When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
From the number on the carb (7042156). Note that rebuild kits can and do cover a wide range of different carb numbers to minimize the number of different kits that need to be stocked. Most will have multiple sets of gaskets or extra parts to allow the kit to cover multiple applications. Be sure to carefully match the new parts and gaskets with the old ones from your carb and don't worry that there are parts in the kit that won't be used. You should also get a new float and filter, which are not included in the kit. RockAuto has all these. Standard Motor Products 503A HyGrade kit is under $13. The float is $7 and the filter is $1.50.
The original CSM is one volume (the Fisher Body Manual is a separate book). Do NOT get a reprint, get an original. The reprints and PDF versions are scans of an original, and details in small drawings (like the wiring diagram) get lost when they get copied. I think I paid about $15 for a 72 CSM on ebay earlier this year.
Interestingly, RA shows that the only application for that carb is 1972 Oldsmobile 350. That's encouraging. It does have the boss for holding the solenoid bracket, also a good sign - ASSUMING the delivered carb matches the photo.
I got the manual and I've got most of the vacuum lines figured out, but I don't know what the two outlets at the top in the back of the carburetor do. There's one larger and one smaller. I'm assuming the smaller one is supposed to be for the line that goes to that switch. What's the larger one for?
The one thing (I think) is nice about a Rochester carburetor is the ease with which it can be worked on. You're going to do just fine on the rebuild. The CSM does contain what you need to rebuild the carburetor as Joe indicated. I might make a suggestion. There are many Rochester carburetor rebuild videos available on YouTube - spend a couple hours reviewing several of the available videos and you'll increase your confidence by watching someone performing a rebuild. Best of luck.
And THERE'S your answer as to why you need a factory Chassis Service Manual...
The DVCS (Distributor Vacuum Control Switch) was often taken out of the equation by many vehicle owners over the years. In other words, they bypassed the switch entirely. Additionally, the term 'modulator', refers to the transmission modulator which you'll find more information in the transmission section of the CSM. When the DVCS is taken out of the equation, many ported the modulator vacuum line into a manifold vacuum on the front of the intake manifold and routed the distributor vacuum advance into the front port of the carburetor. Since the DVCS was removed from the equation, there was no need for the wire to the DVCS and the wire simply cut & taped to the side. Additionally, the choke is sometimes bypassed as well on vehicles - eliminating the need for the stove choke pipe in the manifold cross-over. Folks in Southern climates (in particular) found limited need for the choke and simply bypassed it and blocked it off at the rear of the carburetor. Hope these tid-bits help a bit.
The other is connected to the hard line that supplies air to the choke stove in the intake crossover.
Do you mean the line that goes to the actuator that closes the door in the air horn?
Originally Posted by Vintage Chief
The one thing (I think) is nice about a Rochester carburetor is the ease with which it can be worked on. You're going to do just fine on the rebuild. The CSM does contain what you need to rebuild the carburetor as Joe indicated. I might make a suggestion. There are many Rochester carburetor rebuild videos available on YouTube - spend a couple hours reviewing several of the available videos and you'll increase your confidence by watching someone performing a rebuild. Best of luck.
I bought the reman carb from Rock Auto, though I may rebuild the old one in the future.
Originally Posted by Vintage Chief
The DVCS (Distributor Vacuum Control Switch) was often taken out of the equation by many vehicle owners over the years. In other words, they bypassed the switch entirely. Additionally, the term 'modulator', refers to the transmission modulator which you'll find more information in the transmission section of the CSM. When the DVCS is taken out of the equation, many ported the modulator vacuum line into a manifold vacuum on the front of the intake manifold and routed the distributor vacuum advance into the front port of the carburetor. Since the DVCS was removed from the equation, there was no need for the wire to the DVCS and the wire simply cut & taped to the side. Additionally, the choke is sometimes bypassed as well on vehicles - eliminating the need for the stove choke pipe in the manifold cross-over. Folks in Southern climates (in particular) found limited need for the choke and simply bypassed it and blocked it off at the rear of the carburetor. Hope these tid-bits help a bit.
The DVCS has been bypassed and the choke may have been bypassed, or may simply have stopped working. Not having a choke was fine when the weather was in the 80s, but it's been dipping down into the 40s or even 30s over the last couple of months, and that has made the car take a very long time to start. The only replacements for this vacuum switch I see are selling for $300 on eBay. Do I need the switch with the solenoid, or will the generic ones without it I've been seeing work?
