Ping Sweller

I'm making plans to revive the MZ, namely, throwing a new lump into it.

What happened to the 300 lump?

I was a TC and left it idling on the drive, welding the big end bearing
to the crank.

" "

Is there any difference in the carb jetting between the ETZ 250 and
ETZ300? - I've possibly got a 250 lump to sling in, but it's a bare
engine without the carb.

From the factory book (of which you should have a copy on the disk I gave
you)

ETZ 250
Carb: BVF 30 N 2-5
(the key number is 30 - compare it to the cast and stamped numbers on
your carb)
Main Jet 135
Pri. Jet 45
Start Jet 110
Needle valve 20
air screw 1 turn out
Needle 2 A 531 (C 6) with 5 notches
Needle pos. 3rd from top

The only real diffeences will probably be main and primary jets.