Kz750 trike build engine choices

[biddie_gibbs2.0]

Hey folks! I’m building a custom 3-wheeler using a KZ750 frame and need help picking the right engine. It originally had massive wiring issues and the engine was questionable. So I snatched it out. I’m a heavier rider and working on a budget, so I’m torn between a Predator the whole predator line of engines.

My gut says 420 with a clutch and let her rip. But I’m very unsure. Not sold on having to go the torque converter route either.

Have any of you run these in similar builds? What would you go with—and why? I’m aiming for solid torque, reliability, and low cost. Bonus points if you’ve got pics or performance tips!

Appreciate any thoughts or experience you can share!

View attachment IMG_0745.jpeg

 

[panchothedog]

So we all know what the predator engines look like. A better picture of your whole trike or even multiple ones would help a lot more than so many pictures of the engines sitting on the shelf. Your gut couldn't more wrong. With the size of those rear tires NO centrifugal clutch is going work regardless of engine size. It will burn up very quickly. Torque converters work fantastic. Especially since you say you are looking for torque. It all comes down to dollars. I am certain that you know the prices of the engines. A 30 series torque converter will work with either the 212 or the 224 and can be found for $70 to $80. For the 420 you need to use a 40 series torque converter and they are going to run you close to $200. So it comes down to that age old question. How fast do you want to go? How thick is your wallet? If you're on a budget, I would get the 224 and the 30. You can have everything you need " Brand New " for less than $250. I have several of the 212 engines, and a couple of the 224's. For the little bit extra in cost, the 224 is worth the money.

 

[biddie_gibbs2.0]

Thanks! I like cheap. The 224 with a tc will probably be the move then! I did notice stage 2 kits for the 420 is like $500. I am afraid that if I don’t remove the gov on a 420 it will have torque but be a turd. Like would it be fast without removing the gov hence going billet internally?

I also thought a clutch was the move because I see so many people in the mini bike forums going 60-70mph with clutches.

 

[biddie_gibbs2.0]

Ignore the rod through the swing arm. The correct size bolt is coming in today.

 

[panchothedog]

All of the engines are going to be limited to 3600 rpm with the governor working.
With a 420 you could gear it very high and get more top end speed, but you will be giving up acceleration. The rear sprocket on your axle is very small and would provide a VERY high gear ratio as is. But it will be a pig and only good for max speed runs with a very long stretch to get up to speed. Punch power from a dead stop or low speed is where the fun is. If all you want is top end speed then get a clutch ( and be prepared to buy another one in a week or two). If you want something practical and fun get the torque converter. With either set up you need a 54 or better yet, A 60 tooth sprocket on the rear axle, and a 10 tooth driving it.

 

[biddie_gibbs2.0]

The highest tooth sprocket for a blaster I’ve seen is a 54 tooth. So I probably will have to get a jack shaft setup to assist with this practical power from a dead stop. And you would recommend the 224 correct?

 

[Master Hack]

Put the 750 back in it.
you can thank me later.

 

[biddie_gibbs2.0]

It’s too late to put it back together. I spent months piecing together the basket case it was. I also spent months trying to figure out the wiring with the 25 different slight variations to the exact specifications it was dealing with, using the wiring diagrams. Even if I had completely rewired the engine and rebuilt the carbs, I would have been even deeper in debt. I just want to have fun, and it seems like the mini bike community is having fun too!

Side note: I did have ChatGPT generate what I’m aiming for. See the picture.

 

[Master Hack]

There's that tek shyt again! No clue what that line said!
Nice pic! That would be a handfull with a 750!
Don't underestimate yer power requirements! A few bux more for that bigger engine is a lot less if ya buy now, than if yer buying it later to replace one thats just not up to expectations.

 

[panchothedog]

With a 54 tooth sprocket and a 10 for the driver you should be OK. How tall are the rear tires? With the 30 series torque converter, you can even get a 9 or 8 tooth sprocket, to lower the gear ratio. A 9X54 is the same as a 10X60 which is the industry standard for 18" to 20" rear tires. I wouldn't waste the time or energy building a jack shaft setup. You don't need it, and the plate system torque converters ( where the plate bolts onto engine ) and everything else is self contained are as easy and simple to install as falling out of a chair. I have 212 and 224 predator engines ( not stock ) on big heavy 2 seat off road karts with torque converters. On asphalt they will top 45 mph, not quite 50. They accelerate
Very strong, will climb any hill, and I've even seen my son and overweight daughter in law ( easy 440 lbs ) drive around with plenty enough performance to have fun. There certainly is truth about what Master Hack says about the bigger engine. But the bigger engine and 40 series is going to cost around $580 as compared to $250. Only you can decide.

 

[Denny]

670 that is going to be heavy!

 

[biddie_gibbs2.0]

So a decision was made…..

I bought the 459cc. Here are my reasons:
1. It was what I wanted but I was trying to talk myself out of it. Trying to be cheap and settle.
2. It has electric start
3. It can sit at 3600rpm all day and I won’t remove the gov and it *should* be reliable
4. No doubt it has the power and torque to really move me and the bike.

That’s my Ted talk. Thank you.

 

[samlevy0515]

Predator 420 is the sweet spot. Add an oil cooler to prevent heat soak on long rides.

 

[biddie_gibbs2.0]

I have a ton of parts coming in. So hopefully I can make some major headway on it. I bedlined the frame with duplicolor bedliner. I love the feel and look of it.
Only thing I haven’t thought out yet is the seat.

 

[ezcome-ezgo]

This would look cool:

 

[Master Hack]

Just FYI pics of 5mb or less will get ya an actual thumbnail instead of that symbol thing

 

[Master Hack]

Same pic 9 mb on the left

 

[ezcome-ezgo]

So techy.

 

[Master Hack]

So techy.

I know! Thanks! I'm proud of my computer knowledge and willing to share.
Next l'll probably want to cover the basics of dial up internet service! Stay tuned!

 

[biddie_gibbs2.0]

Sooooo…….

Definitely have an issue. I had the engine centered in the frame but when I installed this massive 40 series tc, I didn’t anticipate the sprocket to be between driven and the mounting plate. And it was dead in line with the frame. I don’t like the engine offset in the frame and I am drawing a blank. On the 30 series the sprocket is behind the plate opposite the driven.

now that the engine is offset to one side , it’s slightly slightly pass the inside of the frame but definitely still a problem. Maybe I can cut the bottom of the mounting plate for the tc, but I would have to offset the engine even further to one side. Is there a solution I am not seeing?

I had the thought maybe I went too big with the 459 and the 40 series. But I wanted to be good power wise. Turn key and roll!


View attachment IMG_0996.jpeg