# My jon boat setup tell me what is wrong



## Big_Kahuna (Aug 25, 2013)

=D> 1980 Monarch 14ft x 48in short transom 15in
8) 1980 15HP Johnson with 9 1/2 x 10 prop (what it came with from manufacture) short shaft 15in
 Mini Jacker provides 3in lift 
:x So that puts my anti-cavitation plate 1/2in above keel.

So what went wrong. Today think I had a blowout (spun hub on three week old prop. Had to baby it back to boat ramp as it would not go over 5mph. Got home to check my lower end oil that's good. Looked at prop but can't tell it's slipping just by looking at it.

Me, wife, some fishing gear full tank of gas 5,000 rpm @ 16mph. This motor should be in the 5,500-6,500 range.


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## lckstckn2smknbrls (Aug 25, 2013)

If you put a mark on the prop and a corresponding mark on the hub. Then take the boat for a short run then check the position of the marks on the hub and prop.
Also check to see if both cylinders are firing.


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## Big_Kahuna (Aug 25, 2013)

[url=https://www.tinboats.net/forum/viewtopic.php?p=327363#p327363 said:


> lckstckn2smknbrls » 25 Aug 2013, 21:39[/url]"]If you put a mark on the prop and a corresponding mark on the hub. Then take the boat for a short run then check the position of the marks on the hub and prop.
> Also check to see if both cylinders are firing.



Ok I'll check that once I make it back to the water. If it turns out to be spun, how could this happen meaning no taggle lines didn't run into weeds or stumps. Am I looking to replace the prop every three weeks?


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## jethro (Aug 26, 2013)

Pull your prop off and check the shear pin. You may have snapped it, but the remains may still be in there causing enough friction to maintain some shear until you throttle it up. I've had shear pins go with nothing more than throttle. They can get corroded and old and just go. I'm no expert here, but most of the lower units I've been through have a buffer or something between the prop splines and the lower unit output shaft, so it's unlikely you would have trashed the prop no matter what happens unless you hit something and have visible damage.


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## thudpucker (Aug 26, 2013)

IF that prop's not down far enough into the water, you'll be sucking air. Cavitation it's called. That will damage something. :x 
Take that lift out and let the engine down some and see if the problem don't lessen for you.


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## shawnfish (Aug 26, 2013)

[url=https://www.tinboats.net/forum/viewtopic.php?p=327360#p327360 said:


> Big_Kahuna » Yesterday, 19:30[/url]"]=D> 1980 Monarch 14ft x 48in short transom 15in
> 8) 1980 15HP Johnson with 9 1/2 x 10 prop (what it came with from manufacture) short shaft 15in
> Mini Jacker provides 3in lift
> :x So that puts my anti-cavitation plate 1/2in above keel.
> ...




im curious... if you have a 15 inch transom on your boat and your motors a short shaft and you have a mini jacker that provides 3 inches of lift how can your cav plate be 1/2 inch above your keel? them numbers tell me your cav plates 3 inches out of the water. 15inch transom with a short shaft motor(15 inch shaft) should make the mini jacker useless and put your lower right where it needs to be. correct? as for only getting 5,000 rpm's how are you coming up with that #? tachometer? if so you need to try a prop with less pitch or re arrange the weight in the boat. but really 16mph is not bad for your set up and a 15hp motor. id guess that if you can get 1000 more rpm's you would be at 20mph or maybe a hair more....


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## lckstckn2smknbrls (Aug 26, 2013)

[url=https://www.tinboats.net/forum/viewtopic.php?p=327435#p327435 said:


> shawnfish » Mon Aug 26, 2013 11:31 am[/url]"]
> 
> 
> [url=https://www.tinboats.net/forum/viewtopic.php?p=327360#p327360 said:
> ...


Not all short shaft motors or short shaft transoms are exactly 15". I have a minijacker on my short shaft boat/motor, then when you add in the extra height from the setback it very easy to get 3 or more inches of lift.


