Im stumped, a little help please (jetting)

Well, My bike has been cutting out on me ever since i bought it, and I beleived it to be too rich, because it was fouling plugs often and blew some black smoke even when warm, but I thought, no big deal, my pipe will be here soon. Well, I put my TA on and it worsened, so I took it to work and put it on the EGA (Exhaust Gas Analyzer) and it was lean! VERY LEAN! And before all this i dropped the needle 1 clip and went to a 40 pilot(42 stock) to try to lean it out. So, i went back to the 42, and went back to stock needle position. Still way lean. Then i raised the needle twice and its still really lean and isnt getting any better. It runs great low end and top end, just at about 1/4 throttle where the needle jet is, it cuts out. Does anyone know anything about the slow jet, not the pilot, but the other jet that looks like a min but its not. Ive tried everything, any help or ideas would be appreciated.

Jetting is:

168 main

42 Pilot

stock slow jet(72 if i remember)

Fuel screw at 2 3/4 turns

Needle at 6 clip from top.

Totally stock and a Thunder Alley Pipe



I don't know about much about the jet you speak of, but I find it wierd that you are that lean with your current settings.

I have an 01 with the TA and I run:

168 main

stock needle / stock position

40 pilot

fuel screw 1/2 turn

I don't know if that helps at all, but just thought I would share that with you since we are so close to one another.

Matt, look at my jetting and pilot! It confuses Wyatt and I too. But it runs like a bat out of hell! It had the same symptoms you describe. The jetting resolved most of everything and the BK/GB mod. I do run race gas always as Houston's gas is oxygenated and if you change brands/pump all of my settings go out the window. Try the pilot change. I have a 45 if you want to try it.

In fact after reading your post again. You say your fuel screw is 2&3/4 out. This is an indicator the pilot is too small try a 45 or a 48. Once that is resolved it will help in the transition onto the needle. Remember that there is an overlap of pilot,needle and main. Each will have a small effect overall

Your "Slow Jet" is just used for starting. Once its running the slow jet isn't really used any more unless you still have the choke on. From there 0-1/4 throttle is on the pilot circut. 1/4 to 3/4 is on the needle. And of course 3/4 to WFO is all the Main jet. I don't know what your elevation is and that is a huge factor on getting jetting right. But, if your 2 3/4 turns out on the pilot screw you really need to put a larger Pilot it it. Anything over about 2 turns out is a good indicator that your pilot is too lean. Your test show that it's lean too and a 45 or 48 pilot and 170 or 172 main may not be a bad try. However, if you go to a 48 pilot, you need to match it up with a 100 pilot air jet. The stock 75 pilot air jet isn't designed to run well with 48 or larger pilot jets. That's my two cents worth, hope it helps a little.

Thanks for everyones input. The only problem is at 1/4 to 3/4 throttle, which is the needle jet, as noted above. I have 168, and am going to try a 170 just to see if it increases power output, but it runs fine top end. I will try to go to a 45, and possibly 48 pilot jet, but I beleive the problems are more in the needle jet. I have the fuel screw out farther to try to help since it is lean. My buddy at work ( the head tech) said it could possibly be a bent float, which mine looks to be in good shape, but I dont not have the tools to measure it, Ill ask him tuesday if he has it. I think I am going to try a 45 pilot.

Fastest1, would you be willing to sell me your pilot, so I do not have to order one and wait on it? Also, i will try to locate/order a bigger "slow jet" since I am bumping up the pilot. But until then, could I run the stock slow jet with the 45 pilot, just to see if that fixes it, or do I need to up-size the slow jet as well? Once again, thanks a bunch for the input.


P.S. I am at sea level. And mine bike is one of the weird ones like Fastest!, we set it up with the stocker according to other bikes similar to mine and same elevation.

Before you do any fiddling with the carb be sure that it is clean!!

