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Thread: Trouble with jmax XS

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    Member DanielApplin's Avatar
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    Default Trouble with jmax XS

    I have a 2008 160hp jmax extreme shallow and am having problems with cavitation. I have a solas 14/20 impeller that is fit nicley to the sleeve which is in good shape. It seems to cavitate more in bigger chop but today I took it to finger lake to do some load/weight testing and the boat seemed tonbe sucking air lighty loaded and then could barley put 1500 pounds on step and seemed to be slipping and not pumping water to full potential, which really seemed to hurt the ability to step more weight. I know the jet units on these boats really are a downfall but i have seen a 20 foot sea ark with a 150hp jet drive step 2800 pounds, can someone explain that to me? I am taking the sleeve and impeller I AFF to see if they can tell me something I don't. Any suggestions or knowledge about this cavitation and weight hauling problem would be awesome to hear thanks for any input.

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    Stinkin thing what the heck

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    Member tjm's Avatar
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    Any damage to the bottom of the boat? If not, most likely culprit is impeller/sleeve...you've got a tiny pump and it doesn't take much wear to lose a noticeable amount of performance..
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    Member DanielApplin's Avatar
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    There are a few dents along the edges of the boat on the left side and up towards the bow but nothing huge, do they just need to be pounded out if nothing else?

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    Member alaskabliss's Avatar
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    Does that have a oring or seal on the housing? I have not looked at your style boat in depth but know the jet ski's have a oring that when it fails you cavitate all day long and have the same issues you are having. With that train of though, could there be a seal or something allowing air in. On my H212 I have had a stick as small as a flat toothpick stuck in between the impellar and sleeve and couldn't get on step, maybe another thing to look at.
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    Member HCL's Avatar
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    I agree with T, check the impeller and sleeve. These rivers up here are like running in Lapping compound and it dont take long at all to wear enough clearance to cause issues or notice a differance.
    Mike

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    Member DanielApplin's Avatar
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    Dropped it off at AFF today and am hoping that is all it is.

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    Member DanielApplin's Avatar
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    Thanks for the suggestions guys. I got the rebuild impeller and ss sleeve from frontier fabrication today and tested it out. Impeller seemed to help a lot and cavitated way less and was able to cruise at lower rpms while staying on step, but the motor is now only hitting 8400 rpms wot when it was hitting 10200 before new impeller. Could the impeller be causing this or is it something else just being a weird coincidence? Thanks - Dan

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    Member tjm's Avatar
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    Tighter impeller = lower rpm's
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    Member DanielApplin's Avatar
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    Top speed also went from 43 mph to 34 mph with new impeller

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    Member tjm's Avatar
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    Ouch... Maybe too tight for that pump ...
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  12. #12
    Member DanielApplin's Avatar
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    Thanks tjm, I guess I assumed the motor would spin then same rpms regardless

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    Member DanielApplin's Avatar
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    Ya it was really really tight when I put it in it was actually rubbing a little bit on sleeve, do they need to grind on it for me some more?

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    Member tjm's Avatar
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    Just a little rubbing is ok, but i dont know anything about that jmax motor...perhaps the torque is so weak that you are rubbing enough that it is jus holding the motor back too much...i know those motors need to spin up, and that little impeller probably need to be spun up pretty high too for you to get your top speed back...

    I don want to lead you down the wrong path, nut i'd probably clean up the impeller just a tiny bit and re-test it...you'll get your rpm's back for sure if you take enough metal off so just be sure you don't put yourself right back in the same predicament by getting too aggressive with your file ...also i have no idea about how finicky those high rev impellers to balancing...be careful there too...
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    Member DanielApplin's Avatar
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    Thanks man, I'm probably going to test it out a couple more times, touch it with a file untill its just right, then I'm sending it out of state to get a thicker replica made of this impeller so I don't have to deal with this all the time. Dan

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    Member alaskabliss's Avatar
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    I wouldn't touch the impellar with a file. On the 212 the impellars are so tight that they will tell you to start them and not shut it down till the horrible sound of grinding metal stops and then the impellar is as tight as it can be. Sounds like the impellar was repitched in the process of being rebuilt. Your RPM's shouldnt be lower. They should be the same as the day it came off the show room floor. I had a similar issue last year with AFF but my RPMs were too high. He repitched it and lowered the RPM's but my fuel burn went up 1-2 gph. She shoots out of the water though no matter how loaded down it is. I would go talk with them again and let them know whats going on. And don't file it!
    Ignorance is not Bliss, it's insanity

  17. #17
    Member tjm's Avatar
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    I'm sure there's quite a difference between a 212 and the little pump on the JMax...I'm sure there's an even bigger difference in the motor you were spinning the 212 with compared to the motor in the JMax....

    Letting her just grind and squeal until the noise goes away might bugger up the sleeve a bit too...i don't know what the sleeve is made from but if the impeller is stainless and the sleeve is aluminum then probably not the best way to get the impeller to fit...

    Do the job right, file it until it fits as snug as possible without grinding/squealing....keep in mind that shaft isn't exactly a precision instrument, it is not spinning the impeller perfectly perpendicular in relation to the sleeve, so you might have room on one side but still be rubbing on the opposing side...

    if your not making noise then look elsewhere for what is dragging down the rpm's... Almost certainly the drop in rpm is partially due to less cavitation too...That motor isn't exactly a torque monster so I'm sure it wouldn't take too much to bog it down....
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    Member alaskabliss's Avatar
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    I have a bigger motor for sure but the same principles apply. You want that impellar as tight as possible. I also have a bigger pump so logic would say that the little motor will spin a little impeller that is tight just fine till it fits itself into the sleeve. Were not talking about inches oversize but mere thousands of an inch.
    If the boats top speed and rpm's are down you have a problem. I don't believe for a minute that a tight impellar is doing it. I do think it could have been pitched differently then stock, on purpose or not. Filing the impeller down before talking with the person who rebuilt it could void any warranty. Look up the clearence tolerences and it isn't much at all and preferably non.
    Ignorance is not Bliss, it's insanity

  19. #19
    Member tjm's Avatar
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    Quote Originally Posted by alaskabliss View Post
    You want that impellar as tight as possible.
    agreed

    Quote Originally Posted by alaskabliss View Post
    Look up the clearence tolerences and it isn't much at all and preferably non.
    if you look up the clearances I think you'd be surprised...they are usually quite large (opinion) and would benefit from being tighter than 'spec'...

    looks like Daniel gets 2 opinions for the price of 1

    I'm relaying what I observed in the 10+ impeller rebuilds/swaps on my boats....this exact thing happened every single rebuild, just not to the extent of losing 2000 rpm's...usually a couple hundred though...

    bet 'cha a nickel that the impeller is 100% the reason for the drop in rpm's ...

    take care...
    T
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  20. #20
    Member DanielApplin's Avatar
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    I appreciate the input guys, I haven't filed it and was going to talk to AFF this week and see what they think about the 1700 rpms loss. I believe the pitch was changed on the 14/20 solas that was given to them. It was grinding at first but not it isnt making noise and i checked mu plugs and throttle cable and such to make sure that wasnt the issue. It seems like that motor makes a lot of its power between 9000-10000 rpms which I cannot come close to reaching. I took the boat up to the cabin close to kroto and moose creek forks, then a ways up moose creek and was happy with how well it does, was driving it pretty hard and only took 6.5 gallons of gas to get from deshka landing to forks, about 33-34 miles, then today returned with a 1300 pound load of kayak floaters and seemed to do just fine, but I feel with even a thousand more rpms it could be much better. Boat only cavitated over the smaller chop in the big su on return trip, which I think I can get used to. Thanks - Dan

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