Getting ready to order parts and nee help please

[speed1]

We are at the final stage of finishing our kart and would like your professional opinion on what to get...
Here is what we have so far: 12 t clutch and a 6.5 hp HF engine...

We would like to do a live axle in the back , for maximum speed what size sprocket and tires should we get? Is BMI a good place to get parts from? Thanking you in advance ... Bob

 

[klicky96]

How much ground clearance do you want? What are you using this kart for? Yes, BMI is very good, this is where a lot of people here order there parts, as well as me.

 

[speed1]

We will be using the kart mainly to ride in the street where I live and also finding an empty cement parking lot just to have fun with my 7 yr. old grandson , as far as clearnce goes the minimum would be ok , we have a kart now with a 6.5 hp on it that goes 25.4 mph (per gps) It has a large spocket in the rear, I would like for this one to go faster...Bob

 

[r_chez_08]

I would say you could gear for 30 if it is just used on the flat.

 

[klicky96]

We will be using the kart mainly to ride in the street where I live and also finding an empty cement parking lot just to have fun with my 7 yr. old grandson , as far as clearnce goes the minimum would be ok , we have a kart now with a 6.5 hp on it that goes 25.4 mph (per gps) It has a large spocket in the rear, I would like for this one to go faster...Bob

I would get a 60T rear axle sprocket, #35 chain. I would buy 15" wheels to give you enough ground clearance. This would give you a 5:1 gear ratio, and with the size of the tires, that would be fine.

 

[klicky96]

Also, your engine is mounted backwards. The shaft should be on the left, facing to the west side of your kart.

 

[speed1]

r_chez do you mean a 30 t sprocket? , Kicky96 the engine is not mounted yet...Sorry for these questions I am not completely understanding...

 

[r_chez_08]

r_chez do you mean a 30 t sprocket? , Kicky96 the engine is not mounted yet...Sorry for these questions I am not completely understanding...

nonono
I mean gear for 30mph, depending on your choice of rear tyres the gearing will change.
See here

I would get rears an inch or two larger than the fronts.

Your kart really does remind me of my frame before adding a roll cage, except yours is "tapered" if you know what I mean (IMO that looks better!)
Mine was just a simple ladder frame on the base.
My kart was inspired from this-

Heres my frame:

See the slight similarities?

 

[speed1]

r_chez, now it's starting to make sense...We built this frame to accomadate the seat that I had bought on Ebay 6 yrs ago, it was up in the attic collecting dust , so we put it it on the ground , got a piece of chalk and did an outline of the frame to fit the seat and yes I do see the simularities on your kart...Thanks for your help, I would like this Kart to do around 30 / 35 mph...Bob

 

[r_chez_08]

Don't forget... You can always remove the governor. This gets you at least 5000rpm before the valves float. If you decide on doing this, please bear in mind that these engines are only meant for 3600, failure can happen and has happened using stock parts running at above governed rpm. What the rpm and condition of the parts were when failure happened is another factor. As with any other motorsport, there are safety concerns.

However, thousands of yellow 6.5hp clones run with stock rod and flywheel at 5800rpm flat out. Not many fail. It's your call

You can also undo the screw on the throttle lever to get you to ~4250rpm.

 

[speed1]

Well I bought an extended warranty for 2 yrs on the engine for $20 that'll replace it if anything goes wrong with it....I don't know what a Governor is or where it's at on the engine or how to remove it and with the warranty I'm willing to try it...I really do appreciate your knowledge and help...Bob

 

[landuse]

I would get a 60T rear axle sprocket, #35 chain. I would buy 15" wheels to give you enough ground clearance. This would give you a 5:1 gear ratio, and with the size of the tires, that would be fine.

I would put a 72T sprocket on the axle. I would be hesitant to go for a 60T sprocket. I know everyone has their own opinion on what will work, but if you go for a ratio of 5:1, you will be putting unnecessary strain on your clutch for a paltry 5mph gain in spead. The 15" tyres won't help the clutch either.

My recommendation (for what it is worth), would be to go for the 72T sprocket (if you have clearance room for it). You can still use the 15" tyres then. This will give you a ratio of 6:1, which is more ideal