Pinking (pinging)

[a101960]

Does anyone have any ideas or observations about eliminating pinking (pinging)? I have an  ally big valve head, a 389 carb fitted with 23 pilot, 420 main jet .106 needle, and a number 3 slide. I have retimed the engine so many times now that the mag drives jumps off the shaft just by whistling at it! At 35 degrees (15/16) BTDC the engine is way over advanced, and the same applies at 34 degrees. I have tried 32 degrees BTDC and there is no pinking but the engine is flat and has no performance. Today I intend to set the timing up at 33 BTDC. I have tried it at this setting before but it still pinked on gradients. This has been an on going problem for ages and I can honestly say that it is detracting from the pleasure of riding the bike. I am paranoid about damaging the engine. I have considered swapping to a manual mag. This would allow some adjustment but, I am beginning to wonder if the compression is to high. I do not know what pistons are fitted, but they have slightly raised crowns and are flat topped with small cut outs in them, so I am guessing that they are probably  eight twenty five to one. Before I go to the expense and all the hassle of fitting new pistons does anyone think that this might be worthwhile? While I realise that fettling is part of the territory that goes with owning an old bike, I am getting a bit tired of constantly playing with the timing and getting nowhere. When the engine is set at 35 degrees BTDC it goes like….er…a rocket, but the engine always feels harsh, it also intermittently kicks back when starting. To not put to finer point on it I am getting so fed up with it that I am contemplating getting rid of the bike and buying something that is a bit less of a Prim Donna. By the way I always run on 99 RON petrol.

[a101960]

Some additional information: I have had the mag and auto advance unit checked out by Tony Cooper ( I actually visited him) and he said to me that he would be quite happy to fit the mag and A/R unit to his bike, so a clean bill of health on that then. The plugs I use are either Champion N4C or B7ES.

[Josh Cox]

Do not claim to be an expert, but if it was me, I'd:

Ensure the fuel is less than 12 months since purchase ( preferably highest octane at the bowser ),

Screw the mixture "full Rich" (screw all the way in ?),

Clean and regap plugs.

Does the the pinking happen when the engine is cold or hot, or both ?.

Is the pinking both cylinders ( run the engine at rpm, spray CRC or similar of the top of the exhaust pipe at the cylinder head, if one cylinder is running hotter than the other, the burn/smoke difference will be noticable, you could use an infared heat sensor to tell you this, CRC is more fun).

Does it pink at a certain RPM, at any stable RPM or whilst varying RPM ?.

Look forward to your response, don't give up on the old girl, this is her having PMT.

[a101960]

The pinking happens under load, going up gradients for example when I open in top gear to maintain speed. If I change down then it seems to go away. I use the highest octane petrol that I can get my hands on. The exhaust pipes are still chrome with no discolouration. After a run there is a very slight yellowish discolouration that vanishes once the motor has cooled down. The plug colour looks O.K. to me (coffee colour). Incidentally when I set the timing up I use an electronic LED module so it is about as accurate as could be reasonably expected. I am running the mixture a bit on the rich side. I am totally stumped!

[A10Boy]

When was the last time it had a de-coke?

[manosound]

Is "15/16" at 35 deg. a typographical error? I can't say I know the angles that go with the distances, but "5/16" is more likely. If you are timing near 15/16" BTDC, it sounds like you might have the timing wheel incorrectly attached. Since you seem to have eliminated the usual suspects, another thing that comes to mind is the possibility of timing gears being off a bit, maybe one tooth.

One thing I am rather certain of, your bike is not haunted. There is, indeed, a reason for the problem and you will eventually find that reason. Maybe someone who is not guessing, as I am, will give the exact answer while I'm typing. There are lots of bikes out there with higher compression than yours that don't ping (I am in the U.S., after all, so, not "pink"). Mine is one of them at 9:1. I think I can speak for a lot of members here in saying, "hang in there, we enjoy the company."

Richard L.

[Triton Thrasher]

Have you tried raising the needle in the throttle slide?

