jhonson outboard

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jhonson outboard

Postby green head2 » Mon Oct 03, 2005 6:26 pm

I have a 40hp jhonson seahorse on my boat Im hoping someone might be able to ansewer my question I just bought the boat this summer And only have had it in the water twice Between idle and half throttle the boat moves great But if I open it up the engine revs up but the boat slows down or barley moves I dont know alot about outboards or boats really And where I live there is only one guy that works on them He went through my engine tuned it up rebuilt the carb changed the plugs But it is still doing it He said he has never heard of it But he is a small engine repair guy not really a boat man sticks to lawn mowers ATVs Just a few boats a year Any Ideas I thought mabey the prop But I would not know what size to go to Bigger smaller I need help Thanks
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Postby Smackaduck » Mon Oct 03, 2005 6:38 pm

Sounds to me like your prop is either blowing out of the water, or the prop is spinning on the hub. If your motor is trimmed all the way down, i would be willing to bet that the prop is spun off the hub. :thumbsup:
As far as prop size i would find a prop manufacturer and tell them your specs and they should be able to get you the best prop for the situation.
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Postby green head2 » Mon Oct 03, 2005 7:22 pm

What do you mean spun off the hub You think the prop is to small Or that something is broke thanks
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Postby bkejwanong1971 » Mon Oct 03, 2005 9:31 pm

that would be my bet too ,,,,,,,prop wrong size or worn down too much ,,,or is worn out ,,,,,,,,,,try a new prop ,,,,,,,get rite size very important
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Postby ol' yeller » Tue Oct 04, 2005 6:47 am

Do you have a stainless or aluminum prop? If it's stainless I would bet it's a spun hub. There's a rubber hub inside of the center of the prop. If the rubber is old or the prop has been hit hard it will cause it to slip. Try putting the motor in gear at home and see if you can spin the prop by hand.
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Postby gsphunter » Tue Oct 04, 2005 7:27 am

Adding to what yeller said, make sure the shaft isn't spinning when you spin the prop. You're checking to see of the prop will spin indepedent of the shaft.
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Postby Evil_McNasty » Tue Oct 04, 2005 11:28 am

Is the motor bogging down? If it engines is still getting full rpms and it's going slow, it's prolly a prop issue. But you didn't say what the engine sounds like.
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Postby green head2 » Tue Oct 04, 2005 11:37 am

The engine revs up no bogging back firing I just start slowing down but the engine is wound up I could probably swim faster than it pushes the boat But when I drop it back to half throttle it takes of again I will look at the hub when I get home thursday Also A buddy of mine said I could be to low or high in the water There is a plate right above my prop How far above or below the bottom of the boat shpuld that be Thanks for all your help
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Postby Evil_McNasty » Tue Oct 04, 2005 11:46 am

Yeah that sounds like a slipping hub problem. Assuming you have that type of hub.

The cavitation plate should be out of the water while running at full throttle. There are 2 things to avoid when raising the motor. (1) Getting to the height where the water intakes are not getting enough water. This causes low water pressure and therefore allows your motor to overheat. Watch your wp. (2) Overreving due to the prop exiting the water. This is a no brainer, if you are jacked up high, are trimmed up, and the hit some chop where the prop has blow out, you are too high.

PM me if you have any detailed outboard/boat performance questions. I've been running and working on performance boats for years.
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Postby pwhnts5 » Tue Oct 04, 2005 12:16 pm

Sounds like a hub slipping, but it could be another issue. Is the motor a short shaft or long shaft model? What is the transom height of your boat, 16" or 21"? If you put a short shaft on a 21" transom this could happen, or if you put a long shaft on a short transom it can also cause this problem. Check that out. The cav plate on the motor should be about in line with the bottom of the boat.

