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MG MGA - Weber a cure for running on?

Hi people.

Probably a well-worn subject but I'd love somebody to solve a conundrum for me.

I run both Weber DCOE45 and SUs (alternately!) in my MGA Mk1 1500.

When I run the SUs which have been kitted and overhauled,
I get running-on despite a 700rpm idle. Plugs are brown, car runs great. Just always runs on at the end of a drive.

If I run the Weber, I get no running-on even though idle is 1,000 rpm for around town.

Why would this be?

Engine is about 8,000miles since rebuild, running stock manifold for the SUs when shopping and a SKRacing carb and manifold (Weber style) Extractors and larger bore exhaust for fun.

Thanks,


Baz.

B. S. Bromley

strange - I found that timing/distributor faults caused running on -if not deposits in the combustion chambers.
Cam Cunningham

Hi Baz
I have had the same problem in the past and was advised by long time mg specialist garage owner to avoid this engage gear and as you turn the ignition off just ease the clutch up to create drag on the motor and this stops it , i always felt embarrased when the engine ran on ,he could give no cause as everything was set correctly, hope this helps
Cheers Colin
c daly

Colin,
You are "spot on" for the cure,,,, we do this with the TD,, Just make sure that your other foot is on the brake! Running on is also called Dieseling,,
SPW
STEVE WINCZE

Baz - seems like the SU's might be running leaner than your Weber. Lean will burn hotter, thus more likely to run on.

- Ken
KR Doris

I have had this problem with my car running SU carbs, Installed a rebuilt distributor from Advanced Distributor and timed the engine, adjusted the idle, and the problem was gone.
JP Jim

Weber is never a cure for anything. Check the mixture on the su and set dwell and timing.

Jim
AJ Mail

If you have excessive run on you probably have carbon build up in the combustion chambers and hot spots - verty common with early heads.

The only proper way to deal with it is to remove the head and have it 'decoked' and have the sharp areas that promote this sort of thing smoothed.

An interim measure is as suggested - either put your foot to the floor right after you turn it off (the rush of cold air often limits the time it runs on), or do the clutch thing toi stop it if it bothers you.

The Weber is not, IMHO, a suitable carb for a 1500 on the street - far more trouble than it is worth (maybe 2-3 BHP at top end where you probably rarely run it anyway). They are fine for racing (and also very decent for street when properly set up, which 95% of them never achieve).

The stock SUs do an excellent job on the car.
Bill Spohn

This thread was discussed between 18/05/2013 and 29/05/2013

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