Wow thanks for the many responses.

261 is installed in a Chev 1940 right hand drive Canadian military truck..... engine is from a 1959 5 ton fuel delivery truck.

Truck engine is rebuilt stock.. stock 59 flywheel and starter.....plugs are new AC 45..... dizzy is Pertronix inside...carb is rebuilt YF which runs just super.... stock 216 air filter.

It ran fine before I replaced the PCV pipe with a new one..... may have a small air leak....will check with a unlit propane torch.....

Idle screw may be set too richhhhh as I am still getting some black stain at the exhaust.

Throttle linkage has been sticking and I intended to install a stiffer return spring on the linkage as the throttle doesn't return tight against the idle screw ...

Keep in mind that the throttle linkage has to go right through the floor panel... to the front of the engine..... across to the left hand side just below the water neck/above the fan pulley..... back to the bell crank then up to the carb.....

My bet is 99% on the idling being too fast due to sticking linkage that keeps the carb plate partly open....and the mixture screw too rich.

Thanks for all the help.

On the timing issue....setting up the timing in the tight confined of the semi COE engine bay.... almost impossible to see the marker and position the timing light. Chap in New Hamshire came up with the following idea. On top of the bell housing is a small sheet metal cover.... you remove....set the engine at absolute TDC.....paint a vertical mark on the clutch cover assembly.... run a stiff wire between the two screws that normally hold the flat cover. Now sit back comfortably with the timing light aimed 90 degrees to the wire and the painted mark on the clutch cover. In our case the floor bellhousing cover is not yet installed.... I aim the light and tell my able assistant to rotate the dizzy to the right setting.... tighten up and the job is done.
why is it that GM never documented that approach in there manuals.

Thanks for all the assistance guys it will make next weekend more enjoyable.

Bob C.

Bob C.
CMP Heaven
The Hammond Barn