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Old 10-14-2007, 09:29 PM   #1
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4 barrel carburetor

While I was coming back from a camping trip, I noticed that my 4 barrel would not kick in as I was climbing a mountain. I had the gas pedal stomped down all the way, but nothing. I have never worked on a 4 barrel carb before, so I don't know about them. Does this thing have linkage that might be disconnected, or maybe a vacuum hose? What are some possibilities that may be causing the 4 barrel not to work?
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Old 10-14-2007, 11:23 PM   #2
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Is it the carb, or is your transmission not dropping down a gear?
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Old 10-14-2007, 11:27 PM   #3
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. . . and check the distributor also, maybe the spark advance is bound up.
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Old 10-15-2007, 12:49 AM   #4
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Hi, I have some possibilties for your four barrel concern. If you have a carburetor with vacuum secondaries and you have the gas pedal on the floor, you virtually don't have any vacuum to open them. At a slow engine RPM with a heavy load [going up hill] you would just bogg down with that much carburetor opened up. If you have a mechanical four barrel carburetor, they have an upper butterfly similar to a choke that will stay closed if there isn't enough vacuum to pull them open. And finally, most four barrels have a choke block that won't allow the secondaries to open when cold. And a choke problem [adjustment] can cause this to happen when the engine is warm.

Good Luck.
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Old 10-15-2007, 02:49 AM   #5
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In the Chevy vintage I'm used to, 70s to early 80's, theres a mechanical linkage to open the 2nd valves, and a kick down cable that goes down to the tranny to drop a gear when the pedal is on the floor.
That way you get sizable increas in throttle and a lower gear for accellerating and passing.

If the tranny is kicking down but the 2ndary barrels are not opening, then you should still notice it downshift with rise in your engine RPMs and modest acceleration.

If the tranny is not kicking down, but the 2ndary barrels are opening, then you might get modest acelleration, probably not much change in the RPMs, but you might see the gas guage visibilly move

If you take the air cleaner off when the engine is warm, you should see the top butterfies open (choke is off). Have someone step on the pedal and you should first see the butterflies on the small bores open, then the valves on the big bores open when its all the way down.
you can do this with the engine off if it has a mechanical linkage, if its vacuum actuated then you need the engine on.
Make sure you dont have any loose hair/clothing when looking down the carb. Those 454s will suck the eyeballs out of a parrot.

Similarly, you should be able to find a cable that attatches to the throttle linkage somewheres, and trace it down to the tranny. I think theres a linkage with a little lever on the side of the tranny. You should see that move on the last 3/4" or so of travel on the gas pedal.
(dont hold me to that last part, its been almost 15 years since I had a chevy)
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Old 10-15-2007, 10:57 AM   #6
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on rare instances, the base gasket can catch the secondary plate and keep it from opening. i wouldn't look down a running carb without safety glasses and covering my hair with something that won't burn ;-)
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Old 10-15-2007, 12:55 PM   #7
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i would consider all above responses but make sure that parrot has a helmet and glasses on.
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Old 10-15-2007, 01:14 PM   #8
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Quote:
Originally Posted by 345bill
i would consider all above responses but make sure that parrot has a helmet and glasses on.
The parrot also needs a safety harness and a Confined Space Entry Permit.
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Old 10-15-2007, 01:28 PM   #9
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hello jaG,

