OEM carb swap 1983 / 1986

69hurstolds

Geezer
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Jan 2, 2006
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Wow. Didn't realize there was such passion about baseplates. I couldn't tell you about Chevy baseplates. I'm not a Q-jet expert. I've only had one spare from a 454 from a 1976. But none from a 305 CCC carb. The 2-point, 3-point, and 4-point adjustments for the carbs are about how to tweak them on the vehicle to tune them to final specs. In the end, the engine doesn't care how it gets fuel when it needs it, as long as it's getting what it needs. For the most part, the calibrations can be tweaked on any of the CCC carbs to get you where you need to be for the final application. AFAIK, most all E-jets are set as lean as possible for emissions purposes anyway. Primary jets/rods can be swapped out as well as secondary rods/hangers if needed, but from what I've seen, there's not much difference on primary jetting between the V8s. And ALL the E-jet secondary seats are the same. Just the rods are different. Also, for example, Olds has a 1/2 turn wrap setting on the secondary air valves, where the Chevy, I think, is nearly twice that. Ideally, you just want it not to bog when you get into the secondaries and you shouldn't "feel" the secondaries kick in. You may hear them, but you shouldn't feel them.

For the air horns, I've found Chevy and Olds are virtually the same in comparable year applications. I got a new Chevy air horn with the rich stop which could be used on the Olds 3-point carburetor. The only differences I've found are the filtered air port not present on the back of the Chevy one since the Chevy didn't need it for the E-choke, but can be drilled and fixed if needed for a hot air choke. I know, I did it. E-chokes can be put on an Olds (plug the vacuum port in the choke housing if you do) but it's harder to put on a hot air choke on a Chevy since it has no vacuum hole, you would have to drill one into the float bowl- yikes. If your air horn is a 2-point adjust, the rich stop screw hole is not drilled/threaded, and to use it on an Olds 3-point system (and some Mopars) you would have to drill and tap that. Another Yikes. Good luck.

The IABV "tower" holes where it actually pulls in air are in different locations, but again, that means nothing as Chevy's in the front above the IABV, and Olds is on the side. And the final difference was already mentioned. The Chevy used no air bleed restrictors for the main primary (as seen through the top of the air horn) where the Olds did. I used some well tube restrictors from my hosed up float bowl with smaller .030 holes and drilled them out to the proper hole size .047 before I realized you could actually buy these from the Q-jet shops.

FWIW, even the lettered IABVs are set with the tool and if needed, adjusted if needed. Typically the lettered IABVs are set with the tool and left alone and all the idle mixture is controlled with the mixture screws. But there's a caveat in the procedure that says if you can't get it exactly right with the mixture screws, you can tweak the lettered IABV until you get it right. With the non-lettered ones, you tweak both the IABV and idle mixture screws. WHY they did that stupid sh*t I'll never know. To that point, 305 in the 84 F-body specs says to set the IABV with the gage alone, suggesting they have lettered IABV. What's the difference between F-body carbs and G-body carbs for the 305? 🤷‍♂️

Ok, back to the subject at hand. Sorry I got derailed. Follow the ports. Match up the porting from your float bowl to the air horn, or from the float bowl to the baseplate, depending on what you're swapping. 95% of the time, they'll be the same. Check port SIZES as well. Just because they're there doesn't automatically mean they'll match up and be correct. going from tiny to big or big to tiny may make a difference. Check 'em with drill bits or small gage wires. I did that with my Frankencarb and the Chevy ports and Olds ports/tubes and all that junk matched right up. If there's an extra vacuum port you don't need- plug it. If there's a vacuum port you need that ain't there- if you're desperate enough- drill it. Just know what you're doing with it.

There's another thing you could do for your other carb and that's remove both baseplates, grind off the factory stakes in the primary throttle shaft blade screws, remove them, and then swap the primary shafts. It's a bit more work, but then it won't matter how the baseplates are set up. The throttle shafts are pretty much all the same on the CCC carbs, regardless of E or C models. The only difference is the throttle shaft main lever which is staked on to the end of the throttle shaft. NOT and easy fix to swap that. If Rochester would have figured out a way to attach those primary levers on without being pressed and staked, that would make carb swapping infinitely easier.

