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MG MGB Technical - Pinging - from Fuel mixture?

Besides incorrect timing, can the engine ping under lean or rich conditions when the timing is correct?
Thanks
Samuel Sullivan

A lean mixture can cause the engine to ping even with correct ignition timing. This is assuming the advance curve is correct also, as incorrect advance rate is probably the most common cause of engine ping. There are also many other things that can cause ping such as : Engine temperature, local boiling in the cooling system (usually because of a crook pressure cap), local hot spots in combustion chamber, too hot a range of plugs, and even an engine using oil increases the chance of ping.
Denis
Denis4

Have you checked that your vacuum advance is working?
Ian Buckley

And centrifugal advance for that matter. Even if the timing is nominally correct at the stated dynamic rpm it could be way off at other points in the rev and throttle opening range. But as a USA car, unless pre 71 it's going to be low compression, which are much less likely to pink/ping anyway. So much so that sometimes the only indication of over-advanced timing is that it stalls the starter.
Paul Hunt

Timing is 10 btdc, vac works,18v engine, fx needles, NGK plugs,centrifugal works, HS4 carbs, stock cam, 18V engine .060 over. The idle is rich but at cruising speed the car goes lean.
Samuel Sullivan

How many miles are on the engine? If a lot, maybe it is carbon buildup on the surfaces of the pistons that is causing preignition. RAY
rjm RAY

'Works' maybe, but how do the *curve* characteristics compare to specification? That is the important thing.
Paul Hunt

Sam
Paul is right on the job here, You have to check that the mechanical advance is working to specs with a timing light and with the vac. advance disconnected. Simply checking base timing and full advance is not enough. It's the middle bit that counts--- I'd hate to think how many B's are out there with rusted off advance springs in the dizzy and happily pinging their way around the place You mention your car has rich idle (why) and that it leans off on the road-- Do you mean leans off to normal level or too lean------Air fuel ratios-?
Cheers Willy
By the way Mr Buckley if the vac. advance isn't working it will only cause a retarded ign. compared to optimum at part throttle conditions resulting in reduced part throttle performance only-- This will not cause pinging unless the engine gets to an overheated situation.
WilliamRevit

This thread was discussed between 01/10/2009 and 04/10/2009

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