Detonation And Preignition ?

[zzzzed]

I have recently swapped my standard points distributor for a Mallory electronic distributor

First issue was I had to reduce the timing from 10 degree down to 5 degree to stop detonation

Second issue is that I am now getting preignition after longer drives.

Could the stronger spark be making the fuel mixture lean?

I am running British Su carbs from an Austin Healy on a standard l28.

Edited February 6, 2016 by zzzzed

[Jason89]

Try colder plugs. You may have more heat in the combustion chamber due to a better burn.

[RLY240]

Sounds like the new dizzy has a greater mechanical advance, do you know what the total advance is?

The Nissan ones are stamped on the weights, ie 7 on each weight totals 14 deg advance.

Roger

[zzzzed]

Sounds like the new dizzy has a greater mechanical advance, do you know what the total advance is?

The Nissan ones are stamped on the weights, ie 7 on each weight totals 14 deg advance.

Roger

That wouldn't make it preignite though would it.

I thought it might be a carbon build up and now it is burning hotter the carbon is making it preignite

[zzzzed]

Hmm I think the total advance of the dizzy is around 22 degree

[peter mc]

First. Spark dose not cause a car to run on .as soon as you turn the ignition off theres no spark ...can i ask did you turn the idle screw up after you had to retard the timing. .? Also combustion chamber may have hot spots in it from running retarded timing

[zzzzed]

I havnt touched the idle speed.

I might up the timing a couple of degree and see if I can add a bit of fuel to the mix to try stop the pinging

[oldmates260z]

I have had similar issues with my L28 with flat tops....found my dizzy was only going to 20-25 DBTC

 

You should check Ignition timing- should be around 34-36 degrees at 4000 rpm

[zzzzed]

Ahh ok. I think I need to get it on th dyno and let some one who knows what they are doing have a go.