Understanding my automatic choke

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Understanding my automatic choke

Post by Scotbag » Wed Jan 22, 2020 10:05 pm

Dear Fellow Scimit-tzars

As a complete and utter novice....I’m learning my engine really slowly and working my way through the issues I have getting this car to start and stay running!

A question about my automatic choke... should it be set open when starting her or should she be set closed?

I’m being told it should be open and perhaps it staying open and never getting hot enough to close is my issue...
But I’m looking at her and even after pumping the throttle 2-3 times...she remains closed and won’t fire up?

I’d love to hear any advice re: that.

Many thanks

Deano



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Understanding my automatic choke

Post by rebel alliance » Wed Jan 22, 2020 10:08 pm

Flaps closed to start , if they don't shut after 3 pumps to the floor then the linkages and cams want servicing or cleaning...or just buy a new carb



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Understanding my automatic choke

Post by Roger Pennington » Wed Jan 22, 2020 10:16 pm

Yes, definitely closed to start, *but* note that it stays in the position it was last in when the car was run (normally open, if the engine got warm) until you do at least one pump on the throttle. The pump on the throttle will cause the choke plates to close, and squirt in some petrol, ready for starting. Normally a couple more pumps (to add more fuel) don't do any harm. The crucial thing to remember is that you *must* pump the throttle to set the choke.


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Understanding my automatic choke

Post by AJL Electronics » Wed Jan 22, 2020 10:25 pm

Once the engine starts it will open the flaps slightly to admit air. As the cooling system warms up the flaps open under the influence of a bimetallic coil in the water chamber. If it drops out too soon or too late, there is an adjustment. Don't mess without good reason though, they work far better than having to play tunes on a manual downgrade.


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Understanding my automatic choke

Post by Scotbag » Wed Jan 22, 2020 11:35 pm

Okaaaaay so then the choke is perhaps not the issue. Thought I was onto something there.

I have spark so I wonder why she’s not firing up🤔 got a mechanic coming tomorrow. Hopefully he’ll find the fault.

Thank you for the advice.



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Understanding my automatic choke

Post by Scotbag » Fri Jan 24, 2020 9:21 pm

Hmmmm my mechanic has let me down this week. So if I’m tinkering this weekend. I have spark....the choke does seem to be in the correct set position..the staring procedure is correct....any body know what I can try as she won’t fire up??



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Understanding my automatic choke

Post by rebel alliance » Fri Jan 24, 2020 9:47 pm

Get a new mec..no wait we stopped that years ago. Back to the car firstly any fuel in the carb ? If you look down the carb and open the throttle do you get two jets of fuel out of the accelerator pump nozzles



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Understanding my automatic choke

Post by scimjim » Fri Jan 24, 2020 9:47 pm

If you have fuel, air and a decent spark, the only thing left is timing (valve and ignition).


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Understanding my automatic choke

Post by AJL Electronics » Fri Jan 24, 2020 10:14 pm

Drop a tablespoon ish amount of neat fuel down each barrel. Then see if it tries to start. We can go from there.

You have got plenty of fuel on board I assume?


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Understanding my automatic choke

Post by Scotbag » Fri Jan 24, 2020 10:48 pm

All top advice. I have fuel yes, though I’ll keep an eye on that. I’ll try to get a look down the carb. Might have a classic car mech coming over to help tomorrow.

I was advised to try something that I think was pretty dangerous...but interesting! Force open the carb flaps and turn her over...now there was a few flames....(that cannot be good) but she fired up. Kept going for quite a while but stalled when I dropped below 10k revs.

Does that help explain anything?



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Understanding my automatic choke

Post by halfpenny » Fri Jan 24, 2020 11:26 pm

10k revs !!!!



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Understanding my automatic choke

Post by Scotbag » Sat Jan 25, 2020 7:39 am

Typo...1k revs....imagine 10k revs!!!!!



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Understanding my automatic choke

Post by willholderogri » Sat Jan 25, 2020 7:46 am

Reset the choke by pushing the throttle twice and see if it will restart .it sounds like you may have a sticking choke which in time if it does not open will flood the engine and foul the plugs . You opening it manually may have freed it so it's worth trying to start it again.


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Understanding my automatic choke

Post by AJL Electronics » Sat Jan 25, 2020 9:03 am

It does sound like flooding, or ignition problems. Starting with the throttle held open, does it start and run? Could be carb needle sticking, or is there an electric fuel pump I wonder?

Have the plug leads been taken off at all?

Do you have a continuity tester so that we can check the static timing?

Does it run points? Have you checked the gap?


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Understanding my automatic choke

Post by rebel alliance » Sat Jan 25, 2020 10:29 am

In my opinion if this carb looks to be past its sell by date and your willing to pay a mechanics fees you might as well spend that money on a new carb for £330 approx



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