Question: Rochester QJ set up

[fecraly62]

I am restoring a 1974 with 454 and auto trans. Previous owner changed the carb (a commercially rebuilt QJ from 1975) and it is causing me problems, Did the OEM carb (fed version) for this engine have a carb idle stop solenoid installed?
Main problem is difficult start when cold; won't idle/run unless I keep foot on accel pedal to hold revs up until warm/hot. Runs OK and restarts OK when hot. What needs to be adjusted/repaired? Thanks in advance for help. Jim

 

[tracksnblades1]

I am restoring a 1974 with 454 and auto trans. Previous owner changed the carb (a commercially rebuilt QJ from 1975) and it is causing me problems, Did the OEM carb (fed version) for this engine have a carb idle stop solenoid installed?
Main problem is difficult start when cold; won't idle/run unless I keep foot on accel pedal to hold revs up until warm/hot. Runs OK and restarts OK when hot. What needs to be adjusted/repaired? Thanks in advance for help. Jim

Fecraly 62, Does your 74 have air conditioning? Does your solenoid work? Do you have a service manual for Qjet carbs? Can you verify you have the correct cfm model for your 454?

 

[tracksnblades1]

I am restoring a 1974 with 454 and auto trans. Previous owner changed the carb (a commercially rebuilt QJ from 1975) and it is causing me problems, Did the OEM carb (fed version) for this engine have a carb idle stop solenoid installed?
Main problem is difficult start when cold; won't idle/run unless I keep foot on accel pedal to hold revs up until warm/hot. Runs OK and restarts OK when hot. What needs to be adjusted/repaired? Thanks in advance for help. Jim

Do you have the divorced choke style on your 74? The divorced type had a bi-metal coil some mechanics called the choke stove. This sat bolted on the exhaust heat riser that ran under the carburetor pad on the passenger side between the valve cover and intake manifold center. Other styles of chokes were positioned here as well. Try to determine if you have all of the choke rods, choke pull off rods, and secondary lock out rods. If you have all these rods properly installed and a working choke coil and choke pull off you can properly set up your choke/choke pull off. Your will need a service manual or a Qjet rebuild kits instructions for your model carb and is best with your application. The Qjet had a reputation that was usually created by a lack of understanding. This carb has excellent economy and satisfactory performance when properly set up. They also have excellent cold starting and warmup characteristics, however they will never remote start without fully depressing the accelerator pedal fully first to set the choke. If your handy with carbs, rebuild yours first. Check for the latest primary and secondary bowl plug updates. Bowl leaks are apparent with a warm engine that starts flooded after setting for prolong periods. A properly adjusted unloader rod can mask this problem.
The proper cfm Qjet for the 454 will run great. Never as strong as a Holley but you might be able to pass a few gas stations with the Qjet.

 

[lars]

If you have a non-original, commercially-rebuilt Q-Jet, you have at least a dozen problems that cannot be troubleshot via forum posts: Your carb needs a complete teardown, inspection, and replacement of all the damaged and altered parts that the commercial builder stuck you with. Drop me an e-mail request for my "Commercially Rebuilt Q-Jet Problems" paper for a complete listing of all the issues that are likely with your carb. You need more than an idle stop solenoid to fix your idle problems... You can also drop me a note for my Q-Jet Tuning Paper, which outlines all the correct choke adjustment and setup procedures for the carb. But you're going to have to fix all the crap done by the commercial builder first.

The proper cfm Qjet for the 454 will run great. Never as strong as a Holley.

I have dyno data that proves this differently - a propery set up Q-Jet will run identical to a properly set up Holley of the same size (750), and will, in fact, produce significantly more torque below 3500 rpm than the Holley. I'll be running yet another Q-Jet versus Holley dyno test for a customer in a couple of weeks, and I'll post the facts and data once again to prove that point...

Lars
V8FastCars@msn.com

 

[fecraly62]

Fecraly 62, Does your 74 have air conditioning? Does your solenoid work? Do you have a service manual for Qjet carbs? Can you verify you have the correct cfm model for your 454?

Car does not have A/C. Current carb (not the original) does not have solenoid. My inquiry was to see if the OEM carb had a solenoid. I believe the correct carb has ID 7044225. My intent is to find a correct OEM carb

 

[fecraly62]

If you have a non-original, commercially-rebuilt Q-Jet, you have at least a dozen problems that cannot be troubleshot via forum posts: Your carb needs a complete teardown, inspection, and replacement of all the damaged and altered parts that the commercial builder stuck you with. Drop me an e-mail request for my "Commercially Rebuilt Q-Jet Problems" paper for a complete listing of all the issues that are likely with your carb. You need more than an idle stop solenoid to fix your idle problems... You can also drop me a note for my Q-Jet Tuning Paper, which outlines all the correct choke adjustment and setup procedures for the carb. But you're going to have to fix all the crap done by the commercial builder first.