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## BoatingCop (Aug 27, 2013)

That engine does not use a shear pin. It has a hub system but on these props the hub is hammered into notches making it nearly impossible to spin a hub. I'm almost willing to say with 100% certainty that you are cavitating. 

If that is the stock prop and it was not have the plastic converging ring on the end if the prop it will likely cavitate. If its an aftermarket prop, the end of the prop MUST be flared pretty good otherwise it will almost certainly cavitate. Can you post a picture of you anti cavitation plate in relation to where it is at the bottom of the boat?


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## Big_Kahuna (Aug 27, 2013)

[url=https://www.tinboats.net/forum/viewtopic.php?p=327363#p327363 said:


> lckstckn2smknbrls » 25 Aug 2013, 21:39[/url]"]If you put a mark on the prop and a corresponding mark on the hub. Then take the boat for a short run then check the position of the marks on the hub and prop.
> Also check to see if both cylinders are firing.




I have done this but haven't made it back to the water yet.


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## Big_Kahuna (Aug 27, 2013)

im curious... if you have a 15 inch transom on your boat and your motors a short shaft and you have a mini jacker that provides 3 inches of lift how can your cav plate be 1/2 inch above your keel? them numbers tell me your cav plates 3 inches out of the water. 15inch transom with a short shaft motor(15 inch shaft) should make the mini jacker useless and put your lower right where it needs to be. correct? as for only getting 5,000 rpm's how are you coming up with that #? tachometer? if so you need to try a prop with less pitch or re arrange the weight in the boat. but really 16mph is not bad for your set up and a 15hp motor. id guess that if you can get 1000 more rpm's you would be at 20mph or maybe a hair more....[/quote]

If the transom was squared up I would say that would be right but it's on an angle. It's 1/2 above the keel with jack plate. According to the Johnson manual I should check it with a light load. I did and I got 5200rpm @ 20mph just me boat and some fishing items.


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## Big_Kahuna (Aug 27, 2013)

So far what I have checked, got fire to both plugs. Checked both plugs and one looked fouled (oil) so I have changed them. Eyeballed the prop marked it now waiting to get back to the water. I will update with results. [-o<


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## Big_Kahuna (Aug 28, 2013)

[url=https://www.tinboats.net/forum/viewtopic.php?p=327647#p327647 said:


> Big_Kahuna » 27 Aug 2013, 23:30[/url]"]So far what I have checked, got fire to both plugs. Checked both plugs and one looked fouled (oil) so I have changed them. Eyeballed the prop marked it now waiting to get back to the water. I will update with results. [-o<




Ok here is the update. Must have been the fouled spark plug. Now running Champion I did have NGK's in it. In the river going up stream 5600rpm @ 18mph. Going downstream 55-5600rpm @ 21mph. I had different tach when I gave the first set of numbers using tiny tach this time. This was just with me in the boat, anchor, gallon of fuel, three life jackets, fishing net, some tools. So look as if every thing is the way it's suppose to be. Thanks for the help


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## JMichael (Aug 28, 2013)

I'm curious how you mistake an engine running on one cylinder (one plug fouled) for the sound of a spun hub or cavitation which would be over revving.


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## shawnfish (Aug 29, 2013)

[url=https://www.tinboats.net/forum/viewtopic.php?p=327729#p327729 said:


> Big_Kahuna » Yesterday, 18:09[/url]"]
> 
> 
> [url=https://www.tinboats.net/forum/viewtopic.php?p=327647#p327647 said:
> ...




when the engineers design outboards(and im not sure but probably any engine) they start with the spark plug and design everything around that plug wich in 1980 were champions. I ran NGK's in my 80 Johnson 25hp for a while because the parts store didn't have my plugs in stock and when I put the champions in I could notice how much better the motor idled and ran. if your max operating range is 5500 to 6500 rpm's
and your running at 55-5600 rpm's at those speeds you are making your motor work a lot harder than it should have to and is putting more wear on the engine than normal. with a 55-6500 operating range your motor should be putting out about 1000 more rpm's for it to run like it was designed to run. if your wide open at 5600 rpm,s you better change to a prop with less pitch that will let you run right around 6500 rpm's or that motor will not last long putting all that strain on your powerhead,shaft,gears etc.....


