I am in aprocess to service my Cutlass -69 3502bbl carb. There are two slots in the throttle body gasget.
I noticed these slots are leaking air directly in the carb throttle body???? Is it supposed to be that way?
Kuva0066_zps3add8fb1.jpg
Kuva0067_zps058ff90f.jpg

 

No, this is a leak and should not be there. Carburetor rebuild kits usually come with extra gaskets that are similar to each other but are slightly different. This allows the kit to fit a variety of carburetor versions. Whoever rebuilt your carburetor either had the incorrect kit or selected the wrong gasket.

 

When I rebuilt my Tri-Carb the rebuild kits had several gaskets to choose from. Looks like someone rebuilt that carb before

 

+3. Wrong gasket.

How did it even run?

Check all settings and dimensions carefully (use the specifications in the Chassis Service Manual) in case other things were screwed up.

- Eric

 

Yup wrong gasket,i had the same issue with a 4gc core i bought,the new kit had the same wrong gasket that was removed, i ended up getting another kit from a different source.Nick

 

Common sense says it's a leak, but Carb repair data sheet has a picture saying they are "Vapor Vent Passages", what ever that means?


My repair kit is car specific, American made, designed for -69 Cutlass 350 2bbl. It is not an universal kit. According to carb tag and also carb number stamped on the carb body, the kit should be the right one.


Car was running and idling good. The reason I started servicing was the sticking cold start butterfly. Also the gasgets were not good any more.


Does anyone has knowledge about these "Vapor Vent Passages"??
(Sorry for lousy pic quality)
Kuva0069_zps792c927e.jpg

Kuva0068_zpsb4651c0a.jpg

 

Suit yourself.

If you are so certain you're right, then why did you ask?

Those grooves are for a different casting.

- Eric

 

x2

 

Yes sirs I believe you and common sense are right. For unknown reason there must be wrong gasget in this set. All the codes seems to match. Need to grab one of those universal kits and find a right gasget. It is a strange co-incidence that the old gasget is similar.


Does anybody have a glue what these "Vapor Vent Passages" should do?

 

Interestingly, GM shows the gasket you have as being right for that car, which leaves open the very real possibility that someone over the past 45 years screwed the wrong stamped aluminum tag onto the wrong carburetor.



A quick search shows that O'Reilly lists two kits for that car, one from Warner (#10332C, $27) and one from Walker (#15468D, $24), and that both contain the correct gasket:


- Eric

 

You may also find this manual helpful (sorry, it's all jpeg scans)

- Eric

 

FINALLY AT LONG LAST SOMEONE ELSE NOTICED THIS

I noticed it years ago, before the internet.
When I was able to, I put forth an inquiry like the above on the internet- but no one knew anything at all about these passages, there was not even a mention of "Vapor Passages" to be found.

To me, it seemed ABSURD to allow dirty unfiltered air into the engine in this manner, therefore I ASSumed that the carbs like that [and by now I had seen several] were rebuilt using the Wrong Gasket from a kit. But as I recall my kit had the gasket for dirty air entry, and other gaskets that did not work for one reason or another- too thin, holes wrong, etc. I ended up sealing the Dirty Air passages with RTV or similar, on the principle of allowing dirty air directly into the engine is WRONG.

Now the plot thickens.
In a lot of parts I bought came to me an NOS new in the box carb like that.
Guess what?
Dirty Air Passages, RIGHT FROM THE FACTORY.
I have photos of this carb- though it sold long ago.

To summarize, then:
It is NOT just a matter of rebuilders putting in the wrong gasket, these carbs CAME LIKE THAT.
No one knows WHY the factory would allow DIRTY AIR right on into the engine.
Unless there's a good reason not to, I recommend closing off the Dirty Air Passages during your rebuild.

 

With all due respect, I'm not buying it. This would result in a MAJOR venturi vacuum leak, and wouldn't even allow the mixture at idle to be set properly at the factory. This would have been found out on day one.

 

I want the pictures, Chris.

- Eric

 

http://www.oldcarmanualproject.com/m...3__2G_0008.htm

On p.7 of that manual they talk about constant bleed purge ports that suck air out of the fuel tank canister. From the figures they show, it looks like the throttle body you have doesn't match the rest of the carb that uses the constant purge setup.

I have the feeling you may have a frankencarburetor. Disclaimer: I have never worked on these carbs. Take a look at the manual and ask others here.

 

It will idle ok,the air leak is above the throttle plates, it will affect off idle venturi vacuum or part throttle cruise mixture mainly causing a lean condition.all the port openings need to match the main body and throttle body.Imo someone has been there before.Nick

 

No, sir. The Dirt Passages are above the throttle blades and while they might affect main venturi flow slightly, they cannot really alter any idle conditions. The Constant Feed Purge Canister ports shown in http://www.oldcarmanualproject.com/m...3__2G_0008.htm are BELOW the throttle plates, so are not this feature.

