Hello,

I've been suffering this problem since I got this machine some months ago, and I think I finally solved it.

New paper feeded ok, but paper previously printed tended to feed about 2/3 on the machine and then jams.
The ligther the paper, the worse the problem. Cardboard feeded ok
It was worse at low speed

There is some threads about problems like that, and a lot of usefull information, but nothing I tried worked for me.
I changed feed rollers and pad, cleaned paper sensor, timming and guide rolls, inspected the clutch spring in the timing roll, check overall timming... everything looked ok, s thought it has to be a paper incompatibility or something inherent to the Riso world.

Last weekend the problem got worse to a point I couldn't complete a zine print, so I moved my drums to another RP3700 and found that the paper was not the problem; everything worked fine without a single jam.

I spent a time trying to understand the feed process, and I saw that the problem could be related to the paper feed clutch, as sometimes pushed the paper too far into the second feed section, bending too much the paper and causing the jam. I tried to change TM parameters with no effect, so I tried to clean the clutch as I wait for a new one and... it worked!
Now I see how it is supposed to work, I realise that clutch never stopped when it should, but always pushed the paper too far in an aleatorius amount and caused the jam when excesive bend happened
Since cardboard and new paper are stiffier than previously printed paper, I think clutch stopped pushing way before and I've managed to print till now.

I hope this can be helpful for someone