yet another jetting question

[SuzookKING]

Will a main jet change of 6 to 8 sizes leaner (from a 128 to a 113 or possibly smaller *Keihin jets*) have a major effect on needleclip positioning?

 

[Rich Rohrich]

It will depend a lot on the final taper of the needle, you should get a copy of James Deans Keihn jetting chart. It will prove to be quite useful.

 

[SuzookKING]

his xcel sheet doesn't cover the carburetor (PE68B A *28mm) I am using or at least I haven't found the needle (F1343H 24N AAC is stamped on it) I am using listed. I haven't been able to cross this particular needle over either. :whiner:

 

[Rich Rohrich]

Send JD an e-mail. He's like a needle encyclopedia :)

 

[SuzookKING]

he is a carburetor "Tailor" of sorts :)

 

[bclapham]

does james dean have a web site with the info on. i rember i tried a link from the 2-stroke forum before but i couldnt get it to work

thanks

 

[SuzookKING]

http://home.att.net/~wbarrow/jd/jd_index.html <---is his site

 

[RJH]

We have tested needles many times with, lets just say, extra large mains on Mikuni carbs. The Keihin has a slightly different taper style needles but the principal is the same. The area we need to be concerned about is where the needle leaves the jet needle. There is never a common answer with jetting as we all ride in different conditions and styles etc. Your dropping your mains huge ,I guess, because the carb is on a different engine? That means the main was wrong so if the needle was set up for the other condition then it is probably wrong as well. Also depending on the carb design flow. For example, carbs like the Keihin (some only) and the TMX and TM American are set to run with a rich mid and lean top end. You will find the TMXx from Japan on modern day bikes have a very lean mid range and rich top end. As an example our YZ125 would run probably about a 160?? with a PWM or American Mikuni but would be hard pressed to get under a 400 with the Japanese TMXx style carb and the pipe we use. In testing – we have gone from a 460 main to a 390 and dropped the needle (leaner) by two clips as well!!! Again – with our setup and our style and our conditions. So – it’s really good to hear you are into testing but there is no magic setting or standard. With the old VM’s or even the TM you can change that rich / lean % at will (with experience) but not with your carb. If it was me I would simply drop your mains and set the needle couple notches richer and ride it and make changes. If someone’s paying the bills – leaner out till she seizes then go up one – but it’s safer to start rich and work down. Bob Hogg PS – how come you dropped so many sizes? :cool:

 

[SuzookKING]

the size drop was from a major fuel switch as I am playing "hydrocarbon blending man" with MTBE as an oxygenator. I am trying to get baseline carb settings using 2 different fuels (one non-oxygenated and one HIGH on oxy content). And yes, I pay the bills so I prefer to start rich and progress to the dark side :flame:

 

[RJH]

Sounds cool - that stuff was used to improve air qualityand was first introduced in gas on the west coast to to get rid of some smog. At first it ate up a lot of lawnmowers and weedeater carbs etc. but new plastic material was introduced to work with it. The Honda 4/ kart racing guys had trouble because the engines ran so lean and all carbs were made stock to work with it. Main jets were a tech item so racers restricted the air correction jet to richen it up and that worked. So I guess you would have to really lean it out. You may need to flatten out the cutaway on your slide as well. Only if goes "waaa" when you open from an idle - I guess.Bob