Jump to content

Gripper timing


tztwofifty
 Share

Recommended Posts

On 7/17/2018 at 4:55 AM, section swept said:

The closer the timing to top dead centre the more likely the engine is to start and run backwards. Advancing the ignition point to say 4mm before top dead centre ( occurring earlier) reduces or eliminated this. Retard ( move ignition point closer to top dead centre and there is a more noticeable kick back and a likelihood of the engine running in reverse. Petrol burns at the same rate irrespective of piston and crankshaft speed/ revolutions so starting the burning ( ignition ) sooner before the piston reaches top dead centre allows the engine to make better use of the fuel. Retard the ignition point ( move it nearer to top dead centre ) and the piston may  have gone over top dead centre before complete burning has started. That’s why with a mechanical advance the ignition moves away from top dead centre or the original timing point so then at say 5000 rpm the ignition might be occurring at 15+ degrees btdc. So on a relatively slow running two stroke with fixed timing ( no means of advance or retardation) the closer to top dead centre the ignition the more  initial throttle response the harsher or peppier the engine responds. The closer to the tdc position that the ignition is set means that although the Kickstarter spins the engine in the correct direction of rotation any tardiness in the operators kick may just allow the engine to start in reverse. I can see the point that you are making and was aware of that at the start, ignition advance potentially causing reverse running. Let’s face it we are talking about some really old engine design with very basic ignitions...just large lawn mower engines...even they now have a simple advance and retard map in their electronic ignition systems. Let’s just let our man with the Gripper which has leccy ignition experiment for himself, not sure if that has an ignition curve map. Hey it’s been interesting discussing with you this topic, just out of interest I run a Sherpa 250 with the ignition set at the manufacturers spec of 2.8 mm btdc, but with the vagueness of the contact breakers wear with the heel rubbing against the flywheel ignition cam ( felt pad oiled...high melting point grease on inside of heel....polished cam) after a few hours running the timing will possibly have gone off due to wear and the points closing up a little. More maintenance/ tuning but easier to fix if a fault develops. Your Sherco 200 will be running leccy ignition? ??

 

Interesting, but are you certain retarded timing causes backwards running.  I was always led to understand if the timing is too advanced, the engine kick back and provided the kickstart is not engaged, this is the initial engine firing that sets in motion the backwards direction.  After that, the timing is firing after top center, and look out when you let the clutch out.

Link to comment
Share on other sites

 

12 hours ago, pmk said:

 

Interesting, but are you certain retarded timing causes backwards running.  I was always led to understand if the timing is too advanced, the engine kick back and provided the kickstart is not engaged, this is the initial engine firing that sets in motion the backwards direction.  After that, the timing is firing after top center, and look out when you let the clutch out.

Yes because the closer to tdc the piston travels the more likely it is to go staight back down the way it came...backwards rotation.?

Link to comment
Share on other sites

 
  • 10 months later...
 
 

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
 Share

×
  • Create New...