Needle shims Mikuni VM28 73 RD350

[Karl squire]

Hey, question about Needle shims, I think a shim or 2 for the needle would be beneficial but I know nothing about them and need a bit of education.

Are they measured in MM or in fractions of an inch?.

I will go and measure this my self but does anyone know off hand what the measurement is between clip segments on the needle?

Does anyone know what the sizes are the shims come in.

I had my carbs set on the 2nd clip, it was good but seemed a bit rich, so I changed it to the first clip, definitely better but seems to have a bit of a flat spot or a lean bog in the 1/4 to half throttle so I was thinking of shimming the needle up a bit.

[m in sc]

i think i used m3 washers that were .020" in the past, but TBH, i rarely use shims in a final tune.

[Karl squire]

i think i used m3 washers that were .020" in the past, but TBH, i rarely use shims in a final tune.

lol I was wondering if anyone used washers, I was thinking about going to an electronics store and see if I can get any. hmmmmm I'm surprised I thought it would be more common to use spacers. Thanks for chiming in, I appreciate it. I just get concerned about going too lean, I know what the out come is when your too lean at the top end, not sure of the consequesces of being too lean in the mid range so I'm trying to tread carefully. Mind you these are china pistons so I'm not too worried but on the other hand that bike is running good, its a fine line. lol  

[SoCal250]

Shims for Mikuni are 0.5mm and designed for 1/2 step increments in needle clip adjustment. I've never heard of anyone using them except for racing applications where every last bit of tuning is applied.

The Sudco catalog lists these specs for the shims: .106" I.D. x .250" O.D. x.020" (0.5mm) thick

[svgarage]

Economycycle has them for a buck a piece. As SoCal250 mentioned, they're 0.5mm in thickness. I just put some in the other day, so my needles are at position 2.5 now.

[m in sc]

one thing to watch out for with needle shims, when they are installed make sure the needle can still wiggle a bit freely. if not, you can wear out a jet tube or needle very fast. .02

[svgarage]

one thing to watch out for with needle shims, when they are installed make sure the needle can still wiggle a bit freely. if not, you can wear out a jet tube or needle very fast. .02

Definitely! I did check for a little play. All is good over here!

[Hawaii-Mike]

If you buy washers from the hardware store, compare their thicknesses to make sure they match.

[Karl squire]

Thanks everyone, I did a plug chop, ok I have not done the chop part yet its still sitting on my bench ya know procrastination, so depending on what the plug says I'll get the shims Thanks everyone for chiming in.

[teazer]

Plug chop means chopping the throttle to get a reading that is not masked by riding back to the pits.  It does not involve cutting the plug up.  Buy a cheap plug reader.  It's a loupe with a light. I got a replacement from Summit racing after my last one died from over use.

https://www.summitracing.com/parts/nxo-00-56007

That's the one I got.  It is much better than the one I have used since Pontious was a pilot.