Small outboard jets

YeeHaw · #1 11-21-2018, 02:54 PM

Looking to repower my 16' misty river tinner with a jet for river running. I currently have a 25 two stroke that does a great job doing what I ask and plan to stick in that category. So my question is what are the pros and cons of running a setup like this and what would be considered best bang for my buck for an outboard?

skidderman · #2 11-21-2018, 05:59 PM

You lose a lot of hp with a jet. A 115 becomes an 85 & so on. I once had a 19ft jet with a 115/85 outboard jet. Was too slow for my patience and it you suck up rocks or weeds you won't go anywhere until cleared out. Pros are will go in shallow water. Be warned though that the outboard jet could still hit a big rock but once you learn to navigate rivers properly it should not happen. I didn't keep mine long so am limited on experience. Went to an inboard jet after that boat.

Oldan Grumpi · #3 11-21-2018, 06:35 PM

I tried what you're contemplating, and I wasn't happy with it. The jet pump does indeed cost you about 30% of the engine horsepower, but there are additional downsides.

There is no 'neutral', as there is no gearbox. It's sucking from the moment you hit the starter, and while you can balance forward and reverse with the 'reverser', it's sucking sand and gravel through the pump all the time. Sit at shore and wait for a brief warmup? You're pumping sand, even if you're not moving.

Also, mine was terrible for plugging off with weeds against the grill, and a good part of what went through the grill went into the engine. I frequently had to unplug the tattle tail hole with a piece of wire.

For a tinny in water too shallow for a regular outboard, I'd check out the Pro Drive 'mud motors' that they sell at Explorer Industries in Edmonton. Apparently they take a real beating, and seem fairly efficient compared to a jet leg.

I don't think an outboard jet is a good idea unless you go whole hog with a tunnel hull, and get the pump inlet somewhat higher than the bottom of the boat, like in the Explorer boats. As long as that pump is the lowest part of the boat, it's going to be the part that hits the rocks first.

Flight01 · #4 11-21-2018, 06:51 PM

If I had my time back I’d have went with a 50/35 in 2 stroke.
Yes 2 stroke. While I love the smooth running 25 factory MERC jet I could use a bit more power without the weight. I’d need to take more gas but think I’d come out ahead. Providing I didn’t explode the 2 stroke.

With a 16’ misty not designed for jet, I’d suggest a 50/35 in 2 or 4 stroke but keep in mind weight to power ratio. Height and angle of attack will be crucial when setting up your engine height. Do it right and it will be a fun boat. But still not a jet boat

Positrac · #5 11-21-2018, 07:15 PM

In a small Outboard go 2-stroke. Smaller, lighter and no chance to float a valve when it sucks air and cavitates, and it will at times.

Intakes on the smaller outboards are robust enough and the motors light enough that they bounce up when they hit an object. Once you move up into the 50hp range to get 30hp at the pump they don’t bounce up as quick due to weight & thrust, so they tend to take chunks out of the intake. A spare intake is a must and it would be good to know how to change it on the side of the river.

As for tunnels, a properly designed one works great and I wouldn’t have another Outboard Jet without one. Well, unless I went back to a 14’ Jon with a 25hp at the head. The one I had worked pretty good but even then I looked at how to put a tunnel in it before I finally just bought an Explorer.

Lots of recent info on here as the subject comes up a few times a year. A quick search should get you the info you’re looking for.

Flight01 · #6 11-21-2018, 07:16 PM

Trimmed down
2 gas cans and 400lbs of me and buddy upstream 30km/hr

Flight01 · #7 11-21-2018, 07:18 PM

Trimmed up
1 gas can and 400lbs of me and buddy.
35km/hr upstream

Tannerdog · #8 11-21-2018, 07:36 PM

First off, if your Misty River is a V bottom, it will not work well with a jet leg. The intake needs a flat clean sheet of water coming off the back of the transom in order not to suck air and cavitate. You would have to mount the motor with the intake below the bottom of the V and rocks/bottom will be an issue. I had a 15' tracker jon (flat bottom) with a 25 merc 2 stroke and it was barely adequate. Under powered for sure and that boat only weighed 110 lbs. dry. I currently have a 16' G3 with a tunnel. Will be twice the weight of your tinner but also has a 115/90 outboard. Runs great but would be under powered with any smaller of a motor.

Supergrit · #9 11-21-2018, 09:16 PM

Myself I would not do it if your going to get outboard jet get a tunnel haul I have older roughneck boat with tunnel go in shallow water and the jet leg is hard to damage. With out a tunnel the jet leg would be below the boat.

pikeman06 · #10 11-21-2018, 10:00 PM

What these guys just said. A v hull is not a river boat unless you got the horses. I got a 70 horse 2 stroke on my 16 ft misty can't even imagine it with a 25. Never mind the jet leg hanging down there. Make sure you got the power when you need it. Nothing worse than halfway thru a set of rapids and you can't point it where you want to go and get there quick. It's tuff to explain until you've been there.