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

Worn out needle jet will cause a rich condition...I know first hand...

I glanced back through the thread and didn't see the following mentioned, but apologies if it has been. The main jet definitely can affect low throttle openings. It can do so by its absence. If the main jet has vibrated out of its holder and dropped to the bottom the bike might still run, but it will run badly due to being too rich.

I've only experienced this problem once (with a friend's Matchless G80CS) so I don't know how bikes in general respond. It was a decade ago so I don't remember the details of the symptoms, but I do remember that it started with great difficulty and ran very badly. It's easy to check for -- if the jet falls out when you remove the cover at the bottom you've found the problem.

Something that is never covered in the Monobloc literature is the importance of making sure the pilot jet is seated in the body. It is the very first thing to check when having problems with this carburetor. If it is not seated, and fuel is leaking past it, the instrument will be very rich at low throttle openings. Probably not the problem but well worth mentioning.

Forgot its a Monobloc, MagnetoMan, i had encountered the same on a friends 650 AJS with a loose MJ in a Monobloc.

The jets are all seated fine; I made sure of that when I was checking the numbers on them. I think I will start by replacing them all, then move to rebuilding the float and replacing the slide, etc. If worse comes to worse, i can always buy a new carburetor and end up with a spare for parts. Incidentally, i was examining the carburetor further and noticed that the connection between the carb and the head is as follows:
Carb/Paper Gasket/Cork Gasket/Paper Gasket/Head

Is this correct? I have a feeling that someone was over ambitious with stealing leaks in this motor.

Also, there is no washer where the fuel line comes into the float; not upon a visual inspection at any rate. Also, the tickler seems to function normally, but occasionally, fuel not only comes out of the tickler, but out of the intake holes on the carb inlet.

Alright,I finally got the primary chain cover gasket in the mail and was able to take the bike out for a ride for about ten miles, reaching speeds up to 55mph and here's my report:

Firstly, I installed a 210 main jet. 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.

Running at speeds above 50 is pretty smooth running, but below that feels somewhat inconsistent, like ever so slight changes in power. Sitting at idle requires fiddling with the spark or throttle to keep it running, otherwise it seems to miss step for a few seconds before cutting out.

That's very likely due to an air leak where the exhaust pipe enters the head.
Which raises the question, retard it from what value? How many degrees BTDC do you have the magneto set when it is fully advanced?

The carb gasket arrangement is suspicious, paper, cork, paper , it may be you have an air leak at this joint, with the motor running spray WD 40 around this joint and listen for motor changes.
its better to have solid phenolic spacer between the two paper gaskets, this acts as an insulator to prevent heat boiling up the fuel in the carb.

Magneto man makes two very good points, exhaust leaks wont help and your timing should be a known figure.
You still havent told us the slide cutaway number.
have you tried adjusting the pilot air screw for a smoother idle once the motor has warmed up?

Amals do not have minds of there own, they are inanimate objects. They respond to tuning adjustments like any other carb.
They do suffer from ham- fisted owners who overtighten the mounting Fasteners and warp the bodies,this can cause bad things to happen , like the throttle sticking open.

The slide is a 3-1/2. Also, the needle is on the lowest notch, which I believe it's incorrect. Shouldn't it be something like the second notch down from the top?

Try raising the needle clip two notches and see what effect it has

Well, I stripped the carb down, cleaned it out, reassembled it without going crazy tightening it down, raised the needle two notches, eliminated the paper/cork/paper connection and installed a phenolic spacer and gave it a go. It's definitely running better. Throttling up from idle still has a slight hesitation, but idle is smoother and the smoke is gone. I plan on replacing the needle and pilot jets just to cover all my bases, but so far the results look promising. I can't ride it at speed at the moment because I've got a clutch issue that's needs sorting out so I've got it disassembled on the bench. Once I've got that back together I'll take it for a spin and give an update on the results. I should have the new jets by then too, which should eliminate another point of error. Incidentally, the slide and block fit neatly with little play and are not in a poor state. Ditto for the float & needle(s). The mesh fuel filter was dirty, but I've cleaned it out and added a filter between the tank and carb to help things from getting clogged.

next time you get the motor warmed up , raise the idle speed a little using the throttle stop screw then screw in the pilot air screw a quarter turn at a time , wait around 15 - 30 seconds between each adjustment, the optimum setting is when the idle increases, and steadies. lower the the throttle stop to normal idle speed and try on the road. . Normally the correct pilot air screw setting is around 1.5 turns out. You said it was set at 2.5 turns out earlier.

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.

Okay, update time:

I have replaced all gaskets and jets in this carburetor, keeping the slide and the jet block. I also reused the float and float needle as they were both in fine condition. The main jet is size 210, the needle jet is size 106, and the pilot jet is size 25. The needle is currently in position 3, and the pilot air screw is currently adjusted 2 turns out from the seat.

