xj650/750 carb joints

i have a xj650j and i was looking online for the intake boots (carb joints, carb to head boots, whatever they're called) i was looking at a couple different vendor and it looks like the part #'s for the 650 and 750 are the same. i have the YICS engine, i don't know if that makes a difference or not. i've asked this question before, i know, but if it's true that they are the same i could get them from a local shop right away instead of ordering them online (which i hate doing) anyway any info would help. thanks

 

Nope, not the same. On the 650 the intake holes all slant the same way. On the 750, two are opposite: \ \ \ \ versus / / \ \.

 

Actually, HALF the 650's are the same, half( the early years??) are different. Take a look at your 650 and see if it's / / \ \

 

Wow. Did not know that. I had three 650 engines and they were all the same. I always learn something new on this forum.

 

my 650 is this //\\. i'm just wondering about the sizes really. are the 750 carbs bigger than the 650 or is the engine size the only difference. these may seem like a stupid question but i would like to find out.

 

XJ650, XJ700, and XJ750 engines:

NOTE: the non-YICS (1980-81 and 1982 XJ650RJ Seca) left side (cylinders #1 and #2) manifolds differ from the YICS (1982-84) manifolds in the orientation of their mounting:

* non-YICS engines have the intake manifold mounting bolt holes in the cylinder head aligned in this manner:

<#1 \ \ \ \ #4>

* YICS engines have the intake manifold mounting bolt holes in the cylinder head aligned in this manner:

<#1 / / \ \ #4>

This is why the left side (cylinders #1 and #2) intakes differ between the YICS and non-YICS engines, and why they are the same for the right side (cylinders #3 and #4) in-between all 650 non-Turbo engines!


NOTE: all intake manifolds differ between the left side and the right side versions in two critical manners:

* intake manifolds, when installed on the engines, "curve" inwards towards the centerline of the bike.

* they also curve "upwards" (as well as inwards).

This combination of both upward and inward curvatures of the intake manifolds is why it is not possible to simple swap left side (cylinders #1 and #2) and right side (cylinders #3 and #4) intake manifolds.....some people think that you can just "flip upside down" a right side manifold and it will become a left side manifold (or vice-versa). This would be true is there were only the "inward" curvature to the manifolds; however, the "upward" curvature prevents such swapping from occurring (as the swapped-side manifold would be curving "inwards and downward")...........and you'll never get the carbs to fit correctly into such mis-aligned manifolds, and on the slim chance that you do get them to fit, you'll end up with major vacuum leaks at that joint.

 

I'm using the original 650 carbs with 750 jetting on my bike and it runs great. I've have wondered about airbox differences, though.