2-stage acceleration

[sp949]

My 1971 Spica 1759 Spider seems to have a strange issue. It starts and runs fine both hot and cold. However, especially when starting cold, it is sluggish to accelerate to @ 2000 RPM, but, after that, it accelerates without problems. I am also noticing that either the throttle is too hard to open, or that it kinds of struggles to get past 4500 RPM.
Running the engine statically, I see no problems; throttles open all the way, the SPICA pump has no issues and it is set up correctly. The only clue I have is that the plugs (NGK BP6ES) insulators are dark gray instead of brown, but the ground electrodes are burning clean with no deposits. I have electronic ignition, the ignitin timing is set to spec, and the engine has 70,000 original miles. Timing reaches the point M on the pulley by 4000 RPM, but will not go any farther.
I am thinking that the Marelli distributor is not advancing as it should under acceleration, but the weights and springs move freely by twisting the shaft.
Is there any recommended test to see if the springs should be replaced due to age and deformation? are they even available as spare parts?
Thanks,
Val Barone

[Roadtrip]

It does sound more like an advance issue, but just double check to make sure that the injection pump is timed correctly.

[sp949]

Quote:

Originally Posted by Roadtrip It does sound more like an advance issue, but just double check to make sure that the injection pump is timed correctly.