Automatic Choke

Could anyone tell me how to check that the automatic chokes are working correctly on my twin carbs?

I do appologise for posting daft questions on here but I’m not used to petrol engines with carbs, dizzys etc. Bit of a learning curve but I’ll get there!

Remove air cleaner
Engine cold - chokes should be shut
Engine hot - chokes should be open
A bit simplistic, but its a good place to start.

Cheers Alan,

So just to get this right then, remove air filter and look down the carb. I should see the choke flap shut, this means that the air fuel mixture is richer for start up right? As the engine warms up the flap opens making the mixture leaner right? I think I’ve got it.

Is it O.K to run the engine with the air filter removed?

I’ll go and try this at lunch time.


I beleieve your carbs are dual Solex? If so, from the top of my head I’d try this first…
From cold, press the accellerator pedal to the floor once, then release.
Turn your ignition on, but don’t start engine.
Go to the engine and check the terminals connected to the choke heater elements.
Pull the spade connector off each terminal one at a time - there should be a small but visible spark when you touch them together. This means there’s power to the element.
Reconnect, wait a while, and you should feel some heat.
Then, check each carb to see if the choke arm is moving away from the cam, while the cam is held open on it’s highest step by the throttle stop screw. This means the bi-metal strip is working too.
Wait a couple more minutes, until there’s a bit more heat from the carb body near the element, or at least until the arm isn’t moving away from the cam anymore, then open the throttle linkage by hand.
Both cams should drop until they touch the arm again, and the throttle stop comes to rest against the lowest step of the cam. This means the choke is fully open.
If you need to adjust the tension in the bi-metal strip, release the three screws holding the plate locking the choke heater element and turn it accordingly.
Ideally, the arm should be just touching the cam at its lowest point when warm.
Switch off ignition, have a cup of tea, then go back to engine bay.
When you open the throttle by hand, the cams should be lifted by the arm until the throttle stops come to rest on the highest step again.
This at least means your choke flaps are operating correctly, all other things being equal.
If your getting too much or too little choke when driving, adjust as before in smaller increments, but make sure the choke flaps are fully open after the engine is warmed up after at least 3 minutes running. You shouldn’t be needing any more choke after that!
This is the technique I’ve used with single Solex engines before. I hope it applies to the twin carb engines too.
If not, er, over to Alan…

O.K guys this is what I’ve done so far,

  • checked the voltage to the chokes. O.K

  • checked that the chokes heat up. O.K

  • checked that the flaps are shut when engine is cold. right hand flap stuck open but closed with a click after manual persuation (is it possible that the flap has stuck open on a ratchet after last engine run?)

  • checked that the flaps open as the engine warms up. they do but very quickly. both flaps were fully open after about one minuite. right hand flap much quicker to open.

I don’t know my way around carbs so if anyone has a decent diagram of the choke mechanism indicating the cam, arm etc that would be a real help.

cheers and thanks for everyones patience so far!

Just one more thing…

I’ve been looking at some photos of the dual carbs on and I seem to have a bit missing. I don’t have the dashpot on my carbs, how important is this? What do they do?


Er I don’t think you should have a dash pot. Can you post the exact URL, it may be some kind of emissions guff.

excact URL is:

this thing is shown on all three of the first photos and is labled on the third.

I think you could be right about it some sort of emmissions thing as these web pages are American. Have you seen this site before? it’s pretty extensive, I suspect this guy isn’t married!!!


Never seen the site before, its comprehensive !!

  • no chance of getting married until he gets professional help.
    Yes its Good Ole Uncle Sam’s emission tosh, it doesn’t actually save the planet it just gets the vehicle past the tests at the time - it actually produces less CO (good) but uses more fuel (bad) - Doh!
    If you did have this stuff, the good news is you can remove it with a spanner and set your carbs up properly.
    Picture 2 on your URL shows the air by-pass adjustment; its labelled “idle speed screw” - with your engine hot, use this to set your idle and nothing else.

dashpot is just a damper to slow down the closing of carbs as you lift your foot. therefore cleaning emmisions but also slowing down engine braking if it was me i would remove