Yamaha ET250 Keihin Carb adjustment proceedures

Been dialing in my 1980 Yamaha ET250 recently, put on a Mikuni VM34 for awhile but decided to go back to the original Keihin carburetor. The Mikuni did work well but I had no oil injection with that setup and I really did not want to have to mix gas all the time. This sled is my daily driver... The sled always did run good with the old Keihin, so I rebuilt it with new diaphrams, new lines, thorough cleaning,etc and put it back on. I set the fuel level to proper setting with the sight glass, set pilot jet to where it should be. It runs ok now but is still a little boggy on bottom end (not too bad though) and backfires through carb quite often. Tried adjusting pilot jet with no success. It runs reasonably good now, but has worked better. I have read almost every manual online of these carbs and studied them to the best of my ability. I even printed most every one of them and refer back to them often. I was wondering if anyone has a Yamaha ET250 manual or the proper carb tuning instruction for one of these carbs. It is a Keihin CDX-38-32 , used only on the ET250 Yamahas. I have a fair amount of experience and I would say alot of patience with these old carburetors but this one really has me baffled.... I know these can work well because this one once did.
Any help would be appreciated. Thanks in advance!!

Correct me if I am wrong should not a a rich condition will usually backfire out the exhaust and a lean on the intake side when letting off the throttle ? What do your plugs and piston wash show ? http://www.smellofdeath.com/lloydy/piston_diag_guide.htm

Hi, thanks for the info. Plugs show what I would say is a perfect burn... coffee like clean, brown color. Of course this is after being run at all throttle ranges. I have not removed the head nor piston to read the piston like you are showing. Sled works perfect from 1/4 throttle thru top end. Just has that 2 second bog at first until RPM's slowly come up. Usually backfires only through carb, not exhaust when engine is holding back going down a hill or when decelerating. Never ever did this before. Overhauled carb because it was bogging really bad. I have definitely made an improvement in it but just not 100% there yet. Pilot jet adjustment in or out seems to give very little response either way...

Was wondering if you had any luck with the bog, I have the same sled with he same problem. will start ok and after the bog it runs great

Thank you

Pro

I ended up switching to a Mikuni VM34. Works much better now. Lots of forums on here that show how to do this.