plug chop

[jhg1958]

I am almost embarrassed to post this but I am a but stuck.  When I was running in the A10 GF I had no problems but now I am opening her up I have found that the engine starts to stutter.  It revives if I close the throttle rarely cutting out.  At first I thought is was lack of fuel but I have opened up both taps and the problem remains.  Then as it occasionally backfires I retarded the ignition by a few degrees.  Lastly I thought it was an electrical fault and in fact I blew a fuse due to fault on the horn/dip switch.  After rectification it still stutters.

The 1961 GF has electronic ignition, and a new Amal carb.  The charging system is working well and the battery full. I have carried out a plug chop stopping the engine when the stutter occurred and have included a photograph.  I think the engine is a little rich as it starts up without choke or tickling the carb.

Where do I look next?

John
   

[Rex]

That doesn't look like a rich plug. It's either brand new or running lean.

[limeyrob]

What main jet are you running and what needle position?  For now move the needle up a slot and see what difference it makes.

[Worty]

Definitely looks lean - very much like the Kwaka plugs which is supposed to run lean.

[jhg1958]

Needle in the middle position

Needle jet 106
Main jet   250

The plug is new about 50 miles.  Here is a picture of the old plug just taken out at the end of a run.

I will try moving the needle.

John

[muskrat]

G'day John.
The plug after the plug chop still looks lean. What number slide?
Could be rich on pilot hence starting cold without tickle or choke but still lean further up the range.
As Rob said, lift the needle to start with.
Cheers

[Kickaha]

but now I am opening her up I have found that the engine starts to stutter.  It revives if I close the throttle rarely cutting out. 
 

I had the same symptoms on my Ducati, it was caused by being too lean on the main jet

[morris]

Had a similar issue once. Too restrictive (home made) air filter was found to be the cause.

[jhg1958]

I must admit I found it hard to believe that moving the needle one position would make much difference.  I moved it up (raised the needle) one position and the problem has gone away!

I need to admit I made one other change before I tested the bike.  Not a brilliant idea I know.  When I put the electronic ignition in and rewired the bike, I was reluctant to put a key switch in.  So I fitted a remote controlled relay coming off the lighting circuit.  It has worked really well disabling the bike with the a press of the remote button.  I realised that these items are not meant for motors especially one as old as this with the terrible vibration.  So I bypassed the remote.  So it could be this.  One day I will put the remote back in and see if the fault returns. 

For now the plugs look not much different so I am happy with the change to the needle position.

John