jet sizes

[lvpg]

What does the number represent when sizing jets? I relize the larger the number, the larger the hole--- but is the 140 an actual measurment [such as 1.40mm or .140inches]? Or, is it an arbitrary number like a shoe size?

My dealer only has jets to 137.5 and I want a 140. I also don't want to wait for a delivery [this is where trouble usually starts]. I would like to drill out a smaller one to 140.

Thanks for any help

[DBragg]

dont bother drilling, its not accurate enough. just order the jet if its not a locally available item. insist on genuine mikuni or kehien jets (or what ever brand carb you have). accuracy in carbs is everthing.

not sure on the sizing issue.

[Desertskyy]

DBragg is right on. Only use genuine Mikuni jets. Other aftermarket jets have been known to be off and thus makes it real difficult to get the bike running right when you think that you have a particular jet in the carb. Be patient. When you have it all set up right you will have a great time riding it. I also saw on your other thread that you are running the needle in the 5th groove. I think I was running my in the 4th groove when running the Calif desert on my 92 DR 350. You may need to look at the needle for future adjsutments. Also a 140 main sould be real real close in main jetting choice.

Good luck

[trickwarrior]

Wait and get the right jet. All jet sizes are not the same IE 140 dynojet jet is not he same as a 140 mic. I thing you will want to go to the 4th groove. Dynojet makes a great kit for 75 bucks that will come with all you need. Good Luck. <M>

[BCRider]

Jet's are relatively cheap and easy to change. If you're closer to sea level I think that you'll find as I did that the 140 isn't rich enough and you'll need a 145 or even 150 before the plut shows signs of a bit of "coffee and cream" brown on the tip of the insulator. So get the shop to order in all three sizes so you've got them to work with. If they are more than $5 each look for another shop. Often they'll have a box full and you can buy the first one then exchange them during your tuning process provided you don't mar the screwdriver slot. Pick up a driver that just fits and no more so you avoid deforming them

With the 140 I went out for a long uphill on the highway, cut the ignition and pulled the clutch in, coasted to the side and pulled out the plug to check the main jet mixture color. This is called a "plug chop". With the 140 the plug was paper white and far too lean for safety and engine life. When doing a plug color run you want to be at full or near to full throttle for about 30 to 40 seconds to get a good and truthful color reading. If you don't have a handy hill a couple of good runs up through the gears finishing with a full throttle run up and similar ignition cut and clutch pulled in at around 60mph will do the trick. Just check your 6 for any SUV's bearing down! ! ! ! Even a few seconds of idling or lower throttle running will change the color and mask what you're trying to find out.

I'm actually up to a 155 now and it's still a bit lean. But for running in the hills it's rich as I found out two weeks ago. I'm probably going to put in the 145 for the next higher altitude run I do and put in the 160 for the motard riding with it at sea level.

[lvpg]

I ended up with a 142.5 jet. I left the needle in the 5th position and turned out the pilot screw to 1 1/2. I did the stock airbox mod on Jesse's site and had 16 disks in the super trapp. The bike started much easier. I took it for a few laps around my block, but this bike is not set up for street. From idle, the bike cracks hard and clean when bliping the throttle [in neutral]. No delay or bog. I had 12 disks in prior to the rejet and I believe it had more low-end snap [just estimating]-- so, I pulled 2 disks. All in all it was a nice little project. I do have one question which I'll post in another thread.

Thanks for everyone's wisdom