Timing a 420

[Charles]

I was wondering if I can use a timing light on the 420.I think it would work but would like to hear from the experts.Thanks

[Swawpy]

Hi Charles- I just went through this awhile back on my 40c. On the right hand side of the flywheel housing there is a small cover attached with a single screw. Remove the cover and you can see the flywheel. On the flywheel there are two marks (spark and TDC), you will have to bump engine or turn over by hand to see them. Hook your timing lite up (positive ground) and rotate distributer till it flashes on "spark" at full throttle. Thats it, or thats all I remember anyway. I bought mine and it was timed to TDC instead of spark, ran great once I got it timed correctly.

[Charles]

I just timed mine with the light at DC on the flywheel while running.Not sure if thats rightdoes run ok

[snoopy]

My book on m-mc says to use the DC marks when installing the oil pump and SPARK when setting the distributor timing. I used SPARK when setting my MC with a timing light and it runs just fine. I would think that settting it to DC would cause a reduction in power. You need to have the spark fire a few degrees before top dead center.

[Swawpy]

Charles- my 40c ran also, but not well enough to push dirt. When you re-time it to SPARK you will have a new machine. It will run stronger, start easier, and hopefully push like crazy. The exhaust note will not have such a labored bark and should sound much smoother.

[Pammark]

Always remember that any fuel takes time to burn. That is why you time an engine a little advanced before TDC. By time the engine rotates to the top, the time passed and full power is established.

If the distrubutor has a vacuum advance or centirfugal force advance mechanism, plug the vacuum and run the engine real slow not to work the centrifugal mechanism.

If you pull the distuributor and need a quick-n-dirty adjustment just to get the engine runing, rotate the engine to a few degrees before TDC. Adjust the distirbutor and points gap to just open. This is when the spark from the coil will form. When the circuit is opened, the magnetic field in the coil colapses and the spark is generated. Time better after the engine is running.

Low octane fuels burn faster then high octane fuels. It is the reverse concept than what most people think. Racing engines want low octane to burn faster for faster RPM's. If you burn cheap gas (normally low octane) the fuel might burn so fast as to ping as the combustion occurs before the engine is at TDC. It is trying to run the engine backwards. My Dad used to say, if an engine pings just a little bit under load, your timing is right on. Plus a engine that pings so very little is a good engine. Engines with poor compression, valves, and retarded timing will not ping.

Extensive pinging may indicate very cheap gasoline, wrong timing or a carbon build up in the combustion chamber. Carbon will glow from the previous cycle and pre-ignite the current cycle.

Mark

[Ray III]

I was under the impression that carbon build-up decreases combustion chamber volume and increases compression to cause pinging. I don't know about the carbon glowing, could be true too.

Race engines actually use higher octane fuels, the higher pressures in those engines make the high octane fuel burn faster.