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:
Remove OEM carb, plug oil line with nail or something similar to stop it dripping
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.
Cut either bend down till you have only the 90 degree bend left
Fit carb to OEM Manifold – now it’s time to start plumbing it in
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)
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