pinking

[charles.bulloch]

My VH pinks horribly in town. It idles OK and runs fine at full throttle. I have fitted a bigger main jet (220) and raised the needle. Ignition is at 1/2 inch btdc. The pinking is much reduced if I retard the ignition on the lever. It never used to need retarding after starting. Is this modern petrol? Pictures of the plug attached, does it look OK? Its a B6EV.

Is it worth richening the cutaway? Not easy as it is a Bratby carb.

Charlie

[Keith.owen]

Hi,
Could be that 220 is a bit small, but that really is not going to effect most of your running which is probably going to be on the cutaway/ needle jet. If you are worried about it, just remove the main and run without it; it only comes into play above about 3/4 opening. This will quickly tell you - but I think it is not going to be the problem.

Fortunately you have manual advance / retard so it shouldn't be an issue as long as you use the adjustment. Are you sure that the mag sprocket disn't slip when you wre tightening it up? Are the points set correctly?

Do you have some massively high C;R piston?

The colour doesn't look too bad !

I once read that if you suspect ignition it's probably the carb and vice versa.

Keith

[Brian_Walker]

Take off the points cover and view the cam ring advance/retard movement in the magneto when moving the lever, I have seen issues where the cam ring is jammed or spring too weak and not returning leaving the the ignition fully advanced. I have mine set at 5/8" on full advance. (9:1 piston)

[nevhunter]

If there's any chance your plug is too hot change it for a cooler one. Sustained wider throttle operation will bring it on. It doesn't help your motor to have it happening. Nev

[david.anderson]

Charles
Pinking. How long since you gave the bike a valve grind and decoke? The build up on the spark plug is suggestive that there may be a large carbon build up on the piston and head and if that is the case that will be the cause of the pinking.
Apart from that how recently did you check the ignition advance. If the point rubbing block has worn and the point gap is less than the initial setting (should be .012”) the ignition will be advanced.
And when you check the point gap can you get any movement in the armature shaft as that will vary the point gap when the engine is running. The magneto armature runs in cup and cone bearing. The end plate of the magneto is shimmed to ensure the knock is taken out, but there should not be any preload. With a little wear in the bearings it is very easy to get quite a knock in the shaft. I have seen armatures that I could move to vary the point gap by .010”.The fix is to remove one or two of the shims behind the magneto end plate ie adjust the shims to take knock out without preloading the bearing.
David

[charles.bulloch]

Thanks for the replies, everyone. The head was off recently to get a new valve guide and the timing has been checked. I'll try another carb. and even a cooler plug. And check for play in the armature.

Charlie