XS500 single carb manifold, jetting?

Jramos13

Jramos13

Been Around the Block
Hi guys!!

Im working on a tx/xs project, its a 1973 tx500 frame with a 1977 XS500 engine so i wont have a problem with the head crack issue, im planing on converting it to a single VM34 carb by building a custom 2 into 1 manifold, but jetting wise in a bit lost what a good starting point should be with pilot, main, neddle, neddle jet and slide, the mikuni i have came from an old snowmobile and the jets it has dosnt have any marking on them

any tips or ideas are greatly appreciated!
 
I found this from the mikuni catalog, so i guess its what mine should have:
 

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you might get an idea of a starting point from CXman he does conversions
its going to be a long tough road,lots of hours testing,not a wise modification if you have no experience tuning carbs
the stock setup is a better bet
 
if the parts inside are mikuni brass they will be marked

you may need a magnifying glass to find them

a 34 will work its a little small and in the end wont give you as good economy as 36 on the highway

let me know what you have for brass and what throttle slide

post a pic of the carb so i know which 34 you have
 
cxman said:
if the parts inside are mikuni brass they will be marked

you may need a magnifying glass to find them
Click to expand...

Right. Authentic Mikuni parts have the component spec and always the factory emblem which is a square with another quarter size square in one corner. If a part does not have that, throw it away and get an authentic Mikuni part to start with so you can compare apples to apples. Non factory Mikuni parts are notoriously unreliable. A single carb would be cool, but the combination of building a custom manifold and the tuning work is vastly more work than keeping the original set up and working from there. You can certainly do it though. I'd expect the 34mm to be on the small side too.
 
Yea, the carb is a mikuni copy, but it is actually a 34mm i meassured it, the box came from a snowmobile store and it was marked as 34mm, i had some original mikuni internals like a pilot and a neddle jet and they fit just fine, so i can get sone mikuni internal, what would be a good start point jetting wise? I had some vm30 for a cb35 i used to have and these look preatty damn good for a copy, here are some pics:
 

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thats a copy i cant help you those things flow differently from one carb to the next so there is no stable way of telling you

that looks like a chinese knock off and it is missing the fuel retaining cup on the jet needle between it and the main
 
I undestand, the chinese will not be as precise as the jap version, but if it was a real mikuni what would be a starting point? Since i allready have it it worth a try, if i doesnt work i can just buy a 36mm

ts has the retainer, its the lip at the end, looks like part of the needle jet but its the retainer thing,
 
3.0 slide

q2 jet needle

6dh4 needle

40 pilot

240 main

2.0 air correct

and if you were close to me i would just tell you to haul it over i would get it running and stick my a/f ratio gauge

on and go for a ride as i have every jet and internal part you could need here and it would not take long to dial in
 
;D I would like to "see" all this go together, but if I were you I would get an old Webber 45 DCOE and stick it on... you might have better luck :eek:

19600.060__48981_zoom.jpg
 
that weber even with 32 mm venturis would be way to big for that motor

been there tried that
 
Apreciate it cxman, i will post yodate when i get the manifold together itmight be in one or 2 month since in rebuilding the xs500 engine now, if it doesnt work i will fallow your advise and get a 36mm

For the needle jet is 159 q2?
 
Well i decided to fallow oyur advise and ditch the mikuni copy to go with a 36mm carb,

I found a keihin PE 36 carb at a good price, are they any good?
 
they are ok but i am not sure you will find as much jetting info for that as a vm36 mikuni
 
Jramos13 said:
Well i decided to fallow oyur advise and ditch the mikuni copy to go with a 36mm carb,

I found a keihin PE 36 carb at a good price, are they any good?
Click to expand...

i see cxman is here 8)
you are in the hands of a savant and should cherish your good fortune !
i have some used 36 vm can do for a fair price if you are interested in a used one i can put one together with jets and slide i will dig around but may even have all of the right numbers that cxman says to start with
would you want the long or short airbell ?
 
he would like the long bell with a 3.0 slide if you have it


and my answer to your question about the kehin is mikuni
 
bah bah bah i found a 34 -strike one ! another 34 strike 2 !! then.... then a 38 STRIKE 3 !!!
they sit around for years, they all ,look the same..... till ya need one :'(
 
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