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1978 camaro 5.0 rochester 2 barrel carb. Idle-air mixture screw settings
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chevyguy78
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Jan 23, 2008, 8:42 AM
Post #1 of 6
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1978 camaro 5.0 rochester 2 barrel carb. Idle-air mixture screw settings
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I have a 1978 camaro LT. It has the original 5.0 engine with the 2 barrel rochester. When I bought the car, it was in need of a carb kit, so I bought one and rebuilt the carb. What they didn't tell me was how to set the idle air mixture screws on the front of the carb. I took it to a guy at the parts store and he adjusted them, but I don't get much of a response when i step on the gas. You can hear the carb reacting, but it feels like the car is sluggish. Can you please tell me how to adjust these screws the right way so I can get better performance out of my car.
chevyguy78
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Jan 23, 2008, 9:22 AM
Post #2 of 6
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Re: 1978 camaro 5.0 rochester 2 barrel carb. Idle-air mixture screw settings
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Have the tamper-proof plugs been removed? The original screws use an odd socket to adjust. The screw head looks kind of like a rectangle sucked in at the middle sides - I forget the name of it. Base setting would be about 2 and one half turns out from closed to perhaps 3 turns out. This may not be your problem but worth a try. If a base setting doesn't behave there's other things to chase down rather than trying to cover something up with that adjustment which is partly why they put plugs over them originally to keep you out of there!
Remember that they only affect idle an just part throttle for a while and not midrange power or full power request - AKA - WOT.
You may need to get a carb adjusting kit for this as those are hard to get at while on the car,
T
(edit) I remembered the name of the screw head! It's called "clutch" head - pretty sure........
(This post was edited by Tom Greenleaf on Jan 23, 2008, 9:29 AM)
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Guest
Anonymous Poster
bergeconst@aol.com
Jan 23, 2008, 11:46 AM
Post #3 of 6
(7163 views)
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Re: 1978 camaro 5.0 rochester 2 barrel carb. Idle-air mixture screw settings
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the heads on the screws are straight head screwdriver. what else could it be if not this
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Jan 23, 2008, 12:24 PM
Post #5 of 6
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Re: 1978 camaro 5.0 rochester 2 barrel carb. Idle-air mixture screw settings
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Ok: Those are the same just not requiring the special tool. I don't know exactly what year they used what. They are interchangable and a socket with the slotted head screwdriver is helpful to center on stay in the slots for adjustment. Most of the time when I want to just clean out thru those I count how many turns in first, then remove them completely and put back right where they were and fine tune adjustments from where they started. If unknown I just did as I suggested earlier and bottomed them in (tight/closed) and backed out the 2.5-3 turns. Cars will vary on what is best. Richer doesn't mean better or more power and a lot of folks used to do that. They need to be just right.
An old way was to close them in till idle suffered and back out till it reached max rpm and back one turn was a way. In older vehicles than this you could just do those with your fingers and folks were messing them up all the time. They can cause emissions problems so when all is right the adjustment shouldn't need fiddling with anymore and indicates something else should be fixed and not just cover up a problem with those.
An issue with carbs all along was the floats were either brass and soldered seams or a composite floating plasic that this should use. They could get heavy and sink - fuel level would be higher in the bowl and would run too rich. There are scales to weigh the floats to know if you have a problem. At the age now that would be more of a problem than when these were newer.
They started using tamperproof things to discourage fiddling with them but that also was an obsticle to just removing them to clean the thing out for a rebuild or whatever reason it might be clogged up in there.
Hope I didn't just confuse you on this,
T
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way2old
Veteran
/ Moderator
Jan 23, 2008, 4:54 PM
Post #6 of 6
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Re: 1978 camaro 5.0 rochester 2 barrel carb. Idle-air mixture screw settings
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The adjustment you need to be concerned about is actually the jets setting. You can purchase different size jets and needles which will give more response you are looking for. Tom told you true when he stated the mixture screws are called idle mixture screws for a reason. They only affect the idle of the motor.
Being way2old is why I need help from younger minds
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