic wear rings are 7.396 to 7.398 this allows for .023 to .025 clearance (WR to wear skirt) Much beyond that can produce high RPMs vs speed such as you descibe in your post . By my estimation (former 70's mopar tech) the Chrysler 400 probaly made about 300 hp in stock form this should turn your Jac "b" around 4400 and their "a" a little a less maybe 4200 From what i can gather you still have low end "tire spin"? Call if we can help you as well... Tom
Just got off the phone with ya Tom :) tons of thanks to everyone, I jutswapped out my Tach again and gonna head to the lake for a test run on a brand spanking new tach.
Will give a update once Im back and dried off.
~Terry

[oldbuck40]

ob40,
Aren't the A impellers hard to find, looks like a propeller and is made out of stainless steel and are expensive?
i have never priced one so i wouldnt know on that! i just got lucky it came that way when i bought the boat!

[oldbuck40]

What kind of HP are we talikng to turn a jacuzzi A to 6k?
Man i have no clue what its putting out!
496 BBC BDS 8-71 Blower under driven and 2 850 demons

[jetboatperformance]

Terry heres some more info.. Tom
http://i147.photobucket.com/albums/r319/jetboatperformance/Misc/DSC07204.jpg
http://i147.photobucket.com/albums/r319/jetboatperformance/Misc/DSC07205.jpg
http://i147.photobucket.com/albums/r319/jetboatperformance/Misc/DSC07206.jpg

[BrendellaJet]

What kind of HP are we talikng to turn a jacuzzi A to 6k?
A lot!. Ive turned mine to 5500(with plenty of pedal to spare of course:D ) and it gets scary fast very quick.
If anyone is interestd I've got a stainless Jacuzzi A for sale. NOS from NAMJ/Jacuzzi.

[bulldawg art]

A lot!. Ive turned mine to 5500(with plenty of pedal to spare of course:D ) and it gets scary fast very quick.
If anyone is interestd I've got a stainless Jacuzzi A for sale. NOS from NAMJ/Jacuzzi.
I'm interested in your loader:D

[SmokinLowriderSS]

What kind of HP are we talikng to turn a jacuzzi A to 6k?
I don't have a Jac chart, but a Berk A is just short of 700 HP to do 6-grand. 680 and change.

[BrendellaJet]

I'm interested in your loader:D
LOL, buy the boat and you can have it!
Ill try to pull the loader out this weekend and take some pics/measurements for you.

[tbcseod]

Well, it was infact a fualty RPM guage - started out turning a hair over 4k - then while waiting for a spot to open up at the dock to load I got side tracked when a truck wound up about 60 feet further back from the loading ramp than it was ever ment to be................. Cut my hand diving down to tie on to it to try and drag it out......... the closed down that ramp and as I was heading acrost the lake to the other ramp something went in my engine. started popping, RPM dropped by about a grand, and a lound POP!:( it came in under its own power but I spun a bearing or something. Guess its back to working on the engine for the winter........... Sigh.........
Thanks again for all the input and advice - without it I wouldnt have tried a 3rd RPM guage and still wouldnt have knowen if it was right or not.
~Terry

[bulldawg art]

LOL, buy the boat and you can have it!
Ill try to pull the loader out this weekend and take some pics/measurements for you.
Thanks. I can't wait....need to feed the pump;)

[malcolm]

I was going to guess 4200, that's what my old 403 Olds used to pull to with the B. ;)

[moparjet]

i turn a wj with a 'b' to 6000....and yes it hauls the mail