is it necessary to replace the stock pilot jet with this #40 when doing the jetting? I already ordered the following and just realized that the pilot jet is missing on the list:
16009-1912--------Needle-Jet,N1TC

92143-1667--------Needle Collar (required for N1TC needle)

92037-1401--------Clamp, Needle Jet (Clip, required for N1TC needle)

92063-1069--------#125 Main Jet

92063-1074--------#128 Main Jet

 

When running the larger main jets around #130, and air lid removed, some people have reported a stumble just off idle when sticking with the stock pilot jet. You may not have a problem if you keep the lid on and stay around #125-#128. Give it a try with the stock PJ first, but you may want to have a #40 standing buy just in case.

 

I'm still running the stock pilot with a DynoJet #124 main. I'm going to go back to the DynoJet #128, but for the record, here's how my bike runs:

First, here's my current air/fuel pathway:

KDX snorkle, OEM airfilter, Backfire screen, OEM #35 pilot, DynoJet #124 Main, DynoJet 032 Needle, Clip @ 2, F/A screw @ 2.00, Big Gun Evo X w. Vortex Insert @ SA screen.

Starting - It's a bitch. Needs to crank a lot and run for a minute or 2 with the choke on.
Idle - Idles nice, but dies with any throttle until warmed up.

After it's warmed up:

Low/Mod/High - All good
Acceleration - Excellent (13t sprocket, 7/32" drilled carb slide, and 3/8" crankcase vent do wonders ... medium difficulty to do a throttle-only wheelie)
Deceleration - Good (occassionally there's a slight pop, but you have to listen for it)

I haven't checked the plug, but I'm pretty sure that I'm running lean. I plan to install a UNI filter whenever the dealer gets one, and replace the Vortex Insert with a Quiet Core Insert. I'm also contemplating what I want to do about the backfire screen. Regarding the backfire screen, so far that's been an "all or nothing" type mod ... is there an intermediate mod (e.g. using a needle to enlarge some of the screen holes; removing the lower sections, or just 1 section; etc.)? After the air/fuel path has been updated, then I'll re-jet. (Unless a pumper carb is in the cards before next season starts!!!)

 

Mike,

I hope the "7/32" drilled carb slide" is a typing mistake on your part. It should be 7/64ths. Slighty more than twice the proper size will cause issues.

 

Oops, my bad!

Yep, you're right - 7/64". (At least I remembered that it was 7/something-or-others!)

 

Okay, now that we know that Mike didn't trash his slide, I have a question about this particular mod. Like many others here, I did this mod based 100% on the recommendation of the learned masters here. Now that is done, though, I would like to know a little bit more about what I have done and why it works. All I know is that this mod is supposed to improve throttle response. Beyond that I think it has something to do with equilibrating vacuum in the carb. For all I know I may even be off base with that statement.

Here are my questions:

1. Exactly what does drilling the slide hold out to 7/64 do that improves throttle response?
2. Are there any negative effects to drilling the hole?
3. How did we arrive at 7/64? Would a little bigger or a little smaller be better or do we know that this is the sweet spot?

Thanks,
Chris

 

CWGOFF, do remember what part number you used to order the #130 main jet??

Was it 92063-1075? (shows in the Kawasacki parts listing as "main jet, 2nd, #130")??

Thanks,

PS: Like you did, I'm planning on going to the third clip setting and am also going to put in a #40 pilot jet which I don't see in your list of mods. My reasoning is because I'm putting in the K&N filter and either majorly opening my air box or running with the lid completly off. Since there will be more air to leverage and I'm going with the #130 main, I figured I'd also increase the pilot jet a bit. (Adding the #40 pilot jet doesn't seem necessary if using a #125 or #128 main jet from what i can see..)

 

DS,

Yep, that's the part # for the 130. Actually, you and I are on just about exactly the same page right now. I am waiting on my #40 pilot from ronayers.com to get here. Once it does I will tear into the carb for the 3rd time and intall it. While I am in there, I am going to check the diameter of my slide hole because for some reason I am doubting myself on whether or not I actually did that mod when I was in the carb the first time. I am 98% sure I did it, but I might have forgotten to do it in the list of other stuff I was doing at the time. I am toying with the idea of bumping the needle clip down to #4 because I really think I have been running lean even with just the double snorkel mod. Once I remove the airbox lid completely, I think I am going to really need to get some juice going. Sounds like everyone has the "no lid" fever right now.

 

Yep,

I'll let you know how it goes.... Parts are on order...

(and so is that damn Quiet core correction....) [:@]

 

Ok, here's my go at the explanation:

As you know, twisting the throttle grip does not open the carb throat to allow more air into the engine - it simply opens a butterfly valve that is downstream from the carb slide. The carb slide is the thing that opens the carb throat to allow more air into the engine. (As you phrased it, its the butterfly valve that "equilibrates vacuum in the carb".)

The carb slide is raised and lowered by vacuum created in the carb throat and acts against the diaphragm that is attached to the top of the slide. The vacuum gets to the top of the diaphragm through the hole in the slide. (That's why the hole is there in the first place.) When there's vacuum on top of the diaphragm, it is forced up by atmospheric pressure underneath the diaphragm which raises the slide and lets more air into the engine. When there's no vacuum, the spring forces the diaphragm and slide back down.

Enlarging the hole in the slide allows the air on top of the diagram to be sucked out quicker by the vacuum, therefore opening the carb faster (i.e. faster throttle response). It also allows air to backfill above the diaphragm more quickly when there's no vacuum and the slide is pushed down by the spring. (This answers question 1).

If the hole is enlarged too much, it can cause an oscillation where the slide will go up and down on its own without any changes in the butterfly valve position. (I think this is because the slide opens too quickly and the vacuum disappears, causing the slide to drop, which creates another vacuum, that opens the slide too quickly, etc. etc.) This, however, is an extreme situation if you go way too large. Before you get to that point, through, if the hole is too big (but not enough to cause oscillations) throttle opens too quickly and causes a brief lean (rich?) condition immediately after opening the throttle, which causes a bit of stumble when trying to accelerate. (This answers question 2, but only if you drill the hole too large.)

How did we arrive at 7/64? Because we said so! Actually, people like DynoJet and others have worked on figuring out what the "sweet spot" should be. Until I can tell the difference between good advice and bad advice when it comes to drilling holes in slides, I'll take the advice of people who's business it is to know such things. (This answers question 3.)

That's my explanation and I'm sticking to it (unless someone has a better one, of course!)