Qjet Accel Pump stuck.

[A 68 Wreck]

Well, all else on this 4MV is working great on the test runs, but, the replacement accel pump I put in is now not returning the entire way up. 3/8 - 1/2" low. I can pull up the rod as it is "free", but is simply drops back down the 3/8 - 1/2". I used a "stock" replacement rod and plunger, and used the old springs. the stock did NOT have the retaining spring under the plunger, which I have seen on line.
maybe a stronger return spring? I did stretch it a bit prior to re-install.
any help would be appreciated! this is the second time it has happened...

thanks.