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Postby green head2 » Tue Oct 04, 2005 12:32 pm

Im not sure if its a long or short shaft the motor is a 1960 seahorse Where do I measure from The middle of the cut in the transom to the bottom of the boat And the bottom of the motor to the prop If its to low Can I fiberglass a 2x4 or two together and then to the transom to lift it to get the plate even with the boat I guess I should check the hub first Then go from there to fix any problems if the prop is not it Again I appreciate all of yalls help I have never had a outboard motor or a boat long enough to have any problems Until I bought this can of worms Thanks
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Postby pwhnts5 » Tue Oct 04, 2005 2:36 pm

Measure from the top of the transom where the motor clamp goes over to the bottom of the hull. If it is 16" or less you need a short shaft, if its 20-21" you need a longshaft motor. Do the same on the motor, measure from the clamp braket where it sits on the tansom down to the cavitation plate, it should be 16-17" for a short shaft, 20-22" for a long shaft. I am not sure, but I think a motor that old is most likely a short shaft.

My gust feeling is that if it is wrong, you have a short shaft motor on a long shaft transom boat, that is what is sounds like to me. The older Johnson's used shear pins, not thrust hubs, so I don't think it is the hub.

Hope this helps.

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Postby ol' yeller » Tue Oct 04, 2005 2:39 pm

One more thing to add to pwhnts5's post is see where the cavitation plate sits in relation to the bottom of the boat. Most outboards are setup to run the cavitation plate anywhere from even with the bottom of the boat up to 1.5" below the bottom.
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Postby twin_teal » Wed Oct 05, 2005 2:39 pm

If you have an older motor and the cavitation plate's set up I'd check the shear pin. My friend used to have a old johny with shear pins and if he sheared one he could go about half throttle and then the prop would spin on the shaft. Pretty much the same thing as a hub slipping but easier to fix.

One real easy way to check if you have a shear pin is to check the prop for a head cone. If you've got a cone you probably have a shear pin. If this happens to be the case I'd almost garentee you sheared a pin which is actually good news cause they take about 5 minutes to fix and their cheep. Another suggestion if you do have shear pins keep a few extras in the boat at all times because if you hit something and shear a pin you can just fix it then and not worry about it.
why have a mud motor when you could have an airboat?
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Postby green head2 » Tue Oct 11, 2005 9:18 pm

I checked the plate this weekend it is dead even with the very bottom of th boat The far sides of the boat are a little higher The back of the boat is a v And the plate is dead even with the little 2 inch ridge at the bottom Hope this is making sense I checked the shear pin it was fine There is no rubber in the prop it self or do I think there would be room for one It was a really tight fit If I twist the prop around you can here the pistons turn over its got a lot of compression against the motor I ran it this weekend and it is getting worse If Im stopped and gun it it runs really fast for about 5 seconds Then slows down but the motor is still reving high Almost like spinning a clutch on a car Grabs then lets go until it slows down Is there a clutch on this kinda motor If so are they expensive and hard to find and replace I sure do appreciate all of you guys helping me out here I wish the boat shop was not 200 miles away Thanks
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Postby Evil_McNasty » Wed Oct 12, 2005 7:37 am

Hmmmm, maybe you should try a different prop. One with more pitch.
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Postby jawilor » Wed Oct 12, 2005 9:36 am

I had a similar situation with my 6HP Johnson. It would run great at idle and low speed, but at full throttle is would really bog down. Turns out the gas line on the carburetor wasn't clamped and gas was squirting out the sides at full throttle. I clamped it with a zip tie and the boat ran great. I realize this may be different than what you're experiencing, but it sounds like everything on your motor has checked out OK so far, it may be time to look at other potential causes.
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Postby jawilor » Wed Oct 12, 2005 9:42 am

Here's a site that will give you a schematic and parts list for your motor
http://ishopmarine.com/ishop/jsp/AsplIsmHomeCcat.jsp?reqFor=29
Follow the parts link and you'll end up with the schematic.
Good luck
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Postby green head2 » Wed Oct 12, 2005 4:19 pm

Thanks for all your help guys I called the honda dealer ina town about 60 miles away from my house Asking about a new prop He told me there is a dealer for johnson in my town I called this dealer up and talked with him for about a half hour He has been working on motors since 1943 And been a dealer here since 1960 I have lived here all my life population is around 2000 And I never knew we had a dealer Kinda funny He is going over to my house to pick up my boat And said he will have it running like new before I get home on friday Again thanks
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Postby Smackaduck » Wed Oct 12, 2005 7:50 pm

Please be sure and let us know what it was for future reference. :smile:
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