Author Topic: misfire at low throttle  (Read 1790 times)

Offline melvyndalby

  • Active
  • *
  • Join Date: Aug 2011
  • Posts: 10
  • Karma: 0
misfire at low throttle
« on: 03.09. 2011 16:31 »
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

Offline t20racerman

  • A's Good Friend
  • ***
  • Join Date: Feb 2011
  • Posts: 232
  • Karma: 7
  • Keep it nailed!
    • The T20 'Super Six' Suzuki website
Re: misfire at low throttle
« Reply #1 on: 03.09. 2011 19:00 »
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
1944 WN/G based trials Ariel
1961 A10 - somewhat modified :-)
1967 T20 Suzuki - heavily modified Classic Racer
1967 T20 Suzuki - pretty standard road bike
2007 KTM 660 SMC - fast and furious supermoto
Triumph Tiger (modern one)

"If I had all the money back that I've spent on motorcycles... I'd spend it all on motorcycles!"

Offline wilko

  • Resident Legend
  • *****
  • Join Date: Mar 2010
  • Posts: 681
  • Karma: 4
Re: misfire at low throttle
« Reply #2 on: 03.09. 2011 19:39 »
Close your points gap a little.

Offline melvyndalby

  • Active
  • *
  • Join Date: Aug 2011
  • Posts: 10
  • Karma: 0
Re: misfire at low throttle
« Reply #3 on: 04.09. 2011 13:48 »
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

Offline muskrat

  • Global Moderator
  • Wise & Enlightened
  • **
  • Join Date: Jul 2009
  • Posts: 11062
  • Karma: 132
  • Lithgow NSW Oz
    • Shoalhaven Classic Motorcycle Club Inc
Re: misfire at low throttle
« Reply #4 on: 04.09. 2011 14:32 »
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
'51 A7 plunger, '57 A7SS racer now a A10CR, '78 XT500, '83 CB1100F, 88 HD FXST, 2000 CBR929RR ex Honda Australia Superbike .
Australia
Muskys Plunger A7

Offline t20racerman

  • A's Good Friend
  • ***
  • Join Date: Feb 2011
  • Posts: 232
  • Karma: 7
  • Keep it nailed!
    • The T20 'Super Six' Suzuki website
Re: misfire at low throttle
« Reply #5 on: 04.09. 2011 16:32 »
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.
 *smile*
1944 WN/G based trials Ariel
1961 A10 - somewhat modified :-)
1967 T20 Suzuki - heavily modified Classic Racer
1967 T20 Suzuki - pretty standard road bike
2007 KTM 660 SMC - fast and furious supermoto
Triumph Tiger (modern one)

"If I had all the money back that I've spent on motorcycles... I'd spend it all on motorcycles!"

Online Triton Thrasher

  • Scotland
  • Wise & Enlightened
  • *
  • Join Date: Feb 2009
  • Posts: 2004
  • Karma: 23
Re: misfire at low throttle
« Reply #6 on: 04.09. 2011 22:53 »
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,
 *smile*


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.

Offline melvyndalby

  • Active
  • *
  • Join Date: Aug 2011
  • Posts: 10
  • Karma: 0
Re: misfire at low throttle
« Reply #7 on: 18.09. 2011 17:47 »
Thanks for everyones advice.The problem was a faulty condenser which was found when I had it checked.
Mel.