New owner, first old bike - b21, issues!

[David Samways]

When you back-firing, do you mean spitting back through the carb or unburnt mixture igniting in the exhaust?

What colour is you exhaust? A photo would be good.

The stiff kickstart is wierd. It could be unrelated to the running - have you checked the primary chain tension?

[Blakeatron]

Its popping out the carb.

Earlier this week the throttle needle was sticking in the carb and i released it with some wd40, wondering if there is something stuck under the needle causing the high idle?

Exhaust is a bit of a bodge, mostly chrome - not got a pic to hand.

Will have a proper look tomorrow at the kick

[David Samways]

Spitting back through the carb could be caused by a number of things including incorrect ignition timing - too advanced. In this case it sounds like it's down to a weak mixture. The needle shouldn't get gummed up. Is the tank lined with something breaking down due to the ethanol content of the fuel - the same goes for fuel lines which will leave a black gummy deposit in the carb. Foreign matter in the carb would also account for your flooding problem mentioned earlier. If the bike's been laid up for a long time, the evaporation of the fuel often leaves a brown varnish or sediment in the carb.

[Steve.S]

It's unusual for the needle to stick. More likely, it's the slide. This can be caused by overtightening the flange nuts, causing the body to distort.
I wonder if the slide is not bottoming on the slow running screw, perhaps the cable is holding the throttle open? Maybe give it a bit of free play?
You should be able to unscrew the slow running screw until the engine stops.
If you're sure the slide is bottoming, then another reason for a fast idle is an air leak. Spray WD40 over the flange with the engine running to check. Also spray grease on the inlet valve stem to check for leaks here. You may be able to grasp the valve collar with a pair of molegrips to check for play without dismantling.
I have found that laying the spark plug on the head doesn't tell you much. What you need is a spark gap tester. This is just an adjustable gap. I made one following the instructions in "The Motorcyclists Workshop", and it's saved me hours of grief. A reliable spark over a 3/16" gap indicates 8,000 volts, 1/4" gap 10,000 volts and 5/16" gap 15,000 volts. Don't go over 5/16" gap as you may damage the windings.
Have you tried screwing in the air screw to cure the spitting back?