Mikuni VM24SS 100 main jets

[Zebedee]

Wanted some 100 main jets for Mikuni VM24SS carbs for my z650.

As many of you know Ive rebut and refurbed my old z650 during lockdown.

Well shes been running rich and drinking fule so im having the choke plungers refurbed and as the carbs were out I thought od give them another clean. I cleaned them last time thyey were off the bike back in the spring.

Anyway on cleaning I’ve noticed that thers some blocked with crud from the tank as expected but also they all have 102.5 main jets? Which might explain the rich running and poor fuel economy?

Anyway anyone have some ‘100’ mains that they dont want need/ want to sell?
Anyone whose upped the main as they’ve fitted pods or an after market pipe may well have some lying around that they dont want?

Thank you

Zebedee

[warren3200gt]

102.5' mains and 15's pilots is stock on UK bikes with airbox and stock pipes. 100's were US market to reduce emissions.
Are your carbs airscrew, fuel screw or both? The mixture range acheivable with the airscrew is greater than one jet size change so you should be able to colour tune it to where it needs to be. Excessive bowl fuel height will also create a rich mixture.

[zed1015]

Fitting smaller mains won't cure rich running at lower to mid rpms.
They will only lean off the top end.
If the float heights and everything else is in spec then the choke plungers are the likely cause.
The last Z650 ones i did reduced the fuel consumption from 29 to 42 mpg..

[Zebedee]

Ah thanks both. Yes Ive got 102.5 mains but ive had the air screw. Screewed out as far as it will go and it seemed eto make no difference.

Ive now bought 100’s off ebay but may well try the 102.5s again I've sent the choke plungers off for refurb and hopefully that might solve the problem.

Thank you.

[warren3200gt]

If the airscrew is making no difference then the air passage is partially blocked. Take the airscrew out and blast some carb cleaner down it. Then put it back in and squirt more into the pilot intake vent. Should clear it.

[Zebedee]

So I’ve checked the Haynes manual and it definitely says 100 for standard jet and as mine is/was running very rich.

So although Ive just had the plungers done (thansk Rob) what do people tgink about swapping out the 102 jest for 100?

Its kinda now’s the right time to do it.

Ive got hold of a carb float height tool so im going to adjust the floast down a bit too, but whats the concencus?

[zed1015]

I'm sure the Haynes book of lies is incorrect.
102.5 is the stock size for every vm24 equipped UK Z650.
I would leave it as is.
Changing the main jet won't affect anything other than outright top end fueling anyway so unless you are showing rich when performing high rpm plug chops it's not your issue.
I would also not reduce the float height below the spec figures, just set them by the clear tube method .

[warren3200gt]

102.5 mains, 15 pilots is correct. 2-4mm from bowl mating surface for fuel height is correct.
All assuming you have stock airbox / exhaust setup.
If your air intake set up is too restrictive or your using cheap pods that block the pilot air intake all the messing in the world won't help.
Oh, and use the Haynes manual under the wobbly table leg or as heating fuel.

[Zebedee]

Well I’ve had the pilots out again and blasted carb cleaner through the air screw and checked that ther’s no blockages ?

Ive set float height but I’m wondering as the Haynes manual says 30 or 31 =-1mm and the Clymer says 23 =-1mmn but again I guess that’s for US emissions regs?

Plungers expected back tomorrow and the carbs now have another new set of gaskets and O rings and jets and pilots and needle valves and everything, so here’s hoping.

But what should the floats be at?

[warren3200gt]

You need to set the float height using the wet method and throw that Haynes manual away.
Float height as I previously posted.

[steve452]

Try these.

http://www.zedrider.co.uk/service--owners-manuals.html

[warren3200gt]

Try these.

http://www.zedrider.co.uk/service--owners-manuals.html

But remember that's an American copy so will show the wrong UK jets.

[steve452]

Cheers Warren, didn't realise that.

It's showing main as 100 and pilot as 16 for a 1976 B1.

However for the Z650 F2, D4, H1 1981 models it's showing 102.5 main and 15 pilot.

I'm guessing it's generally going to more useful that a Haynes doorstop though.

[warren3200gt]

. Can you even get a 16 pilot?