MIKUNI Choke plunger seat replacement and Air corrector jets for GS fours VM's

[zed1015]

UPDATE - Plunger reseating service now available for Mikuni 10mm diameter rubber tipped plungers as fitted to most CV's etc and not just the 8mm ones as initially advertised.
Original post now amended to suit.

[salty_monk]

I will likely bring you mine over next time I visit home

Where are you based in the UK?

[zed1015]

I will likely bring you mine over next time I visit home

Where are you based in the UK?

I'm in North Lincolnshire, Little village in the Isle of Axholme where nobody goes unless they are lost or live there.

Current shipping from the States is pretty fast despite the Covid and all that..
Just received a set of plungers from Florida in only four days.
They will be done and going back out today.

[salty_monk]

I did a few trackdays at Barkston Heath years ago, closest I've got. Not somewhere I can drop off then! I was hoping you'd be near some of mine or the Mrs family, we usually cast a pretty wide net when we come back.

[bwringer]

Just bumping this thread because this service needs to be more widely known!

[roeme]

Eh, so do I understand this correctly; these worn seats cause the choke circuit to leak fuel?

How to test? Cause mine sure as hell don't look like the provided picture. But I have observed a few of the described issues.

[zed1015]

Eh, so do I understand this correctly; these worn seats cause the choke circuit to leak fuel?

How to test? Cause mine sure as hell don't look like the provided picture. But I have observed a few of the described issues.

Yes! They go hard and distorted with age and depending on wear you can suffer anything from slight rich running, sooty plugs to very poor running, idling issues, loss of power and increased fuel consumption etc.
It's tricky to test them ( apart from them being visually indented and hard ) but chances are they are most likely leaking to some degree if they are the rubber tipped type found in MIKUNI carbs and with the use of Ethanol fuel accelerating the seal materials degradation their function will only get worse.
The one in the pic is from a VM slide carb with metering needle attached as used on early GS's and KZs but some don't have the needle as on some Yamahas etc.
There is no downside to fitting new seals as i use ethanol resistant Viton which they originally didn't so won't degrade with fuel contact once done and then they can be ruled out of any future fuelling problems.
I can do any Mikuni plungers and originally developed this to repair the obsolete ones that are no longer produced.
The plungers for some later machines may still be available from the dealers but chances are the seals are Nitrile and not Viton so will still develop problems with modern fuel..

[roeme]

Ah, thanks for the clarification (Luckily, no ethanol fuel around here unless you specifically seek it out).