Carbs too rich by far

[fredtporter]

Hi

I have just obtained a 63 mk2 which is running excessively rich (garage says 12% when it should be 3%?. I can't work out if it's the auxiliary enrichment device that has failed and is leaking fuel when supposedly closed but I have taken it apart to look at the brass disc that opens with the action of the solenoid. Anyone have any idea what it should and shouldn't look like or how loaded the spring should be!? Can't see an obvious problem on inspection. Am tempted to order new parts and fit them just to see if it cures the issue. The richness adjustment screws on the crabs themselves seem to be already at their greatest lean setting. Could it be float levels? Anyone have any tips? Thanks.

[piman]

Hello Fred,

the disc is to shut off the air when the device is deactivated. If you disconnect the solenoid then that deactivates it. However if it is on all the time you hear it by the air going into it.

Float levels are one possibility, but from waht you say I would suggest that the carburettors should be stripped and all basic settings checked. If you remove the dashpots, and switch on the ignition you can do a fuel level check by looking inttpo the jet tubes, the fuel should be about an 1/8" below the top of the tubes.

If you are not happy about dismantling and adjusting these carburettors and it is not the aed, then you will need someone who is familiar with these carburettors.
to check them for you.

Alec

[Tintin]

A restriction in the air intake may also cause over-richness. I assume you have checked that the air filter is clean and the induction system has not been inappropriately modified? Of course this would only apply when running the engine with the induction system all connected up.

Robbie

[fredtporter]

Many thanks. I can turn off the auxiliary in the cabin so I know it's off but was wondering if petrol could still get through the disc if it wasn't faulty or the spring too saggy. Maybe they don't go working like that. It doesn't look faulty on inspection. Better check the floats etc then I suppose

[PPV]

Have you got an additional switch fitted for the auxiliary starting carburettor? As Alec says the disc is to stop the airflow and when you switch it off (or disconnect the connection from the thermostatic switch which controls it you will hear the difference (only works before the engine is up to temp) as the noisy 'hiss' disappears and the if you are not using the throttle the engine may stall. In addition you should hear a click from the solenoid as you do this. With no air going through the aux carb then no fuel should be sucked into the engine. The manual gives a very good description of this and how to set it up. The disc has no adjustment, it is just in the open or closed position. The sliding needle in this carb can be pushed down gently to reduce the flow of petrol and test it that way also in case it is stuck but the full downward movement is limited by the collar that sits above the spring that surrounds/supports the needle.
I would take off the inlet to the carbs and see if that makes a difference, then if not take off the dashpots and see if the top of the jets are close to the bridge in the carbs (nominally should be just below it as the starting point for tuning is usually level with the bridge). If it is lower then the carbs are out of adjustment and will need resetting.
If that looks Ok then it could be that the floats are not shutting off and you will need to take off the tops off the float chambers and check if the floats are indeed floating and that the needle valves are working and are set correctly.
Regards,

[fredtporter]

Thanks all. I'm pretty sure the aed is innocent and that it is a carb issue - floats/needles etc. I shall investigate!

[ChrisDixon]

Yes, put the carbs back to their basic settings, but first check for evidence they are rich, is the exhaust emitting any blackish smoke when the engine is warm. Pull a couple of plugs to see if they are sooty (and while you are at it check they are the correct plugs, basically distrust anything you didn't fit yourself).

[fredtporter]

It's running rough and was measured by local garage at 12% richness when it should be 3 or 4. New plugs just fitted as old were slightly off. Pretty sure mixture is my issue.

[fredtporter]

Retuned the carbs myself and it's running very well now. Not sure I have it absolutely right but what a change from the way it was! Nothing wrong with aed but have changed needle valve and seat in front float chamber and also the fork which appeared to be shedding bits of black stuff into the chamber which can't have been good for the valve which was leaking! New one on me.