Carb jetting help plz

[Cafe Murdock]

I'm running 34mm mikunis with k&n pods n I'm about to put lowbrow customs mufflers on in the next few days n I could use help with jetting big jet is74.0 and small is 42.5 I no I need a bigger jet for start and idle but not sure on the rest carb jetting is kinda new to me on bike carbs n I'm still learning how mikuni carbs work any help would b great thanks

 

[TwoManyXS1Bs]

Post #1 has mucho info to download about VM carbs.
http://www.xs650.com/threads/carbs-carburetors.43/

Have a look at gggGary's jetting compilation.

Post 67.
http://www.xs650.com/threads/help-me-id-these-and-can-they-be-tuned-mikunis.6570/page-4#post-547589

You're in for a barrel of fun, or a world of hurt...

 

[grizld1]

There is no #74.0 in any Mikuni jet. From the size of the pilots jets I'd guess you have OE BS34 vacuum diaphragm carbs, but that's only a guess. The search utility works really well on this site and so does the Tech button: as the old Dylan song goes, "It's all been done before, it's all been written in the book...."

 

[Cafe Murdock]

There is no #74.0 in any Mikuni jet. From the size of the pilots jets I'd guess you have OE BS34 vacuum diaphragm carbs, but that's only a guess. The search utility works really well on this site and so does the Tech button: as the old Dylan song goes, "It's all been done before, it's all been written in the book...."

Yea I figured thats wat they where does any one make a kit with different Jets n sizes n it that'll work on 34mm mikunis

 

[grizld1]

Sure, Keyster makes a kit. It's full of junk Chiwanese brass and guaranteed to make you wish you'd never touched a carburetor. 5twins did a fine job on the "Tuning for Modifications" section of the Carb Guide. Click the link, read don't skim, and order genuine Mikuni jets from Niche Cycle Supply.

 

[Cafe Murdock]

Ok so wat about carb sync useing a vacume gage

 

[TwoManyXS1Bs]

Comparing the vacuum gauge to the fluid tubes.

1 tic mark on the vacuum gauge is 1 psi.

If using colored water in a fluid tube, that's equal to a 28" difference in fluid levels.
If using oil, that'll be a 37" difference.

Just a matter of granularity. Coarse vs fine...

 

[Cafe Murdock]

Ok I've got snap on vac. Gage set from the 70 or so there good reliable gages but I've only ever used them on small blocks n that sorta stuff do I hook my Gage to the back. Barb's on intake tubes or is there a threaded vac. Tube hole sum where on 1980 mikuni BS 34mm carbs my motors got sum bad vibes n Poppin and stutter goin on and I'm hopein a good cleaning and resync with cure a bit of that

 

[TwoManyXS1Bs]

Sorry, I've only worked on the early '71 unlinked carbs. I synchronize by feel, sound, experience.

Can't quite make out the rest of your questions...

 

[gggGary]

Use the barbs on the intakes.

 

[Cafe Murdock]

Use the barbs on the intakes.

Yea

 

[Cafe Murdock]

Use the barbs on the intakes.

Sorry I got confused there for a sec but yeah so do use the vac. Barb's to hook up me gages to sync.