Pings when hot

1977 MGB GT twin SU HIF4 carbs, vacuum advance attached to manifold.

Hi everyone.
Can anyone help me with this?

I recently had a tune up and vacuum advance fitted, the old vacuum advance didn't work. However there was a delay getting the vacuum advance so they fitted it later and I don't think they re-tuned.

After the tune up the car ran very well, but after they fitted the new vacuum advance it pinged a lot & was very perky with a high idle rev.

I retarded the timing which stopped the pinging but even when the throttle stop screws were backed off totally the idle speed was still high (1100 - 1200 rpm). The car now runs hotter than it ever did and pings when hot.

Regardless of the above symptoms the car runs 100% better and is more fuel efficient than ever before.

Many thanks for any advice.

Cheers,
Billy

Edit: Wrong forum dammit!

Retard your timing! Use a strobe timing light and check the timing per the chart:

http://www.autochart.com/MGB_Tune.htm

If after retiming it still does the same thing try colder heat range spark plugs. In rare cases the tip of a too hot plug will continue to glow red hot between compression strokes and preignite the fuel.

Thanks!

look for a vacuum leak it can cause same symptoms!
the clue is the hi idle ..

It may be the WRONG vacuum advance for use with manifold vacuum. If it offers more than 10 degrees advance at the crank (you can check that with a timing light), then that's your problem!!! More advance at idle speeds the idle. Compensating by retarding the timing at idle will only hurt performance at higher rpms.

BTW....Welcome back! I haven't seen you post for a while!

Right, I am going to buy a timing light and a colourtune kit and sort this baby out!

Had a look for vacuum leaks yesterday & could hear the vacuum retracting when I sucked, also tightened up the carb mountings which were a bit loose. Anywhere else to look?

One thing I noticed is that the idle speed does not change when I advance or retard the timing. The idle is really rough too.

Thanks Rick, I have been working nights which turns me into a zombie....

You probably have something seriously wrong (out of tune) if the rpms don't change with timing adjustments. Is your plug wire order at 1-3-4-2 CCW on the cap and 1-4 from front to back on the engine? Sounds like a car with either bad igniton parts or incorrect plug wire order.

Again, get the specs on the new vacuum advance and maybe consider disconnecting it and getting the timing set right. It may be the source of a lot of your problems?

Well, I spent the day at my friends house with a strobe and colourtune kit. Stripped & cleaned the carbs (scary for me), balanced them, colourtuned & set the timing to about 12 deg.
Now she glides along, no hesitation, pulls under load, zippy, and idles smoothly at about 1,000 rpm. Also got a great sound.

Then he took me for a spin in his V8......

Thanks for all the help fellas, I appreciate it.

Edit: Stopped the pinging too!