# New owner of alweld/johnson jet



## RutStrut (Jun 18, 2011)

Just wanted to introduce myself, I am new to the forum, but have been on here reading alot. I just came into a 1644 alweld and Johnson 25 jet tiller. I am not able to find much information on the internet in regards to the motor and wanted to know if anyone had any experience with it and could provide any modification advice or links to other helpful sites. I was told that a carb change would increase the hp on this one? Motor is a newer model with very little use. I will mainly be using it on the rivers in Northwest AR/White, Crooked Creek, Kings and the Sac, Little Pomme, and Taneycomo in MO.


----------



## Jim (Jun 18, 2011)

:WELCOME: Bud!

Thanks for joining!


----------



## Lil' Blue Rude (Jun 21, 2011)

Yeah you can change to a 35hp carbs. You might have to pull the front half off and match the hole in it to the size of the new carb. Don't think it would be hard at all. 
You can polish or atleast take the rough casting marks out of the inside of the jet pump and sharpen the impeller, you can also "cut" the liner. That's pretty much just increasing the angle of the liners leading edge but you don't want to cut it too far up. I normally increase the angle just enough so that the edge is just about to the corner impellers blades. If you polish the pump make sure to not increase the diameter of the pumps nozzle where the water exits because that will cause you to lose some pressure.
The height of the motor and tilt off the motor have alot to do with performance to. That's one of those things that can only be determined by trial and error. You have to adust one thing at a time and check to see which perfomed best.
Good luck


----------



## fender66 (Jun 21, 2011)

Hey RutStrut...welcome to tinboats. Looks like you might be from Missouri? (might want to add that to your profile)...there are quite a few of us from Missouri. Happy to have you aboard.


----------



## RutStrut (Jun 24, 2011)

Thanks for the replies, I am originally from MO but currently live in NW ARK during the week and spend the weekends up in Stockton MO. I inherited this rig and its very basic but I think with a little time I can improve it to meet my needs. I plan on using it for fishing brownines on the King and Sac, trout on the White/Taneycomo, along with eventually giging and bowfishing. Might also try jug and trot lining. Right now I am needing to add some seats for comfort along with an alum perforated floor and then eventually a trolling motor and engine mods. I am also torn between fixing this 36 y.o. boat up or purchasing a 15 ft Blazer and using the johnson on it?


----------



## silver99gt (Jul 4, 2011)

keep in mind, that if you do any pump modifications, if done correctly, you will loose some rpm. Up the carbs and keeping the impeller sharp would prolly be all you would want to do to that engine. If you had some more horse you could shave front side of your pump on the bottom, shave your grate fins on angles, grind the top of the impeller to where it forces the water into the jet at a more direct angle, lots of things. but if i was in your rig i'd just keep it shimmed and sharpened and up the carb and call it a day


----------



## Lil' Blue Rude (Jul 4, 2011)

silver99gt said:


> keep in mind, that if you do any pump modifications, if done correctly, you will loose some rpm. Up the carbs and keeping the impeller sharp would prolly be all you would want to do to that engine. If you had some more horse you could shave front side of your pump on the bottom, shave your grate fins on angles, grind the top of the impeller to where it forces the water into the jet at a more direct angle, lots of things. but if i was in your rig i'd just keep it shimmed and sharpened and up the carb and call it a day


What kinda pump mods are you talking about? Never seen a motor lose rpms from polishing the pump, seen them lose rpms from sharpeneing the top side of the impeller but that's because it's catching more water.


----------



## silver99gt (Jul 5, 2011)

wasn't specifically talking about polishing the pump. there are several modifications you can do. Kinda logic, more water=less rpm. my promax would only turn 5200 rpm. 300 pump with pump mods. and keep in mind a 225 promax is actually a 245 - 250 hp engine. made lots of difference but i lost 500 rpm in doing so. same results with my previous boats.


----------



## fender66 (Jul 5, 2011)

silver99gt said:


> wasn't specifically talking about polishing the pump. there are several modifications you can do. Kinda logic, more water=less rpm. my promax would only turn 5200 rpm. 300 pump with pump mods. and keep in mind a 225 promax is actually a 245 - 250 hp engine. made lots of difference but i lost 500 rpm in doing so. same results with my previous boats.



Please re-explain this....I'm not understanding.


----------



## Ranchero50 (Jul 6, 2011)

Fender, ask yourself, what makes the boat move through the water and how can you measure it? Had this discussion with Mr. Bill O'neal on the Seadoo subforums of PWCToday.com a while back with no real answers.

Is it the quantity of water, the velocity, or the pressure difference of the water coming out of the nozzle? From my understanding at low speeds it's the volume of water pushing the boat but at higher speeds it's the pressure and velocity keeping the hull moving at speed. Higher pressure happens with a restricted nozzle but you can't restrict it too far or the impellor will cavitate because it can't move the water efficiently enough at low speeds to get the hull moving. Kind of a ram jet principle. It becomes very complicated and the more you get into it the more you realise the OEM designs are very good at what they're supposed to do.

If you can find some time, read up on hydrodynamics, Wiki has some good info but it gets into mathematics too quickly and my head starts to hurt. Same for impellor efficiencies and slip angles.

At summer temps my inline flow axial pump is running 6500-6800rpm and with the mild porting and cleanup I did to the housing when I rebuilt it I need to feather the throttle to load the pump correctly (or it'll cavitate). Once the hull hits @20mph the spoon will ram jet the pump and it'll load hard and accelerate to @50mph with very little extra throttle.

I'm interested in what the Hamilton guys are doing too.

Jamie


----------



## Lil' Blue Rude (Jul 6, 2011)

I under stand that more water=more pressure=less rpms, so i'm guessing your removing material from the begining of the pump housing to create more volume for more water? Right or wrong. What did modding the pump gain you? hole shot, top end or both?


----------



## Ranchero50 (Jul 6, 2011)

Just reburring the pump housing I think gained more water, lugging the engine down for less RPM. I blew the wear rings up and couldn't help deburring the bronze bearing box / flow straighteners. They make different bearing housing cones to limit the water coming out of the nozzle. That is supposed to increase the pressure while decreasing the total flow allowing the engine to rev higher.

Here's a picture of mine from the business end.






Rutstrut, sorry to hijack your thread.


----------



## silver99gt (Jul 6, 2011)

Which part are you not understanding?


----------



## silver99gt (Jul 6, 2011)

Lil' Blue Rude said:


> I under stand that more water=more pressure=less rpms, so i'm guessing your removing material from the begining of the pump housing to create more volume for more water? Right or wrong. What did modding the pump gain you? hole shot, top end or both?


It gained a heck of a lot of holeshot. Not much top end but when launching the boat would damn near stand straight up and down. As where most 200s and 225s would blow the impeller. It didn't matter if I had one person in the boat or 6 I never cavitated one bit.


----------



## hotshotinn (Jul 6, 2011)

I have had excelent results with my 20 jet now that i moved the battery backk from the front to the back.I getting morefe boat out of the water when on plain at full trotal than before..The 20 just makes more cence now than beforewhen i was looking at bigger horse power


----------



## Lil' Blue Rude (Jul 7, 2011)

"you could shave front side of your pump on the bottom." That's what I was asking about. Are you removing material from the inside of the pump on the front to create more volume?
As for inboards, that's a foreign to me. I run the upper end of the currnet so I've never been around them.


----------



## silver99gt (Jul 7, 2011)

Let me get some pics.


----------

