misfire at low throttle

[melvyndalby]

My 1955 RGS rep misfires at speeds up to 40-45 mph.After that it performs as it should.Coil ignition has been fitted and the points are set at 15 thou.Can anyone help?
Hear is photo of my bike.
Mel

[t20racerman]

Hi there

Need a bit more info to help out. Where is the misfire - in every gear? Are you saying it only runs above 45 MPH? What colour are the plugs? What is the timing set at? What advance and retard do you have?

Also, is this a new problem that has just arisen or one that it has always had?
Cheers

Adrian

[wilko]

Close your points gap a little.

[melvyndalby]

Hi Hadrian

I've had the problem since I aquired the bike in March.It has coil ignition and the points are set at 15 thou.The carb is Amal and the misfire occurs at about a quarter throttle in any gear.If I open the throttle fully the bike acclerates away smoothly in all gears and keeps on accelerating.The spark plug gap is set at 25 thou (I have trouble starting if they are set at 18-20 thou.The plgs are a grey/black colour.There is no adv and retard.
Cheers Mel

[muskrat]

No advance sounds like the culprit. At low revs the spark is too advanced and as the revs rise they come to the sweet spot in the timing. How is it to start?
Second opinion is a rich slide, and open the plug gap up a bit more
Cheers

[t20racerman]

As a simple first step try weakening the mixture low down with the air screw and/or drop the pin down a notch. This is easy to do and might clear it up, but the advance retard needs looking at as if the timing isn't right you'll never get it to run right.
 

[Triton Thrasher]

As a simple first step try weakening the mixture low down with the air screw and/or drop the pin down a notch. This is easy to do and might clear it up,
 

A rich needle position may well be the cause.

Seriously consider going through the whole Amal tuning procedure though.  It's probably in your manual.

[melvyndalby]

Thanks for everyones advice.The problem was a faulty condenser which was found when I had it checked.
Mel.