Jetting help on a 1996 Virago XV1100 SH Twin Cylinder

I had 4 XS650’s over the last 35 yrs so I can appreciate your sentiments but that is not why I am writing.

I just modified my XV1100 SH (1996) Virago to accept a H-D K&N RK-380B air cleaner assembly. I am thrilled w/ the modification and my OEM jetted carbs are great from idle to 3/4 throttle. After that the bike feels as if it has a miss. I believe that I have to replace the main jets. Another Virago tech forum member did a similar but not identical mod and had to open his main jets two sizes larger. My Hitachi HSC40’s have stock sizes of, Front #122, Rear #128. Does that mean that I should go, Front #126, Rear #132 ? I appreciate your advice.

Your jet size estimates sound correct. When you change an intake or an exhaust you’ll generally go up on the main jet anywhere from 1 to 3 sizes. 2 is probably about right for your bike, but personally I never make jetting adjustments in increments more than one jet size. If I was you I would pick up a 124, 126, 130, and a 132. I’d go up one size on the main jets then give it a ride. If it still stammered at open throttle I’d go up one more size.

Most (imported) transversely mounted air-cooled V-twins like your Virago run the rear cylinder richer than the front to keep it cooler because it doesn’t get a whole lot of air flow. Kind of an interesting solution to a specific problem. Just part of the reason the big twins never have a competitive edge in any racing circuits.

Anyway, thanks for reading the blog. Let me know how it goes.

Lots has happened since the message below.

1- It turns out that the Factory service manual was wrong.  I do not have Hitachi’s I have Mikuni’s.  This is very good because of widespread availability of various jet sizes.

2-  After becoming extremely effective and proficient at removing and installing carburetors I have finalized the jetting.  140 for the front cylinder and 137.5 for the rear, that’s 6 sizes up.  I opened the pilot jets up to 42.5, that’s one size.  If you read your attached post you can be amused that you threw me one.  I thought that my jets were in ass-backward but after I inquired on the Virago Tech Forum  I found that not to be the case.  I was severely chastised.  The front cylinder is richer of the two.

3- My Photobucket slide show is complete.  Here’s the link … 20Cleaner/
Please view it and provide me w/ some honest critique.

4- I synced the carbs w/ a homemade “Manometer” constructed for <$4.00.

That’s it.  If anyone can use any of this info then pass it on.

Great looking bike you have there.

1996 Virago XV1100

I find it very odd that the front cylinder would be the richer of the two. I’m going to do a little reading on that out of curiosity, I can’t think of why that would be. Glad you got it sorted!

Evan Fell


  1. I just want to say thanks for helping me figure out the jetting in my 84 Virago 500. Your remark about import transverse v- twins running rich in the rear cylinder to keep it cool made everything click in my head. The spec for the front jet needle said 5d4 and the rear carb was 5d2. I assumed the front cylinder was richer because it got cooler air. I was wrong, atleast in the jet needle range. The front is leaner in the mid throttle, then it goes richer on the main circuit. The spark plugs came out clean ever since I made the adjustment. Thanks again


  2. I bought an engine that has very few miles but sat in a field for a while, when I opened the oil drain plug nothing but water came out, do I have to tear the engine down and rebuild it? It only had 6000 miles on it when it was parked outsife


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