BS34 needle plate raising 87 KZP 1000

Bike starts and runs incredible....except....I had intermittent missing on roll-on throttle at all rpm's. Plug #2 & #4 sooty after 100 miles. 4 worse than 2. all the standard issues checked...valve lash, timing, air leak,  advancer, spark, (have done wired george coil re-power mod), fuel bowl fuel level clear tube checked, petcock tried on all positions.... Then I take open #4 slide top and find the needle plate stuck near the top. (pictured) I pushed it back in position and rode fine for 50 miles at so w no missing on roll-on. missing returned so I pulled all 4 slide tops and find #2 slightly raised/stuck and #4 raised near top (again) and stuck there. So I lightly sanded the plastic needle plate outside (while turning it in a drill press to keep uniform round). Now all 4 needle plates slide freely inside the slides. So, now it runs good. but sometimes on hard roll-on throttle I get an miss like 1 or more needles are loose from a needle plate still rising then dropping back in position from spring pressure where before they would stick up letting the needles rise and over fuel. My BS34's dont have any clips or anything other than spring pressure holding the needles and needle plates in position. 

How do I keep the needle plates from rising (against the slide springs) and letting the needles move up? 

Notes:
J motor
1075 10.5 :1 pistons 
welded crank
degreed stock cams
stock airbox w UNI Foam covered filter where paper one fits. No snorkel.
stock exhaust and mufflers
Dyna S ignition w green dyna coils
Ricks voltage regulator
valve job w ape studs
compression 185 psi low 195 psi high cold.

Honestly, I have no idea how that could happen unless when the throttle is opened, the needle is getting jammed up in the jet and not moving back down with the piston.
With it all assembled, stick your finger in the carb and gently push the piston up, then pull your finger out and see if the piston and needle will smoothly fall back down.

The slide moves freely. The needle moved freely in the needle jet. I can "finger" the slide up and it falls back down with the needle smoothly within the needle jet. If I hadn't seen it w my own eyes, I wouldn't believe it. I looked at a suzuki BS34 slide and it has a an inner circlip holding everything in place in the inside bottom of the slide....so it reasons they make it that way for some reason....maybe to keep it from rising?

The spring tension should keep the needles bottomed in the slide (I don't think sanding will have helped as it has added more clearance to something that shouldn't move) Are they OE needles as it appears something else is pushing them up (are they centred in the main jets or off to one side?)
It might just be the photo but the needle you show doesn't look straight to me - something must be pushing the needle up (enough to overcome the spring) when the slides return ??

Yes, OEM new Mikuni Y595 needles. I can lift the slides and let them fall with NO resistance or dragging of the needle or slide. Perfect alignment. The motor is not stock with 1075cc, 10.5:1 pistons, and stock cams with adjustable cam timing gears. Cams timed intake 105 1/4 deg exhaust 104 1/2 deg (centerline timing) I'm wondering if there is some pulsing back into the carbs blowing the needles up into the slide? Could the vacuum pulling the slides up also suck the needle and needle disk stopper up?

You say the problem only occurs on #2 and #4. Swap the needle, round plate and spring from #1 and #3 and see it the problem moves with the parts or stays with the cylinders

Is it possible the needle plate should be a tight fit and not slide easily?

F64 wrote:

Is it possible the needle plate should be a tight fit and not slide easily?



 

Thought about that a lot....old part is swollen w age and discolored. originally white. The two that were larger were binding up and not returning (under spring pressure) to hold the needle in place. I still can't figure out why they raised up. This pix is a suzuki BS34 slide inside
 

vacuum may be acting on the needle plate.
That may be why there are holes in the plate????

I would put a couple of drops of superglue on the edge of the needle plate. Not much.. just enough to hold it in place.  It most likely won't hold for long anyways as the gasoline and plastic don't make for ideal bonding.

I'd also make sure the hole in the piston next to the needle hole is lined up with the hole in the needle plate.


Yeah, it may need to be a tight fit.


photo: do the ton
 

Just so you don't feel like the odd man out MReed, I've had the same issue with the needle plates and it was nice to find this year old thread to see that I wasn't alone. 

My 82 1000 LTD would specifically exhibit this missing under load if I would ride the bike and then shut it off (and the carbs would get a good dose of heat from the engine).  I popped the carbs off, took the top off the offending cylinder and there it was, a needle plate stuck half way up the bore, just like you showed!

In my case, I believe the old needle plates were damaged by ethanol exposure (as most of the rubber parts of the carbs showed obvious signs of ethanol exposure) and this narrowed the clearances to the point when heat expansion took place, there isn't enough free play to allow the needle plates to freely bump up and down. 

Before investing in any new parts, I'm going to attempt to give the plates a little more clearance and see if it cures my issue. 

I hope yours got cured.