Yet Another Carburetor Conundrum...
My ride an 01 250 bone stock except:
Modified airbox (loose battery box for removal)
2 washers under needles ~1.5mm
Added fuel filter
Prior to last year (spring 2016) rebuilt petcock & lined the tank, (tank was punctured at fairing mounts)
Idle at 3.5 turns. Idles smooth
Starts in 1 sec w/ no choke
slides operate smoothly.
Needles have no ridges.
No perceptible stumble revving in neutral.
No perceptible vacuum leak - hoses look good
flat spot in the 5500 to 7000 range after a hard full throttle pull to 10k+
Then backing down to the 6k range (60 mph) it stumbles. ~
1/4 throttle
If slow acceleration to 6k seems to stumble less.
Started happening last summer. Prior running was great.
New plugs and 1 new plug boot - for some reason the boot was lifted and the arcing burned through the beryllium copper thread retainer.
Valves adjusted previous spring. 2k miles since. Minor tweek
In the last 2 weeks I have rebuilt the carbs 3x. 2nd time was a 2 hr soak in Berryman. Probed, blew out, spray carb cleaner all passages.
Even adjusted floats to 18.5 mm in case it was a flow issue (no change)
Old float needles... I have some new ones ordered
Bike runs great when cold but after 4 min it will stumble while cruising.
Seems to run great when on the throttle,, Great pull after 7k and up.
Stays strong at 80 mph for 3 minutes +
Have driven with the fuel cap open ( no change )
Any Thoughts
Scouring other posts has not gin=ven me any new directions to try.