Road boss viper

[Gho11]

So i got a road boss 850 viper it needs new belt but all i know is its a comet clutch it is less then 8inches from center of the clutch to center of the jack shaft sorry bout pic couldnt find tape measure

 

[bob58o]

Under 7 inches is not good enough. Is it closer to 7" or 8"?

If it is a 40 series and the Driven Pulley is 7.5" OD and the spacing is 7.25" then this is the belt..
Comet 203783A
https://www.carrollstream.com/Genuine-Comet-Model-203783A-Belt-p/203783a.htm

If the Driven Pulley is 7.5" OD and the spacing is 7.875" then this is the belt..
Comet 203784A
https://www.carrollstream.com/Genuine-Comet-Model-203784A-Belt-p/203784a.htm

 

[Gho11]

Remeasure

I measured the driven pully is 8.5 inches across from from driver pully its 8inches exactly

 

[bob58o]

I measured the driven pully is 8.5 inches across from from driver pully its 8inches exactly

The shortest belt (on this chart) for use with a 8.5" pulley, is a 203786A for 7-5/8"
The next longest belt is 203787A is for 8-3/16"

Can you adjust the spacing? Can the engine slide forward or back without moving the jackshaft?
https://www.gokartsupply.com/tcbelts.htm

 

[Gho11]

Should its set up is like a Murray with a jackshaft mounted on a plate thats between the engine and the engine plate

 

[Gho11]

Now can you tell me how to get more speed i clocked it at 35mph ten tooth on jackshaft im guessing 40 on axle

 

[firemanjim]

Now can you tell me how to get more speed i clocked it at 35mph ten tooth on jackshaft im guessing 40 on axle

Uh its a jack shaft so we would need to know the tooth count of all the sprockets. .
You could probably get away with 5:4 or something like that , with the tc. Don't know your tire size either.... That's needed info too...

 

[Gho11]

Srry bout that its 18inch wheels 10 tooth on jackshaft 64 tooth on axle clocked at 35mph its a 8hp briggs no governor

 

[firemanjim]

10 and 64 give you 6.4:1 final drive. At 4000 rpm and 18" tires, you get 33 mph , but you also have a 10% overdrive so you're looking at 35 mph..... At 4000 rpm.... 40 mph if you wind it out to 4500ish rpm...

 

[Gho11]

What would i get if i swap out 10tooth for a 14 and this is a old briggs

 

[firemanjim]

47 mph at 4000 rpm... Assuming 4000 cuz you pulled governor. You said you clocked it at 35 , so 4000 rpm is what fits the equation.....

---------- Post added at 09:53 AM ---------- Previous post was at 09:52 AM ----------

http://www.diygokarts.com/speed-calculator.html

 

[Gho11]

Can u suggest a sprocket cuz this things old im guessing 20+ years only reasons im keepn it because electric start i accidentally took gov from last person hooked it up wrong so i took spring off its a bad set up

 

[Nosandwich]

can u suggest a sprocket cuz this things old im guessing 20+ years only reasons im keepn it because electric start i accidentally took gov from last person hooked it up wrong so i took spring off its a bad set up

say what????

 

[firemanjim]

Can u suggest a sprocket cuz this things old im guessing 20+ years only reasons im keepn it because electric start i accidentally took gov from last person hooked it up wrong so i took spring off its a bad set up

Put the governor spring back on then! You can,blow the engine like that....
Or take it apart and remove governor correctly and completely.....
Removing governor correctly will increase your mph and HP ....

 

[Gho11]

I will put spring back

 

[firemanjim]

I will put spring back

Screw that..... LoL. ... Yank that bad boy out. Keep the stock valve springs....
Taking the governor out is a REAL "feel it in the seat of your pants " mod! You WILL feel the increase I, speed and power. .... And its not hard to do.
But that's just me.... I always take the governor out of my kart engines. I just adjust the throttle stop down if the kiddos ride.....

 

[Gho11]

I know they still make parts for this engine but ya know no money an not the right tools i got two karts a yerfdog thats giving me problems to

 

[bob58o]

10 and 64 give you 6.4:1 final drive. At 4000 rpm and 18" tires, you get 33 mph , but you also have a 10% overdrive so you're looking at 35 mph..... At 4000 rpm.... 40 mph if you wind it out to 4500ish rpm...

Since he said it was an 8.5" Driven Pulley, I assumed a 40 series Torque Converter.

The 40 series with 8.5" Driven has a range of 2.83 :1 in Low to 1.24 :1 in High Gear, so no 0.90 :1 Overdrive.

AFAIK, 30 series have 6 or 7" driven units and 40 series have 7.5 or 8.5" Driven Units. I don't know jack about the 20 series.

64T : 10T, with 1.24 :1 High Gear and 18" Tires should give you about 35mph at just over 5200 RPM (if I did the math correctly). I don't know much about 8HP Briggs, but if it were a Honda small block, I would say you are hitting valve float (or close to it). Bigger sprocket on the JS should increase the top speed a bit. If you are still hitting 5200 RPM, then you can increase the jackshaft sprocket size until max RPM is under 5000.

With that engine, you can probably get 45-50mph???
You can try a 13T or 14T on the jackshaft. It will probably give increase your top speed and prevent you from floating the valves and throwing a rod by keeping RPMs to a "safer" level. Unless of course the tires are spinning freely.