Classic cars forum & vehicle restoration.

Finch661 · Posted: Fri Feb 27, 2009 5:31 pm Post subject: tuning '76 midget

i have managed to tune my midget (colortuned, carbs balanced, idle set), but for cold starts, i pull out the choke and the rpms only increase by a small about (500-600rpm). what could this be? have i missed something?

thanks

47p2 · Joined: 24 Nov 2007 Posts: 2009 Location: Glasgow

When you pull the choke out there should be a lever on the carb that adjusts the needle jet, this might be needing some adjustment
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Finch661 · Posted: Fri Feb 27, 2009 6:59 pm Post subject:

i dont see a lever, would the "fast idle screw" do the trick?

47p2 · Joined: 24 Nov 2007 Posts: 2009 Location: Glasgow

No don't touch the fast idle screw

Have a look at this picture. You will notice at the bottom of the picture there is a cold start mechanism. When you pull the choke this lever should move and when it does it moves the jet allowing more fuel and a faster tickover
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Finch661 · Posted: Fri Feb 27, 2009 9:16 pm Post subject:

ah im with you! when the choke is pulled, the jets lift up, but again there is only a 500rpm increase, not a lot! i would like a choke idle of about 2000rpm. do you think my mixture is still off??

Penman · Joined: 23 Nov 2007 Posts: 4755 Location: Swindon, Wilts.

Hi
Looking at that picture the lever pulls the jet down the needle, I wonder if the piston is supposed to move up as well and if that is sticking under less vacuum than there is when using just the throttle/butterfly flap.

Could either the vacuum passage or the atmospheric inlet be blocked/restricted?
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47p2 · Joined: 24 Nov 2007 Posts: 2009 Location: Glasgow

Yes the lever does pull the jet down, this allows extra petrol for cold running. However as far as I can remember the piston is NOT supposed to move up at the same time. The piston should be sitting on its rest until the throttle is opened. There should be a small pin under the carb which if pushed will lift the piston a pre-determined amount and it is used to check when adjusting the mixture.

Check that the piston is resting properly on its stop, that it has the correct oil in it and the damper is giving a reasonable resistance. Check the lever is not worn or bent and is moving freely. It might be worth removing the cable and working the lever to see if it makes any difference, maybe the cable requires adjustment.
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Finch661 · Posted: Wed Mar 04, 2009 11:31 am Post subject:

right i managed to get the car working (after much faff) i retuned the car (correct idle, good mixture, synced throttles) and then took on the choke. i adjusted it so that by 1/4 out, the car was fully pushing the fast idle screws (before the screws barely toutched the cam) adjusted so that the engine ran at about 2000rpm. once the choke is pulled beyond that 1/4 mark, the jet seats are lifted, enriching the mixture.

the car still needs fettled, but its a lot happier when cold starting (like today)

many thanks for your help Wink