Jump to content
Sign in to follow this  

Theory of James Dean's Kit and Carb Tuning

Recommended Posts

James,

I ordered one of your kits for a KTM 525 recently. My brother told me just to order jets one size larger but obviously your knowledge and technique goes much deeper then this (in fact, you recommend a smaller jet). Could you do a write up showing the theory behind your kits and tuning for us tech geeks. I know it has a lot to do with the needle tapper but that just wets the appetite.

Also, do you has a swiss type lathe or what do you use to build your kits. I know you don't want to give away trade secrets but any information would be interesting. My brother thought the kit was expensive but I don't think he realizes the expense of running a machine shop. I hope he can appreciate the experimenting and research you had to do to achieve such great results!

I am an engineer for UAB building space flight hardware and rarely get a chance to play with motors even though automotive type stuff is my passion. I would really love to have a better understanding of stoichiometrics of these carbs.

Thanks,

Icemanbhm :cry:

Share this post


Link to post
Share on other sites

The pilot and main jets primarily meter fuel at idle and full throttle, while the needle is everything in-between. In addition, the needles affect both idle and full throttle too, due to the overlapping effects.

The kit needles are custom made and have 2 different straight diameters and 3 tapers each with specified lengths and angles to make the fuel delivery (and power) the most effective thruout the throttle range. These were determined the hard way, by trial and error testing. It helped to graph the profiles and have an understanding of where each dimension affects performance.

The needles are made to a tolerance of +/-.0002" and I check them and reject off-sizes. They're difficult to make consistently at this tolerance, but it's a requirement to get the performance.

You can see some examples of typical graphs used by clicking the banner ad at the top and looking at the jetting guide graph examples. The jetting guide is essentially a write-up and spreadsheet tool showing the methods used to test with different needles and jets. It also shows how to predict jetting for different altitudes. The guide is a "practical" tool without much theory. Understanding the graphs is going to take a course in fluid mechanics to realize the implications. I've basically developed an exponential equation to merge the main jet and needle effects approaching full throttle because these 2 restrictions are in series (I'm also an engineer). Dyno testing was then used to compare results, going so far as to run full throttle tests without a main jet while using the fattest tipped needle made. The bottom line is these are custom kits made by someone who has worked hard at refining the jetting to out-perform any stock parts. They are what I would want as a dirt bike rider, along with some support to help with jetting issues.

Thanks,

James

Share this post


Link to post
Share on other sites

Thanks for the information James! Sounds like a lot of work but I bet you had some enjoyment and satisfaction from your hard work!

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×