proper jetting???

[bklyn400ex]

how can i tell if my 400ex is jetted properly, i have a White Bros R4 pipe, drilled holes in airbox, headpipe welds ground out, 14tooth front sprocket. It seems to be running fine, but its a lil hard to start, the jetting is stock, should i rejet, how can i tell if i need 2, and if i rejet what will be the difference, will i get more speed and power??? thanx

[KAWSAM62]

if its hard to start then proble you need to bump up the pilot to a 40 or 42 and if your piped the main jet will need to go up a few sizes read the plug color to know for sure how this helps:cool:

[bklyn400ex]

thanx man, will this improve performance?

[bklyn400ex]

???

[Texan32]

Yes, you need to rejet. Thy a 160 or 165 main jet and a 40 pilot jet.

[gojk]

Jetting will make or break your motor.

[bklyn400ex]

is there a difference between a dynojet kit or if i go to the dealer and pick up a few jets???

[bklyn400ex]

?????

[GNCC#829]

I am pretty sure that they have differant number for the same size jet.

No need to buy the K&N jet kit, just buy different jet sizes from your local dealer. Our friendly dealer gave us this advice. The sizes on the K&N jet kit do not correspond to the stock carb sizes.

If its hard to start you can go to a bigger pilot jet, also, you can try adjusting your slow jet screw by screwing it out a little bit to see if that helps. Normally you look at your plug to check your jetting - but you can use the butt 0'meter too. If you do some mods and the bike doesn't increase in power like you hoped, then you really want to check your jetting. Normally going to a bigger main jet, and dropping the clip on needle.

[Wheelie]

IMO----A good starting point would be a #40 pilot, drop the clip on the needle one notch and use a #152 or a #155 main jet.

One thing to keep in mind, if the machine seems to lose top end performance/power, it's too rich.

BTW---A properly jetted machine will have more power/better throttle response than a machine that isn't tuned properly.

Good Luck!!

[Str8Wicked]

Hey guys... Just reading this and wondering...


I got a CT Exhaust, I re jetted to a 165 and it runs great. I do find that I have to have the choke on for a while and keep the engine revved up for it to keep running. Will a pilot jet help out. If so which size, which size is stock...


Let me know

[Wheelie]

A pilot jet will help. Stock is #38. A #40 with your current setup works well. If you plan on removing the choke, a #42 might be a good idea.

Later,
Jeremiah

[Str8Wicked]

I don't plan on removing the choke so I'll most likely throw a 40 on it...

thanks guys..

do I have to change the needle or anything also...

[brazilian rider]

Sorry about this stupid questions but I'1m from Brazil and this explressions are diferent. Anyone could tell me what a jet and a pilot jet are?What about this numbers and size like #40 and 165?They refer to what??Thanks

[Texan32]

Braz,

Inside the carborator are little pieces that have cerian sized holed drilled through them. They are called Jets. The control how much fuel passes through them and into the intake. The Pilot jet is what controle the air/fuel mixture at idle. The Main Jet is used in conjunction with the needle to regulate fuel at everything past idle. The more throttle you give, a tapered needle rises out of a tube connected to the main jet, allowing more fuel to flow. At WOT, the needle is all the way out and the size of the main jet will determine the maximum amount of fuel it will pass. Its kinda hard to understand without actually looking into the carb itself. But in the pic, # 39 is the main jet. # 37 is the pilot jet an # 2 is the needle and clip.

Numbers. The 160,165,40...those all correspond to the size of the jet. The pilot jet is the smaller of the two. Factory pilot jet is a 38. Most just put in a 40 because it makes it hella easier to start. The main jet is a 148. When you make modifications to your engine, you will need to change the main jet to allow more fuel to the motor. The needle i was talking about is also adjustable. it has a c-clip on the top of it that can be moved to change the fuel mixture and mid throttle. Like i said, it is MUCH easier to understand what everything is if you tear into one and actually look at it yourself :)