Cold start overfueling

Bin it and replace with a proper carb., like a Weber.

are you sure that 80 (cold start air valve) is opening as it should ? A split diaphragm in that would give the symptoms you have

Nedavno SteveH napisa:

I did. I have Weber 32ADF. But I need few custom parts for it to be able to run it on LPG. Currently I made LPG mixer out of wood :-)

And 32ADF has coolant heated semi-auto choke that seems to keep higher rpm longer than my original carb.

Nedavno Mrcheerful napisa:

Yes I am. Without it open engine would die at idle when cold, as better part of the fuel enrichment during warm-up engine gets from waxstat 75 and electric enrichment valve 82. As it gets warmer coolant is heated and waxstat 75 moves piston 73 to the left and at ~75 Celsius closes by-pas channel.

in that case I would blank off the cold start device and rely on the choke flap for enrichment, you will need to manually keep the throttle open enough.

Nedavno Mrcheerful napisa:

I know I could do that, but I am not very good at it.

What is the function of 78 - cold start air valve (as you named it)? It is open almost always, it closes briefly only when you press hard at the throttle, and that has effect only while the engine is cold. When it is warmed up piston 73 closes by-pass channel completely.

Check the pull down unit and vacuum lines to it. It's a black plastic bit below the choke housing. It should open the choke a little as the engine fires.

Nedavno Yvan napisa:

I forgot. There is another reason, I have a/c, and Pierburg has one device that increases rpm when a/c is on. Weber (at least the one that I have) does not.

Nedavno Chris Bartram napisa:

I will check that, but currently I fixed open choke flap, so pull down unit does not have any function.

While I was testing I used screwdriver to open choke flap fully (from cold), and engine did not die. So my guess is that cold start enrichment device is broken - the one heated by coolant, as I blocked off electrically heated one. But I changed it recently, and it's letting correct amount of air in, since it runs OK on LPG.

Or there is a leak somewhere that I can not see... And that is why I posted here, I thought that someone might suggest where to look for it.

Have you tried the old wafting a little propane from an unlit plumbers torch around the inlet side to find a leak?

it closes when the throttle is wide open to give a richer mixture (like an accellerator pump)

Nedavno Duncan Wood napisa:

No, I did not when it's cold. Above 10 Celsius ambient temperature I do not use petrol, and then it's OK on LPG. Even at lower temperatures I do not have a problem on LPG (except evaporator freezing eventually).

It could be that I have a leak when the engine is cold, but wouldn't that create a weak not rich mixture (and it is reach - I fitted lambda sensor in the exhaust).

Nedavno Mrcheerful napisa:

Yes, I can see that, I just thought that since it's almost always open, and has no use when the engine warms up it's unnecessary, or has a function that I can not see :-)

it will work as an anti stall mechanism

Doesn't it normally read weak when the engines cold? It's a "feature" of lamda sensors.

Nedavno Duncan Wood napisa:

I do not know what do you mean by that, but lambda sensor is only used for running on LPG (closed loop). On petrol it has no function, other than it is connected to a LED voltmeter so I can read lean or rich.

Nedavno Mrcheerful napisa:

I just thought of something. Could it be, if new waxstat is OK, that I have too much opened throttle butterfly 26 compensated by too much closed 46? So when choke flap is closed it draws more petrol than needed (remember choke flap fixed in open position sort of helped).

usually the throttle butterfly is a fixed position from the factory (just off binding shut) and the idle is all through the bypass screw. As a rough amount the by pass screw should be open about 2 to three turns which should give a reasonable idle, if it is too fast (when hot) then the throttle butterfly may be open too much.

Nedavno Mrcheerful napisa:

Yes, but I remember (trying to) adjusting it :-( Perhaps I opened it too much. But I might check it again, here is how:

I'll check that, thank you.