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Whatsup. I recently picked up my second whaler. It’s a 1970 13’ whaler and I threw a 1996 Johnson 50 hp outboard on the back.

A little back story: I purchased the 50 hp from a friend who had it on a water logged 18’ center console (way to heavy for the motor so he upgraded to a 90 hp and I snagged it up)

Currently the 50 hp is over propped I believe. It is equipped with a 13.75 x 15 3 blade aluminum prop (pretty beat up too)

At full throttle I am only pulling 4200 rpms at 27 mph.

I am looking to achieve 5500 rpms and obviously a top speed of 40-45 mph.

Any help is greatly appreciated. I have no idea where to start with another prop. I was debating a 12x13 3 blade aluminum to start.

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My first question would be is what is the shaft length of the 1996 50hp Johnson?
https://www.whalercentral.com/faq.php...p?cat_id=7

You should have a 15" shaft length for your transom.
https://www.whalercentral.com/viewpag...age_id=155

You can look at the motor Serial Number to find out what length it is for sure.
Something like: J50 "L" ??
The L would signify 20" Long Shaft.

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It is a 20” shaft motor.

I have a kent fabrication transom adapter to allow me to run a 20” shaft.

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Here’s the boat

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Here’s another.

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If you are truly going for speed, you will want a stainless steel prop.

I think the diameter is too large, not necessarily the pitch of the blade.

Your target speed will be ~ 36 mph running solo and light.

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I am not too concerned to squeeze all the speed out. But I would like to be able to get the boat to redline or close to it.

Also I will be going with a stainless steel prop after I get her dialed in. I don’t wanna spend all this money on a nice prop and still not be running the correct size.

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You have the 3cyl 50hp which is a LOT of weight for that transom as they were not the strongest from the start. That engine has the midsize gearcase so a larger diameter prop. I would check compression and throttle linkage as something is majorly wrong. I would probably raise it up a hole or 2 as well. I would start with a 13.25 x 17 SST prop, easy to find used for about $100. You should hit 40+. These boats are like barges, they are not going to do 50mph.

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Thanks for the info. The motor has 110 compression all 3 cylinders.

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How about carb linkage? Is it getting WOT? Easiest way to tell is to see how far the throttles open up and then remove the throttle and sometimes the shift cable to see if they will go farther. I don't mean a tiny bit as you can sometimes over throttle them all the way open as the butterflies will start closing the other direction. Basically are you getting all the throttle you want/need? A 3cyl 50 with a 15" pitch prop is not a 4200 rpm engine unless the prop is wrong with markings or work done to it. Should not be hard finding a 17" to try as just about every 3 or 4cyl OMC runs one or a 19". If you were closer I could scrounge one up for you.

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The carbs were rebuilt last season and throttle is 100 % open. We discovered today that she’s not running on all cylinders at full throttle. I have replaced plugs/wires/coils and cleaned up the connections / grounds but not the cdi. Do you have any recommendations? I have yet to water test again.

We also checked timing and it was 2 and idle. 18 full throttle (she hits full rpm’s on just idle revving)

My new prop should be here tomorrow I went with a 12 x 13 pitch.

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A 12x13 is NOT going to fit, don't even take it out of the box.

You asked what prop and I told you where to start. Where did you come up with a 12x13? That is not even for your gearcase. That would fit a 2cyl 50hp which you clearly do not have.

An engine running on 1cyl will hit redline in neutral and do not do that with 2 strokes unless you want to grenade it. Find out if your coils, wires, were bad by sea trial. If not the problem then stator, or CDI is bad. Try running it at night and see if anything lights up.

You are going to have to dig deeper and probably why your bud gave you the engine.cheap as he was tired of messing with it. Good thing is the parts are reasonably cheap and easy to find.