All in all, MOST of the time you can swap stuff over from carb to carb as long as you know which carb you have, adjustment-wise. From what I've seen, ALL E4ME/C carburetors have an M/C solenoid set by gage at 1.304" and a rich stop, if used, set at 4/32". 2-point carbs are built in rich stops, so no adjustment needed. Those two settings haven't changed. Also, all the IABVs are set with a gage, but some are "note 2" which says set with the gage, final adjustment on car.
 
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Clone TIE Pilot

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I have a few spare CCC Qjets including several Chevy ones and one Olds Qjet and both baseplates are setup very differently, more than just different throttle shafts.

As I said before, Chevy CCC baseplates have idle air bypass ports under the throttle plates. Idle bypass air allows the throttle plates to be further closed at idle to prevent main nozzle drip. Olds baseplates do not have idle air bypass ports under the throttle plates, not even the machined taps in the bore. Instead they appear to have extra set of off idle ports just above the throttle plates that Chevy baseplates lack whose purpose I am not sure. If you try to use a baseplate wituout proper bypass air in a carb originally designed for it you will have rich idle and possible main nozzle drip from being forced to crank the throttle plates further open at idle. Bypass air configuration has a huge affect on idle quality. This beside Olds baseplates lacking a vacuum port to hook the EGR valve up to.

Bypass2.jpg


The red arrows in the image above shows the idle air bypass ports I am talking about which Olds baseplates lack but Chevys have. You can also see the EGR vacuum barb in the upper left corner which again Chevy has and Olds lack. What is the OP going to connect his EGR valve to?
 
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1983MonteLS

Not-quite-so-new-guy
Thread starter
Aug 1, 2022
24
3
I swapped it out fairly easily, and as mentioned I didn’t get a true feel for it all because I ran out of gas, what are the issues I’m going to run into leaving this carb hooked up?
Wow. Didn't realize there was such passion about baseplates. I couldn't tell you about Chevy baseplates. I'm not a Q-jet expert. I've only had one spare from a 454 from a 1976. But none from a 305 CCC carb. The 2-point, 3-point, and 4-point adjustments for the carbs are about how to tweak them on the vehicle to tune them to final specs. In the end, the engine doesn't care how it gets fuel when it needs it, as long as it's getting what it needs. For the most part, the calibrations can be tweaked on any of the CCC carbs to get you where you need to be for the final application. AFAIK, most all E-jets are set as lean as possible for emissions purposes anyway. Primary jets/rods can be swapped out as well as secondary rods/hangers if needed, but from what I've seen, there's not much difference on primary jetting between the V8s. And ALL the E-jet secondary seats are the same. Just the rods are different. Also, for example, Olds has a 1/2 turn wrap setting on the secondary air valves, where the Chevy, I think, is nearly twice that. Ideally, you just want it not to bog when you get into the secondaries and you shouldn't "feel" the secondaries kick in. You may hear them, but you shouldn't feel them.

For the air horns, I've found Chevy and Olds are virtually the same in comparable year applications. I got a new Chevy air horn with the rich stop which could be used on the Olds 3-point carburetor. The only differences I've found are the filtered air port not present on the back of the Chevy one since the Chevy didn't need it for the E-choke, but can be drilled and fixed if needed for a hot air choke. I know, I did it. E-chokes can be put on an Olds (plug the vacuum port in the choke housing if you do) but it's harder to put on a hot air choke on a Chevy since it has no vacuum hole, you would have to drill one into the float bowl- yikes. If your air horn is a 2-point adjust, the rich stop screw hole is not drilled/threaded, and to use it on an Olds 3-point system (and some Mopars) you would have to drill and tap that. Another Yikes. Good luck.

The IABV "tower" holes where it actually pulls in air are in different locations, but again, that means nothing as Chevy's in the front above the IABV, and Olds is on the side. And the final difference was already mentioned. The Chevy used no air bleed restrictors for the main primary (as seen through the top of the air horn) where the Olds did. I used some well tube restrictors from my hosed up float bowl with smaller .030 holes and drilled them out to the proper hole size .047 before I realized you could actually buy these from the Q-jet shops.

