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Thread: New Boater Questions

  1. #1
    Member akshrop's Avatar
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    Default New Boater Questions

    Looking for a little info on jets as I am a new jet driver.

    First off I have an 1852 with 70hp Yamaha 2-stroke (donít hate me, I could afford it). I have put 40-50 hours on it in the last month and a half. I have sucked a lot of rocks and the impeller is most definitely dinged up.
    First: Can I up grade the factory impeller for a little more speed (I already have bigger engine envy). I have heard some of the stainless argument and I take from that, that it will not help performance on any engine less than 100hp, but that it has longer life.
    Next: 4600 rpms is all I get out of the engine. I cruise around 3800-4000. I have heard others talking about much higher rpms. Is there anything wrong with my throttle?
    Last (for today): What is the best way to mount seats, rodholders, cletes, ectÖ? I have already had seat screws pop out.

  2. #2
    Moderator Paul H's Avatar
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    Nobody hates anybody because of what they do or don't have. You have a boat to get you on the water, and that's great.

    I'm not an expert on jets, but here's my thoughts. Most o/b's redline around 6000 rpm give or take. If you're only getting 4600 wot, you either have too much impellor for the engine (or a damaged impellor), are putting too much weight on the boat for the engine, your throttle linkage isn't allowing the carbs to fully open, or you have something wrong with the engine that is not allowing it to make full power.

    Were you able to get higher rpm earlier on in the season, when the impellor was in better shape? A dinged up inmpellor, and improperly shimmed certainly won't help you get going, especially if your engine is on the smaller size for your boat and load.

  3. #3
    Member akshrop's Avatar
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    Default RPMs

    The engine has maxed out the rpms at the 4600ish mark since I bought it new. Roughly 1 1/2 month ago. Should I be taking it back to the shop for a tune?

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    I have a 18/48 jon with a 60/40 merc jet 2 stroke. My rpm's top out around 5,500. I usualy run around 4,600-4,800 rpm's to save on fuel and just to be nice on the engine. With that set up I run about 35 mph down river and about 25 mph upriver. Which for me is plenty fast. I usualy only run with 2-3 people in the boat. And I perfer just 2 counting me. I have sucked rocks from time to time. More so durring my 1st season. But my impellor looks pretty dang good still. On my fourth season now. Haven't had to shim it at all yet. When I get in to shallow water I just pin it and usualy skip right on through. When I know I am not gonna make it and sucking gravel is gonna happen I kill the engine to save from impellor damage. I would think your rpm should be a little higher 5200-5500. But I am by no means an expert on this.

    BTW do you know your MPH? And is your boat welded or rivited? I am thinking of going to an 17/60 all weld with the same 60/40. But I am worried that I'll need more power with the heaver boat.

    Oh yeah. Congrats on your new boat

  5. #5
    Member DMan's Avatar
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    First thing I would do is pull the impeller. Check the Aluminum sleve. If the sleeve has really bad gashes in it replace it. If it has wear marks but is consistent and smooth you are probably okay. Then sharpen your impeller. Search the forum for how to do this as it is important, there is a good thread out there. You only sharpen one side. Then put the impeller back on and make sure you shim the impeller to where the impeller just clears the sleve all the way around. Sometimes it is even necessary for it to touch just a tad and then spin the impeller to set it. Make sure all three or four blades are touching the sleeve evenly. If not it is due to inconsistent sharpening and may need to be balanced and touched up by the impeller shop.

    I know that when I had my jet boat I could tell as soon my prop and sleeve needed work. You get it all perfect and the boat runs great, jumps on step easy, is fast, etc. As soon as you take on a few rock and ding up the edge of the impeller and get a gap between the impeller and sleeve you loose your efficiency to cut the water and suction power. All in all slower getting on step, less rpms, and slower speeds.

    Thats the first thing I would do........... When I had my jet I would go through that a few times a summer. I sucked allot of rocks obviously but just couldnt' stay away from the deshka at low water.

    Derrick
    ... aboard the 'Memory Maker' Making Memories one Wave at a Time!

  6. #6
    Member AKBassking's Avatar
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    Quote Originally Posted by akshrop View Post
    The engine has maxed out the rpms at the 4600ish mark since I bought it new. Roughly 1 1/2 month ago. Should I be taking it back to the shop for a tune?
    Also look at your owner's manual in the specs section. It should tell you the WOT RPMs. It does sound a little low.

    Caution though, the higher the RPMs on your OB over 5K, the better chances you have of "burning" the impeller. My Evinrude 250 WOT is 6600RPM and according to "Outboard Jets" I should not run it at that kind of RPM for very long.

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    Check your impeller and make sure someone didnt stick one in there for a 90hp engine. Normally if you cannot get full RPM then either your engine is not making rated HP or the impeller pitch is to much.
    Also when your wear ring start to go the engine will cavitate more on take off.

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    Member akshrop's Avatar
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    Default Thanks

    Thanks to all of you helping out. I am taking the boat into the shop. They also think that the impellor might be the wrong size/pitch and I have certainly sucked a lot of gravel. Tough lessons can be fun though.

    FSHKLR, My boat runs 23 MPH down river and 20 up with 24 gallons of fuel, three men, and lots of fishing gear. The boat is riveted. I hope to improve that with the proper impellor/tune. I run around 3800 RPM right now. I will keep you in the loop after I get it back in the water. Hope it might help you with your next one.

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    Cool thanks for the info. It does sound like you got a problem. 3800 and only 25 downriver sounds a little low and slow. I just made a trip to alexander creek area and we did about 29 mph down river, not quite at full throttle. Thats with 42 gal of fuel on board, 2 men, a cooler full of food and camping gear for 1 night. back up we were averaging 26 mph, that was at full throttle. We took a too much fuel though. We planned to explore a bit more but the pike fishing kept us busy enough till we got tired of the rain and headed back home. I think we used 7 gal to get there and about 8 1/2 to get back. Not bad at all I was figuring about 24 gal to get there and back. Oh and by the way it looks like my impellor will need some TLC soon. Starting to get nicked up along the leading edge. Still getting the RPM and MPH out of it though. I think I may of been able to get 1-2 mph more if the impellor was perfect.

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