[groily]

Would it be worth running the thing up a hill at speed under load to promote the pinging, cutting it dead while it's doing it and doing a plug chop roadside? If they're far off the coffee colour you describe, then it might well be worth raising the needle a notch. Could also try B8s or N3s I guess, but doubt it would make much odds.
No air leak at carb to head, deliberately arranged to fool you because it only causes grief when the motor's sucking hard? No funny gizmos in the plug leads sold by snake-oil persons as spark-enhancers?
Like Richard, also wondered about your 15/16ths - which would account for no end of hassles, including trying to break your leg when starting. But if you're using a timing disc anyway, does look like a misprint.
I wouldn't put on a manual mag with the deliberate intention of running it at less than full advance most of the time, as the spark weakens appreciably as you retard it. Manual ones are set up to spark best at full advance, fixed ones always spark optimally. Better to do the 'Orabanda slotted-hole mod' (see recent threads) to get some moderate (few degrees) adjustment?

[chaterlea25]

Hi, a101960
My Super Rocket behaved very much like yours for a long time
I would feel BSA fitted a manual mag to the SR etc for a reason!!!! (mine has)
If your bike is kicking back it means the A/R mech is not doing what it should

You are saying you are using 99 octane petrol
Personally I dont believe such a product exists!!! I believe the oil companies dish out any old crap and charge a premium for calling it 99 octane.

To stop my SR from pink(g)ing I used to add octane booster,
I did not find valvemaster plus much good at the recommended dose!! so I upped it 2 or 3 times the reccomdation this gave some improvement,
I had better results using Acetone with a wee drop of 2 stroke oil mixed in
maybe 50ml to a tank full.

The final cure came when I changed out the Lucas mag to a BTH (manual)
This is not a straightforward job,  see the post I put here on the forum.

I really dont know for sure why the BTH cured the problem?
But it gives a way better spark at low revs (kicking over)
and way better acceleration and power, with the same timing figure, 35degrees

I'm just thinking as I write this, have you connected a strobe to your bike
Its a good way to see if there are any misfires when you rev the bike it will also check how well the A/R  unit is working
I have sorted out quite a few mysterious problems on various bikes /cars just by looking
at the strobe light pattern, its very easy to see erratic behaviour on one cylinder at a time
What about the tension on the points spring? maybe the points are floating a bit when the revs are up causing over advanced timing?
HTH
Regards
John O R

[muskrat]

G'day A101960, like John O R says strobing is the best way to time the spark. Pinging and kick back is caused by too much advance at both ends of the curve. I run 31 deg on the A7 with 8:1 and 33 on the A10 with 10.5:1. I also boost our premium (98oct) unleaded with Nulon pro octane boost to about 105 and add a cap of R30 per tank (mmm that smell). A bit of a pain but the ride is worth it. most old bikes will ping on unleaded, even my Rhonda Whore had to be retarded by about 4 deg. Richening the needle & main jet may also help. All the replies have merit, just work your way through them, don't give up. The ride is worth it.
Cheers

[Richard]

John
Dont bother mucking about with it any more, you know its not worth it, give it to me it likes my garage anyway.
Retime it to 32/33 degree's meet up with us on Saturday at the Esso garage at Chisledon tomorrow (Saturday) at 11am  for the Fish and Chip run and then let me see how it goes and you can try my Super Rocket which does not have the big valve head but the standard vales for a S/R then at least we will have something to go by and if it goes as well as mine at 32 or 33 degrees without pinking then you have nothing to worry about.
bring some basic tools and if needed we can raise the needle by one notch which will if I am correct give more fuel when you open the throttle to go up inclines which should stop the pinking if it is fuel related.
Ring me and let me know if you will be coming
Richard

[a10gf]

Be 200% sure the auto advance behaves properly, to eliminate it completely form the equation.

groily:

I wouldn't put on a manual mag with the deliberate intention of running it at less than full advance most of the time, as the spark weakens appreciably as you retard it.

I'm no expert, but seems to me that with a mag in decent condition the spark will always be strong enough as long as timing is roughly within spec (but very high compression could have an impact, am on 7.5. No spark problem at full retard, would not start if so). So IMO, no harm in trying out manual control.

[BSA_54A10]

Get a new slide with a small cut away.
Run up your "test hill " .
If it pinks then pull the slide and increase the size of the cut away.
Repeat till pinking stops.

The original carb was designed to work with "real" petrol which modern "fuel" bears only a vague resembelence to, so all of the factory settings should be regarded as a starting point for tuning and not the correct "set in concrete" correct settings.

Do not use a bunch of different slides unless they are all brand new because different wear in the slides will change the volume of air drawn down the sides so you could end up with more than one variable and these problems are only soluable by changing one thing at a time.