FWIW, even the lettered IABVs are set with the tool and if needed, adjusted if needed. Typically the lettered IABVs are set with the tool and left alone and all the idle mixture is controlled with the mixture screws. But there's a caveat in the procedure that says if you can't get it exactly right with the mixture screws, you can tweak the lettered IABV until you get it right. With the non-lettered ones, you tweak both the IABV and idle mixture screws. WHY they did that stupid sh*t I'll never know. To that point, 305 in the 84 F-body specs says to set the IABV with the gage alone, suggesting they have lettered IABV. What's the difference between F-body carbs and G-body carbs for the 305? 🤷‍♂️

Ok, back to the subject at hand. Sorry I got derailed. Follow the ports. Match up the porting from your float bowl to the air horn, or from the float bowl to the baseplate, depending on what you're swapping. 95% of the time, they'll be the same. Check port SIZES as well. Just because they're there doesn't automatically mean they'll match up and be correct. going from tiny to big or big to tiny may make a difference. Check 'em with drill bits or small gage wires. I did that with my Frankencarb and the Chevy ports and Olds ports/tubes and all that junk matched right up. If there's an extra vacuum port you don't need- plug it. If there's a vacuum port you need that ain't there- if you're desperate enough- drill it. Just know what you're doing with it.

There's another thing you could do for your other carb and that's remove both baseplates, grind off the factory stakes in the primary throttle shaft blade screws, remove them, and then swap the primary shafts. It's a bit more work, but then it won't matter how the baseplates are set up. The throttle shafts are pretty much all the same on the CCC carbs, regardless of E or C models. The only difference is the throttle shaft main lever which is staked on to the end of the throttle shaft. NOT and easy fix to swap that. If Rochester would have figured out a way to attach those primary levers on without being pressed and staked, that would make carb swapping infinitely easier.

All in all, MOST of the time you can swap stuff over from carb to carb as long as you know which carb you have, adjustment-wise. From what I've seen, ALL E4ME/C carburetors have an M/C solenoid set by gage at 1.304" and a rich stop, if used, set at 4/32". 2-point carbs are built in rich stops, so no adjustment needed. Those two settings haven't changed. Also, all the IABVs are set with a gage, but some are "note 2" which says set with the gage, final adjustment on car.
Dang man, you lost me in the first paragraph (total Quad noob…). Anyhow I did swap the baseplate from my old quad to the $20 regal carb thinking what do i have to lose? Since the electric choke looks aftermarket I’m going to guess that the carb was rebuilt… with that said it actually runs much better with the cross carbs. Maybe they rebuilt with some Chevy parts which helps me? Who knows, who cares. This is honestly my Roadkill car I graduated high school with sat for 12 years and got it back to life, so it’s big and ugly and I love it, my favorite car to drive even over my ‘67 Mustang in some aspects. I’ll keep you guys posted on the ride as I plan on taking it around town despite the Smokey exhaust, dents and faded paint. Long live 1995! :)
 

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Clone TIE Pilot

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Dang man, you lost me in the first paragraph (total Quad noob…). Anyhow I did swap the baseplate from my old quad to the $20 regal carb thinking what do i have to lose? Since the electric choke looks aftermarket I’m going to guess that the carb was rebuilt… with that said it actually runs much better with the cross carbs. Maybe they rebuilt with some Chevy parts which helps me? Who knows, who cares. This is honestly my Roadkill car I graduated high school with sat for 12 years and got it back to life, so it’s big and ugly and I love it, my favorite car to drive even over my ‘67 Mustang in some aspects. I’ll keep you guys posted on the ride as I plan on taking it around town despite the Smokey exhaust, dents and faded paint. Long live 1995! :)

What is your air fuel mixture dwell reading?
 

Clone TIE Pilot

Comic Book Super Hero
Aug 14, 2011
3,243
113
Galaxy far far away
The fuel mixture dwell should be varying around 30 degrees in closed loop, trans in drive and idle speed set at 600 rpm. Always use the 6 cylinder scale for air fuel mixture dwell. Its because it sets up nice even 3 standard deviations above and below the mean of 30. 0, 10, 20, 30, 40, 50, 60.

