# 1968 400 HO carb questions



## Shake-N-Bake (Jun 16, 2015)

I have been going through some parts in preparation for an upcoming project and found myself comparing carbs....mostly because I am curious. One unit is 7028268 which my book says is for a 1968 GTO 400 HO auto model. I don't remember where I got it but I think it came off my 1967 Firebird 400 engine so it's obviously played the field a bit. The other carb is a SR carb that I've had on the shelf for quite a while. Tag said it was a 68-70 RA carb which seems correct based on the metering rods and jets that are installed.

My question is about the HO carb. I think the air horn might not be correct. Shouldn't it have the slots in the secondary air valves and the holes in the casting that draws fuel from the wells? I think the longer fuel inlet is something that I added a long time ago because I figured a larger fuel filter would flow better (not sure if that is the case but I was a tinkerer back in the day...)

Does anyone with a '68 HO model still have their original carb and if so....does it have the accelerator ports and signal slots on the secondary air valve flaps? I think someone may have changed the air horn on my carb and if so, then I'd like to change it back so it would be more correct.

Thanks
:thumbsup:


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## dan woodland (Jul 24, 2013)

Hey Shake-N-Bake,

I believe that front vacuum port is for an automatic setup... I'm sure someone here knows for sure.

I am in a similar situation. I have two 7028276 carbs, they are identical with exception of the ports you mentioned in the secondary plates. I'd be interested to hear why the difference.

Excellent post and pictures!!

Dan


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## Pinion head (Jan 3, 2015)

Will go through original '68 and '69 "268" carbs, if you like, and compare to an nos 7028276 SR Qjet I have. Have near 4 dozen '68-72 Pontiac Qjets.

Of note, the 7028268 Qjet was used on base auto 350 horse '68 GTO's, engine code YS, as well as the lower production number 400 HO's (engine code YZ). it will not have the machined notch in the airhorn for the retaining clip for the rubber boot on the acccel pump shaft. The main peculiarity of the '68 Pontiac Qjets is the vac port out the pass side of the throttle body. This port disappeared on the '69 Pontiac Qjets. 

On the 4853 Carter mfg Qjet, it's a fairly broad application replacement, but not a RA carb. Carter never produced RA Qjets for Pontiac, original RA Qjets and SR RA Qjets were made by Rochestor Products. the following Qjets were the Service Replacements for '68 and '69 RamAir Qjets:

'68, all RA application Q-jets: 7028276
'69, all RA application Qjets: 7029270
'70 model 49 state RA cars Ive always ran across 7029270's (need to dbl ck if that was the official SR)
'71's, both RA 455HO applications as non RA 455 HO's used the 7041270

SR versions of these above RA carbs typically were produced up into '75 or '76


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## Shake-N-Bake (Jun 16, 2015)

Pinion head said:


> Will go through original '68 and '69 "268" carbs, if you like, and compare to an nos 7028276 SR Qjet I have. Have near 4 dozen '68-72 Pontiac Qjets.
> 
> Of note, the 7028268 Qjet was used on base auto 350 horse '68 GTO's, engine code YS, as well as the lower production number 400 HO's (engine code YZ). it will not have the machined notch in the airhorn for the retaining clip for the rubber boot on the acccel pump shaft. The main peculiarity of the '68 Pontiac Qjets is the vac port out the pass side of the throttle body. This port disappeared on the '69 Pontiac Qjets.
> 
> ...


Thanks for the info....
Any idea if the 7028268 was supposed to have the signal notches in the secondary air valve along with the feed holes in the air horn? My book also says this carb was used on some 428 engines. Would Rochester have produced a couple of different versions of the "268" carb (YS, YZ and 428 engines)? Seems like there would be different carb numbers if the application was different enough to have secondary acceleration ports on some engines but not others. ??

How do we know that Carter didn't produce SR carbs for Ram Air application? I think I've read that none were made for production vehicles but I hadn't heard about the SR exclusion before now. The tag on the 4853S carb said 68-70 Ram Air and 71 RA455? The "71 455?" was on a second line. However, all of it was hand written so that info could have come from anywhere. I think I purchased that carb from Purely PMD in the early 90's so maybe they were taking a guess as to what application it was for?

