A little stumble at highway speeds

[Traveler]

I recently bought a 71 MC, with 69000 miles a 350 2 barrel,...The car surges at highway speeds, and was missing badly in the mid to upper rpm range.  First thing I did was plugs, wires, cap, rotor reset timing and dwell ( found it way off 4* atdc and 12* dwell).  I didn’t replace the points because I planned to and did installed the Fast XR-i pointless ignition and a new PS2 coil (coil looked to be stock).  Part of the reason for the change was that I wondered if I was losing spark in the mid to upper rpm range causing an intermittent miss. When I examined the plugs #2 cylinder showed signs of oil migration so I pulled the springs on #2 and the valve stems seals were gone, there was very little lateral valve stem movement and about 4% blow by, put new seals on, reassembled.  

Engine holds 20” of vacuum at idle, and starts and idles fine, drops to about 14” at full throttle and then jumps back up to 20” when throttle plate closes.  I have looked for a vacuum leak and found none,  any suggestions.  

[MC1of80]

Surging at highway speeds could be fuel pressure. Did you check/change the fuel filter? Fuel pump diaphragm could be weak from age. 

[Traveler]

5 minutes ago, MC1of80 said:

Surging at highway speeds could be fuel pressure. Did you check/change the fuel filter? Fuel pump diaphragm could be weak from age. 

Thanks for the reply, a mind is a terrible thing to waste, lol. I bought one and never installed it. This may be the problem.. I hope you have a blessed thanksgiving.

J

On 11/22/2019 at 8:54 AM, Rob Peters said:

Joseph, or Joe or J,

I just noticed I have not welcomed you aboard the boards.  We hope you like what you see here and decide to become a full fledged dues paying member and also, next June, bring your Monte to the 2020 Eastern Meet at the Chevrolet Nationals in Carlisle, Pa. where they are featuring  the Monte Carlo for its 50th Anniversary Celebration next June.  If interested please contact me.

rob