Pinking when warm

[Slymo]

My 58 SR is pinking like a MF when warm. It’s got 9:1 pistons (+020” which came with it brand new) and I wonder if the comp is simply too high to run modern juice? I’m running Champion N4 plugs and might try a colder plug and also I can reset the ignition timing but have done that once and even when I dial it back on the lever it doesn’t cure it completely. Do I simply go for flat top pistons or is there an easier way?

[worntorn]

When was the head and piston top last decoked?

Glen

[Slymo]

Literally within hours. It’s spotless in there.

[Clive54bsa]

Retard the timing a bit, Orabanda posted a useful alternative to "book" values on timing. If you search his posts you'll find his research very interesting.
Clive

[orabanda]

And check your mixture; could be too lean.
Lift the needle one notch, and repeat your ride. If the pinking stops; problem solved, if it reduces, lift the needle another notch.

[muskrat]

G'day Slymo.
There's three ways to combat pinging. Retard ignition, richen the mixture or use higher octane fuel.
Try orabanda's method first. If it helps you may also need a bigger main jet. Then if it's still pinging knock the timing back further. Orabanda found the magic number was 32 degrees btdc
My Cafe runs 11:1 on 98 and 32 degrees. It will ping on a hard hill if I let the revs drop so I throw her back a gear.
Cheers

[beezermacc]

I read an interesting article on pinking recently. Apparently the fundamental problem is a 'hot spot' somewhere in the combustion chamber. The effect of this is to create two points of ignition, one is the spark plug, the other is the 'hot spot'. The article stated that the pinking is caused by the two combustion pressure waves colliding. I had always thought that the pinking was simply evidence of pre-ignition i.e. the spark firing too early and the pressure wave smacking the top of the piston too soon.  The most likely source of a hot spot in the cylinder head is the edges of the exhaust valves or the plug tip. Setting theory to one side for a minute I have a Super Rocket which has been plagued with pinking ever since I built it. I have tried everything! Lower compression pistons, retarded ignition, richer mixture, all of which had only minimal effect. However I recently fitted a Mikuni carb which made a big difference and cured the pinking, though I am still running the low comp pistons. The carb is set up for a Super Rocket, which the bike is no more because of the pistons. I can only deduce that the mixture provided by the Mikuni is keeping the top end a lot cooler than previously. The bike runs great in its current configuration. I have another Super Rocket spec bike which runs absolutely fine in standard SR trim. I also have two iron head A10's which both run great. My guess is that the issue with my rogue Super Rocket is the alloy head - something just ain't quite right about it! This particular cylinder head was professionally built so I have been reluctant to blame it. One day I'll return the rogue SR back to its standard trim with a different head to see how much difference it makes. Food for thought.

[A10 JWO]

Are you buying fuel from Supermarkets or Esso , just thinking out loud. I had one that did this only on Esso, not BP. Different additives.   

[beezermacc]

I always buy best fuel available, usually BP or Shell V-power.

[bsa-bill]

Do I simply go for flat top pistons or is there an easier way?

Debatable whether it simpler or not but I cured this on my bike with electronic ignition (Pazon), made starting a lot more reliable also.
probably about the same costwise as a piston change, involves a bit of work ( so does a change of compression).
I would say the a/r mapping is better of course than the standard auto /a/r, only downside I found was you do need to ensure the battery is up to 10 volts so switch ot off when parked.
Other than that it's down to how original you want the bike to be

[muskrat]

G'day Fellas.
There are lots of web pages on the subject. All of them give the same remedies. More fuel (cools the cylinder), better fuel (slower burn), retard ignition, lower compression which will reduce heat.
If you retard the ignition too far this will also create more heat and end up like a dog chasing it's tail. I wonder why twin plug heads don't ping, as it's creating two flame fronts?
Cheers

[worntorn]

With twin plug you retard the timing 5-8 degrees behind the normal setting for single plug, same engine and you still see full power, in fact usually a bit more than single plug power.
Twin plug isn't so much about extra power on it's own, although it generally adds some.
It's about allowing high power tuning without having detonation. The squish band is another big help. The drag racers call them "Quench heads"
The squish band transfers more heat to the head than a nonsquish head does.

Glen

[Bsareg]

I run twin plugs on a 350 bullet which stops the pinking and seems to run cooler, strangely when I tried it on my 500 bullet I couldn't find any difference even though I could switch the second plug on & off and adjust the timing when at speed. I  haven't yet tried it on my bighead Fury as it seems a similar combustion chamber as the 500.

[Slymo]

Good chat thanks folks. For the moment I have lifted the carb needle and will give that a go tomorrow, my next plan is to try B9 NGK plugs which I was going to try first but found I had been sold resistor plugs and I dont want to stuff the K2F's primary windings. I will set up a timing wheel and try the 32 degrees. At the moment Im just using the stick down the plug hole method and I'll admit that isn't foolproof. Will post back on my discoveries but am heatened to hear that it isnt an impossible task.

[Slymo]

Yep sorted. Lifting the needle one notch stopped the pinking immediately. I also dropped the mainject from 250 to 240 and it is much more responsive at wide throttle now. This fuel bears so little resemblance to the old stuff that you really need to go through all three circuits one by one untill it all works well.