I've seen 4853S and 4987S carbs on the same table as a 7028273 Rochester and the 4853S looked identical to the Rochester carb externally, with the exception of the accelerator pump boot/seal thingy. As best as I can tell, the 4853S and 4987S are both listed for 68-70 model year applications but there must be some reason for the different part numbers. :confused

Your SR part number listing is really great info. :thumbsup:
I find it interesting that SR Rochester carbs were a 'one size fits all' replacement across all RA engines for '68 and '69-'70 respectively. According to a helpful "how to" guide posted by Lars, the production versions of the 68 RAI carbs had different primary metering areas for Autos and Manuals and then again different for the RA II engines. Which makes sense because the RAII cam was quite different compared to the RA I bumpstick. Then the RA II carb carried over for use on the 69 RA III in regards to primary metering area....which seems counter intuitive since the RA III cam wasn't nearly as radical as the RA II stick. ???(still can't figure out why Pontiac did that...)

It's worth noting the secondary metering area on all 68 RA I & II as well as 69 RA III engines were the same. (BE rods with short tip .0413 dia)

The 69 RA IV was a bit of a departure in regards to primary and secondary metering area compared to it's RA predecessors. Interestingly enough, the primary metering area REDUCED both at idle (5%)and WOT (9%) but the secondary metering area INCREASED (3%). Very small changes but interesting just the same. 

That same chart appears to show that 1970 was a homogenization of sorts for the RA III, RA IV and HiPo 455 models in they may have all had the same primary and secondary metering areas. In these cases, the primary metering area increased slightly, approaching the 68 RAII size while the secondary metering rod increased dramatically (26% larger than the RA II/69 RA III area. 

The primary metering area in the Carter 4853S unit is nearly identical to the RA II and 69 RA III automatics (2.7332 vs 2.7512) while the secondary rod is identical (BE).....so I am planning on using it in my 68 MT RA II build. I'll probably step the jet up one size since I have a manual trans (like Pontiac did). And then (because I can't leave well enough alone....), I'll probably play with different rods and jets and fine tune per Lars step by step instructions. With luck, I'll end up with a really nice running engine. 

If not, then I'll have to see if my friend will sell me his 7028273 carb for a reasonable price. 

I am still curious about the 7028268 carb....is it supposed to have the slots and acceleration ports in the secondary side? :confused


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## Shake-N-Bake (Jun 16, 2015)

dan woodland said:


> Hey Shake-N-Bake,
> 
> I believe that front vacuum port is for an automatic setup... I'm sure someone here knows for sure.
> 
> ...


I am curious about that vacuum port as well. If the automatic cars need that port then I'd expect to see it on the SR carbs....Does anyone have a photo of the aforementioned Rochester SR carbs that we can compare with?

I don't have my book handy....is 7028276 a RA carb? What are the dates of your units? Maybe one is SR and the other isn't??


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## Shake-N-Bake (Jun 16, 2015)

Pinion head said:


> Will go through original '68 and '69 "268" carbs, if you like, and compare to an nos 7028276 SR Qjet I have. Have near 4 dozen '68-72 Pontiac Qjets.
> ...


Do you happen to have a 1970 RA III or IV carb? I'd be curious to see if it's like the carb on my 70 RA III engine. That carb is unique in that the air horn is fastened with Torx head screws and the integral choke rod tab on the choke flap is removable via machine screw. I always thought that was a pretty cool feature. Made it really easy to change primary rods and jets at the track without having to perform a ballet trying to disconnect and reconnect that rod.


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## Pinion head (Jan 3, 2015)

Yes, the 7028268 Qjet was also used on '68 auto 428 applications, as well. '68 428 B series are actually fairly low production thus didnt mention that application. Compared to '69 B series where '69 Bonnevilles received YH code 428's as standard equiptment, '68 model year use 428's are rare. There are no different calibrations on the 7028268's due to body style. On SR RA Qjets, am extremely certain of the part numbers, have had quite a few SR dated 7029270's and have passed on many others. Also have had dozens of Carter built Pontiac Qjets, and passed on many more. There is a sheet out there that notes the only 4MV style Qjets that Carter built for Pontiac, nearly all are rather mundane applications, same with the 4digit number Carter Qjet replacements.

