As I wasn’t able to find a comprehensive write up on how to do this; I did my research an worked it out. I used a 21mm for a few reasons, main ones being that I found it cheap and local AND I plan on upgrading to 70cc and high flow exhaust later down the track.
• NB: Do your own research as to carb size (they come form 15-21mm) based on your requirements
I completely disassembled rear end of bike (IE fuel tank, oil tank, battery box and underguard all removed). You could probably get away without doing this, but it will make it a lot more fiddley.
Here is the 21mm carb and all identified components relevant to the install:
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Remove OEM carb, plug oil line with nail or something similar to stop it dripping
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Remove stock bracket that combines the choke and throttle cable, I cut with hacksaw and then bent it apart till I could extract, this is because I wanted to reuse the bent pipes. You could just buy some 90 degree bends and keep your stock bracket aside.
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Cut either bend down till you have only the 90 degree bend left
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Fit carb to OEM Manifold – now it’s time to start plumbing it in
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Throttle Cable – reassemble with the small bend piece cut (as above) above the top of the throttle assembly
• TIP: For slide carbs, put a SMALL amount of oil on the gasket that fits in the top housing to stop it fall out when getting the throttle cable/slide/spring assembled -
Main fuel line (larger top line coming from petcock) goes to larger front nipple (in RED above)
• I replaced the main fuel line with 6mm fuel line and lengthened it by approximately 2 inches, you could probably get away without doing this, but I didn’t want to be fighting it to fit. I also put a fuel line clamp on the carb end at the nipple for added safety. -
Vacuum line (thinner diameter hose coming from bottom of petcock goes to the back of the carb – again in RED on pic above)
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Remove nail from oil line and fit to right hand side of carb (See BLUE in pic above)
• You will not see this in my pic as I removed oil line and have moved to premix (if doing this you need to cap the oil injector nozzle). -
I elected to delete choke cable as it would have created more work and it never gets below 10c (50f) where I live, I found a bolt that fit in choke cable fitting, wrapped in plumbing tape and capped it off.
• If you choose to keep - Choke cable was is too short, you will need to use a longer cable hat allows you to refit the 90 degree bend
NB: the 2 x Float bowl vents (in yellow) are left to vent to atmosphere – leave them open.
Hope this helps 