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Thread: J-Max

  1. #1

    Default J-Max

    Okay, just got back from the Copper bear hunting with the 1875 J-Max.
    First off the boat only had about 4hrs. on it when I left so I'm not sure what to expect after it gets broken in or if mileage and perfomance should get better with time. I would think so.
    I initially ran down for one hour at 8000rpm and filled up. It took 6gal. to top off. Speed ranged from between 24mph-30mph but we had serious head winds of around 30mph so I know that had an effect on speed.
    Load was two hunters and more gear than I care to admit taking. I would guess we had about 300lbs. of gear.
    Took a couple wrong turns on the river into some really shallow stuff and kept waiting to grind to a stop but didn't even touch so was happy with how shallow this thing runs.
    The one thing I will say about this boat that I think is a big plus is how quiet it runs. I can sit right over the dog box while running and hold a conversation with another person. Granted we needed to talk loudly but it is no where near as load as the Opt. This for me is a big plus.
    On the trip up river I ran it at 9000rpms and the boat seems to run awsome in this range. It probably was burning close to 7gph in this range but speed coming up the Copper was averaging around 25-26mph with a load and bear might I add.
    I get the impression that this thing will probably burn the reported 3.5-4gph in the 7500 rpm range which for me is not fun enough. I am sure I will be running in the 9000rpm range most of the time so will suffer a higher burn rate than I had hoped for.
    I still have a lot of testing I want to do with this boat and will start recording data with gps and burn rates once I feel it is broken in. My gut feeling is that the Opti is the better sled for the money and performance but after spending time it that boat last year was unwilling to put up with the noise level it puts out. I know some are breaking the code on this with sound silencing materials so maybe that was the route to take. We'll see how this boat does down the road. So far I'm happy with what I've seen but am hoping for better fuel mileage.
    Whacked a nice bear way down by Miles Lake by the way. Oh, yeah. this thing did great even though after I pulled it out it had a bunch of sticks and debree stuck in the intake. The Copper as usual is full of trees, sticks, fish wheel parts etc. so it's like running a slalom course the whole time. Now I've got to go clean the boat and my gear as everything is full of sand from the high winds.. This must be what our troops in Iraq have to deal with on a daily basis.
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  2. #2
    Member AKRoadkill's Avatar
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    You had a bunch of sticks and crap in the intake and it still ran great? Wow! usually it only takes a little blockage to really destroy performance in a jetboat. Does it have a stomp grate?

    Nice bear!

  3. #3
    Member tjm's Avatar
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    Quote Originally Posted by mtnman View Post
    I know some are breaking the code on this with sound silencing materials
    roger that...$50 and a couple of hours work and I can now cruise at 4800 rpm and yak with my buddy without shouting in my 200 opti......

    ....nice bear, congratz...
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  4. #4

    Default stomp

    Yes, it has a stompgrate but it was running well so I really didn't think there was all that much stuff in there. Some of the sticks where jambed up there pretty good but it must have been getting good intake cause it performed well even with all that junk in there. I thought about pulling over and hitting the grate but hate pulling over on that river. The dealer said I'm supposed to shut the engine off before hitting the grate. Seems like I could just put it in neutral and stomp it. Whats the scoop here?
    I may look into sound silencing my dogbox like the Opti guys just to make this boat quieter. If you can pull it off for $50 would like some intell. on that.

  5. #5
    Moderator LuJon's Avatar
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    Congrats on the great hunt and the great boat! Not to mention the nice bear. I am enjoying reading aboout your experiance with the J-Max. On a side note if the "sand" was the consistancy of talcum powder then perhaps you have gotten a glimps into the Iraq experiance.

  6. #6
    Member AKRoadkill's Avatar
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    I also would like to know how to reduce the engine sound in my 210 SportJet. I don't shut it off to stomp it, just make sure I'm in deep enough water with no crap floating around that could get caught in it.

    And LuJon, I can relate to the talcum powder sand in Iraq. Been there twice...REALLY nice when it rains, no? sloppiest, stickiest crappiest mud I've seen anywhere besides the Rex trail!

  7. #7
    Moderator LuJon's Avatar
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    Quote Originally Posted by AKRoadkill View Post
    And LuJon, I can relate to the talcum powder sand in Iraq. Been there twice...REALLY nice when it rains, no? sloppiest, stickiest crappiest mud I've seen anywhere besides the Rex trail!
    Yeah funny I remember trying to wipe it off in some gravel, I ended up with 10lbs of rocks stuck to my boots! Stuff is unreal!

  8. #8
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    Putting the boat in nuetral does not stop the pump from pumping, it just lowers the reverse bucket about 1/2 way over the nozzle. I never use the stomp grate while the engine is running. If there are rocks or sticks or whatever in the grill, if you stomp it the pump is going to suck them right up.

    Nice bear. Glad you like your new boat! Any shots of it on the river?

  9. #9

    Default River Mud

    Doesn't sound like the sand is as bad on the Copper as what you guys are talking about in Iraq. Actually when it rains it becomes almost enjoyable down there as it knocks the dust down for a day.
    Sounds like the thing to do is to shut down before using the stompgrate. Makes sense now that you explain it.
    Another thing about this boat that's interesting is that the center console window folds down. This came in handy on the trip down the Copper as the wind was so bad that the windshield seemed to act as a sail.
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  10. #10
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    Quote Originally Posted by mtnman View Post
    The dealer said I'm supposed to shut the engine off before hitting the grate. Seems like I could just put it in neutral and stomp it. Whats the scoop here?
    Stomp it with the engine running and any rocks in your grate are going to go through the impeller and possibly damage it. The idea with the grate is to keep that stuff out of the impeller not save it to do damage later.


