Questioni have a 1982 cb650 that sat since 1994. i cleaned the carbs, adjusted valves and checked compression which was good. put carbs back on and it started fine but it backfires on # 3@4 cylinder at all rpms. what are the possible problems. thanks mike
Answer
Hi Mike,
Backfires can be caused by a few things. Any emulsion tubes above the
main jets that have not been physically cleaned can be a problem.
They have very small holes in them to atomize the fuel.
Number two is an air leak around the carb manifold rubber holders.
Sometimes these can get pinched during reassembly or might
have hairline cracks in the rubber which leaks air into the intake.
Can check for leaks around the rubber tubes with wd40 or carb cleaner when running.
Number three is any loose exhaust connection or bad exhaust gaskets
that allow the engine to pull fresh air back in and ignite unburned exhaust gases.
Number four is any vacuum hose leaks that allow air into the intake system.
Number five is a vacuum leak on the fuel petcock hose or diaphragm in the fuel petcock.
Number six is an exhaust system that has been modified from stock
and has too little backpressure. This can sometimes be helped by installing
larger carb jets or raising the carb slide needles very slightly.
Number seven is non stock air cleaner.
Basically anything that reduces fuel supply or allows excess air into the intake system
will lean out the fuel mixture and cause backfires.
Try pinching off vacuum or air hoses one at a time and look for anything that
would affect only those cylinders at fault.
Make sure those carbs are getting enough fuel to them.
Check the choke adjustment.
Check battery condition, terminals, and see if the bike is charging well.
The ignitions need full battery power to work well.
WS
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