1970 Carburetor question

[Joe W.]

Greetings!

Spring is here and I'm anxious at getting my car out of storage but
concerned about it's performance and lingering gas fumes. My good friend
loaned me a carburetor from his collection to get my car running until a
suitable replacement could be found. When I bought the car 4 years ago,
it came with a Holley which, was not correct. The loaner, a Rochester
Quadrajet - 7040507.

I have a few questions to ask.
What is the difference between this carburetor (7040507) and
the 7040207 or any other 70-72 4-speed Quadrajet? Is it restricted?
Are there different components in it? Could it prevent the 4 barrels from
opening up completely?

Next, I smelled gas lingering in the garage after I shut the car off.
I wondered if the rubber lines that come off the front of the carburetor
would have anything to do with this.

On the 70' 7040507, there are two nipples, one large and one small.
The larger hose goes directly into the left valve cover. I can't remember
if it goes into a PCV valve or not.

The other, smaller nipple at the front of the carburetor;
I can't remember if it's capped off or routed somewhere to the
right rear of the motor. The car is in storage, away from my home,
so I can't run out and look at it.

Way back when on my 72', 350/200hp 4-speed, I faintly remember
the (2) rubber lines at the front of the Carter carburetor, were routed
differently than the 70' Rochester.

On the 72' Carter, the larger of the two hoses went to a Tee in the
left valve cover, connecting to a PCV valve? The hose on the other side
of the Tee and the other smaller hose from the front of the carburetor were
routed down, somewhere into the left front fender. But to what?

Is my 70' supposed to be routed the same way?
Could this account for the lingering gas fumes?

I don't have any photos to show this,
but I hope my description can help you answer my questions.

Any info would be appreciated.

[Jeff G.]

Re: 1970 Carburetor question

My 69 Rochester has the smaller nipple runing a line to the A.I.R. diverter valve. If no AIR, just cap it off.
I assume you've looked to make sure there are no leaks in the fuel lines, filter, etc.

[Patrick H.]

Re: 1970 Carburetor question

Joe,

The 70 hoses are routed somewhat different than the 72. The large nipple goes to the PCV valve, and stops there. The smaller nipple sort of above and left of the fuel inlet actually connects via a short rubber hose to the metal vacuum advance line that goes all the way around to the distributor. You can find good pictures in Dobbins' "Fact Book" if you own one, or also in a Doc Rebuild catalog or on his site.

http://www.docrebuild.com/dr-r-web/PCV2.pdf

and other pages too.

None of this should account for any gas smell. However, gas smell is very, very common on these old cars. My 72 smells like gas on occasion too. We're just so used to clean newer cars that we forget about it.

Patrick

[Joe W.]

Re: 1970 Carburetor question

Thanks Patrick.

So out of curiosity, where do the hoses from the 72' carburetor and
the tee on the valve cover go to under the left front fender?

Also, congrats on your 5000 posts! Wow!

[Jeff G.]

Re: 1970 Carburetor question

Pat's description is correct for that Dr. Rebuild picture (small block carb?). The configuration is totaly different for my 69. My PVC runs from the front larger nipple like he described, my vacum is from the side. I here's a pic from the passenger side ...

[Patrick H.]

Re: 1970 Carburetor question

Thanks Patrick.

So out of curiosity, where do the hoses from the 72' carburetor and
the tee on the valve cover go to under the left front fender?

Also, congrats on your 5000 posts! Wow!

They go to the charcoal canister in the left fender, behind the wheel.

Yah, now 5002.

[Joe W.]

Re: 1970 Carburetor question

Thanks Gents and for the photos as well.

Joe

[Joe L.]

Re: 1970 Carburetor question

Greetings!

Spring is here and I'm anxious at getting my car out of storage but
concerned about it's performance and lingering gas fumes. My good friend
loaned me a carburetor from his collection to get my car running until a
suitable replacement could be found. When I bought the car 4 years ago,
it came with a Holley which, was not correct. The loaner, a Rochester
Quadrajet - 7040507.

I have a few questions to ask.
What is the difference between this carburetor (7040507) and
the 7040207 or any other 70-72 4-speed Quadrajet? Is it restricted?
Are there different components in it? Could it prevent the 4 barrels from
opening up completely?

Next, I smelled gas lingering in the garage after I shut the car off.
I wondered if the rubber lines that come off the front of the carburetor
would have anything to do with this.

On the 70' 7040507, there are two nipples, one large and one small.
The larger hose goes directly into the left valve cover. I can't remember
if it goes into a PCV valve or not.

The other, smaller nipple at the front of the carburetor;
I can't remember if it's capped off or routed somewhere to the
right rear of the motor. The car is in storage, away from my home,
so I can't run out and look at it.

Way back when on my 72', 350/200hp 4-speed, I faintly remember
the (2) rubber lines at the front of the Carter carburetor, were routed
differently than the 70' Rochester.

On the 72' Carter, the larger of the two hoses went to a Tee in the
left valve cover, connecting to a PCV valve? The hose on the other side
of the Tee and the other smaller hose from the front of the carburetor were
routed down, somewhere into the left front fender. But to what?

