This is a 1972 350SL 4.5L with about 145k miles on clock.

Car was running OK, just a small stumble once in a while and perhaps slightly less power than I recalled, so as a start, I decided to replace some of the original and older stuff.

Changed spark plugs, plug wires, distributor cap, rotor.

When I went to start, it started OK, but on road test had no power - would not go over about 40mph.

Tried switching back to old rotor and cap and slight improvement - Still awful performance.

Checked points gap and it was small, so opened it up a bit - Tried 0.35mm and 0.45mm. No improvement and now I hear slight popping or backfiring sound when driving. PLugs should be OK - they were the proper Bosch plugs and I checked gaps - all 0.032".

I have checked that wires go to proper plugs.
I have removed points (no pitting) and cleaned everything with contact cleaner. I don't have a dwell meter, so can't check dwell.

At my wits end! Any suggestions for things to check before I take into shop?

Questions:
- Bosch pamphlet that came with rest of stuff said something about need to change coil when changing ignition wires because of possible damage to ecu. Not sure what they meant.
- Old (original) plug wires were different - they had hard plastic inserts that seemed to have resistors in them at distr. end. New Bosch wires don't seem to have those.

Graham