Use of the choke when starting from cold

 In Engine General, MGA-MGB, Midget

With modern cars having engine computers to do all the tricky stuff, the operation of the choke is something that many new owners of classics are not familiar with.  Under use of the choke will make the car hard to start, while over-use can lead to flooding and/or fouled spark plugs, so here’s the choke action explained and the procedure when starting your MG from cold:


What the choke control does

The first half of the action only increases the idle speed, and has no effect on fuel mixture.  Enrichment happens only at the end of the choke travel.


How to use it

When starting from cold, use full choke and then as soon as possible push the choke mostly in so it is clear of the mixture enrichment zone.  This is usually straight away with a standard engine other than on frosty mornings, but with a modified camshaft a bit of enrichment may be needed for longer.  In any event, avoid having the choke on enrich for longer than is necessary, otherwise modern fuels can result in permanently fouled spark plugs.  Listen for an even beat to the engine rather than a lumpy one (or in the case of a modified camshaft, lumpier than usual).

Then adjust the choke control position to maintain an idle speed of around 1200 RPM until the engine will run without the fast idle control (usually by the time the gauge reaches the 7-8 o’clock position).

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