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Carburettor Clean

I was having problems with tick over and fuel economy so decided to clean the carburettor.

The tick over problem manifested itself as a reluctance to drop back to tick over and cutting out. On inspection throttle adjustment screw was set ok (not stopping the return), but the actuator (linkage) felt stiff.

This is how the carburettor looked when I removed it. Pretty dirty in there.

This shows the state of the bore of the carburettor and float chamber. yuk!

Here is a larger shot of the same part.

This is the top of the carburettor.

Now we get onto the offending part causing the stiffness in the linkage (and bad probably the tick over). You can see the state of the arm that the choke flap. It was so coked up that the choke would have never worked correctly. Notice the temporary plaster made from electrical tape, I seem unable to go into an engine bay without leaving some skin and blood in there .

So all was cleaned and freed up and is now working smoothly.

The carb was refitted without problems, well almost.

Throttle

The throttle only opens about 2/3. I started by setting the cable up as the manual states (depress pedal, open linkage fully and back off 1mm) but this meant that the throttle wasn't shut when the pedal was released. I ended up setting up the throttle cable on a closed throttle but it does mean that I don't get full throttle at the moment. The problem appears to be that the linkage is worn taking up the throw of the throttle arm.

Air leak

The throttle arm (see pic) is leaking air. The way to check this is to pump the throttle (whilst the engine is off) and check for fuel/air vapour escaping from the joint where the arm enters the carburettor. This will lean off the mixture, If I'm correct, as the revs increase (due to the increased vacuum in the carburettor) pulling more air in. If I am correct this would account for the problems setting up the mixture.

Setting up the carburettor

This was always going to be difficult and if I can't get it right it will probably mean a new carburettor. I tried setting it up anyway. The main thing to remember on these carburettors ('34 pic3') is that you set the tick over using the air bypass screw and not the throttle cable linkage screw. I found that (without changing the mixture screw) the engine bogged down at low revs but was ok as the revs picked up.

I'm going to set up the mixture and see if I can fix (bodge) the air leak with more fuel flow. I wouldn't recommend this to anyone though as if the mixture leans off then the engine can overheat and sieze. It's only a temporary measure until I get it fixed properly