Britbike forum Forums British Motorcycle specific Brands Bsa bulletin board 1952 B33 Rich Mixture issue

Spencer,
you are having a bad run with this bike but anyway I will try to help, this is long winded but read on as I feel some advice you have been given is not correct but you have also been given good advice too.

Be very careful setting the ignition timeing. Make absolutely sure you know what way you advance or retard the timing with the cable as from reading the previous posts you have been told correctly and incorrectly or else I have read it wrong. On your magneto the cable enters the battery side of the end housing, that means you have to pull the cable (which you have been told) to advance the timing, end of story. It does not matter what way you push or pull the handle bar lever, as long as you tighten the cable by either pushing the lever or pulling the lever you will advance the ignition timing. People get mixed up in this because they fit levers from the right hand side to the left hand side of the handle bars. You have to know if its cable tight advance or cable slack advance and lever toward you advance or lever away from you advance.

Another thing, setting the main needle clip in the bottem hole produces a richer setting, not a leaner one. Think about it, you are raising the needle and letting more fuel out for the same throttle setting. If you think any engine is running rich, turn the fuel tap off while it is running and watch closely what happens, does it start to run better or run worse, that will tell you for sure if its rich or lean.
Watching your bike run on your video it looks like the timeing is maybe retarded but its not actually running that bad, that could explain the smoke you seen coming from the engine because it will start to run hotter like that, these bikes leak oil from nearly every joint, a bit of oil on the fins under the cylinder head will soon start to smoke, 5 or 6 seconds of retarded ignition and a couple of revs on my bike produces a wisp of smoke from the engine and exhaust pipe, you would think the engine is pulling a load up a hill as it does not want to rev with the ignition retarded.

Now, here is how I ignition time my B31, its not 100% accurate but it gets the engine running very very close to correct. Set the advance / retard lever and cable to the full advance position. Kick the bike over slowly until you feel the compression stroke. Remove the spark plug. Bring the piston up slowly to the top so you can see it and set it at T.D.C (top dead centre) taking into account there is a dead spot in the crank at the point where the crank rotates but the piston doesn't move, you have to feel for it. Get a vernier caliper and measure the distance from the edge of the spark plug hole to the piston and whatever it is in Millimetres, add on 13 millimetres. I know the vernier will be pointing at a bit of an angle at the piston but is accurate enough for now. Now rock the engine back and take the piston back down and place a piece of thin cigarette paper between the points, rock the engine forward again and bring the piston up slowly until the piston is the distance you measured plus the 13 mm from T.D.C. That means your piston is now 13 mm from T.D.C. At that point your points should just be starting to open which you can confirm if the paper has been released from between the points. If not you can move the points slightly or if it is completely wrong you will have to remove the right hand side engine timing cover and remove the magneto drive pulley from the taper on the magneto shaft with the special puller that threads into the gear wheel.

You will know when you have the ignition timing set right if you have the ignition timing fully advanced with the lever and you kick the bike over compression after priming it without actually trying to start it and the engine kicks back at you, retarding the ignition with the lever will soon show you where it doesn't kick back and that is the sweet spot where my bike starts first kick every time. Retarding it further produces a engine which is impossible to get to fire never name start.

Intake valves are generally equal to or larger than exhaust vales in most engines.

The reasons are the intake charge is more dense than the exhaust charge, therefore taking up more physical space, and the exhaust charge is under pressure so that helps it evacuate the cylinder vs the intake charge being under vacuum to get into the cylinder.

More dense means the same mass takes up less volume.