Matt I will give you my 45 pilot to try and if it works you can keep it. I run a 48 with the stock air jet with no problem. If you are running a 2000 426 have you tried updating to a needle from a 2001? I hear, though I have not put one in yet that they increase midrange hit alot. It is one of the next parts I order. I would like to hear your bike run to see what the problem is. Splendora on saturday? We can fix it trackside! I will pm my phone#.


Not sure if you tried this, but make sure your carb is totally clean. If a tiny spec of dirt or even air filter oil gets lodged in a passage you'll go crazy trying to jet.

Im going to 3rd the carb cleaning idea.

At sea level, your jetting should be in the ball park. Im thinking youve got something in the pilot circuit. The jet itself may be clear, but the passages could be blocked by a single piece of sand or even a clump of dust.

Take the 30 minutes to clean the carb. The setting for the float is 8mm from the bowl base. but just to the needle tip, it shouldnt collapse the needle preload plunger. I did mine with it on the bike, believe it or not. You can make a tool out of a cereal box to check the height. Basically, you just cut an 8mm horseshoe and pass it below the float and adjust the tab accordingly.

Good luck

I have cleaned the carb thouroughly twice. Since I didnt ride for 12 weeks due to an injury, when I had it off to re-het, I cleaned it. Then, after messing with the jetting several times, I re-cleaned it very thouroughly! I dont beleive that it is clogged, cus i removed all jets, cleaned them out with carb cleaner, ran a peice of wire through each jet and passage way too.

Fastest1, I cannot make it Saturday, cus I have to work, but I think Mr Berg and I will be there Sunday, let me know.

Matt Sandt

Bit of advice Matt

Make sure the pump is working as it should That diaphram may be damaged and not pumping fuel correctly at low.....

if it has set it may have dried and cracked

Just a thought.

Also make sure that slide plate is in correctly....

Water seems to be popular in the winter months. I got thrown for a loop a couple of weeks ago when I picked up some water at my favorite gas station. Pull the fuel line off hold a shot glass under it and turn on the fuel real quick. Check the bottom of the glass for little droplets. It DOESN'T take much water to make your life miserable.

The wire thing scares me :)

The pump is working fine, and it shouldnt be the diaphragm because it only runs bad between 1/4 and 3/4 throttle, low end and top end, it runs great.

Why does the wire scare you, it clears out in heavy debris from the jets?


I might be able to work it out for sunday! I will let you know. Are you interested in ridng Splendora?

The wire thing scares me too, only because every book I've read says don't do it that way. :) The metal used for those parts is very soft and wire can scratch it and possibly change the performance.

I have used wire before. Not on this carb, but on others.......especialy really dirty ones. What I use is a tip cleaner for an oxy-acetaline torch. It has many different sizes to choose from and it works quite well. You just have to use common sense and not force it where it should not go.

I think we are planning on doing Splendora on Sunday, Ill double check with Mr Berg today. I just pulled a peice of wire out form a wire brush, i didnt feel any resistance, just to help clear things out i guess. I am going to ask my buddy at owrk today if he has a 45 pilot for me to try to see what it does. Ill let yall know.

Wyatt, would you be able to join us on Sunday at Spledora, along with any other Houston, Southeast Texas riders. If you need info on the track, email me at Matt


I've heard your bike run and thought to myself "that doesn't sound right." Your description of the problem seems accurate.

Since you have tried all of the standard jetting tricks, your problem may be a little deeper. Maybe a problem with the carb body or CDI. Or maybe the slide plate has a small crack. It almost sounds like you have an airleak somewhere.

I would ask Mr. Berg if you could try swapping the carb from Garrett's 426 to see if it helps. If that doesn't help then try swapping the CDI too. I've hear some people spraying something (maybe WD40) around the airboots to find air leaks. That is worth a try as well. But I'd do a search on TT using the term "air leak" to make sure it was WD-40 first!

Fastest1 - I didn't realize you used race fuel. That explains the differences in jetting we see. Your fuel must have more oxygen than the stuff Wyatt and I are using.

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