Oh, I did mean to mention that dual plugs indeed work very well!
Comet Timing
- Thread starter Hugo Myatt
- Start date
Here are my thoughts having tried a number of ignition solutions in my 51 Comet and finally returning to a rebuilt original Lucas magneto with a Roy Price ATDS.
1. It is essential to lap the ATDS to the magneto spindle - use fine valve grind pase and be prepared for around 10 minutes plus of back n forth twisting. At the conclusion you must remove every trace of the valve grind paste before reassembly. If you are not using a magneto but some form of cioil ignition that requires a plane gear to replace the original ADTS then that plane gear , likewise must be lapped to the distributor shaft.
2. There is no point having perfect timing at maximium advance if you cannot start your beast. To ensure reliable and easy starting you should set the fully retarded timing somewhere between 3 and 7 degrees before TDC on the compression stroke. Set it later or even After TDC and starting will be difficult - nay exhausting and frustrating. Set it earlier then again starting will be difficult and this time accompanied by viceous kick back through the start lever. I use and swear by a magneto synchroniser to set the timing on my Comet - see MPH number 763
3. With a magneto set the spark plug gap to 18 thou. With a coil based system use 22 to 24 thou gap.
4. Finally make sure your carb is in tip top condition.
Martyn
1. It is essential to lap the ATDS to the magneto spindle - use fine valve grind pase and be prepared for around 10 minutes plus of back n forth twisting. At the conclusion you must remove every trace of the valve grind paste before reassembly. If you are not using a magneto but some form of cioil ignition that requires a plane gear to replace the original ADTS then that plane gear , likewise must be lapped to the distributor shaft.
2. There is no point having perfect timing at maximium advance if you cannot start your beast. To ensure reliable and easy starting you should set the fully retarded timing somewhere between 3 and 7 degrees before TDC on the compression stroke. Set it later or even After TDC and starting will be difficult - nay exhausting and frustrating. Set it earlier then again starting will be difficult and this time accompanied by viceous kick back through the start lever. I use and swear by a magneto synchroniser to set the timing on my Comet - see MPH number 763
3. With a magneto set the spark plug gap to 18 thou. With a coil based system use 22 to 24 thou gap.
4. Finally make sure your carb is in tip top condition.
Martyn
Just a thought, If you LAP the ATD to the spindle, You might find, Like Hugo, you can't tighten the ATD up, I found this once, And all I did was take a few thou' off the thread of the fixing " tube nut", So that the end of the taper goes INSIDE the nut. Cheers Bill.
Dear Martyn,
Whilst generally agreeing with what you have said and accepting that a bike you can't start is a pain in the rear I think that correct fully advanced timing is desirable too. If the retarded setting is too late when your full advance setting is correct then your ATD unit has too much total advance range. With a mechanical ATD you may be able to adjust this by building up the stop tabs on the unit. Using your magneto synchroniser and a degree disc you should be able operate the ATD by hand and measure the advance range fairly accurately.
Whilst generally agreeing with what you have said and accepting that a bike you can't start is a pain in the rear I think that correct fully advanced timing is desirable too. If the retarded setting is too late when your full advance setting is correct then your ATD unit has too much total advance range. With a mechanical ATD you may be able to adjust this by building up the stop tabs on the unit. Using your magneto synchroniser and a degree disc you should be able operate the ATD by hand and measure the advance range fairly accurately.
If I may offer a few thoughts on ignition timing , etc . It's best to have the timing at full retard set at around 4 to 6 degrees BTDC to start the burning early enough promote build up of the pressure in the cylinder to give a healthy thrust on the piston for a firm rotation on the idle beat on the down side . Its believed that the burning process continues for about the same distance down the power stroke as it was on the rising side after the initial plug firing . Think about that .
And with the engine idling there exists a plume of fire out the exhaust port for a distance of 8 to 10 inches which retreats back into the cylinder as the the motor speeds up and the ign. advance comes on line . This explains the bluing of exhaust pipes if allowed to tick over at a slow idle for up to that distance or more . Some new Vincents had very thin exhaust pipes which would begin glowing brightly if allowed to idle for a few minutes . My own new Rapide would do this . Scared me that first time ! Almost bright enough to look transparent , like I could see right through the pipe . Sid .
And with the engine idling there exists a plume of fire out the exhaust port for a distance of 8 to 10 inches which retreats back into the cylinder as the the motor speeds up and the ign. advance comes on line . This explains the bluing of exhaust pipes if allowed to tick over at a slow idle for up to that distance or more . Some new Vincents had very thin exhaust pipes which would begin glowing brightly if allowed to idle for a few minutes . My own new Rapide would do this . Scared me that first time ! Almost bright enough to look transparent , like I could see right through the pipe . Sid .