holley 4150 carb issues and questions

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afstegg

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carb is a 850cfm on a mild 440 with a 727 trans.
the history of carb and engine are as followed.
68 440hp
.20 over flat top pistons
mopar "purple cam"
crane push rods,springs and adjustable rockers
torker manifold
mopar distributor
p/p stock heads

engine was rebuilt @ 20 years ago. was put in car drove around a few miles(less then 1000) then parted.
engine/trans sat in heated garage till I bought it a few months ago.

being that it sat so long I rebuilt carb. I'm thinking I may just need a carb or I looked over something as it was kind of crappy in side. I soaked it a few days in a carb cleaner bucket, blew out passages with air and put it back together(with a renewal kit). the issue im having is a part throttle stumble say %15-20 throttle just off idle. I've adjusted acc pumps and can see it pump fuel threw out throttle travel. its drives fine once past that one spot

things I checked
fuel pressure 6 psi
timing @13-15 deg advanced totals out @ 32
new ballast resistor

im thinking of replacing with a preform or other holley based carb.

what do you guys recommend for a street car?
71 duster 440/727 2500stall with 323 rear gear
mech or vac secondary 750 or 850

thanks
 
mine did the same thing and it was the acc pump cam on the throttle arm you can buy the kit for around $20
 
Part throttle issues are primary side related. Give us the "numbers" you found during the rebuild. Carbs that old could have been modified/tuned many times over the years? Jet#, Nozzle#, Power valves, etc?

Do you have any idea what compression you actually have? A compression test would be helpful? Depending on those results, you may be able to hike your initial timing several degrees and that would surely help with drivability on the street or at the track.

You may not know what cam you have, but vacuum readings at a specific idle speed would help with diagnosing the tune.
 
You didn't say which "purple cam". Does it idle ok in gear? If not, your idle feed restrictions in your
carb may need to be opened up a couple or few thou. If you twist up your distributor to 38° total
will your starter crank the motor ok? That's the first thing I would try. Are you using vacuum adv?
If yes, try it disconnected. Problem is probably in primary metering block, though. You could try an
aftermarket billet block with replaceable restrictions. You will have to measure idle feed and power
valve channel restrictions in existing block with index drills & micrometer to know what size to drill
restrictions to in new block. Good luck.
 
I only pulled heads and did not check cam numbers when I got engine.
As for compression I also didn't check that ether. Was told 10.1 but I'm not %100

Car idles fine, has that lumpy idle and pulls @8" vac. It has 6.5 power valve in front and blocked in rear.

I want to say 76 main jets and 80 rear.

I had vac hooked up but it is now blocked.
 
Turn up initial timing to about 20* which is what madmoparmick suggest with 38* total and see how it runs.

IMO, not enough initial timing is the first place to start with tuning.
 
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