In Evanâ€™s Answers I attempt to respond with sound advice to questions regarding motorcycles sent to me from visitors of this website. If you would like to pick my brain just email me
I don’t want to make a habit of doing multiple Evan’s Answers consecutively, but I have a couple of really great new How-To articles and they won’t be ready until tomorrow. Check back for them, together we’ll take your old bike and make it new!
I just modified my 1996 Yamaha Virago XV1100 to accept a Harley Davidson K&N air cleaner assembly. I am thrilled with 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.Â
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. (No I am not referring to Ducati air cooled twins, they are transversely mounted, but they are 90 degree motors tilted forward allowing for much more airflow.)
Thanks for reading the blog. Let me know how it goes.