C6550 E-721 jam , in ADF

[wild140]

Feed tires replaced about a year ago , I have a new set on order . Does not seem like a feed issue, paper stops half way out from under the feeder only on multiple pages never on singles . seems more prevalent on letter R and legal. Second sheet doers not feed in very far.
Ran through automatic read sensor adjustment in book , it says do not have paper blacking sensor . Is paper suppose to be in tray or does that matter ?
All automatic test pass OK , did not perform manual adjustment.

Looking back at older posts , mentions something about a registration roller drive screw coming loose ? ( might not be this model)

Any other suggestions greatly appreciated

[blackcat4866]

You don't mention how many originals.
You don't mention the condition of the separation roller and the lower original registration mylars.

I've seen these separation rollers flat spot in as little 45K originals.
The lower original registration mylars start out as 14mm wide, then wear down to nothing.

Those are two typical E721 jams. =^..^=