Motorcycle Repair: Honda cm400t, 1980 honda cm400t, smooth acceleration

Question
Chris,

I recently purchased a 1980 Honda cm400t. This is my first foray into motorcycle repair - but I bought a repair manual and have been having fun with it. It used to bog down when accelerating but I took off the carb and cleaned it thoroughly and actually got it back together with no problem. It runs much better now with smooth acceleration, but with a new problem: whenever I start to accelerate or decelerate it spits and backfires repeatedly. It runs smoothly when cruising along at a constant higher speed (above 35 or so) but as soon as I touch the gas up or down, or cruising at a slower speed it starts to backfire and spit out the tailpipes. I'm guessing I have something adjusted wrong in the carb but don't know where to begin. Any help would be greatly appreciated!

Chris

Answer
Hi Chris.
 It sounds like you are well on your way to being a real biker.  Backfiring is not related to the carbs.  It is related to valve and ignition timing.  It's a bit long and complicated to explain in this, but if you check out any of the books out there on basic automotive mechanics, it will explain ignition timing and the notorious Tach and Dwell that are components of it.

 What you need to do is make sure that the valves are adjusted correctly and the carbs are synchronized correctly.
 Now on some bikes, the timing corrects itself as the carbs are synchronized, but on others, you need to do both seperately.  I believe that your bike is in the latter catagory.  Check your manual to be sure on that one.

Now, because of the age of the bike, you might never get it perfect, but it should get better, at least.

Good luck.
FALCON