Trying to diagnose why i have air bubbles in the fuel return line (back of IP returning to spin on filter) of my 300D.

At idle no bubbles show up but as throttle is increased the bubbles begin and increase as throttle increases to almost a froth. No fuel leak visible from above will check underside of IP later today/tomorrow.

No bubbles visible in other fuel lines.
Pressure relief valve is tight (location of fuel return line banjo bolt).
Car idles fine, no shaking or rocking as throttle increases.

I believe this problem existed before, but here is work just performed:
Replaced camshaft - 2 lobes were badly pitted and discolored (lobes 8 & 9)
Replaced rear rocker arm spindle - bent probably a 3/16" over the rear third
Replace cam towers 4 and 5 associated with bent cam spindle
Replaced rocker arms 8 & 9 - discolored and faces showed wear
Replaced timing chain - 2mm method showed 4+ degrees...so while i was in there

Injection Pump in not original to the car, was bench tested/adjusted prior to install several years ago. Car sounds and runs better after above work but still sluggish.

thanks,

chris

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1985 300D, 250k
1980 300SD, 180K