Since doing the latest engine mods, there is a hesitation accelerating off of idle (below 1500 RPM) when the choke has opened, and the thermostat is still closed. Stone cold / choke closed - no hesitation. At operating temperature - same smooth pull off of a green traffic light. In between full choke and thermostat open, you wouldn't take the chance at a stop sign trying to cross through heavy traffic.
The car: '64 Dart /6, points and condenser, 4 spd. 8 1/4" - 2.45 rear end out of a '72 Cordova. 205/50 R17 tires. Engine turns at 2K RPM at 60MPH.
Before the mods; It had a Holley 1920 - 1 barrel, and factory exhaust. Timing was 2.5 deg BTDC. Plugs and inside the exhaust tip were a bit sooty looking. It always started at the first bump of the key cold or hot. Mileage was 18MPG and it wouldn't pull a blanket off the bed. Approaching any type of incline on the highway under 70MPH required downshifting to 3rd. No downshift and the car would slowly decelerate.
The mods :D; Tube headers routed via 2" pipe to a 'Y' at the transmission cross member, and 2" exhaust out the back through a Magnaflow type muffler. Shaved the head to a static 8.6:1 compression with multiangle valve job. Modified the stock 1 barrel intake manifold to fit a NOS Carter BBD #6465S for a 1974 318 (It still smelled new!). The choke is an aftermarket electric unit. Also added a water fed, intake heating plate. Timing is now at 11.5 deg BTC. The car pulls GREAT from 2K RPM on about any incline and accelerates like never before (for a /6). First tank of gas came in at 30 MPG. It starts great cold with a couple pumps of the throttle and will fire right off if I turn it off hot and start it right back up. After sitting warm for ten minutes or so, I need to add some throttle and crank on it before it will fire off.
Looking for the cure; I went through the carb twice and adjusted everything to factory specs. The air hole in the butterfly was filled. I've confirmed twice that there are no vacuum leaks. The idle mixture was adjusted lean to a slight RPM drop. Increased richness through max RPM and then slight RPM drop, then back lean half the turns from lean RPM drop to rich RPM drop. With the idle adjustment screw turned all the way off the stop, the engine turns 650 RPM. The plugs are all the prettiest buckskin tan I've seen, and the exhaust smells 'funny' like a bad catalytic converter or something (new exhaust?). With the air cleaner off, the carb has a high pitch whistling sound at idle that I've never heard a carb make before.
I'm guessing I have a lean transition from the idle/low speed circuit to the main metering circuit when the choke is off and the engine still a little cold. Out of desperation I cranked the choke so far closed that at wide open choke and thermostat open, the choke plate was still partially closed. At this constant enriched choke position, there was no hesitation off of idle in the low to mid-engine temperature range.
I'm in need of a lesson. Raise the metering rods? use a bigger hammer? :BangHead:
