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

A 376 on a B33 should be 1 1/16" bore.

No air filter, main jet 260, needle jet .1065, needle position 3. Pilot jet 25

With air filter - 210 main jet, the rest the same.

Coming off idle, if the pilot jet is correct, check float level and slide cut away.check wear on the needle, verify needle is correct length for a 376 carbie.

Modern fuels do affect jetting from 1950's specs, but the change is incremental, not drastic.

Your bike should have a 289, which is a seperate float bowl carbie. But the 376 was used on later B33's

Forgive my ignorance, but is my current 106 needle jet the same as ".1065"? I searched the latter and couldn't find any results (unless I'm just looking in the wrong place)

Try replacing the pilot jet, it may have been cleaned out over enthusiastically and enlarged .
What setting is the pilot air adjuster screw at?
What slide number?, it sounds like it may be too lean.

What throttle slide cutaway do you have? The book say 3.5

Also is the carb in good condition with little wear?

The .106 needle jet will be slightly leaner than the .1065 and from what you describe isn't therefore the source of your problem.

It might also be useful to take the bike for a run so you get up to normal road speeds and then see how things go.

lots of carbon monoxide means rich, and it might substitute for an A/F gauge. if you bring in a box of doughnuts in the morning, they might do a series at different rpms for you on the rollers.

How does it run without the air filter?

I tried oiled foam filters and concluded that they have to be pretty big, to avoid restriction leading to over-rich mixture.

I have found that a restrictive filter requires a bigger slide cutaway and an adjustment to the pilot screw and throttle stop.

If that improves running at slow speeds, but it's still rich at over 1/3 throttle, drop the needle by a notch.

Id take the air filter off and try it then.

Main jet has 0 influence on Idle and just off idle mixture. It is all bout float level, pilot jet, slide cut away and mixture screw setting......

Just sayin'

You need to be flat out with a wide open to 3/4 open throttle before the MJ has any real effect.

Deceleration and shifting causes popping noises.

Also, I have to retard the spark about halfway on the lever or power is almost nonexistent and stalling will occur at idle.

I've been waiting on a new gasket set and jets for this issue. I figured that replacing everything I can will at least rule those things out of this problem persists. The pilot jet got here today and comparing it to the old one, someone clearly did some tampering. On the old jet, the hole drilled trough the sides was obviously drilled out larger. I'm curious to see what differences I'll find when the needle jet arrives.

Good idea with the upload.
What's condition of the engine ?
Did you take a bike to the normal operating temperature before the film ?

That really sounds like it is way too retarded.
To be 8 stroking as bad as that you would not be able to see through the clouds of black smoke.
The really hard bang happens because the exhaust valve is opening when the fuel is only 1/2 way through burning.
There are 2 different magneto ends used on BSA's and they are interchangeable .
Early pull for advance cable enters at the back and late pull for retard, cable enters near the cylinder.
Me thinks you have timmed the engine on full retard.

The excessive oil from the breather can also be due to retarded spark forcing excessive gas flow past the exhaust valve guide down into the sump .
Sudden oil leak will be a blown head gasket, or a blocked breather tube on the oil tank ( Mud wasps )

If you have a timing light with an inductive trigger ( clamps to the spark plug ) you can slip the primary cover off and mark the cush drive nut at TDC with a blob of white out.
Put this mark at the 12 O' clock position.
Rotate the engine and put another one at your timing point , also at 12 O'clock.
So now you have 2 marks on the nut about 1/4" to 1/2" apart.
Start the bike and look at the marks with the strobe lamp.
If timing is near right there will be one dot near the 12 O'clock position and another a little to the left when the light flashes.
If you have timmed it full retard then 1 or both of the dots will be to the right of 12 o'clock.
Crude rude & unsoficticated but good enough to verify the timing.
While you are there play with the advance / retard lever and watch where the dots appear.

When I use to ride the A 10 I had a timing disc glued to a strong magnet which I placed on the cush drive nut to time the engine accurately as it was running 11:1 pistons so if not spot on would self destruct.

yes,
cable slack is full advance,
Because there is no key on the timing gear, the timing can slip both when you are doing up the nut on the pinion and if the engine backfires.
I don't think any two BSA single owners actually do the timing the same way.

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.