MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Timing setting for Oselli Stage 2

I have an Oselli Stage 2 MGB engine in my MGA. The po has set tickover timing to 20 deg advance. It is only a standard dizzy and at high revs seems to be pushing well into the high 40's advance. Does it need a tickover advance as much as that? Obviously I can ramp it down but just wondered.
Graeme Williams

High compression or low? If it's high, then what timing you can run depends on your engine characteristics, distributor curve and fuel grade. Unless you have programmable ignition, or want to spend a long time on a rolling road tuning the distributor curve (swapping springs and maybe weights) the only option is to use the Haynes method and go by ear. Original timing specs depending on the engine and distributor but were pretty conservative catering for a range of engine characteristics caused by component tolerances. Even in the days of leaded petrol you could often get better performance and economy on a particular engine by advancing the timing a little - I did using the vacuum gauge method, and Haynes says to accelerate at full throttle in top from 30 to 50, and set the timing so that pinking is only just apparent. With unleaded and high-comp engines the timing often has to be backed off a bit even with 97 to 99 octane, and almost certainly will if you use 95 octane. The original curves even for standard engines are largely irrelevant now.
paulh4

But 20 deg seems very advanced for tickover! I'm more used to around 8 deg static. My worry at 20 deg is it's probably going to be overadvanced at 3000 rpm and a quick check with the timing light suggested way over 40. Ok I need to do a proper set-up but before I started just wondered whether 20deg seemed high to anyone else. (In my mindset a maximum advance is around 34/38 deg).
Does this sort of engine set-up need something different?
Graeme Williams

Hi Graeme, is that with vac advance attached?
Peter
Peter Burgess Tuning

And where is it attached to? If the inlet manifold then that would be about right. If connected to a carb then the idle dynamic should not be much more than the static, depending on the distributor curve.
paulh4

My fast road 1950 engine was set at 9 btdc static on a rolling road. Any further advance didn't do much for power and it doesn't pink.
Stan Best

This thread was discussed between 09/12/2017 and 16/12/2017

MG MGB Technical index

This thread is from the archives. Join the live MG MGB Technical BBS now