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'77 Aspen w/Carb issue- Hesitation at Full Throttle
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Author:  InThePink [ Thu Feb 21, 2008 11:11 am ]
Post subject:  '77 Aspen w/Carb issue- Hesitation at Full Throttle
'77 Aspen wagon with the Super Six 2-bbl Carter BBD (the type with the removeabel plate at the top/front which allows you access to the accellerator pump). Rebuilt by previous owner, but there's still a stumbling or hesitaition issue when you push the accelerator to the floor.

What I do know- the fast idle cam works correctly as does the choke pull off. The choke plate closes as it should after stepping the throttel down when cold. At partial throttle acceleration (0-60%), everything is fine, no issue. N.O.S. fuel sending unit and fuel filter recently installed by me. Air cleaner element is clean.

Problem- At full throttle (i.e pedal to the floor), the engine almost dies, coughs and hesitates, then after a few seconds (two or three) finally kicks in. Makes no difference if it's from a standing stop or while the car is at speed.

Specs- Stock with a 2.5" aftermarket high-flow cat and 2.5" exhaust rearward. Timing is 10* at idle and is advancing correctly as far as I can tell with the timing light hooked up. No vaccum leaks at the carb, either. The only thing connected to any carb port (besides the vac advance line) is the air temp sensor which runs to the air cleaner base. EGR vacuum port (on the EGR itself) is capped.

My thoughts- Kickdown linkage works fine, car cruises great. I changed the ignition coil to an Accel Super Coil and there was no noticeable difference. Plugs are clean as are the contacts in the dist. cap and on the rotor button.

I have adjusted the accelerator pump rod as mentioned in this thread: http://www.slantsix.org/forum/viewtopic ... ht=#150680

...but it seems to have little effect on the stumbling/hesistation issue I'm having.

My gut tells me the engine is not getting enough fuel or air, but I've had issues with this carb on my van ('77 360), so that problem was eliminated by going to a 4-bbl setup...

Let me hear your suggestions, please.

Casey
Author:  SlantSixDan [ Thu Feb 21, 2008 2:45 pm ]
Post subject: 
The rebuild might not have been done carefully or properly, or a new fault might have developed. Does the car start to accelerate for a second and then gasp and stumble (step-up/metering system), or does it gasp and stumble the instant you put your foot down (accelerator pump)?

See the large Carter BBD operation and repair manual (pdf) for detailed info on the carb's systems.
Author:  InThePink [ Thu Feb 21, 2008 4:58 pm ]
Post subject: 
Quote:
The rebuild might not have been done carefully or properly, or a new fault might have developed. Does the car start to accelerate for a second and then gasp and stumble (step-up/metering system), or does it gasp and stumble the instant you put your foot down (accelerator pump)?
It gasps and nearly dies when the pedal hits the floor. I adjusted the accelerator pump rod to the extreme in both directions and took a road test after each adjustment, but felt little change either way. I set it back to the middle of the adjustment range and same thing- still have the bog.
Quote:
See the large Carter BBD operation and repair manual (pdf) for detailed info on the carb's systems.
Yeah, I checked it out earlier today. I'm familiar with the carb's workings, but not the troubleshooting aspects. I've been through similar issues with my Edelbrock 1406 (600cfm) carb on my van's 360, so I've changed rods and jets before and fiddled with the accel. pump, too.

Are rods and jets available for the Carter BBD carb?

I will probably end up getting another rebuild kit, tearing it apart and verifying all is as it should be, but I was wanting some advise of someone who has had similar issues before I do a full rebuild...which may or may not even solve the problem.
Author:  volaredon [ Fri Feb 22, 2008 8:52 am ]
Post subject: 
Hey Casey is this the one all the pictures are about on Mopowerstyle? Put some here too!
Author:  Doc [ Fri Feb 22, 2008 9:40 am ]
Post subject: 
Are you sure it's a carb problem and not a EGR or vacuum advance / timing problem?
Will the stumble go away or get better if you crank a bunch of initial timing advance into the system (a quick test)
DD
Author:  InThePink [ Fri Feb 22, 2008 4:57 pm ]
Post subject: 
Quote:
Are you sure it's a carb problem and not a EGR or vacuum advance / timing problem?
Will the stumble go away or get better if you crank a bunch of initial timing advance into the system (a quick test)
DD
I haven't tried rotating/advancing the distributor yet, but as mentioned above, the timing does appear to be advancing correctly under throttle.
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