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MG MGA - Running on problem

I have an 1800 3 main in my A and have an lot of problems with run on. I am switching to HS4 carbs this spring and was wondering if adding an anti run on valve would solve my problem.
Thanks for any advise you can offer.
Kris
Kris Sorensen

Kris

Can you get the tickover down to 8/900rpm, with the timing just off pinking. Then before switching off ignition, try allowing 30-40secs to cool down the hot spots. Also try depressing clutch as you turn off, the extra drag of the clutch bearing can help kill it.

These things helped on my 'cammed' MGB engine. Remember, the anti-run on valve can fail and you don't go anywhere! So a last resort I reckon - course it does work, but just another complication...

Pete
Pete Tipping

The anti-run on valve only stops the symptoms, not the cause of the problem. Search the archives - there is a wiring repair that can be made to eliminate the problem as well. It works as well as, or better than the valve.

You may want to verify that you don't have an ignition timing problem. You may also need to decoke the head.

Jeff Schlemmer

Hi Kris. The 3 main MGB engine was basically a displacement enlarged MGA engine, and had no smog equipment to speak of. This engine should shut down without run on! I would first check the carbs for correct mixture, and perhaps even err a bit on the lean side if necessary. I would also lower the idle speed a bit. I would also adjust the ignition timing to factory spec, to see if that eliminates the run on. If run on still persists, then perhaps try experimenting with "modifying the factory ignition timing. Perhaps in "altering" the factory recommended ignition timing, you will find a setting that eliminates the run on, but still allows good performance. Sometimes "properly" setting the ignition timing either statically or with a timing light,for some reason, does not remedy running problems! If all else fails, it is possible that there is a large build up of carbon deposits in your engine, and that they are causing the run on condition. In that case, you could try chemically removing the deposits by using a proprietary product such a Shaler's "carb out", or you could remove the cylinder head, and manually remove excessive carbon deposits. I would try the least invasive options first. Good luck! Glenn
Glenn

This thread was discussed on 08/02/2006

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