Custom crf450r sodi kart build

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Dav1s

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Hi everyone, i'm in the process of building a sodi kart with a 2005 crf450 4 stroke engine, i have the engine mounted on the kart chassis and i'm trying to work out the best route to go with chain and sprockets, i did initially think it would be best to just use the gearbox sprocket and chain from the dirt bike, 520 pitch but after seeing a few other comments on threads i'm wondering if i should just go with the 428 pitch chain, the axle on the kart is a 30mm with 6mm keyway, and the split 428 pitch 30mm sprockets are readily available, but i'm not having any success finding a 428 pitch sprocket to go on the crf450 gearbox output shaft, this has 17 splines.

Can anyone advise on a sprocket that would be suitable? is there off the shelf options? also would the what number of teeth on the rear sprocket would be about right gearing wise?

Any help appreciated.

Thanks
 
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panchothedog

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Thinking that there is quite a difference in tire diameter between the bike and the kart. You will probably want a smaller axle sprocket. Other wise might end up with a very low gear ratio. I also would vote for staying with the heavier chain.
 
anderkart

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There's several shops that build custom counter sprockets to your spec's,
here's a link to one: https://sprocketspecialists.com/product/front-sprocket/

I don't know where your going to find any #520 or #428 axle sprockets with built-in hubs (or separate componets) for sale with suitable shifter racekart gearing, that are made to fit a 30mm racekart axle. I've seen a few older shifter racekarts with 40mm. axles, but most all of them have 50mm axles.

But if you can find (or custom build) a suitable 30mm-bore sprocket hub, you'll find #428 & #520 pitch, split-axle sprockets in suitable tooth counts at this site:


Looks like your engine has max hp at around 9000rpm.
Just for comparison, the Honda CR-125 (a very common shifter-racekart engine) achieves max HP at around 11,000 rpm, so your in the ballpark there.

The common gearing that the guys that race CR-125 shifter karts use are:
Counter sprockets that range from 16 to 19 teeth.
And axle sprockets that range from 21 to 28 teeth.
This gives them a lot of deferent combinations to achieve the best compromise between good acceleration & whatever top speeds are needed to match the length of the tracks straightaway's.

I'm not sure if your planning on competing at a racekart track or just riding around for fun, but I'd imagine a good gearing for your kart to try first would be somewhere around a 19-tooth counter sprocket & a 25-tooth axle sprocket. That should have amazing acceleration & achieve somewhere around a 60mph+ top speed with 11" tall rear tires.

PS:
I hope your Sodi kart has front brake's, your probably going to end up needing them (y)
 
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Dav1s

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Hi folks, apologies for the major delayed response!

Thanks for the advice, i've went with the 520 chain as id prefer it to be as strong as possible, less chance of any breakages and stretching with the power/torque also, i ended up going with a 13T counter sprocket and a 22T axle sprocket and it seems to be pretty much perfect!

as regards to front brakes, no it hasn't got any, so i'm in the process of making a front brake setup for it just now, once that's done i will get it to the track for some testing and i will get a better idea of the gearing, top speed etc, but from the little testing i have done it should be pretty rapid!

I'm also trying to finalise the fuel system, as i've just been running it with a temp gravity fed fuel tank above the engine, but want to use the original kart tank, but obviously this is below the carb, so there will be no flow of fuel, ive been looking at the various mikuni pulse/diaphragm fuel pumps, so trying to figure out the best way to do it.

does anyone know if these suitable and if so how would you hose it up and setup the fuel line so there is ample fuel to the carb, but not too much?

I thought a fuel line from the pump to the carb, with a t-piece in that then flows back to the bottom of the tank, so there would be the constant weight/head of the fuel in the tank against the returning fuel, if that makes sense

Thanks Craig

crf450 kart.JPGIMG_9220_edited.jpg
 
anderkart

anderkart

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Here's a pic of the fuel system I installed on my old racekart. My carb's needle & seat couldn't handle the pressure resulting in flooding, so I plumed the fuel pumps 2nd outlet to a tank return with a briggs & straiten 1/4" shut-off valve installed in-line; so I could meter how much fuel was allowed to return. I also installed a 1/4" marine primer bulb in the pumps supply line to make cold starts much easier.




1699280432804.png
 
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Dav1s

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anderkart said:
Does your intake manifold have any locations where you could install a 1/4" barbed fitting?

View attachment 143386
Click to expand...
not that i can see, there is a very short rubber coupling between the carb and the engine, so i'm thinking i will need to have a longer rubber coupling and fit a bulkhead type fitting into that coupling
 
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