77 Cutlass 260 v8 stumble and hard start when hot ??
 

Hello, I picked up a 1977 Cutlass Supreme with a 260v8. The car has only 40k original miles. It starts perfect when cold. I pump the gas twice and it fires up smooth and idles high. Once warm I kick the pedal and the idle drops to normal just as should. When pulling away from a stop I get the slightest stumble and then it pulls smooth all the way to 80 mph. At idle when I come to a stop it has the slightest rough idle in the engine. When driving it is powerful and smooth with no pop,skip,fart,smoke, Nothing but the slight stumble when pulling from a stop and the slight rough idle. Once driving for a while if I shut the car off and wait a few min then get back in to go it is hard to start. It cranks powerful but does not fire right away. I have a new fuel pump, starter, and battery. Does the stumble sound like an
accelerator pump? and if so would this cause the hard hot start?

Thanks

It does sound like an accelerator pump, but I don't see how that would cause the hard start. I would look at the choke, and make sure the throttle body is clean. Also, check for a small vacuum leak.

Is this the stock carb? Does this have A/C ? Replace the carburator or go threw all your vacuum lines. Also i would check your timeing out and see what that is doing. Advanceing it a 2-4 Degrees might help or check your primary float level. On a car this old with less miles the rubber rots or past owners made bad adjustments. Have someone put car in drive and hold brake while you listen and feel under the hood for hissing or sucking - vacuum leak, one will bog you out or the other will give slight acceleration( A/C Vacuuming ).

ACCELERATOR PUMP SYSTEM
The accelerator pump system consists of three main components:
the pump diaphragm, the pump cam and the pump nozzle.
This is the carburetor system that is most responsible for having
good, crisp, off-idle throttle response. Its purpose is to inject a
certain amount of fuel down the throttle bores when the throttle
is opened. By accomplishing this purpose it acts to smooth the
transition between the idle and main circuits so that no stumble,
hesitation or sluggishness will be evident during this transition
phase.
The first adjustment to check is the clearance between the pump
operating lever and the pump diaphragm cover’s arm, at wide
open throttle. This clearance should be around .015". The purpose
for this clearance is to assure that the pump diaphragm is
never stretched to its maximum limit at wide open throttle. This
will cause premature pump failure. Once this clearance has
been set take a good look at the pump linkage and work the
throttle. Make sure that the accelerator pump arm is being activated
the moment that the throttle begins to move. This will
assure that pump response will be instantaneous to the movement
of the throttle. These adjustments can be made by turning
the accelerator pump adjusting screw that is located on the
accelerator pump arm together with the pump override spring
and lock nut.
The amount of fuel that can be delivered by one accelerator
pump stroke is determined by the pump’s capacity and the profile
of the pump cam. The period of time that it will take for this
pre-determined amount of fuel to be delivered is affected by the
pump nozzle size.
A larger pump nozzle will allow this fuel to be delivered much
sooner than a smaller pump nozzle. If you need more pump
shot sooner, then a larger pump nozzle size is required. During
acceleration tests, if you notice that the car first hesitates and
then picks up, it’s a sure bet that the pump nozzle size should be
increased. A backfire (lean condition) on acceleration also calls
for a step up in pump nozzle size. Conversely, if off-idle acceleration
does not feel crisp or clean, then the pump nozzle size
may already be too large. In this case a smaller size is
required.
info via Holley