coleman ct200u with a honda gx420 tops out at 43mph please help

#1
iv been working on a coleman ct200u mini bike with a honda gx420cc motor on it and a torque converter 1inch shaft 30 series

this project was one hard task no matter what direction i went with the build i was held up by obstacles from the gas tank not fitting and having to mount behind the seat
to the motor being so big the placement on the frame was problematic

i could use some help or input on how to get more top end speed with out building the motor any more

running a straight pipe exhaust with the aftermarket intake filter

i upsized my jet to a .043 but i bogg out when full throttling it
didn't have any bigger jets so i found a supper small drill bit and turned it into a .045 or .046 i believe not sure by drilling it out just a hair bigger
tomarrow i will be pulling the jet back off and drilling it out a little more then test riding

i was running a .042 jet and it would only get up to 20mph i then switch to .043 witch helped lot but after drilling it out is when i hit 43mph
i do believe changing the back sprocket would help but just dont no witch direction to go for a better top speed


THE PROBLEM
i can only reach 43mph over a longer distance of travel about 1/4 mile

i seem to pick up more speed when i gradually throttle almost like the torque converter needs time to catch up

PLEASE throw at me anny advise you can for jetting size or sprocket size
im looking to get atleast 60mph

i am running a 50 tooth sprocket on the rear with a 420 chain
stock gx420 carb

if i had to chance to redo the build id skip the POS torque converter they are trash unless you buy the real one
mounting the torque converter was very difficult the mounting holes dont line up and the torque converter hits the oil dip stick
not to mention i had to cut the bottom half of the torque converter off because of it hitting the frame
 

toomanytoys

Well-Known Member
#5
Never had an issue with the china torque convertors. Your issues are mostly because you are using a tav on a bike that was never designed to use a tav with a motor that wasn't made to be used in that frame. To install a tav with a 6.5 on the frame you have to raise the motor up 1" to clear the frame. Not cut the bottom off the mounting plate. This also let's you orient the backing plate correctly to hit the proper bolt pattern.

You have the governor bypassed and im assuming without billet parts and upgrades valve springs. Valves are going to float around 4k rpm. Which seems to confirm as you are hitting 43mph. Floating valves are going to make the bike feel like it's missing and chugging.

Jetting is different every where. All relative to elevation.

Speed is directly related to rpm and gearing. You need more rpm to gain more speed. Or more power to pull taller gearing at the same rpm.
 

SAS289

Well-Known Member
#7
If you are only concerned with top speed, you will need to gear the bike for that
When you think about it the gearing should already be there once the TAV shifts to "high". What's not there is enough RPM needed for 55 or 60 MPH. With that gearing on a 19 inch tire he should only need around 4800 RPM or so to get 60 MPH according to a speed calc.

Not sure why his big block can't handle the load at higher road speeds.
 
#13
I'd toss that front end.... speed is irrelevant if you get thrown off at speed due to inherently poor handling suspension ( or lack of it) You might have selected the worst handling frame to put big horsepower on as an experiment. I'd suggest a Megamoto 212 frame kit if you're serious in the sport. @ least the suspension won't get you killed... BE CAREFUL!

link below

https://www.gopowersports.com/go-power-sports-blog/mega-moto-212-minibike-kit-install/
 

toomanytoys

Well-Known Member
#14
I'd toss that front end.... speed is irrelevant if you get thrown off at speed due to inherently poor handling suspension ( or lack of it) You might have selected the worst handling frame to put big horsepower on as an experiment. I'd suggest a Megamoto 212 frame kit if you're serious in the sport. @ least the suspension won't get you killed... BE CAREFUL!

link below

https://www.gopowersports.com/go-power-sports-blog/mega-moto-212-minibike-kit-install/
A lot of guys have fast rigid frame bikes. Nothing wrong with a ct200u frame for handling.

The megamoto frame was not a favorite of mine..
 
Top