Aftermarket carb on XR100!!

You will have to do a bit more than a carb and pipe to whip a TTR125. My boy had a hot XR 80 which was half XR100 but with 14" and 17" wheels. It was fast but the TTR125 is a much better starting point and a lot faster and handles better when modified.

On the XR100 with a 120cc bore, you will need a cam and pipe and I would go to a 26mm or even a 28 mm VM Mukini. There are a lot of early model Mukini flange mount carbs out there which with minimal mods fit up. The main problem is aircleaner. You have to run a pod unless you go to a CR80 frame. Check out Powroll, Webcam, BBR Socal XR sites for parts and info.

Good luck

I think that the top end speed on the xr100 or ttr125 depends on how high you are willing to rev it. I (on my xr) could always beat my friend's ttr at top speed, and he weighed 30 lbs less.

Pete, I live nearby you. I ride with a friend on some property of old dirt trackers. They've been swapping parts from different bikes, quads, 3-wheelers, etc... for years. I know that they've done stuff with xr100's. I'll try to see if I can get any info for you, and maybe find a way for you to get in contact with them if you are interested. Just let me know.

Jeremy

Should have mentioned that I was speaking MX. A bike length in a drag race translates into a long way in a 12 minute moto! Kinda puts you last rather than first. 28mm carbs are popular on the XR120's over here. All are well modified motors that can use it. They are ridden by juniors. The flat slide carbs seem to have bog / flat spot problems with the guys that used them and they now use round slides including a 28mm Delortro.

BBR's carb kit for the TTR is a 26mm Kehin. I have had good sucess with both 24mm and 26 mm on the TTR and a 24 mm on a 95cc XR 80 was excellent.

I would like to try a 28 mm on the TTR but the head would need to be well ported before that would work. Trouble here is finding somebody who has actually worked on a modified TTR and getting over the TTR poping. Heavier valve springs help a lot but I have decided that its the CDI thats the real limiter at the moment. Well it is until we find out if the bottom end can take the revs, at the moment it is surviving but add more revs and power and ???????

The XRs can rev better than a TTR thats for sure. Add valve springs, heavy porting, lightened flywheel to a good cam and they are quick little motors.

I don't know what the valve sizes are in the 100/120 engines, but we were running 26-28mm carbs back in the mid '70s on the SL/XL125 engines. Their stock carbs were 22mm.
Swiss