Hi Guys,

A quick question. What causes the air fuel ratio to change on my bike? It was running fine last week and is now missing and back firing. I assume this means the ratio is off? It's an 85 Evo.

Thanks

 I'll have to get it looked at, I'm next to clueless mechanically. Do ignition problems cause the same sort of backfires and splutters? Thanks

clean fuel tank &  jets as well as carb bowl  1st  & put in a new set of spark plugs @ least

90%  of carb problems are electrical. 

If it runs fine one week and then goes to chit WITHOUT you touching anything then its most likely a tank of bad petrol or Ignition issue or something wrong with the carbby.

Is it running rough when you start it or when your crusing at 80/100 or when your WOT?
Is it running on both cylinders?
What do the spark plugs look like? Post some PICS!

 Thanks for all the tips guys. I took the plugs out today and they are black with soot. Too rich I'm assuming? Was also told today the carb may be too big for the motor? It's an S&S shorty on a stock Evo motor. Thanks again for the help

Well the sooted up plugs WILL make it cough and splutter as the spark gets shorted out etc. Replace the plugs and you should be good...BUT that does not address the root cause which by the sounds of things is the carbby settings.

A S&S Super E should be fine on a stock(ish) Evo (A Super G on the other hand is WAY too much). I would google the jets etc for a Evo and also download the S&S tuning manual from S&S in the USA - its bloody awesome!

 I'll do that mate, thank you.

 hi S&S E is a good carb for the EVO 80 c.i. just set it up proper

I had a similar problem when my bike had original carb on it (87 softail) turned out to be the rubbers on the intake manifold. Having an S&S you probably have a better intake manifold so may be irrelevant.

 Hey mate, still haven't got around to having a good look at it as have been working. Once I do I'll post what the story is.