QuestionHi Bill,
I have a 1984 Honda VT-500. It is my first bike. It runs great when I run through the gears fairly rapidly. Once I get to 6th gear, and level off on the speed, any slight throttle will cause the bike to sputter and act as if it is not getting any gas. This problem seems to get worse under loads such as against a strong headwind. I have re-built the carbs, replaced the coils, plug wires, plugs and cdi boxes. Any help you can give me on where to look next will be greatly appreciated!
AnswerMark, I don't have specifics on the jetting for this model, but noticed a the online microfiche services that there are different jets for front and rear cylinders. I hope you were watching carefully when you rebuilt the carbs.
6th gear is highway cruising speeds and not for around town, of course. Part throttle carburetion is metered by a combination of the idle mixture screws and the needle taper. "Jet kits" often have larger main jets and needles with narrower tapers, so the engine can get more fuel. Factory jetting was done to satisfy DOT standards and is often lean at part throttle settings. You can try to turn out the idle mix screws just a bit and/or remove the needles and put a thin washer under the head of the needle, so it will be raised slightly in relationship to the carburetor slide. DO be sure that your main and idle jets are correct for the front and rear cylinders, first. You may get a benefit by going up one size on everything, especially if you have changed the intake or exaust system from stock.
Also, at part-throttle, the carb synchronization is critical. It MUST be set with a mercury stick or vacuum gauges that are accurately calibrated. CV type carburetors are very sensitive to any kind of alteration or being out of synch with each other.
Bill Silver
http://chuck.kichline.com/ascot/default.htm
http://www.geocities.com/motorcity/speedway/5284/5284p2.html
