Topic: Back Firing?

[campbmic]

Hey I am fairly new to bikes, I picked up a 1975 CB550 about 2 months ago. I tore the carbs apart and broke a piece so I went to a local pick and pull and got a used set. I was too afraid to mess with them, they were gunked up and I put them on the bike. The bike sounds like its about to explode whenever I start it. I have a little black smoke coming from the exhaust and one of the exhaust heads. It has a 4 into 1 exhaust by the way.

When I got it running it back fired quite a lot and ran very unevenly, some of the pipes were super hot, others were kind of mild. Everyonce in a while a fireball would shoot out of the exhaust when it back fired.

Is this bike toast? What does backfiring mean?

[the technological J]

no your bike is just outta wack with any luck you should be able to tune it  and have ur way with her.... if its not a valve problem.... if you know of anybody that cleans carbs go for it... if not get some sea foam and run it  every tank for a while..... download a manual and do a 3000 mile tune up (valves timing points.. just make sure the carb screws are set at the right level) but take her for a ride after that and let her clean herself out

[w1sa]

All sound like nothing is as it should be, to properly operate the engine. Out of service/tune carbs, engine service, leaky exhaust gasket(s) etc.
It's not practical to just install wreck yard carbs on your bike, especially since you won't know their internal set-up or condition. If your bike falls into a similar category you've increased the chances of failure or possible damage by subjecting the engine to further abuse.

As mentioned, Search the manual,service and tune-up procedures and acquaint yourself with doing that and also clean, inspect and set-up the carbs (per service instructions and available posts)in a condition to do the engine justice.

You'll be surprised at the different results.........

Ignoring any other yet unknown/possible hurdles

[OldSchool_IsCool]

Which pipes are hot and which are only warm?  The ignition on these bikes are pair the cylinders.  If a pipe and it's pair are only warm, then you may have an ignition problem and not necessarily carbs.  The back fire would then be the result of unburned fuel from the warm pair hitting the hot exhaust from the hot pair when they merge in the accumulator leading to the single muffler.

[TwoTired]

These bikes respond well to a complete tune up.  And, this ought to be done before any carb work is accomplished.