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I have an idiling issue on my 69 427 4bbl. Everything is fine when I first start and run the car. When I shut it down and say go into the store, I come out and restart it, it idles very low 500 RPM and vacillates. If I do not give it gas it will stall. This continues for a bit, once I have been able to run through the gears it clears up and resumes normal idle at 800RPM at the next light.
Any ideas what might be causing this and what to do about it?
I have an idiling issue on my 69 427 4bbl. Everything is fine when I first start and run the car. When I shut it down and say go into the store, I come out and restart it, it idles very low 500 RPM and vacillates. If I do not give it gas it will stall. This continues for a bit, once I have been able to run through the gears it clears up and resumes normal idle at 800RPM at the next light.
Any ideas what might be causing this and what to do about it?
Thanks
Hans
Instead of starting it the second time, remove the air cleaner and see if gasoline is dripping into the carburetor throat.
From: At my Bar drinking and wrenching in Lafayette Colorado
You have a commercially rebuilt, hacked carb that likely has a long list of problems. E-mail me for my paper about the commercial carbs to get an idea of all the things that will be wrong with that carb. And I assume you know that it's not a '68 carb or even a correct 4MV model-series carb... it's a 1980's vintage M4M truck carb.
Lars V8FastCars@msn.com
You have a commercially rebuilt, hacked carb that likely has a long list of problems. E-mail me for my paper about the commercial carbs to get an idea of all the things that will be wrong with that carb. And I assume you know that it's not a '68 carb or even a correct 4MV model-series carb... it's a 1980's vintage M4M truck carb.
Lars V8FastCars@msn.com
Hi Lars,
Thanks for the note.
I actually have hated this carb since it was installed. Always been an issue. I should not have taken the reccomendation on it.
I have the original Rochester that came with it. I need to have it rebuilt and someone knowledgeable to look it over. I was told at one point it was leaking around the base and warpped. I would certainly like to get the origial back on......
I actually have hated this carb since it was installed. Always been an issue. I should not have taken the reccomendation on it.
I have the original Rochester that came with it. I need to have it rebuilt and someone knowledgeable to look it over. I was told at one point it was leaking around the base and warpped. I would certainly like to get the origial back on......
From: At my Bar drinking and wrenching in Lafayette Colorado
One more thing: If you have the original 1969 intake, be aware that it requires the use of a special 3-piece gasket "set" between the carb and the intake. Failure to use the special gaskets, with the stainless steel middle gasket, will result in exhaust gas ingestion into the intake, vacuum leaks, and the bottom of the carb getting so hot it will boil the fuel right out of the carb and cause damage to the bottom of the carb.
Post some photos of the carb you believe to be the original carb. The '69 427 carbs are very good... And very rare... They sell for around $2K in rebuildable condition. I can tell you if the carb is correct and if it is a good candidate for rebuild. Post the carb number as well.
Lars
One more thing: If you have the original 1969 intake, be aware that it requires the use of a special 3-piece gasket "set" between the carb and the intake. Failure to use the special gaskets, with the stainless steel middle gasket, will result in exhaust gas ingestion into the intake, vacuum leaks, and the bottom of the carb getting so hot it will boil the fuel right out of the carb and cause damage to the bottom of the carb.
Post some photos of the carb you believe to be the original carb. The '69 427 carbs are very good... And very rare... They sell for around $2K in rebuildable condition. I can tell you if the carb is correct and if it is a good candidate for rebuild. Post the carb number as well.
Lars
Hi Lars,
Thanks for the response and effort. I will get some pics up on it tomorrow.
Here are the pics of the original carb. My vette was born in November 69 all other numbers are matching. The only thing I did not have was an alternator, but the kind folks here helped me with that. On the side, stamped into the body (not on a disc) is “7029215 EH, then below that “2979”. From what I can tell, this tells us its from the late 60’s (702), produced in 1969 (9), it’s a QJ 4 bbl meeting Federal standards (2), Chev division (1) and the 5 is an odd number indicating a manual xmission. 2979 means it was produced on the 297th day of 1969.
Other identifying numbers:
On one of the base ears: 37983
On the base in a circle: 7037600
Back near the secondaries in a circle: 7038524 and “GM” and “RP”.
From: At my Bar drinking and wrenching in Lafayette Colorado
Your 7029215 carb is a Q-Jet used on 1969 Chevy, Chevelle, Camaro and Corvette 396 and 427 engines with manual transmission. It was built on Friday October 24th,1969, which makes it unlikely that it was ever installed on a 1969 production car. It has been commercially rebuilt, so it is likely to have multiple problems, which is probably why it was removed from the car. If the carb still has it's original throttle plate and has not been hacked too badly, it can probably be repaired and brought back to serviceable condition. I did not see any photos of your intake manifold mounting flange configuration - are you using the correct 3-piece gasket set for the '69 intake?
