wfc
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Hi there, I got seriously enthusiastic a while ago about minibikes. I had never seen one before untill about two months ago. They (like gokarts) just dont seem to be relevant out here in South Africa. I know, its crazy, but sadly true! Anyway, I am in the process of building a monster of an offroad kart driven by a yz490 two stroke motor. I bought a new carb for it on ebay from the States and had some time while waiting for it to arive. I just happened to have a good honda gx240 just waiting to be used, and a friend gave me this Yamaha xt250 without an engine..... I decided not to strip the bike for its parts, but try and see whether it would work with this engine. Some day I might find the right motor and return it to the bike, but in the meantime I might as well have some fun
I needed to install a jackshaft, as the sprocket on the bike, and the sprocket on the clutch both didnt line up, and were different in pitch. This was also my first attempt at a jackshaft. Finding the sprockets was a lot harder than I expected.
The bike runs now, and everything seems to work out quite well (mechanicaly). The problem I have at the moment is that the gearing is way out. The thing has a top speed of over 74mph! I think that may be more than it did with the Yamaha engine! That also means that the gearing is wrong for low down power, an pulling off is quite slow.
I know that I have to play around with sprocket sizes to remedy this. Currently I have 10 teeth on the clutch, 12 teeth on the driven side of the jackshaft (from the clutch), 10 teeth on the drive side of the jackshaft (to the bike sprocket) and 47 teeth on the bike sprocket.
I am trying to find a bigger bike sprocket around 60 teeth, but that isnt all that easy, the highest I can manage so far is 52 teeth. What could I change on the jackshaft sprockets to bring the gear ratio in line with good torque? Would a larger sprocket on the driven side increase my gear ratio?
I am attaching some pics of how everything is set up. Any advice would be great, so thanks for chipping in.
I needed to install a jackshaft, as the sprocket on the bike, and the sprocket on the clutch both didnt line up, and were different in pitch. This was also my first attempt at a jackshaft. Finding the sprockets was a lot harder than I expected.
The bike runs now, and everything seems to work out quite well (mechanicaly). The problem I have at the moment is that the gearing is way out. The thing has a top speed of over 74mph! I think that may be more than it did with the Yamaha engine! That also means that the gearing is wrong for low down power, an pulling off is quite slow.
I know that I have to play around with sprocket sizes to remedy this. Currently I have 10 teeth on the clutch, 12 teeth on the driven side of the jackshaft (from the clutch), 10 teeth on the drive side of the jackshaft (to the bike sprocket) and 47 teeth on the bike sprocket.
I am trying to find a bigger bike sprocket around 60 teeth, but that isnt all that easy, the highest I can manage so far is 52 teeth. What could I change on the jackshaft sprockets to bring the gear ratio in line with good torque? Would a larger sprocket on the driven side increase my gear ratio?
I am attaching some pics of how everything is set up. Any advice would be great, so thanks for chipping in.
. Thanks for the tip on the head mod. I was aware of it, and it is number one on my priority list after i manage to get the motor mounted. Right now I have to redo the back swing arm part of the kart as it had a 200cc Suzuki on with electric start, so right now it isnt wide enough to handle the kick starting needed to get the monster to awaken! I will post the pics soon in the Gokart section.