ignition timing question

[eds240z]

what should i set my timing at? i have l28 with p90 head. stock block. ported head with stage 3 msa cam. triple webers. distributor is the mallory unilite electronic no vacuum advance. trying to tune me carbs but wanted to make sure timing is correct. i did a search but i saw diff #s from everone. also am i suppose to check timing at 2 diff rpm's? i read at one thread they said check at idle & 3000rpm. if this is so, how do i adjust at higher rpm and not throw off idle timing? don't know much about distributors but seen somewhere about something about weights. does mine have weights? duh..uh... kinda feel stupid asking that ? but don't know much about distributors. thanks for any info!!!

[trippintl0]

The distributor has little weights inside of it. As the distributor turns faster and faster, the weights slide out towards the edge. The design of the mechanism causes this to advance the timing more than the base timing.

 

Base timing (or initial timing) is what you set the distributor at by loosening the mounting bolts (that bolt the distributor to the engine) and rotating it.

 

Centrifugal advance (or mechanical advance) is determined by the tension on the springs that hold the weights in and the length of the groove for them to slide in.

 

Typically people will use 10-20 degrees base timing, and 32-36 degrees total timing (on the L series engines). Changing spring tensions will cause mechanical advance to activate quicker or slower. There are many modifications possible but most likely you'll be better off to research more, or just set total timing at 36 and forget about it.

[eds240z]

thanks for info!!!

[morbidsunroof]

I set timing at 10 btdc. Some Mallory dizzys have adjustable "spread" and I have gone as high as 42 total in a race car. My favorite tuning aid is the MSD cockpit adj. timing control. With max total set at 46 and starting at 36, whack the knob briefly to max. while under hard pull in third. If power dips you are close to good but check for lean condition. If power spikes, you are probably too rich. Jet down the mains and repeat. I did all my jetting using VP C-12 as it doesn't leave junk on the plug that confuses the plug read. I was told by an Edelbrock engineer that pump gas is a recipe of garbage loaded with dissolvable solids that plate out on the plug (kinda like the lime buildup on the bottom of a teapot) If you see particles on the plug with VP, it is piston material. Ideally after a hard run, a new plug should look like it just came out of the box but under a magnifying glass, should have one teeny, shiny ball on it. For the street, I much prefer a vacuum advance dist.