Plug Chop?

[bill harrison]

How do you do one?  My RGS, I think, is slightly weak.  I think looking at the book that the first thing to do is to raise the needle one notch.  I also have an exhaust gas analyzer but don't want to sit with the bike on the path stationary for too long.

[stu.andrews]

Go for a ride. Work the bike as you would normally for several miles. Whilst riding, declutch & cut the ignition straight away. As soon as you stop, whip out the plugs & read the colour of the centre electrode & insulator. It should ideally be a light brown. The outside ring may be a little more black. A white centre needs instant richening before damage occurs to valves & pistons. Try richening the pilot airscrew first by a quarter to half a turn. If this does not make much of a difference, raise the needle one notch. It depends on how much throttle you are using as to whether the pilot airscrew or the throttle needle will have an effect. If you Google Amal tuning tips, there is a mine of information.

[bill harrison]

Go for a ride. Work the bike as you would normally for several miles. Whilst riding, declutch & cut the ignition straight away. As soon as you stop, whip out the plugs & read the colour of the centre electrode & insulator. It should ideally be a light brown. The outside ring may be a little more black. A white centre needs instant richening before damage occurs to valves & pistons. Try richening the pilot airscrew first by a quarter to half a turn. If this does not make much of a difference, raise the needle one notch. It depends on how much throttle you are using as to whether the pilot airscrew or the throttle needle will have an effect. If you Google Amal tuning tips, there is a mine of information.

Thanks Stu,

went for a ride, did as you suggested and plug is white.  Have managed to en-rich the mixture slightly on the idle but will go and try raising the needle one notch.  have read the "book" and seems that the main jet only comes into play at nearly/full throttle  although as the needle is fitted in the jet this seems counter intuitive!

[bill harrison]

Ended up moving the clip 2 notches as the needle was in position 1 of 3 and I think it should have been in the centre (no2) position.  Ran another plug chop and it looks good, maybe slightly dark but I'll take that whilst its running in.  Strangely my old beast, a standard a10 with iron head (1954) runs fine but has a blue LH exhaust, sure enough the mixture is weak on this side but fine on the other.  I've done the tappets, although they may not be perfect, any other suggestions?  Not too fussed as she's a clonky old "original" condition bike with plenty of patina!

[morris]

Strangely my old beast, a standard a10 with iron head (1954) runs fine but has a blue LH exhaust, sure enough the mixture is weak on this side but fine on the other.

Hi Bill, do a search on the forum involving the words "induction bias" I think you'll find that nine out of ten are suffering this. Some live with it, others fit an anti bias gasket.

have read the "book" and seems that the main jet only comes into play at nearly/full throttle  although as the needle is fitted in the jet this seems counter intuitive!

The needle itself slides in the needle jet, not in the main jet. Therefore, changing the needle's height doesn't affect the main jet.

[stu.andrews]

Whilst it's running in, let it run slightly rich to keep it cool. The bias gasket is normally the answer to uneven mixtures as has been said. You'll get it right!