I have dyno data that proves this differently - a propery set up Q-Jet will run identical to a properly set up Holley of the same size (750), and will, in fact, produce significantly more torque below 3500 rpm than the Holley. I'll be running yet another Q-Jet versus Holley dyno test for a customer in a couple of weeks, and I'll post the facts and data once again to prove that point...

Lars
V8FastCars@msn.com

Thanks for the info. Current carb, and OEM manifold set up for divorced choke. Choke sets OK when press accel pedal for cold start; just won't keep running unless I keep accel pressed until it warms up. I already have a copy of your paper on commercial rebuild problems--very illuminating. I will contact you at above address for the QJ tuning paper you mentioned. Much thanks. Jim

 

[tracksnblades1]

Facraly 62, Sorry I lost focus of your question. The old oem part number for the 74 vette solenoid I believe you will find is GM part#19974117. The OEM carb numbers are 7044225 and 7044221 auto/ manual respectively. Looks like yours may be factory. Like mentioned above this carb must be properly set up for ideal cold starting performance. My intent is not to raise agruements but to merely help. On the divorced choke models the bimetal coil provides the tension to close the choke through properly adjusted rods and linkage. There was no way of increasing the tension like on other models. Make sure your coil is the correct one and in good condition. In your last post you indicated in cold start your choke sets and the engine starts. If it dies after it starts, check your choke pull off ajustment. We used to check this on the car, cold engine off, set choke, verify fast idle cam is staged, with a vaccum pump hooked to the pull off pot, check the air valve clearance against your model# and application. Verify also that your pull off vacuum pot is plumbed to the correct vacuum source. This was easier and more accurately mearsured with drill indexed bits rather than the measuring methods reccomended. This adjustment is critrical for proper cold warm up. If you know what a fat choke engine sounds like, you will know when the air valve clearance is to little. Most mechanics of the time liked this condition so they didn't have comebacks when the temperature really dropped. I didn't like this condition due to the wash down and sooting. I hope this helps. I can't stress the importance of verifying your carb has been calibrated and adjusted correctly, no voodoo here. Obtain a service manual for your carb so you have what the manufacturer warrantied, no BS. There has been a multitude of articles, writings and the sort published about these carbs. Ranging from excellent to BS. In closing I offer no defense on my comment of the Holleys perfromance. There are those still that believe these carbs are superior to FI also. Any carb can be modified to achieve almost ideal fuel curves and atomization that allows vaporization only to occur in the compression cylce. I have not read mister Lars Papers as refered to. I will. I will monitor his dyno tests as available. If convinced I may concur and reject the findings of the greats like Smokey, Barry Grant, NASCAR and the factory big three engineers who chose the Holley on their max efforts. AGE QUOD AGIS Do what you do, Well. Only the Best

 

[lars]

A propery set up Q-Jet will run identical to a properly set up Holley of the same size (750), and will, in fact, produce significantly more torque below 3500 rpm than the Holley. I'll be running yet another Q-Jet versus Holley dyno test for a customer in a couple of weeks, and I'll post the facts and data once again to prove that point...

Lars
V8FastCars@msn.com

Here's the engine almost ready for transfer to the dyno for the Q-Jet/Holley test run. I'll be doing the Q-Jet setup and test data first, and will then transfer to the Holley to get the Holley at exactly the same A/F ratio for a direct comparison test. This was the first start-up of the new engine: The distributor was dropped in at 36 degress total timing, the carb was primed, and the start button was hit. All the numbers are looking very nice, so it should be a good dyno pull for a mild street engine for a 4-speed car. Trying to get the 23rd lined up for the dyno pull... I've been swapping between the Q-Jet and the Holley on the run stand, and I can't tell any difference in throttle response or mixtures between the two carbs right now - this 26-second video has the Q-Jet running:

'76 Firebird Motor - YouTube

As you can see, a correctly set up Q-Jet will fire and run very nicely, even with no choke. The cam in this engine is a little lumpy, but the engine actually idles at 800 rpm at 12 inches of vacuum and maintains a perfect 14.5:1 idle mixture with the 1976 "smogger" carb. IFR's have been opened up a tad, jetting has been corrected, and the carb has been set up exactly as outlined in my "Quickie Performance Setup" section of my Q-Jet paper.

I will monitor his dyno tests as available. If convinced I may concur and reject the findings of the greats like Smokey, Barry Grant, NASCAR and the factory big three engineers who chose the Holley on their max efforts.

