Help me understand carbs better....

How do you determine if you need to go bigger or smaller on the pilot jet?
If you have your air/fuel screw adjusted lower than 1/2 turn or over 2.75 turns you need to change the pilot air/gas jet, depending on which your carb has and what it adjusts. Since you never said what carb you have, you need to figure that out.
How do you determine the number of turns for the fuel screw? By testing after installation.

When raising the needle by moving the clip, how does that change the richness or leanness? Ah, the needle is tapered isn't it, moving it up makes more fuel flow through the main jet (which the needle sticks into)... are you sure you want to get into all this?

From the diagram, what's the throttle valve cut away? That is the opening in the slide when it is all the way down that lets a min amount of air through.

On a side note, I've heard that people are drilling the slide bigger. What hole is this? What does it accomplish? I think it leans it out if your enlarging the slide. But I don't think that is what they are doing. Better research some more.

Thanks for your help

 

I believe that is the hole in the upper portion to allow the diaphragm to move quicker. The 09+ DJ kit comes with a softer spring to accomplish the same thing. KLX300 DJ kits come with the drill bit for this.

 

cmott is correct, you drill the slide so it moves quicker as you move the throttle and the newer kit supplies a weaker than stock spring to do the samething. You would not want to drill the slide and install the weaker spring. Most of these bikes I've seen are fine with the stock pilot some of the big bores get by with it just fine also.

 

Ok, thanks guys.

I ordered an exhaust on March 30. I bought a stage 1&2 jet kit and rejetted the night before the exhaust was to arrive. Long story short, the exhaust never came and is lost in transit. Problems with shipping address being different then billing....

So my 250S with he stock carb is very rich. I have done Marcelino cam mod on the bike as well. I followed the directions, replace the needle, spring, clip on the 3rd. 128 main, screw 3 turns out. Left the pilot at 35.

I did my first wheelie and **** my pants. lol. I rode around a few times. The bike rode ok on pavement. But off road, the bike ran like **** under 4000 RPM and awesome above that.

I'm rejetting tonight and gonna drop down to stage 1 settings which either going to be 116 or 120 main and everything else is the same according to the directions.

I just want to learn more about carbs and get a better understanding. I've searched and search the forums and internet. I just had those questions that I could never find a solid answer for.

Thanks

 

What would happen if you do drill the hole and put in the DJ spring ???

 

My 250S has the stock carnb with drilled slide AND shortened spring. Nothing untoward has happened as a result.