bkm
05-03-2016, 04:47 PM
This is actually off of my CR250, but still applies to trikes. If you've read my thread in bikersville regarding my quest to convert my 86 cr250 into a dedicated woods machine then you already know I'm searching for throttle response and low end power. I ride very tight steep trails that seldom require 2nd gear so instant throttle response and torque are at a premium.
I switched to a Rob Selvy prepped Mikuni tmx38 carb and after the proper jetting, it's a pretty snappy carb that gets the job done, but seeing as how I have a lathe and a spare 38mm keihin PJ carb laying around I decided to experiment. With the help and guidance of onformula1, I decided to make a 36mm reducer for the outlet side of the carb to increase velocity and promote low end power. I machined it out of delrin.
http://uploads.tapatalk-cdn.com/20160503/b775d4c1a19857a78df120f647a6cda2.jpg
I then went to work on the inlet bell and decided to machine a 30 degree taper first. http://uploads.tapatalk-cdn.com/20160503/24139f449e60e87a20fe6e4af41619a1.jpg
I then blended the throat into the taper and smoothed the entry with 400 grit emry cloth.
http://uploads.tapatalk-cdn.com/20160503/cacc903ae9506d8221601b734fcbd01a.jpg
The 30 degrees was something I looked at and decided to try. I'm not a professional machinist or a carb guru by any means. In the tradition of Hot-Rodding I wanted to see if my experiment works. Milner gave me a great starting point jet wise, so after a good cleaning and reassembling I will test it back to back against the TMX. There will be no way to cheat because where I ride if you have lazy throttle response or no low end power, you're not going to get very far.
I'll hopefully have some input in the next few weeks.
I switched to a Rob Selvy prepped Mikuni tmx38 carb and after the proper jetting, it's a pretty snappy carb that gets the job done, but seeing as how I have a lathe and a spare 38mm keihin PJ carb laying around I decided to experiment. With the help and guidance of onformula1, I decided to make a 36mm reducer for the outlet side of the carb to increase velocity and promote low end power. I machined it out of delrin.
http://uploads.tapatalk-cdn.com/20160503/b775d4c1a19857a78df120f647a6cda2.jpg
I then went to work on the inlet bell and decided to machine a 30 degree taper first. http://uploads.tapatalk-cdn.com/20160503/24139f449e60e87a20fe6e4af41619a1.jpg
I then blended the throat into the taper and smoothed the entry with 400 grit emry cloth.
http://uploads.tapatalk-cdn.com/20160503/cacc903ae9506d8221601b734fcbd01a.jpg
The 30 degrees was something I looked at and decided to try. I'm not a professional machinist or a carb guru by any means. In the tradition of Hot-Rodding I wanted to see if my experiment works. Milner gave me a great starting point jet wise, so after a good cleaning and reassembling I will test it back to back against the TMX. There will be no way to cheat because where I ride if you have lazy throttle response or no low end power, you're not going to get very far.
I'll hopefully have some input in the next few weeks.