Just a shot in the car because im at soccer with my boys.

The 76 engine usually has a secondary electric pump. The don't think the 240 chassis has one. Is the secondary pump required and is the mechanical pump on the 260 engine strong enough to meet fuel demands

Why the difference in the previous 4500 rpm & the later 3500 rpm. Was the difference caused by creeping the rpms up on the 4500 & stabbing the throttle on the 3500? Also, did pulling on the choke make any difference? Mechanical pumps alone will supply plenty of fuel for round top carbs on a L26 if the filters are maintained.

Channeling Occam (actually William - I had to look it up) and Einstein and KISS - are you sure that the throttle blade is opening completely? It's called a throttle for a reason.

Why the difference in the previous 4500 rpm & the later 3500 rpm. Was the difference caused by creeping the rpms up on the 4500 & stabbing the throttle on the 3500? Also, did pulling on the choke make any difference? Mechanical pumps alone will supply plenty of fuel for round top carbs on a L26 if the filters are maintained.

Typo sorry. Mac rpm is 3500. I did not get to try the choke, we had a bad storm so the Z stayed in the Garage. Fuel filter is new and clear.

Channeling Occam (actually William - I had to look it up) and Einstein and KISS - are you sure that the throttle blade is opening completely? It's called a throttle for a reason.

Yes opening completely