I know Barry Grant quite well - he provided support and technical sponsorship of my "Tuning for Beer World Tour" seminar series, and I featured his products extensively. The use of specific carb products in sanctioned class racing is mandated by the sanctioning body: Smokey couldn't run a Q-Jet on a NASCAR if he wanted to. GM uses non-GM carbs, such as Holleys, for marketing purposes, as pointed out in several of the interviews I have done with GM engineering and marketing personnel over the last 30 years. Cliff Ruggles and I have both achieved the same dyno results from extensive testing of these carbs: With the exception of the Edelbrock "Performer" carbs (obsolete Carter AFBs), any modern carb of the same cfm flow capability can be set up to perform and run virtually identical to any other carb. So run the carb you are most proficient at tuning and setting up. Since parts for Q-Jets are getting scarce, the default performance carbs are quickly becoming the Holley, ProForm, QuickFuel and BGs (if BG can get their production line up and running with a reasonable level of quality again).

 

[lars]

Be sure to check out the new post, "400 Dyno Data - Holley & Q-Jet Comparison".

Lars

 

[LanceB]

"As you can see, a correctly set up Q-Jet will fire and run very nicely, even with no choke."

Funny you mention that. I haven't had a choke on my 81 qjet in years and it runs pretty good. I even drive it in the winter too if the roads are clean. Funny story on how that choke got removed. We also tried the same set up on my brothers 77 and it never ran right. He threw in the towel and got a Holley.

 

[White75]

When are you going to have another Tuning for Beer tour? I can have a few cases of Shiner Bock for you if you come to the Houston area.

Here's the engine almost ready for transfer to the dyno for the Q-Jet/Holley test run. I'll be doing the Q-Jet setup and test data first, and will then transfer to the Holley to get the Holley at exactly the same A/F ratio for a direct comparison test. This was the first start-up of the new engine: The distributor was dropped in at 36 degress total timing, the carb was primed, and the start button was hit. All the numbers are looking very nice, so it should be a good dyno pull for a mild street engine for a 4-speed car. Trying to get the 23rd lined up for the dyno pull... I've been swapping between the Q-Jet and the Holley on the run stand, and I can't tell any difference in throttle response or mixtures between the two carbs right now - this 26-second video has the Q-Jet running:

'76 Firebird Motor - YouTube

As you can see, a correctly set up Q-Jet will fire and run very nicely, even with no choke. The cam in this engine is a little lumpy, but the engine actually idles at 800 rpm at 12 inches of vacuum and maintains a perfect 14.5:1 idle mixture with the 1976 "smogger" carb. IFR's have been opened up a tad, jetting has been corrected, and the carb has been set up exactly as outlined in my "Quickie Performance Setup" section of my Q-Jet paper.


I know Barry Grant quite well - he provided support and technical sponsorship of my "Tuning for Beer World Tour" seminar series, and I featured his products extensively. The use of specific carb products in sanctioned class racing is mandated by the sanctioning body: Smokey couldn't run a Q-Jet on a NASCAR if he wanted to. GM uses non-GM carbs, such as Holleys, for marketing purposes, as pointed out in several of the interviews I have done with GM engineering and marketing personnel over the last 30 years. Cliff Ruggles and I have both achieved the same dyno results from extensive testing of these carbs: With the exception of the Edelbrock "Performer" carbs (obsolete Carter AFBs), any modern carb of the same cfm flow capability can be set up to perform and run virtually identical to any other carb. So run the carb you are most proficient at tuning and setting up. Since parts for Q-Jets are getting scarce, the default performance carbs are quickly becoming the Holley, ProForm, QuickFuel and BGs (if BG can get their production line up and running with a reasonable level of quality again).

 

[lars]

When are you going to have another Tuning for Beer tour? I can have a few cases of Shiner Bock for you if you come to the Houston area.

There's been a lot of interest in putting together a new series of Tuning for Beer Seminars, so I'm considering it. I've had some medical issues that have prevented me from pursuing this, but I'm healing up now, and may be able to do a few tours again soon. If it comes together, I'll be sure to let everyone know so we can select some locations: We haven't done one in the Houston area yet, so that would certainly be a prime candidate.

Lars

 

[White75]

Glad you're on the mend. Hope you decide to do it and do one in the Houston area. I'm sure between all the different forums, you'll get a lot of takers from the area Count me in for 2 vettes
Hope to see you soon!!!

There's been a lot of interest in putting together a new series of Tuning for Beer Seminars, so I'm considering it. I've had some medical issues that have prevented me from pursuing this, but I'm healing up now, and may be able to do a few tours again soon. If it comes together, I'll be sure to let everyone know so we can select some locations: We haven't done one in the Houston area yet, so that would certainly be a prime candidate.

Lars