86 ATC 250R jetting help

[pantera1975]

Where should I start with jetting in this thing. I believe its a stock unported motor FMF pipe no air box lid and stock carb with 91 octane fuel and 32-1 klotz oil. It had a 42 slow and a 142 main it it when my friend bought it. We are in Wisconsin about 600 FT elevation an its in the 70's. It wont idle last fall I had a 52 in it just for starters and a DGH needle. Its has a complete dead spot just off idle and dont have any power then it reves way out you cant ride it 1/4 throttle. Its been awhile since I rode one with a FMF pipe.

[GO OVRIT]

If its running away just off idle like that I would go up a few sizes on the pilot.  Where's the air screw?  In neutral you want to be able to hold a steady rpm at 1/4 throttle.  If it bogs, you're rich.  If it takes off, you're lean.

[fearlessfred]

I would start buy cleaning carb and making sure all jets and passage ways are clear before changing jets

[pantera1975]

Its all cleaned What need should I use I have quite a few different ones.

[the cosmic avenger]

I'd go down to like  a 45 or 48 pilot and a 152 main and clip the needle on the  bottom. The pilot and needle overlap more than people think...

[fearlessfred]

You should start by using 45 or 48 that c a suggested get the bike warmed up and adjust the air mixture screw ,there's a couple of ways of doing that but the simplest is finding  the highest idle by turning the air screw always go back to the point that you got the highest idle ,if the idle becomes to high, lower idle and readjust air screw again .If your airscrew ends up being between 1 and 2 turns out the pilot jet is correct. Your slow circuit mix's air and fuel together for the correct ratio and should not be used  to adjust anything but idle.the motor needs to run clean enough to pull itself up into the rpms to start getting a draw across the nozzle to pull fuel.a motor that's running too fat on the slow circuit will stumble to get its self going,to lean will bog