With your idle air bypass now effectively blocked off by the incorrect baseplate your idle mixture wil likely be rich. This is similar to what the carb reman guys do. They often block off bypass air to enrich the idle mixture for a more generic tune to trick their customers. Rich idle mixtures can mask problems. Probably better check for nozzle drip too.

Also those stickers are not the carb ID numbers. Qjet ID numbers are stamped on the driver side of the main body and begin with 170.
 

69hurstolds

Geezer
Supporting Member
Jan 2, 2006
6,633
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I have a few spare CCC Qjets including several Chevy ones and one Olds Qjet and both baseplates are setup very differently, more than just different throttle shafts.

As I said before, Chevy CCC baseplates have idle air bypass ports under the throttle plates. Idle bypass air allows the throttle plates to be further closed to prevent main nozzle drip. Olds baseplates do not have idle air bypass ports under the throttle plates, not even the machined taps in the bore. Instead they appear to have extra set of off idle ports just above the throttle plates that Chevy baseplates lack whose purpose I am not sure. If you try to use a baseplate wituout proper bypass air in a carb originally designed for it you will have rich idle and possible main nozzle drip from being forced to crank the throttle plates further open at idle. Bypass air configuration has a huge affect on idle quality. This beside Olds baseplates lacking a vacuum port to hook the EGR valve up to.

Bypass2.jpg


The red arrows in the image above shows the idle air bypass ports I am talking about which Olds baseplates lack but Chevys have. You can also see the EGR vacuum barb in the upper left corner which again Chevy has and Olds lack.
While you can never say never or always say always with GM parts and the stupid sh*t they do, wait until you see a weird CCC baseplate I have stashed away somewhere, once I can find it. It has an EGR port on it right on the corner like you show in the pic. And an Olds throttle shaft lever. I got it specifically for the primary throttle shaft, but it's totally useable on other Olds carbs if you block off that corner port. It's NOS but without a box. Factory stakes on the torx head blade screws and all. But I have NO earthly idea what carb it's supposed to fit originally. I'm thinking early version Olds before EGR solenoid? EGR on later Oldses had the EGR solenoid to take care of things which got its vacuum from the front of the float bowl port on the driver side.

Problem with the GM tech manuals- most of them will show you an air bleed port or whatever and then note "on some models" or "not on all models". Well, that narrows it down. So you have to do your port matches to find out exactly what you're working with. You can usually do workarounds on the calibrations IF, and I stress IF, you know what you're doing when "modding" these kinds of carbs.

I'm not here to argue which is better and every nuance about these stupid carburetors. Clone TIE Pilot makes some very valid points about ensuring you get the appropriate ports to match up when you start messing around and swapping parts. But you have to KNOW about the differences, if any, before you just start slopping stuff together and whether it makes a difference on how the carb reacts. "Hope it works" is not a plan. I was lucky enough to have a VIN 9 carb air horn to match up with the Chevy NOS one I decided to use (which, coincidently is the same air horn the 5204 carb uses). The three differences mentioned before was outlined and anything that needed to change for the Olds application was a relatively easy mod, IMO. And I went over both air horns with a fine-tooth comb. I don't expect it to work any differently than an actual air horn made for an Olds.

And just an oh, by the way. The stickers on the back of the carb are just the last 4 numbers of the carb original part number. Add a 1708 in front of them, and that's your part number. But be careful. I've seen a 6008 decal on a 6009 carb before. Quality is job #54. Keep in mind, ACDelco service part catalog numbers were very likely different, and if you get one, it should still have the original part number stamped into it.

As an FYI, 6008 (17086008) is an 86-88 VIN Y Olds 307 carb. 5204 (17085204) is a 1985 F/B/G body with 305H engine. Your car should have came with a 17083204 carb.

Good luck.
 
