Motorcycle Repair: bad fuel mileage, black soot in muflers, air fuel mixture, goldwing interstate

Question
Mark,
thank you,
the bike only has 9000 original miles ,it sat in a garage for years, then a mechanic went through the carbs recently, cleaned and set float levels,would you still say the needle jets may be the problem with only 9000 miles on the bike? also when I first got it it was flooding. After rideing down a bumpy road it started running good,it has run good ever since,, then I noticed the low fuel mileage and black soot in the exhaust.
Dean

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Followup To
Question -
where should I start in troubleshooting my fuel mileage on my 84 1200 Honda goldwing Interstate, it is only getting about 25mpg. a mechanic did a carb, overhaul and put on a new choke cable,lots of black carbon inside exhaust.Runs fine no hesitation, starts without chokeing. no smoke on startup or after running. but definatly too much fuel going through the engine.
Answer -
Hi Dean,

Excesive fuel consumption is associated with worn needle jets. These jets are precision machined round. As the jet needles travel within the needle jets, needle jets wear in an oblong shape allowing excess fuel to pass.

Needle jet wear may be obvious in severe cases. Also, look for evidence of fuel leaks.

Respectfully,
Mark Shively  

Answer
Gasoline recipes breakdown very quickly. Varnishing, affectionately termed, occurs within as little as 3 weeks. Mileage is irrelevant with this common condition.

When a needle valve's interior spring becomes gummed (varnished) by gasoline, proper operation of needle valve is diminished and may be rendered useless. This condition would cause float bowls to continuously fill and overflow with gasoline. The result is gas leaking from overflow ports, airbox filling/leaking gasoline, and crankcase filling with gasoline.  

The bumpy road may have caused sticky needle valves to free-up and restored somewhat normal operation. The same could be said for the now rich air-fuel mixture. Some changes may have occurred by varnishing/sticky needle valves which in effect, have caused a change in the fuel service levels in float bowls causing the excessively rich running condition. (In laymans terms: float heights may have changed. Fuel levels are higher-richer mix.) Just one theory.

Check needle valves by pressing the float pins. Should move with no resistance. Once gummed, springs may easily become gummed again even after cleaning. Check needle valve tips (machined tips) for evidence of circular wear mark/groove. Rubber type tips may become brittle, cracked, or shrink/expand. I prefer to replace needle valves to limit repair comebacks and promote customer satisfaction.

Respectfully,
Mark Shively