Different stock main jets on my xs 400!!

[jacopo8]

I just dismantled the carburetors of my 1981 xs 400 se to clean them and replace one of the diaphragms and i see that they have different size main jets and different jet needles!
I live in italy and no one can really explain this to me!! I'm really confused!!

 

[Recreateme]

Do you mean the left jet is a different size from the right jet ? or that they are the same but different from what you expected to find?

 

[Scorpio1963]

What bike cause if its a maxum or seca they do have 2 different sizes.117 and 137 I think someone can correct me if Im wrong.If it a xs special bother mains should be the same size 137.5 this will vary from year.

 

[xschris]

An 81 sohc bike should have 135 mains on both sides.

 

[xschris]

I just dismantled the carburetors of my 1981 xs 400 se to clean them and replace one of the diaphragms and i see that they have different size main jets and different jet needles!
I live in italy and no one can really explain this to me!! I'm really confused!!

Post some pics so we can see what you have.

 

[jacopo8]

I mean i have a 127.5 main jet on the right carb and 117.5 on the left!!
My bike is a 1981 xs 400 4g5 se "special"!

 

[Lupe]

I do not have a parts list for a XS400 SE here, so I can not tell you what size you need. There are different main jet sizes in different european countries.
The reason might be different emission regulations or different climate conditions.

On a XS400 2A2 the size varies between 132.5 and 142.5 (Italy), but those carbs are slightly different to the SE carbs.

On your SE right and left carb should have the same main jet size.

EDIT: oops, too slow. 10 points difference sounds strange, even the new XS400 have only 2.5 as far as I know. Maybe someone put together carbs from 2 different maschines. Or somebody tried to fix a problem with gas supply on the right carb.

 

[jacopo8]

I don't know why they are different, i mean why should a cylinder run richer than the other?? I was thinking about the fact that the fuel comes from the left carb and the vacuum tube of the petcock (i don't know how to call it, anyway it's the one that sucks the air when the fuel flows) is also attached at the end of the left carburetor! I would really like to understand that because i'm rejetting the carbs for pods and open pipes and it really sucks to search for asymmetricall parts, it's like rejetting two different bikes!!!!!!!

 

[Lupe]

That's what I meant with my last sentence.
If you look at a lot of old XS you will find that on many of them the right exhaust pipe is darker than the left one. Means the right cylinder runs leaner.

You should have a close look at the hose between the carbs where the fuel runs from the left to the right carb. And make sure that the pet cock really opens.

 

[jacopo8]

The petckock is ok and i FULLY dismantled the carbs to clean them, the holes and passages are all super clean now! The hose between the carbs is open and clean. I just think i wil try with both 127.5 main jets...what can happen? The pilot jets, pilot screws and air jets are both the same size!

 

[Lupe]

have a look at the spark plugs and exhausts and you will see... you got to do that anyway

 

[jacopo8]

Ok thank you for suggestions man!!

 

[XSLeo]

I think on some models the airflow was restricted on one side by the air box design as it fits around the battery. This restriction in air flow requires a different jetting.
Leo