Major problems timing my engine, Please Advise!! Options

[yarin]

Here is a little history:

'72 914
69-70 bus block according to what people said on here based on the serial #
1.8L heads, spark plugs straight up
Not sure what displacement is, maybe 1.8, maybe 2.0
Weber 40s. centrifigual advance

The car was running OK, not great, but acceptable up until an autox last weekend. AFter that it would backfire like crazy. SOOO i changed the following: plus, wires, rotor, cap, points

I set the points to 50 degrees with a dwell meter

I do believe i see these timing marks:
(IMG:http://www.pelicanparts.com/techarticles/914_timing_carbs/pic1.JPG)

Let me number the questions:

1) Do I have vacuum retard? There are no vacuum lines anywhere. How does this affect my method of timing?

2) is there a way to check centrifugal advance? If i push on the plate in the distributor it moved about .5cm.

3) Do I time this engine at 850rpm or 3000rpm to the 27 degree mark?

4) I have a timing light with advance. Do i set the light to zero and adjust timing to the 27 degree mark? Or do I set the light to 27 degrees and time to TDC? My TDC looks looks a little different than my 27 degree mark.

I tried everything! 0 deg(with light at 27 advance), 27 deg(with light at zero adv, and 27 deg with light at 27... def not it), 34 deg(with light at zero), somewhere in the middle.

My results: severe backfiring at 34 degrees. No power at all at any other combination, just not smooth. I know that either the carbs or valves might be off. But i'd like to get it timed first.

Comments, suggestions?

Someone please help!

(IMG:http://www.914world.com/bbs2/html/emoticons/headbang.gif) (IMG:http://www.914world.com/bbs2/html/emoticons/screwy.gif)