What causes honda cb750K motorcycle to backfire intermittently?

Question

The bike will run great for an hour or a day, then start backfiring below 3500 rpm. Then it will crank slow like the battery is low. Then it might run great for 1/2 hour or so. What gives? (Carbs have been rebuilt and thoroughly cleaned, new plugs, battery)

Answer 1

Test the stator, the lack of proper current could be draining the battery a little and cause a miss fire which in turn causes the gas to build up in the pipes. This happened to me last year.

Answer 2

Timing

Answer 3

Make the plugs are the right ones and in properly. Sometimes there's sludge in the gastank from sitting over the winter. Batteries need a lot of charging time too.

Answer 4

What year is your bike? Honda made the CB750K from '76-'82.
The early ones had points and the timing isn't adjustable on the newer ones. I can't tell you what's wrong with your bike if I don't know which one you have. Also, how many miles does the bike have?

Answer 5

1. Valve/cam timing slightly off.
2. Many miles, may be slight build-up of carbon on valve(s) causing preignition.

Answer 6

I've had a similar problem - a completely random misfire, failure to fire or poor running. Then runs fine for while. It turned out to be a coil.

Answer 7

Sounds like the battery is bad, or the charging system isn't keeping it charged.

Answer 8

new oil may help, but sounds like a timing propblem to me- check the timing, and make certain everything is tightened properly- timing may slip if not.

Answer 9

the idol needs to be set lower than, it sounds like it doesn't wanna idol, try giving it more oxygen at idol, make the mix a little leaner.
Best of luck to ya!

Answer 10

Needs an oil change.