Is my 70' supposed to be routed the same way?
Could this account for the lingering gas fumes?

I don't have any photos to show this,
but I hope my description can help you answer my questions.

Any info would be appreciated.

Joe-----


For the most part, if not entirely, the differences between the 7040207 and the 7040507 are with respect to internal calibration. As far as differences between earlier or later Q-Jets, that's another whole story.

Keep in mind also that both the 7040207 and the 7040507 are extremely rare carburetor part numbers. Actually, the 7040207 is extremely rare and the 7040507 even more rare than that. You must have a very good friend to let you use one as a "loaner" (or, he doesn't know the value of what he loaned you).

I'd be very interested in your posting good photos of the 7040507 from several angles.

[Patrick H.]

Re: 1970 Carburetor question

Joe-----


For the most part, if not entirely, the differences between the 7040207 and the 7040507 are with respect to internal calibration. As far as differences between earlier or later Q-Jets, that's another whole story.

Keep in mind also that both the 7040207 and the 7040507 are extremely rare carburetor part numbers. Actually, the 7040207 is extremely rare and the 7040507 even more rare than that. You must have a very good friend to let you use one as a "loaner" (or, he doesn't know the value of what he loaned you).

I'd be very interested in your posting good photos of the 7040507 from several angles.

It's an 07040507 service replacement dated about 1976 (?) that came on my 71 when I bought it.

Patrick

[Joe L.]

Re: 1970 Carburetor question

It's an 07040507 service replacement dated about 1976 (?) that came on my 71 when I bought it.

Patrick

Patrick-----


It may be that the 7040507 was used as a SERVICE carburetor for other applications. I am unaware of that use, though. As far as PRODUCTION use, it was used only for 1970 with L-46 and NB-2. However, if it was so-used in SERVICE, then I suppose it's not as rare as it might seem. At least, a carburetor of that part number with a SERVICE date might not be so rare. With a date that would have been used in PRODUCTION, it's extremely rare.

[Patrick H.]

Re: 1970 Carburetor question

Patrick-----


It may be that the 7040507 was used as a SERVICE carburetor for other applications. I am unaware of that use, though. As far as PRODUCTION use, it was used only for 1970 with L-46 and NB-2. However, if it was so-used in SERVICE, then I suppose it's not as rare as it might seem. At least, a carburetor of that part number with a SERVICE date might not be so rare. With a date that would have been used in PRODUCTION, it's extremely rare.

Yup.

The "0" was added in front to designate some service carbs - but you probably knew that.

[Clem Z.]

Re: 1970 Carburetor question

according to the delco/rochester part manual the 7040207 is a non calif corvette carb and the 7040507 is a calif only corvette carb. i see no different internal parts

[Joe W.]

Re: 1970 Carburetor question

Gentlemen,
If you would please, tell me the reason for a service replacement?
Did Rochester have a problem with that particular model of carburetor
and or in general and the "service replacement" was used to either fix and
or replace the problem?

If Yes, were measures taken to improve this particular model - 07040507?

Patrick, you stated 07040507, I didn't remember seeing the first zero stamped
on the carburetor. Are you adding the zero because there is a Julian date
beneath the serial number, designating it as a service part?

Thank you.

Joe

[Jim T.]

Re: 1970 Carburetor question

Joe Weise you asked about service replacements. My 68 does not have the origianl QJet carb because it was replaced the first few years after leaving the factory.

I still have my 70's original QJet that could of been replaced due to the QJet's fuel bowl leaking into the engine.

While my 70 was still under factory warranty, the dealer removed it for inhouse repair.

Repair did not hold up, fed up with QJet fuel bowl drainage I put a 650 Holley spreadbore 6210 double pumper on my 70 and my 68 in 1974. Gaining instant starts after sitting overnight or two days are great with no drainage of fuel bowls into the engines.

[Dennis D.]

Re: 1970 Carburetor question

Patrick-----


It may be that the 7040507 was used as a SERVICE carburetor for other applications. I am unaware of that use, though. As far as PRODUCTION use, it was used only for 1970 with L-46 and NB-2. However, if it was so-used in SERVICE, then I suppose it's not as rare as it might seem. At least, a carburetor of that part number with a SERVICE date might not be so rare. With a date that would have been used in PRODUCTION, it's extremely rare.

I answered and posted these pics on another forum. Should have asked this a long time ago.Maybe someone can set the record straight.

I researched the advance tube on the 207 for a couple of years to duplicate, and in the process noticed some differences in the 207 and 507. Someone here was kind enough to send me that photo during my research, and did not get the number. Only that it was from a very correct L-46.
In the pics I believe the first photo is of a 507 and the second a 207. You'll notice the capped off tube extending out the side on the top photo. Not there on the lower photo.(my original 207)

My question is did the 507 being a L-46 california version, have a smog system? It appears from what I'm told that the 69 207 did, and that capped off tube should have a hose to the smog pump.