I’ve had my quadrajet rebuilt with a kit from Cliff and it initially (drive home from the shop) seemed ok. I tried to drive it to work Friday and it ran very very rough, spitting and sputtering more the further I went. When warmed up, it is idling high at about 1100-1200. My mechanic suspects the choke is not working properly. Would an electric choke be a wise choice? I see kits are available. This is for my 70 350/350. Carb # is 7042902 with rebuild parts to make it as close to the correct 7040207 as possible.

 

You have a 4MV divorced choke carb - it cannot be converted to electric because the choke coil is not part of the carb. The 1975+ M4M carbs are integral choke carbs that can be converted to electric. If your engine is stock with the stock intake manifold, there is no reason that the stock divorced choke should not operate correctly if it is correctly adjusted and set up. You have a problem with the adjustment, setup, or rebuild - not a problem with needing an electric choke. You can replace your divorced choke coil with an electric coil mounted to the manifold, but I would strongly suggest you fix the actual problem before throwing conversion parts at it. Throwing conversion parts at it to compensate for a bad setup and rebuild is simply a really bad idea.

You stated that you "have had your quadrajet rebuilt," indicating that some "mechanic" did the work. There is a problem with the work he did. It needs to be properly repaired: If your "mechanic" was not qualified to correctly set up the choke and verify its proper operation, I can assure you that he was also not qualified to rebuild the carb. I'll bet good money that you have multiple issues with the "rebuild," none of which will be solved by installing an electric choke system on your intake manifold. In fact, it's likely to cause you additional problems.

Lars

 

In review of your initial post, I noticed that you have a 1972 carb (7042902) that you claim to have rebuilt to make it "as close to the 7040207 as possible." The 1970 and the 1972 carbs have completely different choke pulloff systems, with different secondary airvalve levers and linkages. If you have installed 1970 choke pulloff components on the 1972 carb, your choke pulloff system will be inoperable. What have you actually done to make the 1972 carb "as close to the 7040207 as possible?" The 1972 has completely different air bleeds in it. Have you drilled out or plugged air bleeds..? Making the 1972 carb like the 1970 would require very extensive modifications - this is not just a jetting change issue...

Lars

 

“make it as close to the correct 7040207 as possible” is per Cliff Ruggles who assembled the rebuild kit that was used in my 7042902. No drilling or other extensive mods were made.

 

Cliff is a good friend of mine, and I'm sure he gave you good parts. Based on the symptoms and problems you're having, the person using those parts and doing the "rebuild" did not set things up right for you.

Lars

 

As a note, I do have the capability to test that carb for you, identify any issues, correct the setup, and assure that it's running right. You can contact me via e-mail for info on this. Cliff and I work together on these carbs, and we use the same setup methods, specs, and techniques. Also, if you post or send me some photos of the as-installed configuration of the carb (especially the choke side) I may be able to identify superficial issues.
Lars

 

My guy has been doing auto mechanic work for many years so I’m fairly confident the kit was utilized correctly. It did seem to run very well on my initial 12 mile drive home. One thing he did question is the rod between the carb and the choke mount on the manifold. It does not look correct. Thanks.

 

I can see from your one photo that your carb is a badly hacked commercially rebuilt carb that has significant problems and issues - e-mail me for a paper that outlines just a few of the issues your carb will have. I can guarantee you that your builder did not correct all the issues and problems with that carb. A "rebuild kit" will not fix the issues that your commercially altered carb has. For example, your carb has a choke system on it that is neither from a '72 or a '70. It is a typical "mix-n-match" commercial carb that has parts and components on it from various random years and makes. Your choke system is from a 1969 carb. The rest of the carb will be pieced together from other mis-matched years as well.

Yes, you are correct: Your choke system is badly mangled and not set up right (in addition to not being the correct choke system for the carb). Your secondary airvalve rod, which also controls the choke pulloff system, is also bent, altered, and misadjusted. You are correct in your assessment that your choke system is not operating correctly. Your "mechanic" should have caught that and repaired it correctly - he obviously does not have any experience on Q-Jet carbs. You can also e-mail me for a paper on how to set up that choke the right way.

Let me know if I can assist.

Lars

 

Here are a few more shots of the carb.

 

Oh, goodness... that's a badly hacked "mix-n-match" carb pieced together and altered with a bunch of various years and makes. The throttle plate is not even a Chevy part, and has had a Chevy throttle lever screwed onto the primary shaft after the original non-Chevy lever was cut off. The secondary linkage has been so badly altered and mangled that the secondaries are inoperable. The choke system is 1969, and someone fabricated an inoperable choke rod from a clothes hanger, jamming your choke and making it inoperable. The airhorn appears to be from a '71. Not to sound like an ***, but that entire carb is a basket-case that doesn't have any serviceable parts on it. You need to use that carb to practice your hook-shots into your garage trash can. Your "mechanic" should have spotted this within the first 3 seconds of looking at your carb.

