Look between the IP and the engine's block. There's a set screw with a
lock nut; it's the throttle idle stop. Aft of it is the throttle full
throttle stop screw. With the engine OFF work the accelerator - idle to
floored - and watch the lever behind the IP. Be sure the linkage is free
and that the lever is in fact bumping against the idle stop and the full
throttle stop BEFORE you adjust anything.

I suspect the problem is in the linkage adjustments between the firewall
and the levers on top of the engine. Each lever and pull rod has a
specified length and changing engines may have thrown off this geometry.
Or the two rods on the top of the motor may have been exchanged. I urge
you to consult a M-B manual for the specifications or you'll be
tinkering with this for some time.

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© 2007 T.G.Lambach. Publication in any form requires prior written
permission.

They screwed up the linkage when the valves were adjusted. And, the
linkage has ball and socket pivot / connection points that ought to be
lubed from time to time.
--
© 2007 T.G.Lambach. Publication in any form requires prior written
permission.