Engine jerking, poor acceleration

Sounds like the choke isn't opening up a bit as soon as the engine starts. I don't know the BMW carb, but often a vacuum operated diaphragm pulls on a linkage to instantly open the choke a bit as soon as the engine fires, then there's a more gradual opening that's controlled by temperature and that could just be a crude bimetallic spring with current going through it to warm it up over a few minutes. A bad connection is enough to stop it working. Knowing BMW it might be more complicated than that but the general principle may still apply.

Nedavno Steve B napisa:

But what when the engine warms up? Choke flap is completely open (I checked that).

And you are correct, BMW made this carburetor quite complicated. It has fully automatic choke operation, with a lot of mechanical components to reduce emissions.

"Yvan" wrote

HT leads?

Hello again Yvan. Still trying to get this one going?

You've obviously got a very rich mixture when cold. Is the float level correct and does the float valve seal properly?

remind me, what carb is this? a 2BE?

Is the black smoke still there when warm, or does it just run badly?

What colour are the plug electrodes? (Black probably...)

Nedavno Knight Of The Road napisa:

I think not. I can also run on lpg. I than have some other problems, some (light) jerking, and good acceleration. And lpg is more sensitive to spark problems.

Nedavno Chris Bartram napisa:

Yes. I am in a proces of fabrication of bottom adapter plate for mu weber, but I am also still trying to get the original pierburg to function properly.

I do not know. Runs relativelu OK at idle, acceleration is the problem.

No. Rest of the world had 1.8 litre and 2BE (or 2B4 I think), while we here got 1.6 litre and 1B2.

It just runs badly.

I have to check that.

????????????

Accompanied by the sound of a chisel on slate Steve B, managed to produce the following words of wisdom

If it's a Pierburg carb then it's about normal behaviour.

Either fit a Weber or give in.

Without jerking, presumably?

Nedavno Pete M pise:

I am in a proces of doing that (fitting Weber).

Nedavno Knight Of The Road pise:

I have LPG conversion. So I can use gasoline or LPG (liquid propane gas, I think).

Nedavno Ian Dalziel pi¹e:

:-)

Did I spell something wrong, or it is just a word that has more than one meaning?

Liquefied Petroleum Gas, ITYM.

Chris

If it jerks on a steady throttle opening then it is more likely to be an ignition fault than a fuel fault.

Nedavno Mrcheerful pine:

No it jerks only when accelerating.

Nedavno Chris Whelan pi¹e:

You are right. Thank you. For more check here:

in that case it needs to be richer

Nedavno Mrcheerful napisa:

:-( Too rich when cold and during warm-up at idle and light load, too lean when accelerating.

I hope my adapter plate for weber will be finished soon :-)

just increase the main jet size a little, that will not effect very small throttle openings