Tuning unsettled idle on 351/mikuni
 

Can't get a steady idle. Within a reasonable range on the screw the idle still jumps from 1k to 2k sporadically. Cold or hot doesn't matter still does it. If I crack the throttle while idling it will settle then jump again. How to diagnose?

Adj the air screw.

OP, which Mikuni and what gas tank are you running?

whichever one bill sells in the kit...

ims tank

First, I'd agree with durielk that the air screw adjustment is the first approach. If that doesn't address the problem, I'm not familiar whether the modified TM33 Bill uses has an air "jet" like the TM36 that I use. If the air screw doesn't clear up your problem, you'll have to experiment with the air jet and/or pilot jet.

Did this problem just start after you've been running this bike with this setup, or is this an initial setup and tuning effort?

The reason I asked about the fuel tank, it's not uncommon for aftermarket tanks to affect the throttle cable and/or throttle linkage wheel on the carb which can do some funky stuff to the idle returning to normal. You just check for adequate clearance for the cable(s) and the carb linkage.

air screw meaning the pilot screw on the front of the carb? Bill sent it 2.5 turns out, I have it bumped to 3.

The idle screw is in some sort of tubing - any possibility it could be distorted or kinked?

I take it the "tubing" you mention is just the remote idle adjuster link to give you easier access to setting the idle. It's possible there could be a kink or such but probably not likely.

Again, has this bike been running for awhile in its current configuration or are you just now getting this carb and setup running for the first time?

got about 200 miles on the kit, so setting up and dialing in. Been tackling several issues one at a time and I'm down to this one now.

On the air screw, did you adj it or just turn it to 3? (and it is on the bottom of the carb, not the front, where is the front, doesn't that connect to the head?)
The plastic thing is a remote idle adjustment, you will want that accessible.
I would
1 adj the air screw
2 make sure the throttle cable is not hanging up somewhere so that the linkage is sitting on the idle adjustment platform at all times.

i will check the idle linkage tomorrow.

The only screw i adjusted was the pilot screw which is part number 38 in this diagram:

http://www.mikuni.com/pdf/tm33.pdf

and I turned it an extra half turn bc it seemed a little lean and I was troubleshooting another issue (which turned out to be something else so now it's set back as bill set it)

so the air screw is part 14 in that diagram and appears to be in the throat of the carb which means I need to remove the boot (again) to get to it ugh. What am I shooting for...certain number of turns, or trial and error? Do I want to open or close it?