"I want the pictures, Chris."
=============
Patience.
I have a brake repair to do on a kid's car that must be ready to drive on Monday. And I must get to the local boneyard today [Sunday].


"Imo someone has been there before.Nick"
====================
This was my initial thought as well. However, after having seen MANY, MANY such 2-bbl carbs like this, typically with no sign of having been apart [tag still in place, screw heads not mangled, etc.]... and then finding the *NOS* carb with this configuration... the only plausible explanation is that for whatever reason, these carbs CAME THIS WAY and it's not just a whole lot of idiots picking the wrong gasket during a rebuild.

Speaking of which, in the pic above of gaskets and kit parts, I see THREE types. I vaguely recall my kit having
1) the one with Dirt Passages, which seemed wrong
2) the one with differently located small passages, shown center above, was not usable due to those

Since I did not have
3) what appears to be [on the right above] the correct combination of No-Dirt-Passages and properly located small passages...
I had to improvise and seal the Dirt Passages.

 

A junkyard that's open on Sundays? Now THAT I don't believe.

- Eric

 

Yes the vents are factory, and are as described above, vapor vents. Before emissions regulations prevented their use in new cars, they were standard equipment on the 2GC. A gasket with the vent slots is the correct original replacement for older carbs.

 

http://www.u-pullandsave.com/Price_List.cfm#4

"Yes the vents are factory, and are as described above, vapor vents. Before emissions regulations prevented their use in new cars, they were standard equipment on the 2GC. A gasket with the vent slots is the correct original replacement for older carbs."
===============
"Correct" as in what the factory used, sure.
I still say, it's not emissions to worry about, it's what may be drawn IN there that concerns me. Why bother putting an air filter atop the carb if you are allowing whatever floats by at the aft side of the carb to be drawn right on in?

That's crazy.

Factory craziness.

PS no luck on the pix yet. I have gigs and gigs of photos, and so far searches for "carb" got too many hits, "leak" found some used carbs with this feature, and "NOS" also has too many hits, not enough time to go over the rich tapestry of PadNOS junkyard finds and other people's NOS parts for sale or for examples of what stuff looked like new...... I need a date range or better word to search for. Will try "weird" next, see what pops up.

 

Just came from my carage and checked that the carb no. in the aluminium tag matches to stamping in the carb body. It may be still possible that someone has taken the throttle body from another carb. Still, all the passages seems to match between the TB and other carb.
Also the gasget passages matches perfetly tho those on carb. For now, I ended up sealing these "dirt" passages with RTV sealer.

 

Gasoline turns RTV to slime.

 

Yes that might happen, I'll keep it on eye. Seals are mostly outside of the carb, I'll watch and see what happens, and replace with some other material if needed.

 

OK, let me throw in a little more information to chew on. I've got 7-8 2bbl carbs from 1970-72 and a couple from 68-69. None of them had the vents in the gasket. Then I looked at a 1966 330 with California emissions. I pulled the engine from a running/driving car. It did not behave like it had a bad vacuum leak. Could the internals of the carb been adjusted to allow for this extra air? I've not pulled the carb to see if this goes right down the intake as it would seem. But check out the pictures.

P5110327.jpg

P5110322.jpg

P5110318.jpg

P5110324.jpg

 

OK. I hate to eat crow, but after my research I'm rolling over on this one and believing that these slots were indeed in at least the '66 & '67 Olds CALIFORNIA 2bbl cars. Timewise, this was at the beginning of the looniness that has become the California emissions system. After thinking about it, these slots would introduce air (and debris), but that the mixture-at-idle screws would be able to comp for it. At cracked throttle to WOT they wouldn't make much difference (except for the debris part). I'm sure this kluge help GM get past some ill-founded emission standard.

I bow to Octania, the Roman god of petroleum!

 

I am amazed about the amount of knowledge you guys have here. Can someone tell what year my carb is based on it's number 7029156?

 

7029156:

• 70: Rochester Carburetor
• 2: 1960s
• 9: 1969
• 1: 2-Jet, 49-state emissions (not California)
• 5: Oldsmobile
• 6: Automatic Transmission (even numbers)

- Eric

 

'69-'70 Olds. Whenever you want carb info like this, just Google the carb number along with the manufacturer (i.e., "Rochester").
http://www.carburetion.com/CarbNumbe...Number=7029156

Here's 67442nut (on this board) showing the same carb:
https://classicoldsmobile.com/forums...7029156-a.html

...and here's the whole world of carbs!
http://carbkitsource.com/carbs/catal...ile/index.html

 

Wow! Thanks, Eric! I think it is the original carb of my car. What I don't know, did someone change the TB-part from an older 2G. I doubt it, I guess the vent slots were still present on 1969.
Anyhow, the vents are now blocked and without adjusting anything, the car seems to work ok. Maybe the positioning of the vents is desingned so that they do not cause lean mixture in any rpm. I'll sleep better knowing these dirt suckers are blocked.

 

Ragtop, thanks for sharing great, helpful links!!!