info about jet pump conversion

I have a 59 ci Mercury 3 cyl short shaft tiller . I want to put a jet pump on it . for fishing in some rocky rivers that destroy props and lower units . it is sitting on a jackplate with 12"of setback on a 15x 56 Edge 8 degree v The motor has been ported , flywheel shaved and mid has been drilled . It will spin a lot faster now so I prop it to keep the rpms down to about 6000 with a fishing load .I will have to raise the motor 5" with a pump , I have that much travel with the plate and motor holes just wondering about the 12" set back having an issue . What about rpms with a pump ? Does the pump load a motor like a prop does? Would I have a problem with a ported motor ? I've read somewhere with some Johnyrudes ported don't fare well with a pump on them
Thanks for any info
Ed

It all depends on how the motor was ported. jets need torque, honestly don' think your going to make enough power to need a different size impeller. My omc 60/40 is ported still turning the 6 7/8. I would buy a stainless though. If the ports where raised up enough that torque suffered then the jet wouldn't be a good thing but if it still hit hard coming out of the hole then you should be fine. Shouldn't need a bigger impeller. Never seen a 60/40 merc turn enough rpm to need one unless it had a 50 shot of nitrous hooked up. Think you'll need a jack plate with less set back too. not for sure but think it would cause problems.

Thanks for the reply ,well this thing is a beast with a prop hole shot is VERY fast with the shaved flywheel . I was told it should be making about 80+ hp , how true that is I don't know . I do know I used to run a 14 pitch prop at 5500 now I turn a 17 at 6000 with all my fishing stuff and a two BIG fishermen . It will run up to 7400 now empty with that prop done it once or twice .Its got a lot of grunt! I didn't know how much of a load a jet pump puts on a motor . I was thinking the stainless impeller would load it more with an extra blade and all + wearing better . I 've seen outboard jets with a plate from the transom to just in front of the shoe thought I may be able to do something like that and bolt it to the jackplate kinda extend the bottom. I was gonna do that anyway for my prop . This jet pump idea is a temporary thing to fish some water we can't get to with out tearing up a lower unit and prop , its the same price ,just not tearing stuff up to do it . If things don't work I can always sell it
Ed

I think that much setback will cause problems, too much water will bypass the pump. The plate you see helps a little, but mostly keeps water from coming up the transom.

Get a 3 blade stainless. they run better then a 4 blade in my opinion. Is yours a hyrdro tec port job?

Well its like a Hydro tec port job , the same port map and set up . I didn't know there were three blade stainless impellers I've seen the 4's . When you say they run better , in what respect ? I could see where they may be lighter would that be an advantage ? I have so many questions about this setup . I spoke to a nice young man at Trout Marine yesterday , he said the set back may a problem . ideally it would be better closer to the transom but a plate bolted to jack plate will help , he suggested at least 18"wide . He agreed that the motor should work ok ,I know I will hook up the rev limiter again. I can see a problem over reving if it cavitates . Two feet of the center keel has been removed to clean flow to the prop set up . I've read where that was a good idea for the jet as well . My goal is ....If I can get on a plane , run 20 mph or so with a fishing load and get in and get out with out destroying parts I' m good with that . I know if were making a permanent switch to a jet , I would get it closer to the transom , now I need that flexablity .
Right now I can hear those fish calling "catch me Eddie , catch me ! "
Ed

From what I've messed with the stainless impellers the 3 blades have better top end then a 4 blade and have a better holeshot. 4 blade might have better holeshot on certain setups but I've run 2 different 4 blades in 2 different motor (40/28 and 60/40) on the same boat, both times I lost top end and the holeshot was a little more sluggish. The 3 blade stainless seem to be better quality then the Wooldridge 4 blade impellers in my opinion. I'm sure you'll be able to get the performance you want from your boat pretty easy, just feeding the pump with that much set back will be your only hurdle. Don't know if bending a little lip down on the sides of the spray plate might help channel water to the jet.

is there a particular make or manufacturer or distrubitor for the 3 blade stainless impeller ? I spoke to Brian at outboardjets , he was a lot easier to talk to than the young lady I spoke to there., very helpful .I think a jet pump is in my future . now all I need is funds
Thanks
Ed

Wooldridge makes the 4 blade stainless, I think mercury makes the 3 blade stainless. You can buy them pretty much where ever they sell OBJ parts at. Well worth it in my opinion.

thanks for the info i'll be sportin' a squirter soon !

Ready to see how it runs.

ordered a new jet lower from outboard jets 8 week delivery time !