Here is what you need to do:

1. Fire your "mechanic." If he's a friend of yours, politely tell him that you'll drink beer with him, but not have him working on your car.
2. Remove and disassemble that carb. Retain all the parts you obtained from Cliff, the jets and the rods. Throw everything else away.
3. Locate a good, used, rebuildable, unmolested carb for your '70 and have it rebuilt by someone qualified, using the parts you got from Cliff. Again, you can e-mail me for info on how to locate a good carb.
4. Procure a correct, reproduction choke rod that can be correctly adjusted and set up to your new, rebuilt carb after having done the steps above.

Lars

 

Wow, I had no idea it was THAT bad. The guy I bought the car from struggled with the carb as well. Now perhaps we know why. Step 3 you mentioned will be the difficult part for me - I have no idea where to find a suitable carb as a replacement. I’m not overly hung up on originality when it comes to the carburetor, either. At this point, I want a reliable, smooth running, high performance Vette to drive. Whether that’s with a quadrajet or otherwise really makes little difference to me. I know Holley makes a spreadbore QJet unit. Maybe that’s a viable option. I also would entertain the notion of boxing this one up and sending it to you or Cliff and have the Cliff parts installed on a fresh QJet if you or Cliff have one or one could be located. I just don’t want the process to drag on. I want to be driving the car, not having it worked on. If you can offer any detail on the latter, including estimated expense and timeframe, please let me know. Thanks as always for reviewing my situation and offering up your expertise. Much appreciated.

 

Neither Cliff nor I want that carb - it cannot be salvaged. As much as I regret telling you, it's complete junk, and there is no cheap and easy solution to your situation. As noted multiple times in my posts above, I'll wait to hear from you via e-mail to see what you want to do and how I can best assist.

I can offer technical assistance and tech advice here on the Forum, and I always make every effort to do so. However, your issue is far beyond the scope of simple tech advice, and I cannot recruit business and services here on the Forum. Often, when cases like this pop up, I will offer to take on your case and post a comprehensive article about it for the benefit of the Forum subscribers, and this benefits everyone.

Since it does not appear that you are able to perform extensive repairs and modifications on your own, I would not suggest getting into doing custom mod work by swapping over to an aftermarket carb if you are relying on the "talents" of the "mechanic" you are currently using. That would certainly be a recipe for disaster. I'm even hesitant to offer assistance, since it appears you are relying on incompetent people for basic services such as simply hooking up a choke correctly or identifying a hacked and destroyed carb.

I realize you "don't want the process to drag on," but you have chosen to get involved with a half-century old antique automobile repair project. It will be costly and time-consuming. That's the nature of antique cars... You're going to find bad parts, incompetent people, and lots of cost. That's the fun of it...

Lars

 

@djs70vet I don't know if you're wanting to keep your car original, or just get it running so you can drive it.
If it were me, I'd get it running for now, then spend time/money finding an original carb, if originality is important.

There are a couple of Q-jets listed in the C3 parts for sale forum, one of them may be good enough to send to Lars for him to work his magic.
I found them with a quick search for "Rochester" in the title.

 

Thanks. I will take a look. I’m thinking similarly. I want to be able to get on the road ASAP.

 

For the benefit of those wanting some more info on the problems associated with these "mix-n-match" commercially built carbs that are pieced together with various different makes and years of parts, here are some things to look at and why these carbs cannot be made to work.

As noted, the OPs carb has been pieced together with parts from different carbs. The float bowl is stamped 7042902, which is a 1972 Vette 350 California carb. The OP owns a 1970 Vette, which should have a 7040207 (if it's the high performance engine option with manual trans). He has indicated that the '72 carb has been set up to mimic the '70 specs. The jetting on the stock 1972 carb is 74/45 (jet/rod), and the jetting on the '70 carb is 76/44. We might, then, assume that his '72 carb has been re-jetted to the 1970 76/44 specs.

