Thread: Thermo Spreadbore Carter carb.

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Is a 750 cfm Carter carb w/109,000m. on it worth fixing/rebuilding? I have 72 Caprice w/ a 454cid engine,& minor mods, and factory dual exaust, my Carter carb gets bogged down when I floor my car. Then the carb making a popping noise, and the car looses power, tell I release the gas pedal.It sounds like its either not getting a enuf air flow, or flooding. But it seems fine in less I floor it. I have used carb cleaner the spray version, and in the gas tank kind, and it still stalls. Some one said it might be the heat activated choke on top of the intake manifold, but they didnt know how to check it out,and thiers not many books on Carter carbs, so thanks for any help. Old Chevy

I assume you are talking about the Carter Thermoquads. These are not really a bad carb, I've ran them for several years.

They can be a bit tricky to rebuild and there are a few a couple of tricks to it.

The problem you are describing however sounds like the secondary are opening too quickly. I think you will find that will find that you have a bad vacuum pot. There should be a vacuum pot on the passenger of the carb that is hooked to the secondary air valve. Pull the line on the pot put vacuum to it and see if it pulls the linkage, and holds vacuum.

the way he talked this was the carb. that came on the car, from the fact. just wondering what yrs chev. used the Carter Thermoquads on their motors ?

Originally posted by DennyW
I worked on a lot of them on chryslers.

me to, but hes working on a 1972 chev. 454, more than likely a Q-jet

Originally posted by Mike P
I assume you are talking about the Carter Thermoquads. These are not really a bad carb, I've ran them for several years.

They can be a bit tricky to rebuild and there are a few a couple of tricks to it.

The problem you are describing however sounds like the secondary are opening too quickly. I think you will find that will find that you have a bad vacuum pot. There should be a vacuum pot on the passenger of the carb that is hooked to the secondary air valve. Pull the line on the pot put vacuum to it and see if it pulls the linkage, and holds vacuum.

I checked the vacuum pot, and it does pull the linkage back, and holds it, but it may be loosing vacuum when I drive it, I cant tell though. Thank you for your help. Now I can try some tests, on this vacuum pot.

I think it's a replacement carb. because the millege. From my research I cant find out what was the stock carb. brand was.The car is a 72 Caprice, and in the factory book it only says its a four barrel carb., and it does'nt mention what brand it was.

Originally posted by lt1s10
the way he talked this was the carb. that came on the car, from the fact. just wondering what yrs chev. used the Carter Thermoquads on their motors ?

My memory's a little foggy (but what else is new), I seem to recall seeing a couple of early/mid 70's GMs with factory Thermoquads. Also rare, but I've seen factory Quadrajets on 460 Ford engines. Go figure

Originally posted by OldChevy
I think it's a replacement carb. because the millege. From my research I cant find out what was the stock carb. brand was.The car is a 72 Caprice, and in the factory book it only says its a four barrel carb., and it does'nt mention what brand it was.

that Carter Thermoquads wouldnt bolt to a Q-JET intake.as far as i know and i went to every GM carb. school GM had in 1972. Q- JETS is the only 4 brl. GM used for a lot of yrs. late 60 until 1985, then they stop putting carb. on them. but it does sounds like the secondary are opening to soon. its hard for me to tell you how, but you can check them by tying the back butterflies closed(so they cant open) and go drive it if that fix the problem then ill try to tell how to do it. tap on the big back betterflies and see if they are loose

Originally posted by Mike P
My memory's a little foggy (but what else is new), I seem to recall seeing a couple of early/mid 70's GMs with factory Thermoquads. Also rare, but I've seen factory Quadrajets on 460 Ford engines. Go figure

not trying to cut in on you here mike, im saying i never saw one, and that dont mean it didnt happen, but i was at GM dealershops for guite a few yrs and never saw one.

lt1s10, naw I don't take it as as a slam, like I say my memory's a little foggy. If I did see it (and do THINK I have) I wonder now if it was part of a high altitude package. I live at 4500 feet and while most of the older cars I've worked on here have had the "normal" systems on them there have been a few odd balls, and when we looked closely, they had the high altitude emission stickers on them (the 76 Merc 460/Rochester that was a regular customer comes to mind).

Your suggestion on tying the secondarys is a good one for trouble shooting.

As far as fitting a Q jet manifold I do know they do bolt right up (Ran a couple on BB and SB stock intakes).

Originally posted by Mike P
lt1s10, naw I don't take it as as a slam, like I say my memory's a little foggy. If I did see it (and do THINK I have) I wonder now if it was part of a high altitude package. I live at 4500 feet and while most of the older cars I've worked on here have had the "normal" systems on them there have been a few odd balls, and when we looked closely, they had the high altitude emission stickers on them (the 76 Merc 460/Rochester that was a regular customer comes to mind).

Your suggestion on tying the secondarys is a good one for trouble shooting.

As far as fitting a Q jet manifold I do know they do bolt right up (Ran a couple on BB and SB stock intakes).

thats im bad about saying this is the way it is and somebody will come by every time and prove me wrong so i try not to say anything is 100 % anymore

".........about saying this is the way it is and somebody will come by every time and prove me wrong so i try not to say anything is 100 % anymore......"

Same here. One of the great things about the site is the vast amount of experience that people bring to it, and the way info is exchanged without it turning into a pissing contest (generally).

Originally posted by Mike P
".........about saying this is the way it is and somebody will come by every time and prove me wrong so i try not to say anything is 100 % anymore......"

Same here. One of the great things about the site is the vast amount of experience that people bring to it, and the way info is exchanged without it turning into a pissing contest (generally).

i agree and some times i come across the wrong way but i try not to.