Reducing top end speed

[Canadian Kid]

Good day all I need sounding board for my thoughts on how to reduce top end speed.

Recently purchased what I believe is a doodle bug, and with the current gear and engine set up the online calculators show me a top speed of 31mph (stock tires, 1:5 ratio and 3600 rpms). Way too quick for my 8 year old.

So here’s what I’m thinking…. Stock tires, 1:6 ratio (maybe even 1:7 if I can find a cheap enough 84t #35 sprocket), and limiting rpms to about 2000. Dial back idle to 1200ish RPMs (is this even possible on a non-pristine engine) and replace the standard springs in a clutch to allow for these modified rpm levels, more like 14 mph.

Is my thinking sound? Have I missed anything critical?

Let me know
Thanks, Julian

 

[capguncowboy]

decreasing speed will increase acceleration, which can turn the bike into a wheelie machine. Reducing RPMs is your best bet, but you'll need to get a clutch that engages at lower RPMs to he doesn't cook it running at 1500 RPMs

 

[ole4]

What engine is on it? I thought the doodlebug came with a 99cc 3 hp motor, would be hard to hit 31 MPH. Let us know what engine the thing has. You can adjust the governor adjustment screw to limit RPM which is what I think you were alluding to. So can you tell us:
1) is governor still installed
2) ID of the engine
3) current gearing on rear and clutch (tooth count)
4) Tire diameter.

 

[Canadian Kid]

What engine is on it? I thought the doodlebug came with a 99cc 3 hp motor, would be hard to hit 31 MPH. Let us know what engine the thing has. You can adjust the governor adjustment screw to limit RPM which is what I think you were alluding to. So can you tell us:
1) is governor still installed
2) ID of the engine
3) current gearing on rear and clutch (tooth count)
4) Tire diameter.

I can give you this but you'll likely come to the same conclusion I did...

1) is governor still installed Yup
2) ID of the engine 5hp briggs
3) current gearing on rear and clutch (tooth count) Clutch 10 tooth, Rear 60 tooth
4) Tire diameter 14.5

Equals 30ish mph

yes, I was getting at the adjustment of the governor plus the addition of littler clutch springs

 

[KB2ROCKET]

just something to think about
ratio calculators are pure math and math is EVIL :devil2:
what I am trying to say is the calculator doesn't consider the weight of the vehicle or the rider or wind resistance or friction or slippage of the clutch
so take the bike for a ride and then adjust the governor . use a weaker spring on the govenor if you have to
or you may even fashion some type of throttle stop to keep the carb from opening all the way
some times this can be done by just bending the stop at the carb
these are basically free
heck you could even make a restrictor plate that mounts where the carb gasket goes
I can think of lots of ways to make things slower