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MG MGA - Fuel - Engine Pinking

Finally got my MGA through its MOT - only one problem is the pinking from the engine.

We think it is the fuel. Engine is a 1800 MGB engine, with unleaded head. Garage think it is the fuel pre-combusting before piston reaches top..

What additive do people use ? I assume this is a common problem..?


Aleks Stojanovic

Fill it with super unleaded for a start.

Steve Gyles

...and then check the timing isn't too far advanced...

Pinking is detonation of the mixture as opposed to what should happen, i.e.., it burns!! There is no need for an !800 MGB engine to pink under normal circumstances. But......
Running too lean a mixture will up the combustion chamber temps which can cause premature detonation.(Potential Hot spots don't get cooled enough by the incoming fuel). Check it.
I set a speed (1200 or so) by using the throttle cable stop in the footwellThe SU tuning info for these engines was to adjust the mixture to get the best/fastest engine speed, then richen the mixture slightly to ensure the mixture isn't too lean.
Too advanced an ignition timing, maybe, retard it by degrees until it stops pinking.
As Steve said you can try higher octane fuel, but unless the head has been skimmed drastically or high compression pistons have been fitted, your engine should run happily on regular petrol.
Allan Reeling

I don’t understand the relevance of your comment “I set a speed (1200 or so) by... in the footwell”. Can you explain further?
Mike Ellsmore

Simply setting a speed controlled by the throttle, i.e., as the carbs would be in use, rather than using the throttle stops to set a tuning speed. Sorry but I was thinking B where there is a pedal stop in the footwell which can be adjusted to put tension on the cable. Might not be there on your A, but there is usually an adjustment on the throttle cable somewhere to adjust the free play which can be adjusted up. I've used a clothes peg before now, as per choke control "repair".
Allan Reeling

Pinking is often due to carbon deposits in the combustion chamber, usually due to leaving the choke on too long. Only solutions are to use more expensive gas or pull the head, fix it and don't do it again.

First, of course, make sure the issue isn't due to an incorrect timing or mixture setting.

Any MG in proper tune with factory compression will run regular gas with no ping.
Bill Spohn

As Bill says pinking can be caused by carbon build-up in the head.

In an otherwise OK engine, you have three factors to consider: Timing, compression ratio and mixture. If timing is too advanced, compression high or mixture too weak then the chances of pinking increase - and you may not hear it above valve noise. Your engine will probably run hotter too. Factory timing values are not necessarily good for modern fuels.

The short term fix is to make the mixture a little richer, and retard the timing in small increments (changing compression ratio is a big job) until it stops pinking. The long term fix is to take it to Peter Burgess and have it set up properly so that the settings are correct. When the sweet spot is found your performance will be transformed. It's not a long way from you to Derbyshire!
Dominic Clancy

I'm totally with Dominic, I would absolutely recommend that you book your car in with Peter Burgess for a set up session on his rolling road dyno.
He is not only brilliant at setting up the B Series engine, he is also an absolute gent
Worth every penny
Colyn Firth

This thread was discussed between 22/06/2018 and 28/06/2018

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