These are tips picked up after running two-stroke Ner-a-cars for about 10 years now.
Updated October 2008.
Use of air slide while riding.
Having studied the recently purchased copies of the B&B literature more closely, it gives advice on the use of the air lever.
On starting, it should be completely closed, and the throttle about 1/4 open.
When warm, it says "The carburettor then becomes practically automatic (except at low speeds) and the air lever is used from one half to full open, according to the temperature of the atmosphere, and will only require slightly shutting for slow running, or when slowed up on a hill." It also suggests "the air lever is opened a little before the throttle lever is moved" to prevent choking. Their 1923 book "All About Two Strokes" says "There is always a certain amount of "lag" between its operation and the result." It carries on to say that if it's opened too wide, it causes "popping back".
With this in mind, I now run with the air lever about 3/4 open when riding, which seems to be about right, and it doesn't "pop back" or four-stroke.
Binks carburettors.
It has recently come to my attention that the later English Model B's have single-lever two-jet Binks carburettors fitted as standard, and this possibly coincided with the change to the steel flywheel/Bosch magneto ignition.
Brown and Barlow Carburettors.
Following the purchase of some 1922/23 B&B Literature, I have discovered accurate information!
The B&B carb fitted to the Ner-a-Car is a Type TOD.
The main jet for a 2-stroke can be a 28, 29, or 30.
There are various dustcaps on the inlet, varying from 9-hole to a 12-hole type. Usually it seems to be a 10-hole.
The fuel level should be 0.2" - 3/16" below the top of the jet.
Capillary action draws fuel to the top of the jet, so it cannot be checked simply by looking at the jet.
I have made a screw, drilled right through and fitted with clear plastic tubing, which replaces the bottom 3/16" Whitworth screw on the main jet to check this.
For my carb, and I would guess for most carbs, the level needs to be 15/16" from the top edge of the float chamber (top removed). Mine was way too high!
I have now done several miles on my bike, and have removed the cylinder to check things. The plug and piston crown are a lovely chocolate brown! Perfect!
Tyres.
It would seem that many modern tyres are deeper than the originals. This means that the front tyre may catch the chassis on full lock! We have used a belt sander at the front of the front wheel, and rotated the tyre against the belt to "wear" some of the rubber off. This is a bit dusty, but it works!
I have also found that it is possible to get a "tank-slapper" if the front tyre pressure is low. I run my tyres just above 40 lb/sq.in.
Steering draglink adjustment.
If the ball joint at the wheel end of the draglink is not adjusted correctly, then that can also provoke a "tank-slapper". The adjusting cup onto the ball has 6 slots cut into it. The link has a horizontal and a vertical split pin hole drilled in it. Thus the adjustment can be made in 30 degree steps. I tighten the cone up, then back it off to the next available position for the split pin to be put in.
Lubrication.
I have had discussions with some oil experts. They assure me that modern 2-stroke pre-mix oils ARE suitable for these engines, and it may be possible, and advantageous, to reduce the fuel/oil ratio.
It was thought that the metal crankshaft seal might need a monograde oil, but this is not so.
I am now running 20:1, and have checked the barrel/piston after several miles. Good lubrication, with just a little in the crankcase - Perfect!
Spark plugs.
I contacted Champion and NGK. They say that a suitable spark plug is a Champion D16, an NGK A6, or their equivalent.