Your carburetor should be a GM Rochester quadrajet if its the original unit .
It has mechanical secondaries (throttle plates) that is when you floor the gas
pedal all the way down ,a linkage arm on the rear side of the carb pushes the secondary plates open ,allowing the top butterfly plate to draw open allowing the secondary fuel metering rods to raise up allowing fuel to flow.You can remove your aircleaner ,with engine NOT running and after you have fully warmed up the engine ,idling for 15 minutes or so should be fine ,look at the carb .you can see the rear (large) butterfly plate is closed (normal) push down on your gas pedal slowly and look at the movement of the linkage
on the carb .You can easily see the action of the linkage , The secondary
butterfly may pull open just a little ,you can reach down and push it open
with your finger all the way ,with the gas all the way to the floor ,witha flashlight look down into the secondary part of the carb .you then will see
two large throttle plates opened up ,while looking into it move the gas pedal
up and down some ,you can see the plates moving open and closed .Now
all that said ,sometimes the choke lockout lever is stuck and the secondaries do not open ,so your front (primary choke plate or front (little) butterfly will
be fully open (hot engine) ,if your carb is gummed up that little lever
may be gummed as well .You can use carb cleaner spray to clean around the
carb ,the linkage areas all around it ,Now this procedure of cleaning is better on a cool engine so give it an hour or so to cool down before cleaning .So if do not see the secondaries open ,make certian the front butterfly is fully opened up ,if it does not fully open the secondaries will be locked out by
the little lever down low on the passenger side of the carb.right nearest the mainfold in the center of carb .The secondary butterfly is lightly spring loaded ,so when you open it it will shut back after you release it .Normal
operation for this carb as the secondaries butterfly is opened by airflow demand only .Or when the engine needs more fuel the secondaries are air flow demanded open, then fuel then flows in .If your choke (front butterfly)
is not fully opend up hot ,then your choke is faulty ,the round plastic part
passenger side of carb towards the front it is retained most likely by rivits
to hold the setting from the factory ,anti tamper . You may want to take your coach in to have the carb serviced if your not mechanically savvy on
carbs ,they can be a pain in the butt . hope this can at least help you to know whats going on with your secondaries .you can get a great book at book stores ROCHESTER CARBURETORS its very insightful and helpful .
Kragen or auto zone may have it possibly as well .Now ,you may have
a different carb on there that is not original ,as the GM qaudrajet is the
the only carb that would be factory .Post a photo if what I described is not
what you have on there .If it is a Holley 4 barrel ,the your vacuum secondary
throttle plate diaphram probably is bad .Im running a holley 4 barrel on my
392 IH v-8 .The diaphram went bad ,no secondary action .Secondary diaphram carbs do indeed open under full throttle conditions ,they have to
you . The vacuum signal to the secondary diaphram is routed thru the carb
passages to keep the vacuum signal high to pull on the diaphram .Even at full
throttle you have enough engine vacuum to properly operate the carb .
its designed into the carburetor .

Good luck

Scott of scottanlily
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Old 10-15-2007, 03:51 PM   #10
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Quote:
Originally Posted by richinny
on rare instances, the base gasket can catch the secondary plate and keep it from opening. i wouldn't look down a running carb without safety glasses and covering my hair with something that won't burn ;-)
Hey, Ricky, who has hair? An interesting concept

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Old 10-15-2007, 07:45 PM   #11
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Thanks for all the great info. I am supposed to have a friend come over in the next couple of days to help me with this. I will let him read over all this great info before we get started. Oh, the transmission is not dropping down a gear or anything. When I stomp down the pedal nothing happens period.
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Old 10-15-2007, 08:27 PM   #12
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Quote:
Originally Posted by jagcb750
Thanks for all the great info. I am supposed to have a friend come over in the next couple of days to help me with this. I will let him read over all this great info before we get started. Oh, the transmission is not dropping down a gear or anything. When I stomp down the pedal nothing happens period.
I may have missed this if you said already, but did you notice any difference in your gas mileage? Did it drop noticeably?

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Old 10-16-2007, 10:04 AM   #13
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@safari57: Well, I was going up a steep mountain In eastern Tennessee so I figured my gas mileage was going to be noticeably worse just from this. I never has gotten better than 5 miles per gallon thus far anyways.
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Old 10-16-2007, 01:45 PM   #14
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Quote:
Originally Posted by jagcb750
@safari57: Well, I was going up a steep mountain In eastern Tennessee so I figured my gas mileage was going to be noticeably worse just from this. I never has gotten better than 5 miles per gallon thus far anyways.
Ouch

On our trip to Pennsylvania from Arkansas and back we averaged between 7 & 8 mpg and that includes towing a 2900 lb trailer. This was through the mountains in Maryland on I-68 and West Virginia on I-79. Our 310 has a new generation 6 454 with the Banks Power Pack and 13,000 miles on it.

Guess we don't have a lot to complain about if you're only getting 5 mpg .
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