Jump to content

What Jetting for my 03 450

Recommended Posts

I've got an 03 yz450f. Stock air box, wiseco piston and crank I beileve the head is decked by the PO and it has the zip tie mod and lexx pipe with no spark arrestor right now cuz I some how lost track of it when I repacked it. But I'm at about 3 1/2 turns out of the screw but I have to run it at about 2 1/2 so the screw doesn't fall out. So how many sizes do I go up. I believe there is a 165 main in it now and 43? Pilot but I could be wrong about the pilot, pretty sure they are both stock. Also I have a bit of a hanging idle for 5-10 seconds after I stop. And I get 4-5 big back fires Everytime I completely close the throttle and I had them before I lost the spark arrestor too they just seem bigger then they should be. So if all this is jetting related what should I change to. I've never really messed with jetting. Also I'm at about 500ft above sea level. Thanks for any help.


Share this post


Link to post
Share on other sites

service the hot start, choke, and amump first, replace your worn out slide plate seal and needle jet

now adjust the fuel screw on a hot motor setting the screw at one and the idle as low ad it will go

turn out the fuel screw to raise the idle back up

45p,  165m,  Ncvs/3rd, 50 leak

Share this post


Link to post
Share on other sites
service the hot start, choke, and amump first, replace your worn out slide plate seal and needle jet
now adjust the fuel screw on a hot motor setting the screw at one and the idle as low ad it will go
turn out the fuel screw to raise the idle back up
45p,  165m,  Ncvs/3rd, 50 leak
So replace the orings on the hot start and choke. Or is there more I need to look for and replace. And can I use just general o rings or is there a special seal for those

The seal for the slide seemed good, still soft and fit good, no cracks or tears.

The accelerator pump was in good shape, spring wasnt broke and the diaphragm wasnt torn or hard.

Why replace the needle? Or do you mean the brass piece that the needle drops/slides into. If so how to I replace that? Pull the main jet and and some how tap that piece out?

I understand how to properly adjust the mixture screw

Also I did just have the carb apart and stripped it down and ultrasonicly cleaned it as the bike would only run on choke when I bought it.

Share this post


Link to post
Share on other sites
Needle jet, not Jet needle
They oval out in a couple years
Yah I realized the part you were talking about later after I posted that. Thanks for the help. I'll try some of that and see what happens

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:


×