'66 200 w/'68 dis and 1940 carb- surge/flat spot on tip in

[john tate]

Still playing with the setup w/the Motorcraft 1940 carb and '68 dizzy. Have a few problems:

Carb won't set up on the high step of the cam, or if it does mechanically it just won't speed up like it used to with the Load-O. Have tried the choke anywhere from 3 rich to 2 lean and it makes no difference.

When the car is warming up and throttle is cracked it stumbles big time and then recovers. When it's warm it is better but has inconsistent speed sort of a surging) and a flat spot but only just when the throttle is cracked. Disconnecting the vac advance seems to make no diff.

Every once and a while it will start idling very poorly but if i take the idle mix valve out and spray carb cleaner in there, then replace, idle smoothness returns.

I backed off the vac advance enough to stop my spark knock, but can't seem to iron this out. Is it time to take the carb back off and recheck my rebuild?

New fuel pump, filter, plugs, wires, cap, coil, running stock '68 spec on timing (6 BTDC).

 

[LaGrasta]

although I don't experience all of your probelms, I do also have a flat spot when just cruising casually and steady. I believe it may just be a characteristic of the 1940.

 

[Mercury Mike]

I don't really get that with the 1940. I got a super flatspot with the 1100 though. Hey LaGrasta, so it turns out that I have this '68 distributor, and carter carb, that are both basically new, on this other 200 that I had sitting around that I'd forgotten about. I'm gonna try them. =)

 

[66 Fastback]

Have you checked to confirm TDC and compared with the timing mark on the harmonic balancer? The ring could have slipped giving you a false indication when timing the ignition.

I am not familiar with the 1940 carb (at least I don't think I have had one), but on some carbs, the fast idle and step up cam adjustments are made by bending some of the choke linkage. There may also be a "choke pull off" adjusting nut behind the choke housing. Maybe someone else more familiar with this carb can chime in. My point is that the lean / rich choke adjustment is just one of the many adjustments possible on the choke setting on a carb. Shop manuals give good descriptions.
Doug

 

[john tate]

I did replace the harmonic balancer w/a new one so that's not an issue.

Got a rebuild kit from NPD and followed the adjustments in there to a "T" by making small linkage adjustments, but it still won't set up like it used to with the Load-O dizzy.

Seem to have it tweaked now to where it runs OK. It was rebuilt in '86 and has almost 200K on it now (110K when rebuilt) so I can't complain. Will soon be time to do it again as it is burning a little oil. But for now if I can get it to setup and run better cold I'll be satisfied.

Thanks for the feedback.