    Nice bear

    Quote Originally Posted by tjm View Post
    $50 and a couple of hours work and I can now cruise at 4800 rpm and yak with my buddy without shouting in my 200 opti...
    Where is the thread on that? Most the quiet boat ideas cost $100's not $50.

  11. #11
    Member AKRoadkill's Avatar
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    "Stomp it with the engine running and any rocks in your grate are going to go through the impeller and possibly damage it. The idea with the grate is to keep that stuff out of the impeller not save it to do damage later."

    That makes sense to me. Don't know why I'd figure the stuff would just fall out...with the impeller still turning. I think y'all have just changed my ways, and probably saved me some money on impellers. I don't know how much they afre, but I'm pretty sure I don't wanna be spending that on a regular basis. Thanks for setting me straight!

  12. #12
    Member tjm's Avatar
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    Quote Originally Posted by Crumm View Post
    Where is the thread on that? Most the quiet boat ideas cost $100's not $50.
    no thread...pm me your email and I'll forward the info/pics I sent others...basically just seal up all your open spaces with weather stripping......simple, cheap, and makes a dramatic difference...
    ------------------------------------------------
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  13. #13
    Member Yukoner's Avatar
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    So far I'm happy with what I've seen but am hoping for better fuel mileage.
    What were you running before this rig? Seems like if you can get 7 GPH coming up river with a load, thats pretty good
    Anyone know what the absolute best set up is for jetboats GPH wise??
    BTW, how do you find that rig in chop?
    Looks like a great trip.

  14. #14

    Default Evenrude

    I was running an 18' Alumaweld with a Evenrude 88spl. jet. That's about 115hp engine. It would cruise up river on the Copper about 18mph with two guys and full camp at about 5000rpm if I recall. That was on average and I think I was burning about 8-9gph. Going down I think I was cruising around 22 depending on current and chop. (100% flat bottom boat so chop could get abusive). Not bad but when you loaded it down any more than that it would get sluggish to respond and was a little slow to get on step. Attached a pic of that boat which is for sale and I'm ready to deal as the wife is complaining about my fleet of boats.
    I would have kept using it but my biggest complaint was that it seemed to draft deep at idle and then I would suck in rocks from time to time which had the negative effect of making the boat want to go down river backwards with not alot of control..That is a very bad thing on the Copper River. I have some very bad memories of this very situation which can make you wake up in a cold sweat in the middle of the night. I think that would be the case with any outboard jet. One or two medium sized rocks stuck in the grate and you have no forward propulsion.
    This extreme shallow drafts way shallower at idle and even if I get a couple rocks pinned against the grate I still have good enough propulsion to deal with the situation. I'm still getting comfortable with the boat but so far like what I see. This boat takes the chop better as well as it has an 8* rise to the hull. That's not much but it helps. The 12* rise would have been better for rivers that commonly have big chop like the Copper but they don't draft as shallow which was a big deal to me as there are many side channels I like to run that are very shallow.
    Glad to get the skinny on the stomp grate thing and will definetly be shutting it down to clear.
    I should have paid a little more attention to my rpm's and speed coming back up the Copper. Had the gps going but only checked it a few times as I get focused on just running the river. I did check the time from 32 miles down as the crow fly's which took just over 1 1/2 hrs to make it to the take out at the bridge. In the past in my other boat that distance alway seemed to take right around 2 hrs. depending on river conditions. Also had a head wind when we were coming up the river which is really rare at least for me. Usually the wind blows up the river at gale force, not down. Goggles and windshield solve the problem of the pelting sand.
    It's a great trip but I would make sure to have all of your ducks in a row as there is no help down below Haley Ck and that river has a way of eating boats. It can come up fast over night in the summer if an ice dam breaks which happens every year a couple times. you'll hit the rack and wake up to high water and tons of debree coming down.

  15. #15

    Default flat bottom

    For some reason the computer wouldn't let me attach the photo of my old boat but it's on the swap and sell section under "Alumaweld".

  16. #16
    Member Yukoner's Avatar
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    Who builds the J-Max engine, i have heard its a Yamaha.

  17. #17
    Moderator LuJon's Avatar
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    Quote Originally Posted by Yukoner View Post
    Who builds the J-Max engine, i have heard its a Yamaha.
    If I am not mistaken you are correct and it is a 165 Yami inboard. From what I have gathered it is basically a reworked waverunner motor

  18. #18

    Default 160hp

    Correct as far as I know. It's a 160hp. yamaha.
    I went into the E.River Yamaha dealer to buy an oil filter as I just did the first recommended oil change at 10hrs. use. This dealer does not do boats, just snowmachines, waverunners and bikes I think. Anyway, the dealer didn't know that jetcraft had stuffed that motor into their boats. He ranted to me for sometime on what a great motor it is and basically said if you do the required 100 hr. oil changes and regular maintanance that it should last forever and just get stronger. Seems like along time and wish I could live that long.

  19. #19
    Member Yukoner's Avatar
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    He ranted to me for sometime on what a great motor it is and basically said if you do the required 100 hr. oil changes and regular maintanance that it should last forever and just get stronger.
    Geez, with that AND reasonable mileage, how can you go wrong

  20. #20
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    Its the same basic engine that is in thier R1 sport bike.

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