How Big Are Yours

[cvincer]

The bike is an '82 with  16R  on the headstock (delivered to & lives in Australia).

The carb has a throttle stop screw for the accelerator pump linkage, so think it might be late '82, with a BD34 carb.

The main jets are  BOTH  125

My spare carb has  BOTH  jets  as  120

The Haynes manual  specifies  front carb with a  122.5 jet,  & rear carb with a 127.5 jet.

So can any body please advise  a)  What jet sizes do they have?

                                            b)  What would be the point of having carbs with different jet sizes?
                                     
                                            c)  Wouldn't different jet sizes make balancing difficult?

Here's hoping some friendly  XZ Guru  can provide enlightenment!!

[jasonm.]

the specs you are reading are XZ550 for U.S.A.. But I think they vary by country. If the exhaust is original and good shape. The stock jetting as you stated for 550 works best due the the ODD interior of the exhaust design.  I have cut then up. Take my word...very odd.

[The Prophet of Doom]

a) Jet sizes cause a lot of confusion here,
i) because the documentation is a bit crazy
ii) because idiots who work on these bikes seem to put weird random jets in various holes and then sell their bikes because they don't work any more. 
iii) because air jets and main jets are the same physical size, so easily mixed up.
iv) because people speaking knowledgeably and correctly about US83 models, will mis-inform people with other models.
v) because some documentation (like the US82 parts fiche) calls both the main jets and the pilot air jets "main jets".  The pilot air jets are on the top of the carb, main jets on the side.
vi) because people forget that every time you fiddle with the carbs, you absolutely must check for vacuum leaks, float levels, re-do the synchronisation and mixtures.
vii) because intake, YICS and exhaust leaks make way more of a difference than minor fiddling with jet sizes

Jet specs vary a bit based on what you are reading

Market	Pilot Air	Main Jet	Source	Comment
Germany 11V	130/130	130.0/135.0	Parts Fiche / Service Manual	50PS Model Different Cams
Europe    11U	120/120	122.5/127.5	Parts Fiche / Service Manual
US RK 83	140/140	130.0/130.0	Parts Fiche / Service Manual	Different  BD36 Carb
	130/130	130.0/130.0	UK Haynes
US RJ 82	130/130	122.5/127.5	Parts Fiche / US Haynes
	120/120	122.5/127.5	UK Haynes
	?/135		Air Box Mod Instructions
Australasia 16R	120/120	122.5/127.5	Parts Fiche / Teardown	Vacuum flapper
XZ400  14X	146/146	107.5/110.0	Service Manual	400 cc model, Difft Cams
	145/145	107.5/110.0	Parts Fiche

b) The US and German models run larger air jets to lean the bike out to reduce performance and create flat spots to discourage motorcycling, and to lower emissions because of the evil EPA. 
The jets are different also to reflect needs of different equipment - Models also have varying Cams, airboxes, carbs

c) Balancing is no problem, but you need to buy or build a manometer.  I think there are instructions for building a $4 manometer on Lucky's site xz550.com.

[Lucky]

b) The US and German models run larger air jets to lean the bike out to reduce performance and create flat spots to discourage motorcycling, and to lower emissions because of the evil EPA. 


??  huh?  knew there was a reason, lol

[cvincer]

Gentlemen, thank you very much for the information & advice,; I'l be digging deeper into the bowels of by carbs.