The DVCS has been bypassed and the choke may have been bypassed, or may simply have stopped working. Not having a choke was fine when the weather was in the 80s, but it's been dipping down into the 40s or even 30s over the last couple of months, and that has made the car take a very long time to start. The only replacements for this vacuum switch I see are selling for $300 on eBay. Do I need the switch with the solenoid, or will the generic ones without it I've been seeing work?
Couple things:
(1) You might increase your understanding of how the hot-air choke assembly works on the Rochester carburetor - it can be difficult to understand from a drawing. I honestly don't see the stove choke tube assembly listed in the 2GC carburetor section of my 1971 CSM. However, there is a diagram of the stove choke assembly listed in the Model 4MC section (which you should look for in your own CSM). But, have a look at this video to gain an understanding of the stove choke assembly:
(2) ..."the car takes a very long time to start." This is a relative statement, but it should fire right up. You might need to 'feather' the accelerator pedal a little longer w/o a choke, but the car should fire right up. Which leads me to suspect you should look further into your tune-up specifications. I currently have bypassed both my choke and my DVCS and my car starts within one second when turning the IGN SW - and, that is in 35F-40F weather (currently). Critical these cars are tuned correctly - Distributor Dwell Angle>Timing>Carburetor is the critical sequence. Make certain you have good breaker (contact) points in the distributor, the dwell is set correctly and the timing adjusted as per CSM specifications. I 'suspect' you'll find with the proper adjustment of Dwell Angle & Timing alone, you'll achieve a much faster start time. There are other items (spark plugs, spark plug wires, spark plug gap, coil wire, etc.) but for now, let's make a simple assumption those items are OK; yet, each of those items can influence starting time, as well.
(3) The specifics regarding function of the DVCS are contained in the ENGINE COOLING section of the CSM as Joe has already pointed out from his image of the carburetor he supplied. Give it a read. As I indicated many bypass the DVCS and you stated your's is bypassed. Do you need it - no. Do you want it? That's entirely up to you. Bear in mind, many who own these vehicles are restoring them to OEM condition; albeit, they don't even make the DVCS any longer. Does yours (if installed) even work? Since it's an outdated device, finding an original is going to cost large dineros - $300. Also, anyone who has ever put a 350 cid in a high-performance application (with MANY modifications to cam, lifters, heads, carburetor, etc., etc.) will have never used the DVCS. Again, read what it does and make a decision if you even want it. Mine is bypassed entirely and the intake manifold orifice plugged with a correct fitting brass inlet plug you can purchase at any hardware store.
Do you mean the line that goes to the actuator that closes the door in the air horn?
The "door" on the air horn is the choke plate. The round "actuator" is the housing for the choke coil. The choke coil is a bimetallic spring that expands when heated. Air is drawn from that tube on the back of the air horn, passes through a tube in the exhaust crossover under the carb, and is sucked into that round choke housing to heat the coil. That air then is pulled into the engine with manifold vacuum, which is why the tube on the back of the air horn draws in filtered air and not just dirty outside air. The U-shaped heating tube under the carb has two ports. One port has a tube that connects to the choke housing. The other port is the tube that connects to the air horn.
This is the door in the air horn I was talking about: the one that lets hot air in from the pipe coming off of the exhaust manifold. I read in the manual that it's supposed to be powered by manifold vacuum, but it's not connected currently. I found the hose that's supposed to go to it and it's blocked off with a screw.
...aaaand I found out why I didn't know what connected to the back. That tube is lost to the ages. Do they make repros of these or do I have to buy a used one?
Last edited by Tiberian Fiend; January 20th, 2019 at 06:05 AM.
Inlinetube.com website is somewhat finicky to use primarily because they have recently upgraded their website and not all items listed in the catalogs are listed in their search engine when you try to find items. None-the-less, here's what I do. At the main Inlinetube.com website, click on the Catalogs, look for the Oldsmobile catalog, the catalog will open and you can browse the catalog. HTH
This is the door in the air horn I was talking about: the one that lets hot air in from the pipe coming off of the exhaust manifold. I read in the manual that it's supposed to be powered by manifold vacuum, but it's not connected currently. I found the hose that's supposed to go to it and it's blocked off with a screw.
