This started last year when I tried the "cut spring" mod to get rid of backfire. It got rid of the backfire but the idle was all over the place, So I bought a new spring. Ever since then when I let go of the throttle, or back it off when coming to a stop, it wants to shut off. The idle drops right off. I have to be very careful, and run it at 12-1300 idle speed. Still sometimes it happens. I occurred to me that I had damaged the diaphragm, so I replaced it. No better. Today I pulled the carb, dis assembled it, used a carb cleaning tool in all the passages, cleaned it with carb cleaner, and blew it out with compressed air. I found nothing. The carb was basically clean to start with.
I have a Raask exhaust with baffles, a K&N slab filter in place of the stock filter, a 55 pilot with bleed holes, and a 150 main with a Dial-a-Jet to assist. I did a plug read today and it is a beautiful tan colour.
When I have the choke pulled out a notch it runs rich, but the RPM falls down to idle as it should. I have set the idle mixture as per Serow's thread. It is 2 turns out.
I can only get the smallest wire in the carb cleaning set through the hole from the TEV to the throat. Is that right, or should I be able to get a larger wire through?
Do I need to go up a pilot jet size?
I am stumped, and starting to get very discouraged.

Try the method I was told for idle mixture screw (also known as pilot screw, NOT pilot jet screw) tuning... here it is, I forgot who posted it:

- with the bike off, turn the idle mixture screw all the way in, then count it two full turns out
- start the bike and using the idle speed screw (left side), bump up your idle a bit (makes things a bit easier to hear, less likely to die).
- back the idle mixture screw out slowly, count 1/4 turns at a time (waiting a tad between each adjustment), until revs start to drop
- from that position, count 1/4 turns in again until the revs drop again (so you'll turn the screw through the "happy idle" range).
- divide the number of turns from "screw too far out and rough idle" to "screw too far in and rough idle" in half, and set the screw there. should be pretty close to ideal jetting if the pilot is the right size.

Routy wrote on 05/12/12 at 19:06:48:


My '07 with stock everything and brass plug also runs and idles ideally, and backfires are rare. Maybe they just got things right in '07?  

Built2Last wrote on 05/12/12 at 18:06:07:

Did that.

Your issue sounds really similar to my fluctuating idle. It's really annoying.

LANCER wrote on 05/13/12 at 06:13:12:

I replaced the small diaphragm.
The butterfly seats perfectly.
I removed the choke assembly. Was there something else to remove?
I cleaned the large diaphragm and found no cracks in it.
I cleaned every passage I could find.
I can only get the smallest wire in the carb cleaning set through the hole from the TEV to the throat. Is that right, or should I be able to get a larger wire through?

I can tell you in a day or two if no one gets back to you when I have my carb apart for the spacer mod, I'm just waiting on the screws to be delivered..

Yep. In the last two days I have studied Mikuni carbs and how they work, and cleaned everything. I would suspect the Dial--Jet, except the plug looks like the mixture is good. The thing is... it was working perfectly until I tried the "cut spring" mod, and no matter what I have done, it hasn't gotten back to normal.