The cut away acts as a acceleration pump and enritchens the mix as you open the throttle.
It is a right royal PIA job to do but worth while .

All of the other stuff, in particular the freshness of the fuel and the addition of acetone are all to be considered.
Basically the compression ratio and combustion chamber shape in your engine are not compatable with modern fuels.
And the same applies to the magneto. It only just has enough power to ingnite the current fuels that have a much lower amount of high volatiles so require a lot more energy to ignite and do not atomize properly in the carb as they are designed  to be pressure injected into engines that operate at much higher cylinder temperatures than your BSA can cope with.
  

[mike667]

Have you tried raising the needle in the throttle slide?

this what i did  and cured my pinging  too, which was occurring similar to yours on my A10. I also had a similar problem in my commando and put in the next size bigger needle jet  - worked beautiful on that also - both changes enriched the mixture, although in different ways

 

[Triton Thrasher]

Get a new slide with a small cut away.
Run up your "test hill " .
If it pinks then pull the slide and increase the size of the cut away.
Repeat till pinking stops.
  

Increased cutaway weakens the mixture, which raises temperature, making pinking worse.

A weak slide doesn't usually cause serious pinking, because it is only controls mixture  up to about 1/4 throttle, or maybe less.  Bad pinking is that which is persistent at moderate rpm (and higher rpm) while the engine is pulling.  Your engine can be damaged badly.

[beezalex]

First of all, we need to clear up what CAUSES "pinging".  What we're really talking about here is detonation and it occurs when the combination of pressure and temperature in the combustion chamber exceeds the spontaneous ignition point of the fuel.  To prevent the fuel from detonating you can do three things:  Lower the pressure, lower the temperature or change fuel to one that has a higher ignition point.   Lean mixture causes excess heat, so you first need to make sure that your mixture is correct...mainly on the needle. Going too rich can alleviate pinging, but it's a formula of diminishing returns and eventually causes carbon buildup which causes an even higher propensity for pinging.  Get your timing right (too much advance can also raise heat), get your mixture right, then if it still pings, decarbonize and polish piston crowns and combustion chamber.  Also, remove any sharp edges from around the valve cutouts on the piston.  This removes localized hot spots and origin points for detonation.  This has worked for me 100% of the time that I have done it.  If, however, this still doesn't do it, you can lower the compression ratio by either changing pistons, installing a spacer under the barrel or installing a thicker head gasket.  1 mm lowers compression by about 1 point.  This has also worked for me in the past until I realized how effective massaging the chamber was.

Good luck.

[mike667]

First of all, we need to clear up what CAUSES "pinging".  What we're really talking about here is detonation and it occurs when the combination of pressure and temperature in the combustion chamber exceeds the spontaneous ignition point of the fuel.  To prevent the fuel from detonating you can do three things:  Lower the pressure, lower the temperature or change fuel to one that has a higher ignition point.   Lean mixture causes excess heat, so you first need to make sure that your mixture is correct...mainly on the needle. Going too rich can alleviate pinging, but it's a formula of diminishing returns and eventually causes carbon buildup which causes an even higher propensity for pinging.  Get your timing right (too much advance can also raise heat), get your mixture right, then if it still pings, decarbonize and polish piston crowns and combustion chamber.  Also, remove any sharp edges from around the valve cutouts on the piston.  This removes localized hot spots and origin points for detonation.  This has worked for me 100% of the time that I have done it.  If, however, this still doesn't do it, you can lower the compression ratio by either changing pistons, installing a spacer under the barrel or installing a thicker head gasket.  1 mm lowers compression by about 1 point.  This has also worked for me in the past until I realized how effective massaging the chamber was.

Good luck.

 excellent points as always alex!

[muskrat]

Good one Alex, indexing the plug can also help.
Cheers

[nigeldtr]

I hope this fits with the thread – if not sorry!

I have been looking around to buy a Road Rocket, but I have been put off a little by the problems associated with high compression, and racy cams. Does it really make that much difference to performance (cam – compression) especially as I will probably not keep the engine bubbling at the sort of revs where a racy cam comes into effect?

Your experiences and advice on what to look out for would be greatly appreciated.

Regards

Nigel

[muskrat]

G'day Nigel,
                It does make a difference to performance BUT. A highly tuned motor puts more stress on its components and needs a bit more fettling to stay tuned. Factory settings go out the window.
Start with a std model and work your way up if you want more go later.
Cheers