...aaaand I found out why I didn't know what connected to the back. That tube is lost to the ages. Do they make repros of these or do I have to buy a used one?
The metal tube for the 2BBL carb is reproduced. OPGI sells them. I'm sure others do also.
The hot air flapper is part of the thermostatic air cleaner. The hose from the actuator on the snorkel goes to a temp sensor on the bottom of the air cleaner. A second hose runs from that sensor to any manifold vacuum source. The system is described in Chapter 6N in the Chassis Service Manual.
The operation was a success, but the longer I drove my car on my test drive, the slower and slower the idle got. Eventually, it got so bad I had to hold the gas down at stoplights just to keep it from stalling. It was leaking fuel from around the gaskets right after I first installed it, then stopped. When I got it back home, it almost wouldn't start. I checked it again and it was leaking fuel from around the gaskets and vaporized fuel was coming up from the bowl. Do I just need to tighten some of the screws holding the carb together, or might there be something else wrong with it? It's too dark for me to go out and fiddle with it right now.
Stopped the gas leaks and turned the idle up, but it still idles slowly in spite of turning the adjustment screws almost all the way out, and the engine slows close to the point of stalling when the accelerator is first pressed. Is this a vacuum leak issue?
Stopped the gas leaks and turned the idle up, but it still idles slowly in spite of turning the adjustment screws almost all the way out, and the engine slows close to the point of stalling when the accelerator is first pressed. Is this a vacuum leak issue?
Glad you found the fuel leaks. Where was the fuel leaking from?
I am 'assuming' you have not rebuilt this original carb which is the 2bbl carb on your car - this is NOT the reman carb - is that correct?
Regarding turning the fuel mixture adjustment screws all the way out and engine remains running slow to stalling point w/ accelerator pressed.
The last item to adjust during a tune-up or whenever performing adjustments are the (1) slow idle and (2) fuel/air mixture. Let's assume (which you haven't stated thus far) the choke is either working or not working at this point (there is a fast idle [cam] adjustment on 4bbl Quad carbs I'm assuming on 2bbl carbs, as well). But, let's move away from the choke for a minute and look at the proper way to tune the performance of your engine.
You only need to read this from your CSM, but I'll state it. The carburetor is the last item you want to adjust after FIRST having established the proper timing of your engine.
NOTE: Set your fuel/air mixtures screws BACK to where they were - they're doing you no good all the way out. In case you forgot where they were, I believe they EACH should be ~3.5-4.0 turns out (at least for a good starting point).
(1) I believe you have a points/condenser distributor (not HEI) - correct? I'm assuming it is points/condenser distributor. Firstly, in order to properly tune your engine it is essential the dwell angle is established correctly. If you don't have a dwell angle meter (and you expect to own this vehicle for any length of time) I strongly suggest you own/borrow a timing light and make the proper adjustments using a timing light. Or, take it to a mechanic who owns one. Your contact points should be new (or in a relatively good clean state) - no pitting, etc. Establish your dwell angle to (I believe it's) 30* degrees @ 1100 RPM (look in the CSM or it is stated on the radiator shroud tune-up tag) - follow the directions. This is done w/ the #1 cylinder @ TDC. Repeat - #1 cylinder @ TDC.
(2) Adjust your timing. For a standard sbo, this should be ~12* degrees BTDC @ 1100RPM. Again, look in your CSM or the radiator cowl tag.
(3) Adjust your carburetor slow idle screw (which I believe should be under load) - e.g. w/ the engine in gear. Put some blocks on the front wheels and set the emergency brake firmly. Set your slow idle to ~1000RPM.
The point here is this. It's paramount you follow the correct procedure: Dwell>Timing>Carburetor - in that order. Then decide if it's still stalling.
ON EDIT: I read backwards in this thread & I guess you installed the CORRECT reman 2bbl carb you purchased from RA. If that's the case, the fuel/air mixture screws should have been adjusted nearly spot-on when you received the carb. Set those screws back to their original position then do a proper tune-up then see how it idles. I forgot to mention, but this is clearly stated in the CSM - remove and plug the vacuum advance hose when performing/setting dwell & timing.
Last edited by Vintage Chief; February 1st, 2019 at 03:05 PM.
January 2nd, 2019, 02:55 PM