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1983MonteLS

Not-quite-so-new-guy
Thread starter
Aug 1, 2022
24
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While you can never say never or always say always with GM parts and the stupid sh*t they do, wait until you see a weird CCC baseplate I have stashed away somewhere, once I can find it. It has an EGR port on it right on the corner like you show in the pic. And an Olds throttle shaft lever. I got it specifically for the primary throttle shaft, but it's totally useable on other Olds carbs if you block off that corner port. It's NOS but without a box. Factory stakes on the torx head blade screws and all. But I have NO earthly idea what carb it's supposed to fit originally. I'm thinking early version Olds before EGR solenoid? EGR on later Oldses had the EGR solenoid to take care of things which got its vacuum from the front of the float bowl port on the driver side.

Problem with the GM tech manuals- most of them will show you an air bleed port or whatever and then note "on some models" or "not on all models". Well, that narrows it down. So you have to do your port matches to find out exactly what you're working with. You can usually do workarounds on the calibrations IF, and I stress IF, you know what you're doing when "modding" these kinds of carbs.

I'm not here to argue which is better and every nuance about these stupid carburetors. Clone TIE Pilot makes some very valid points about ensuring you get the appropriate ports to match up when you start messing around and swapping parts. But you have to KNOW about the differences, if any, before you just start slopping stuff together and whether it makes a difference on how the carb reacts. "Hope it works" is not a plan. I was lucky enough to have a VIN 9 carb air horn to match up with the Chevy NOS one I decided to use (which, coincidently is the same air horn the 5204 carb uses). The three differences mentioned before was outlined and anything that needed to change for the Olds application was a relatively easy mod, IMO. And I went over both air horns with a fine-tooth comb. I don't expect it to work any differently than an actual air horn made for an Olds.

And just an oh, by the way. The stickers on the back of the carb are just the last 4 numbers of the carb original part number. Add a 1708 in front of them, and that's your part number. But be careful. I've seen a 6008 decal on a 6009 carb before. Quality is job #54. Keep in mind, ACDelco service part catalog numbers were very likely different, and if you get one, it should still have the original part number stamped into it.

As an FYI, 6008 (17086008) is an 86-88 VIN Y Olds 307 carb. 5204 (17085204) is a 1985 F/B/G body with 305H engine. Your car should have came with a 17083204 carb.

Good luck.
My 83 G carb is 1708504 - as I mentioned I swapped out the base to the 86 cutlass top. It’s running a little choppy, a bit higher rpm at idle/park, but I adjusted the throttle screw down about 4 turns out which seemed to have got it somewhat steady idle. A few burps out the exhaust, but like I mentioned, the carb I had before wouldn’t even allow
Me to go forward or back without shutting the car off so in my mind, this is much better. I pay attn to the sounds and smells of the motor and exhaust - with the cat still on it, I can’t tell if it’s running lean, but has an odd smell, then again is a carbureted car. I have new cars with no smells and a old straight pipe mustang that gives you C02 😮‍💨🥴
 

69hurstolds

Geezer
Supporting Member
Jan 2, 2006
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If it's a 5204, it came out on a 1985 model, which was 2 years newer than your car's model year. I don't know if the calibrations are the same, but the YEAR CODE says 5, (1985) and all I was saying is your ORIGINAL factory carb should have been a 17083204. NOT a 5204. If the stamping on the driver side of the carb says 17085204, it is not original to your car, whether you want to believe it or not. I don't think they did a back to the future trick on it.
 

1983MonteLS

Not-quite-so-new-guy
Thread starter
Aug 1, 2022
24
3
If it's a 5204, it came out on a 1985 model, which was 2 years newer than your car's model year. I don't know if the calibrations are the same, but the YEAR CODE says 5, (1985) and all I was saying is your ORIGINAL factory carb should have been a 17083204. NOT a 5204. If the stamping on the driver side of the carb says 17085204, it is not original to your car, whether you want to believe it or not. I don't think they did a back to the future trick on it.
Who knows my man - it could’ve been replaced with another model - knowing how shady some mechanics/garages are, they could’ve popped my original off and put on a bum one. I was a naive 19 year old kid 28 years ago, and didn’t have everything documented on paper and in my mind, I just drove the sh*t out of it looking for chicks.
 

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