I currently have the foam air filter installed however I got a hold of an alloy elbow which somebody had mentioned on here might work and it will clear the oil tank however the inside diameter of the elbow is too wide to clamp down to the body of my carburetor and the adapter collar that I have is slightly too thick to fit inside of that flange. So some slight modification is going to be required before I can properly mount an air filter to the carburetor.

I recently replaced the head pipe and the muffler as well because I discovered that a previous owner had modified the head pipe from a rigid frame to fit this one and also modified where the muffler mounts so that they could put an aftermarket muffler in place of the stock one. The problem I now face is that the new head pipe does not seal properly inside of the exhaust port so I have a substantial exhaust leak which is preventing the engine from running smoothly therefore I cannot check to see if my adjustments to the carburetor and the replacement of all of those parts have corrected my richness issue. I can say though that I was able to get the engine running in three kicks despite the bike having sat unused for several weeks. That in and of itself is promising, however there was a surprising amount of smoke coming out of the pipe and the leak at the exhaust port. I cannot decide if this smoke was due to the exhaust leak or if it was still due to the carburetor not being properly tuned. I'm going to be sealing the exhaust pipe tomorrow and then trying to run the engine again. I'll follow up with an update after I get that issue corrected. Thank you all again for your help it's been appreciated and hopefully I'll be able to get this bike back on the road soon.

You can take the pipe to your friendly exhaust shop that makes up exhaust systemsand ask them to expand the end where it goes into the head to restore the tight fit.'
I used to get mine done a little too big and put the cold pipe into a hot head.
Seemed to work well with the B40 & B50.
Or you can buy an exhaust pipe expander and do it yourself but you must buy a good one. Anything on evilly is crap out of China and will break before the pipe expands.

Next you can take the guess work out of your tuning by fitting a colour tune.
They come from a company called Gunsons and work really well as you can see the colour of the actual flame ( check out the video on the web site ).
There is a U-Tube video of some one who mounted a video camera to record what was happening as he rode around the block.

It could well be your tuning is better than your timing.
A retarded spark will give you sooty plugs , soft acceleration and total lack of any power at wide throttle openings.

I decided that uploading a video of the bike running might be helpful. the smoke is a recent development I'm not sure if it's because something is worn out and it's developed a new problem or if it's because I drained about half a cup of oil out of the sump before I started it up and there was still some residual oil left in there. Also I should note that after running this bike for a few minutes there is a fairly significant puddle of oil underneath the bike from both of the breather hoses.

https://youtu.be/Eu6IlHJkLRA

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

The motor was warm when I took the video. I believe that it was up to normal operating temperature at the time. As far as the condition of the engine, I'm not entirely certain as I have not taken it apart. I've only owned this motorcycle for a few months and the gentleman that I purchased it from said that he had ridden it, and that everything was fine, but frankly at this point I think this was just a project that he got tired of dealing with and here we are. It was idling a lot smoother when I purchased the bike, but the condition of the Jets leads me to believe that it may have been tuned excessively rich in order to get it to run at all. It may be unfair for me to assume, but I think I've been had. This bike was sold to me as a running drivable motorcycle, but thank goodness I didn't take his word for it because in going over the bike I found nothing but erroneous repairs slapdash customisations and outright failures in nearly every aspect of it.

Here's the second video with a brief description as well

https://youtu.be/LPePBDso2Do

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.

The magneto is an MO1L and the cable enters from the back side, close to the battery. The way the control works (which I think is backwards), is that pushing the control forward pulls the cable, and pulling toward you, while seated, pushes it back, observed from the points cover. The smoke is grey, so it's certainly oil, but before, the carb was running so rich that black smoke was present, but that has been corrected. Condition of the plug is sooty, but not wet.

I have a copy of The Book of BSA, and planned on timing the engine according to the recommended procedure. I am correct assuming that I should time from fully advanced, yes? On the MO1L,this is with the cable fully pushed in (observed from the points cover),correct?

Should have read the post much more closely.
That is an M series magneto with pull or advance, push for retard.
So you should be timing with the cable tight ( 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.

I gather then that re-timing will be a fairly common maintenance practice? In your experience, can timing be achieved with the head in place or do you recommend removing it.

With a degree wheel on the crank and a wodden skewer down the plug hole I lay a trimming knife ( Stanley to some ) blade flat on the head and make a line in the skewer.
Then rotate the engine to firing position and do the same.
I now have a timing stick the goes in the tool box on the bike.
In the workshop it is the degree wheel on a magnet on the crank.

Very important when doing this is to take the piston back 1/2 way down the cylinder then bring it back up to firing position to account for wear in the drive train to the magneto.

I'll be setting the timing on Tuesday once the pinion puller gets here and let you know how it goes.