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## Big_Kahuna (Aug 29, 2013)

[url=https://www.tinboats.net/forum/viewtopic.php?p=327742#p327742 said:


> JMichael » 28 Aug 2013, 22:57[/url]"]I'm curious how you mistake an engine running on one cylinder (one plug fouled) for the sound of a spun hub or cavitation which would be over revving.



Jay my man never said I was a mechanic. This is my first boat with an outboard. The motor was over revving. Only could go about 5mph with the fouled plug.


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## Big_Kahuna (Aug 29, 2013)

when the engineers design outboards(and im not sure but probably any engine) they start with the spark plug and design everything around that plug wich in 1980 were champions. I ran NGK's in my 80 Johnson 25hp for a while because the parts store didn't have my plugs in stock and when I put the champions in I could notice how much better the motor idled and ran. if your max operating range is 5500 to 6500 rpm's
and your running at 55-5600 rpm's at those speeds you are making your motor work a lot harder than it should have to and is putting more wear on the engine than normal. with a 55-6500 operating range your motor should be putting out about 1000 more rpm's for it to run like it was designed to run. if your wide open at 5600 rpm,s you better change to a prop with less pitch that will let you run right around 6500 rpm's or that motor will not last long putting all that strain on your powerhead,shaft,gears etc.....[/quote]

According to service manual 15HP @ 6000rpm. Tank tested @ 6200rpm. Thinking if I go to a 9 1/2 x 8 that should put me were I need to be is this right?


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## Big_Kahuna (Sep 3, 2013)

[url=https://www.tinboats.net/forum/viewtopic.php?p=327584#p327584 said:


> BoatingCop » 27 Aug 2013, 14:01[/url]"]That engine does not use a shear pin. It has a hub system but on these props the hub is hammered into notches making it nearly impossible to spin a hub. I'm almost willing to say with 100% certainty that you are cavitating.
> 
> If that is the stock prop and it was not have the plastic converging ring on the end if the prop it will likely cavitate. If its an aftermarket prop, the end of the prop MUST be flared pretty good otherwise it will almost certainly cavitate. Can you post a picture of you anti cavitation plate in relation to where it is at the bottom of the boat?




I'll see if I can get one up.


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## Big_Kahuna (Sep 4, 2013)

Here are the photos of jack plate with 15hp Johnson 1/2 above keel. :arrow:


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## Rich27028 (Sep 5, 2013)

something not right here - engine will not over rev with a fouled plug-- 

sounds like cavatation -- -- take jack plate off and set engin cav plate level with keel


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## lckstckn2smknbrls (Sep 5, 2013)

With the 4" of setback your getting from the jack plate I don't think your motor is too high but it might not be at the correct height for your boat motor combo. Drill out a few more of the dimples on the mini jacker and try different heights you my find out your boat needs the motor to be a little lower.
When I first mounted my mini jacker I set it so the anti-cavitation plate was even with the bottom of the hull. The boat ran good so I tried putting a 1" thick wood block on top of the mini jacker. That was a little better so I raised the mini jacker 1" and tried it again with the 1" wood block and finely end did up with the anti-cavitation 2" above the bottom of the hull.


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## Big_Kahuna (Sep 6, 2013)

[url=https://www.tinboats.net/forum/viewtopic.php?p=328538#p328538 said:


> lckstckn2smknbrls » 05 Sep 2013, 22:55[/url]"]With the 4" of setback your getting from the jack plate I don't think your motor is too high but it might not be at the correct height for your boat motor combo. Drill out a few more of the dimples on the mini jacker and try different heights you my find out your boat needs the motor to be a little lower.
> When I first mounted my mini jacker I set it so the anti-cavitation plate was even with the bottom of the hull. The boat ran good so I tried putting a 1" thick wood block on top of the mini jacker. That was a little better so I raised the mini jacker 1" and tried it again with the 1" wood block and finely end did up with the anti-cavitation 2" above the bottom of the hull.




I'll try that and see what I come up with.


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