'70 RA Qjets...currently have an original 7040570, it has the small holes in the leading edge of the primary throttle plates, all the original RA Qjets I've owned had that feature amongst other RA Qjet features.. As far as Torx head screws, they were not used on original '66-81 model Qjets. late '80's before GM V8's received throttle bodys, it's a possibility Torx screws were used, would have to ck with friends who own '85 and 86 Chevy pickups.


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## PontiacJim (Dec 29, 2012)

Shake-N-Bake said:


> I am curious about that vacuum port as well. If the automatic cars need that port then I'd expect to see it on the SR carbs....Does anyone have a photo of the aforementioned Rochester SR carbs that we can compare with?
> 
> I don't have my book handy....is 7028276 a RA carb? What are the dates of your units? Maybe one is SR and the other isn't??



From Cliff Ruggles book on Q-jets:

Service replacement carbs have a Julian date code stamped with the carb number. It is a 4 digit number with the first 3 being the day of the year and the last digit the year. There is a photo of a production 1977 Q-jet which also has the Julian date code stamped on it as well. He states that most all Rochester manufactured carbs have this date code.

The carb also has a plant code, a 2 or 3 letter code.

Carter manufactured Q-jets did not use the Julian date code. Instead used a Letter/Number code ie H8 which is August 1968. Carter carbs were not used on HP cars and were found on the lower HP engines.

With the high prices of RA & HO carbs, many have been restamped and lack the Julian codes or plant codes.

The book shows *torx screws* used on the early 1980's carb top to main body. Not used on earlier carbs. You may have a remanufactured carb where companies dis-assembled the carbs en masse, and then rebuilt/reassembled them using parts that fit, but were not number matching correct as this was not their basis for providing a remanufactured carb. We have seen this here on the forums in the past.

Book by Pete McCarthy & John Angeles states the the RA carbs for the 1968-1974 era (excluding the RA I) used the last 2 digits on the carb as "70" (Auto) and "73" (manual).

The 7028276 Q-jet is not a 1968 RAII carb. It is listed as a Firebird RAI automatic carb. 7028277 was the manual trans version. One year only as it does not appear in any other year or any other car.

The 7028268 Q-jet was used on 1968 GTO automatic cars, the standard 350HP GTO engine as well as the 360 HP HO engine. Also used on the big car 428 CI automatics, 375HP & 390HP. Not used on the Firebird. 

The early carbs had the notches in the secondary air flap and it seems this was changed in the early 70's - Cliff Ruggles.

Carter Qjet 4853S was used on the '68-'74 Pontiacs and is a Service Replacement carb. I would stay away from this carb, as it is a Service Replacement. - Cliff Ruggles.

Hope that helps.:thumbsup:


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## Pinion head (Jan 3, 2015)

Original usage 7028276's were indeed early '68 RamAir auto use Qjets. They were dated with a stamping on the edge of the rear corner of the throttle body. Very very hard to find original RA carburetor. The original application "8276" is not what I was elaborating on in my earlier post.

The 7028276 Rochestor Quadrajet that is the SR for all '68 Ram Air application Qjets and as an SR, will have a 4 digit date code stamped in the side of the float bowl below the correct font stamped ID number 7028276. 

The 4853S is not a service replacement for '68-74 Pontiac Quadrajets. The Carter application SR was limited to generic lower performance '68-70 Pontiac V8's. The SR application was limited, as the Pontiac Qjet airhorn design changed for '71 models, and all '72 Pontiac Qjets had a fixed throttle arm which accepted a pop on throttle cable end, versus the earlier style Pontiac throttle body/shaft with a bolt on linkage arm that utilized a throttle cable pin which took a small cotter key.


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## PontiacJim (Dec 29, 2012)

"The 4853S is not a service replacement for '68-74 Pontiac Quadrajets."

I'll email Cliff Ruggles for you and let him know. Came right off his web. But, good info anyway.


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