ed burke

does anybody know what the difference between a standard 425 carb and a 425 carb with A.I.R. A.I.R. carb is a Ca. car with a smog pump. Is there a different jetting what do you need to plug off to eliminate the smog stuff on the carb. Thanks ED

ourkid2000

Well, the answer to this question has led me on a huge journey through long lost information and parts catalogs but I believe I have finally gotten to the bottom of this. I hope this helps someone as I certainly found it quite interesting and fun to research. I spoke with some of the true Qjet masters out there and not even they knew what the differences were. I figured if they do not know, then no one knows so it was time to get into the books and start digging. It also told me that it's highly likely that I'm probably the only person that cares about this, which is kind of humorous.

I have a 1966 Olds Toronado which originally came from California and is equipped with the K19 system and it uses a different PN for the carb than you would normally find on an original 66 Toronado. According to the 66' CSM, mine should have come with a 7036250 Qjet and the 49 state, non K19 Toro should have come with the 7026250 Qjet. Recently, I was looking for a second Qjet to replace my original and this idea lis what led me down the rabbit hole of long lost Qjet lore.

So what's the difference between 7036250 and 7026250? Well, if you look in "most" Delco parts catalogs you will see that, on the surface, it appears that there is no difference at all. Some of the the parts which could possibly be different seem to be either listed as the same PN or NLA (no longer available) but there's no obvious differences between them. The same "service replacement" carb PN is used interchangeably between the 1966 AIR (K19) and Non AIR Toros so that's no help at all. My first clue came when I looked in my physical original 1971 parts catalog that showed a different PN between the throttle bodies (base plates). The AIR car had base plate PN 7031117 and the non AIR car has base plate PN 7029980. The float bowl PN's showed as the same PN. So, now I'm getting somewhere, as this is the first difference that I have found and it clearly shows that they have different throttle bodies. What's different between the throttle bodies, I wondered? It seemed like the older the parts catalog, the more detail that was available. That same parts catalog kinda alluded to the air horns also being different, as the Non AIR carb showed PN 7031109, however, the AIR carb air horn PN showed NLA. Definitely a clue there that more digging was required.

Then I came across the following note in an old 1973 Delco service manual: " On exhaust emission control carburetor applications, the idle mixture needle discharge holes have been reduced in size. This was done to prevent a too rich idle adjustment in the field should the idle mixture needles be turned out too far beyond normal idle mixture requirements". Ah ha! There's the difference between the throttle bodies (or base plate), the idle mixture needle discharge holes are smaller!

So what else is different? Well, I finally came across someone who had a 1967 parts catalog for the carbs (it's the Black #9 manual - Bulletin 9C-520 Nov 1967) and it's there where I found that the air horns are different PNs. Now, this is the only manual I have come across that shows the relevant information, no other manual that I'm aware of shows this. In that manual the AIR carb has air horn PN 7032941 and the Non AIR carb air horn is 7031109. So now I'm really getting somewhere! The two carbs have different air horns, same float bowl, and different base plates. Lets keep going! So what's different between the air horns then? They look the same to me?

Another clue came from that same 1973 Delco service manual. It states "another feature added to some emission carburetors is an adjustable off-idle air bleed system. A separate air channel is added in the air horn which leads from the top of the air horn to the idle mixture cross channel. An adjustment screw with a tapered head is mounted at the top of the channel and is used to control the amount of air bleeding into the idle system. The off-idle air bleed is adjusted at the factory to maintain very accurate off idle air/fuel mixture ratios. It is adjusted during carb flow tests and no attempt should be made to readjust in the field. A triangular spring clamp forced over the vent tube covers the screw to protect the adjustment from being tampered with and should not be removed. All Service air horns have this screw preset at the factory"

Again, the light bulb went off. I looked at my 1966 original 7036250 and there is indeed a screw on the top of the air horn under that triangular clip. I studied pictures of about a dozen original Non AIR carbs (7026250) including one that still had the original inlet valve and all of them had a sealed off plug where that adjustment screw is on mine. Furthermore, the fact that the 7026250 had the original troublesome inlet valve, would tend to indicate that this is a pretty good 1966 time capsule. The fact that that particular carb had no air screw is pretty definitive evidence. I also studied pictures of a couple 1966 service replacement carbs (PN 7041312) and sure enough, just as the Delco manual states, they do indeed have the screw in the airhorn!

So there it is folks. In 1966, the two Toronado Qjets available had different air horns with one having an adjustable off-idle air bleed screw, different throttle bodies, same float bowl. If anyone needs the reference material, I can post it here.

Note: The jetting of these two carbs is exactly the same. Same primary and secondary metering rods, same primary jets, etc. The only differences I have been able to find are listed above.