79 carbs vs. 80 carbs

[corey]

My bike is a 79SF with aftermarket four into two exhaust and a stock air box. I was going through the carbs the other day and noted 110 main jets throughout all four carbs, while info I gained through this website has told me that those jets should be 137.5. Now why would the PO lower the jet size when adding aftermarket pipes? Wouldn't the pipes warrant increased jet size? I should also not that the PO lived at approximately the same altitude that I do.

One more thing. I should say that the reason I was going through the carbs was to fix a rich condition on cylinders two and three. Could this be a clue?

Basically, I wonder if I have 1980 carbs on my 1979 SF, since the jet sizes that were in the carbs were more on spec with the later model bike. It might be helpful to know that the pilot jets were 42.5 and the air jets 185.

Thanks in advance.

[Ken Talbot]

The early carbs two "T"s between carbs 1-2 and 3-4, the lower one for fuel and the upper one for float bowl venting. The later carbs have only one "T" between carbs 1-2 and 3-4. If the pilot screws in your carbs are the sharp, point ones, the carbs are 78 or 79. If they are the blunt ones, and they are not simply broken off, they are 80-81 carbs.

[TopCatGr58]

Hey Corey,

Like Ken said, the 110 jets and single set of "T"s indicate a later set of carbs, which sounds like what you probably have, especially if you're running rich with those low sized mains!!

Instead of changing jets, you may want to adjust the floats a little first, along with playing with the pilot screws! You're right in that being at higher altitude, you don't need it as rich as you might with the aftermarket pipes!
T.C.

[corey]

Thanks guys... just what I was needing to know. I'll play around with them some more.