4 replies to this topic

[smj]

just fitted mg metro engine into my 1993 mini sprite auto, all up and running thanks in no small part to this forum!!!, the car has my original electronic factory dizzy, which i dropped in and got the motor running, i don't have a timing light so have adopted a drive and check plug colour way of seeing if the timing is something like right, the car pulls like a train(compared to old auto motor) the idle speed seems okay(again apologises for no real data) but the plugs look very very lean, not wanting to damage the car, if i retard the timing will it burn better, or do i advance????? i am guessing! but it seems that the spark is arriving when the squashed mixture is either already heading out the exhaust port, or is being explode a long time before its quite ready??? thanks. JUst as a point the air filter and carb are the ones from the auto car, just sat on an alloy inlet with lcb exhaust, and i know i have no air leaks!

[lrostoke]

burning rich or lean is really down to how the carb is set up.

One method of setting the timing though is to advance the timing test run it and check for pinking under load, try going up a hill in to high a gear. If it pinks retard the timing back slightly try again, do this untill the pinking stops.

[bmcecosse]

As above - plug colour is for mixture - not timing! Advance till pinking - then retard slightly. What colour are the plugs ??

[smj]

after many years of driving and messing about with minis, i am afraid i still have to ask the question, WHAT IS PINKING????

this mg metro engine has a ported and polished head which was bought from local mini guy a while back, i haven't removed it from the engine since buying it so have no idea whats actually been done, and also the already mentioned alloy inlet(mg metro factory one) as i know the carb and airfilter are stock do i need to be looking at setting them up differently to accomodate the head?

[Ethel]

Pinking (aka pinging) is where the fuel spontaneously combusts after the spark plug has fired, it creates a pinging sound when the 2 explosions run in to each other. It means the engine isn't far off detonation when the fuel ignites before the plug fires, also aptly known as dieseling.

Normally you'd set the ignition timing to the manufacturer's specs before adjusting a carb but the fuel air ratio and the ignition advance are interdependent so if the engine is quite heavily modified you'd need to optimise the fuel ratio then set the ignition to optimise the power - a rolling road session being a suitable way.

over advanced ignition generates excess heat as t he pressure builds before the piston has reached tdc, effectively trying to push the engine against its rotation. An overly retarded engine wastes power but is less likely to melt itself.