SiKiD_01 wrote:could some one please explain to me about engine timing (in a carby)
what happens if it advanced to far, (wont start) and what does it do to your engine?
what happens if its retarded to far? (wont start) and what happens to your engine?
i'd just like to get my head around this, as i know how to do the timing with a light gun, but not exactly sure about what's going on.
thanks.
steve
there are two different type of timing you will hear about with relation to 4 stroke spark ignition engines. The type you are talking about is ignition timing or spark timing. This is a measure of the crankshaft angle before (or after) top dead centre of the compression stroke where the spark is discharged, igniting the compressed fuel/air mixture. If it is too advanced, that is, the spark happens too early, before the piston is close enough to top dead centre, the mixture will ignite too early and detonate against the piston crown and cylinder walls. this can cause fairly catastrophic damage. This condition is accompanied by 'pinging', a rattly sort of sound as if someone has put a handful of marbles in your engine. If the ignition timing is too far retarded, that is, the spark happens too late, you will get poor power, very poor fuel economy, and a lot of heat will build up in the exhaust side - valves, head and manifold - to the point where the manifold will glow red hot as the fuel misture continues to burn after the exhaust valve opens. leads to cracked valves, dropped valve seats, cracked and broken manifolds. all bad.
as engine revolutions and load change, the timing is altered (either mechanically, by centrifugal cams in the distributor body, and vacuum advance/retard diaphragms, or electronically, by the ECU for full EFI vehciels) to suit the load and revs.
the manufacturer's base timing setting is usually a safe starting point but it pays to experiment a little - by a couple of degrees extra advance you may gain some power/economy, or you might find that at the manufacturer's recommended base setting you get pinging and poor power, so back it off a couple of degrees and record your results.
Other things that influence your optimum ignition timing will be fuel quality/RON, altitude/air pressure, humidity, ambient temperature, your driving style and the condition of your engine.
now for the other kind of timing - Cam Timing or Valve Timing, well, we'll save that for another day eh?
cheers
Brian
