QuestionWas helping a friend with a bike problem - dual carb shadow. Starts great but runs very weak. Front cylinder gets warm quickly but rear stays cool for much longer time. Has no power and seems like fuel is not getting to rear cylinder carb. Can barely make it up a hill in 1st gear. Fuel filter is good - but not sure about the pump. Seen this one before?
AnswerBob, I don't do a lot of work on "modern" models, but can offer a few hints, I think.
Always start with a valve adjustment and compression test to see if there are any mechanical issues that are causing the problem. If you have good compression about 175 psi on both cylinders, then you can narrow things down further.
The engine has two pulse generators, coils and igniters, so each system needs to be checked individually. Compare each component to the other, using a ohm meter. Additionally, you have for spark plugs and spark plug caps to evaluate. Looking at the spark plugs can tell you a lot about how the cylinder is firing. Black/sooty plugs are too rich. Dry plugs might indicate no fuel.
Spark plug caps should have about 5k ohms reading on a meter.
There is a cover on the side of the carb body that has a diaphragm underneath. This is called an air cut valve and if the diaphragm tears, then you have a big air leak to that carburetor.
There is a screen on the inside of the fuel tank covering the end of the petcock fuel tubes. If the tank has rust/corrosion in it, then the fuel flow could be restricted.
After 15 years, the carbs should be pulled out and cleaned. Sounds like a idle jet is plugged up or worse on the inside.
References for part numbers and illustrations are here:
http://www.ronayers.com/Fiche/TypeID/26/Type/Motorcycle/MakeID/1/Make/Honda/Year
ID/38/Year/1997/ModelID/7317/Model/VT600C
Just remember you have to have compression, spark, fuel and air to the cylinders, all in the right timing and combination for proper running. Any mods made to the air filter or exhaust will usually require rejetting.
Bill Silver
