# OUTBOARD JET FOR MY 25 HP JOHNSON



## BCOWANWHEELS (Nov 13, 2013)

I,AM ABOUT TO PULL THE PLUG AND BUY A OUTBOARD JET CONVERSION FOR MY 1991 JOHNSON 25 HP TO USE ON MY 14 FT STARCRAFT. ANY THOUGHT FROM YOU FELLAS ?
THANKS
BOB


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## BigTerp (Nov 14, 2013)

Just figure on loosing 30-35% of the power you had with your 25hp. So it'd be like running your boat with a 15-17hp prop, more or less. MANY other factors to consider as well.


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## BCOWANWHEELS (Nov 14, 2013)

my 14 ft starcraft is very light and is only rated for 15 hp max so i,am hoping its gonna work. i plan on making the engine into a 35 hp as soon as i can locate the carb and intake also. thanks for your imput.
bob


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## BigTerp (Nov 15, 2013)

Sounds good. Turning your 25 into a 35 will make quite a bit of difference. You should get about 25hp at the pump that way. But as long as a 15 will easily plane your boat, you should be good to go. Check out Outboardjets.com. They make the pumps and have alot of good information about ideal hull types, jet setup, etc. I recently rebuilt a 1994 Johnson 50/35 and installed it on my Tracker 1648MV. Let me know if you have any questions. Good luck!!


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## Xterminator GT (Nov 15, 2013)

Should work great. We've got a 25 that's been converted to a 35 on a 17/42 weld bilt that is at least .100 ga and the bottom is pretty rough on and it works good.


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## BCOWANWHEELS (Nov 16, 2013)

seems everybody is looking for the 35 carb and intake,gosh there hard to find....


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## New River Rat (Nov 16, 2013)

I've got a 25HP Johnson and wouldn't do the lower unit switch on it due to power loss. If I were to go with a jet, I wouldn't settle for less than about a 50HP+ (headHP)


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## Xterminator GT (Nov 16, 2013)

There's no way I would have a 25 if the river I run didn't have a 25 hp limit.


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## BCOWANWHEELS (Nov 16, 2013)

i believe it will be fine seeings my boat is only 127 lbs, motor 115 lbs,gear and me is 350 lbs. fuel is 45 lbs o/j says 850 lbs max and i,ll be far under that. all I want to do is go up river and shut the engine off and fish my way back to the ramp about 3 miles. I,am a old fella and going fast is in the "old" days. I have a 18' raysoncraft ( LP ) low profile and A "G" MODEL both V-DRIVES with a 468 chevy's if i feel the need for speed (which is hardly ever anymore)
BOB


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## BigTerp (Nov 18, 2013)

Speed isn't really the issue with outboard jets. Being able to quickly get on plane and stay on plane is what'll enable you to run the shallows well. If your under what Outboard Jets says as far as weight goes, then you should be fine. They make the pumps, so they know what they're talking about. Once you get everything squared away, I seriously doubt you'll want to ever go back to a prop for running the river.

How is the weight currently setup on your boat? Is your motor tiller or remote steered? The only issue I can see is if it's a tiller and you also have your gas tank in the back of the boat, you might be a bit stern heavy.


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## BCOWANWHEELS (Feb 25, 2014)

well i,ve found and bought all the parts to make my johnson 25 hp a 35 hp also i,ve bought everything to convert my long shaft to a short shaft. now i need to locate a jet unit. new there extreamly expensive and 3-4 months to get. i,ve about got my transom redone and my jack plate built. i,ll have some pictures to post soon 4 you,all
bob


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## Boat2fast (Feb 26, 2014)

If you want a FULL 35hp, you have to use a 35hp block. The ports are different(you should _see_ the difference). Same with the late model 25 vs. 30hp. Some years had a different head...1983 for instance. The carb is just the part people can see.


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## BCOWANWHEELS (Feb 26, 2014)

IS THERE ANYWAY YOU CAN POST A PICTURE OF THE 35 HP EXHAUST PORTS ?


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## Boat2fast (Feb 26, 2014)

I didn't take pics when I had the blocks apart side-by-side. Small round ports on the lower hp blocks, Big oval shaped ports on the 35 and 30E blocks.


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## BCOWANWHEELS (Feb 26, 2014)

oh well the smaller exh ports will just make more lower end torque and really is what I need anyway. I,am not building a hi-rpm engine. I,ll do some rescherch and see what I can find though


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## Lil' Blue Rude (Feb 27, 2014)

Looking forward to see how it all turns out. Always love a outboard jet build. You could always square up the ports a little. Not too sharp because it will shorten the ring life but it would add to the power with out losing torque like raising them would.


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## Boat2fast (Feb 27, 2014)

BigTerp said:


> Speed isn't really the issue with outboard jets. Being able to quickly get on plane and stay on plane is what'll enable you to run the shallows well. If your under what Outboard Jets says as far as weight goes, then you should be fine. They make the pumps, so they know what they're talking about. Once you get everything squared away, I seriously doubt you'll want to ever go back to a prop for running the river.
> 
> How is the weight currently setup on your boat? Is your motor tiller or remote steered? The only issue I can see is if it's a tiller and you also have your gas tank in the back of the boat, you might be a bit stern heavy.


Listen to BigTerp. Call Outboard Jets.

Jets need HP, lots of it. Horsepower is a function of torque and RPM. The more horsepower you put into that jet, the more water it squirts out the back. That is what you need to plane a jet powered hull...from what I understand. 

I had a 25Mercury Jet once. It ran great but made much noise and little speed. I used it once and sold it. That day I decided 'If I ever set up a jet boat, it's going to have the biggest engine and the widest hull I can put together.'

That is pretty much all my experience with jets...for what it's worth.


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## wills (Dec 23, 2020)

Where is the best place to find a used jet pump for my 1987 25 hp


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