We also know that the carb's throttle plate is not a 1972 or 1970 throttle plate since the throttle lever has been cut off and a 1972-style throttle lever has been screw-attached to the primary shaft. So the idle air bypass hole sizes in the throttle plate are not correct for the carb. But of greatest concern and intrigue is the airhorn on the carb (the "top" of the carb). The airhorn is not only the incorrect year (it's neither a 1972 nor a 1970), but it's also off of a Marine carb. Here is the airhorn on the carb:
If you look down the primary venturies, you can see the 2 airhorn attach screws (incorrect silver phillips screws in the bores). Just forward and outboard of those screws you can see air bleed holes. Those are the upper main air bleeds. Note that they have brass bushings pressed into them to "size" the bleeds. Chevy Q-Jets up through 1969 used these brass inserts to restrict air bleed into the main fuel discharge circuit. This is the reason that a 1969 and earlier Q-Jet can use main metering jets in the 66 - 71 size range. Starting in 1970, Rochester removed the brass upper main air bleed restrictors, and simply left the upper main air bleeds wide open at .120" diameter. To compensate, the primary jets were bumped up to sizes typically in the 74 - 77 size range. If a 1970-72 float bowl is used with an airhorn equipped with upper main air bleed restrictors, and if the 1970-72 bowl is set up with the jetting for that bowl (in this case with either 74 or 76 jets), the carb will run pig-rich at all conditions other than idle. It will run terrible.

But, wait... look at the photo again: Just forward and inboard of the main air bleeds you can see additional air bleed holes in the OPs airhorn. These holes are upper idle air bleed holes. Rochester had 2 different configurations for upper idle air bleeds: Early (pre-1968) Chevys and many of the Buick/Olds/Pontiac carbs had these air bleeds in the airhorn as shown in the photo above. After 1968, the Chevy air bleeds were moved to the float bowl, and were drilled from the idle fuel down channel into the venturi of the carb. Here is a 1972 airhorn that should be on the OPs carb. Notice the large .120" diameter main air bleeds and the lack of idle air bleeds:


If an airhorn with idle air bleeds is used on a float bowl that also has idle air bleeds, the carb will do nothing but suck air through the idle metering system, and the idle mixture cannot be controlled by the idle mixture screws. Since the carb will not idle properly, the idle speed will typically be cranked up to get the carb to idle on the main discharge circuit, resulting in some very poor idle quality with erratic and rough idle.

Look also at the OPs airhorn photo above and notice how the forward casting wall around the choke tower wraps around the bowl vent tube (which is installed backwards). Chevy car Q-Jets never used an airhorn configuration like this. The airhorn is off of a Marine carb. The 1972 Chevy car Q-Jet airhorn looks like this:


The 1970 car is similar, but has the hole in the forward surface for provision for the idle vent system:


So not only is the airhorn on the OPs carb not a 1972 or a 1970, it's not intended for a car carb. By having air bleeds incompatible with the float bowl being used, the carb can never be set up to idle or run right, no matter what you do with setup and jetting. It's possible that the commercial builder may have plugged or smashed the air bleeds in the float bowl (often done by commercial builders using a drift punch and a hammer to smash the air bleeds closed and destroy the bowl casting), but this just further hacks the carb, making it generally unusable.

Further mix-n-match issues on the OPs carb is, obviously, the choke system. Here is the system installed on the carb:
It is a 1969 choke system with a 1972 fast idle cam installed.

Here is a 1969 choke system with the correct fast idle cam for a '69 (Service Bulletin steel replacement cam):


This is a correct 1970 choke system:


...and here is the 1972 choke system that should be on the 1972 float bowl. Notice that the 1972 system requires a 1972 airhorn with the non-slotted lever in the secondary airvalve lever, further "giving away" that the OPs airhorn does not belong on the 1972 bowl:


So watch out for these commercially assembled carbs. Many of them are not only unserviceable, but actually cannot be rebuilt or saved without replacing the major components of the carb.

Lars

 

Cliff and I are working with Dan to come up with a good carb and solution to his problem... more to come - possibly in a new thread that will be linked from here. Stay tuned, and don't change that channel..!

Lars

 

Cliff had a very nice, used, original, unmolested, rebuildable 1969 Hi Perf Vette Q-Jet (7029207) available for Dan. As noted in my ramblings above, the '69 carbs were the last year for the small primary jet carbs with the main air bleed restrictors installed in the airhorn. These carbs provide very responsive fuel metering due to the small main air bleed sizes, and can be used with great success on a variety of performance engines with very easy tuning and adjustment. Dan is having this carb shipped to me directly from Cliff, and he will be shipping me his Mix-N-Match carb as well so I can salvage the parts from it that Dan procured from Cliff for the failed rebuild attempt. We're also going to make sure Dan is provided with a good, correct choke rod to replace the coat hanger travesty currently installed on his engine... This setup should get Dan's '70 L46 350/350 up and running the way it should. Continuation story link to follow next week once I receive the carbs from Cliff and Dan. Pretty cool when a cooperative plan like this comes together...

Lars

 

 

Lars,

You continue to go above and beyond for this community. I am sure that Dan will be amazed by the performance of his car once he gets the new carb installed.