Your 7029215 carb is a Q-Jet used on 1969 Chevy, Chevelle, Camaro and Corvette 396 and 427 engines with manual transmission. It was built on Friday October 24th,1969, which makes it unlikely that it was ever installed on a 1969 production car. It has been commercially rebuilt, so it is likely to have multiple problems, which is probably why it was removed from the car. If the carb still has it's original throttle plate and has not been hacked too badly, it can probably be repaired and brought back to serviceable condition. I did not see any photos of your intake manifold mounting flange configuration - are you using the correct 3-piece gasket set for the '69 intake?
Hi Lars
Thanks for the note
So if my car was manufactured in Nov of 1969 you believe this is not the original?
I will contact you via email to finish the discussion of that is ok.
I have for the past couple of years wanted to get the original #s matching Rochester QJet back on, from what I understand from the P/O it was the one it was born with.
Following the above discussion thread, I sent it along to Lars to see if he could save it. I have received it back last week but needed to get a Divorce Choke and a proper spark advance vacuum hose set up as the "truck carb" had an e-choke installed and the vacuum line was not correct for the 69. Just got those in so I will be installing it this week. Will post some picks of the install and how she runs later. For now, I am posting the process and Lars' findings (some screwy stuff!! Like a spring from a ballpoint pen....)
The elapsed time including UPS ground shipping to and from Virginia to Colorado was a mere 16 days the actual work by Lars only took 3 days the rest of the time was shipping....
One item of note for those seeking a Divorce Choke for a 69 427/390 or likely other carbs, I did manage to find it in a "kit" will all parts included (instead of having to buy it in pieces) at Carbs Unlimited https://www.carburetion.com/
First - Review of Initial Findings. I have your carb torn down and ready for ultrasonic hot tank cleanup. The following issues were noted:
Commercially rebuilt carb
Warped airhorn - airhorn gasket not seating/sealing
Fuel filter installed in carb - you are running 2 fuel filters in series, which will cause a high-rpm fuel starvation problem. I will omit the in-carb filter upon assembly and credit you for the filter not required
Badly misbalanced idle mixture settings
Incorrect secondary rods installed
Lock washers installed on airhorn hardware, damaging the casting. Lock washers were not used on 4MV carbs
Incorrect power piston spring installed - spring is from a ball-point penand has the power piston locked in the full-rich position at all times
High float setting - contributing to fuel leaks
Idle vent valve bent and altered to remain closed at all times - valve inoperable
Secondary throttle linkage altered to open secondaries over-center
Second - Cleaning and Initial Work All parts are in stock, and carb will go into assembly and setup operations once cleanup is complete. I'll keep you posted on progress. The carb has come out nice and clean from the ultrasonic hot tank process, but removal of the dirt and grime is revealing a bit of corrosion on all surfaces. I'm going to run this through the de-oxidation/de-rust process to get this looking a little better for you - this is a nice carb, and it would be a shame to not try to get it looking as good as possible.
I have been able to do a bit of work to the airhorn to get it to seal a little better against the warped float bowl. As long as the two pieces have the same amount of "twist" and "bow" to allow sealing of the gaskets, the carb will run just fine. I think I got it. We'll see how it performs in test.
Third - Complete and Ready to Ship - Final Findings, Fixes and Test Results
Your carb is ready to ship out via UPS.
The carb checked out really well after repairing some significant items and correcting some setup issues – see attached invoice for a listing of all issues found and corrected.
The tip-off to problems with the carb was the fact that the secondary throttle shaft had been removed by the previous builder and re-installed with aftermarket screws. The secondary throttle shaft was binding severely, and would jam in the wide-open position. It turns out that the builder had installed shaft bushings on the secondary side, which is a very odd thing to do - the secondary side should never need shaft bushings... Further, they had not reamed the bushings to size, so the secondary shaft was severely binding in the bushings. After I did the machine work to the bushings to make the shaft fit, it was obvious that the shaft was also bent, so I straightened the shaft. Once assembled, I attempted to align the throttle blades in the secondary throttle bores, but they would not align properly in the bores for a good seal. Testing the carb in its "best-aligned" condition confirmed that the carb had an inherent air leak through the secondary throttles at idle. This may be the "carb leaks" comment that you have received, and is probably what they improperly attempted to fix by installing shaft bushings. I replaced the throttle blades and obtained a much better seal - the carb showed a significant improvement during test, but still suffered from a fuel "dribble" on the secondary side at idle. This made setup and tuning impossible. After assuring good alignment of the replacement throttle blades, I did the Pontiac "trick" with the secondary airvalves to eliminate any low pressure region in the secondary venturi plenum, which also provides a much better secondary fuel enrichment "shot" when tipping into the secondaries. I removed your stock airvalves and fabricated a pair of airvalves to the Pontiac spec, so your original airvalves and throttle blades are being returned to you with the carb. This solved the secondary "leakage" problem, and the carb is running perfectly with an outstanding level of performance and throttle response.
In this configuration, I ran the carb through all modes of operation from cold-start, hot re-start, idle, and no-load cruise. I also tested for secondary operations and WOT transition. Idle is glass smooth, off-idle response is crisp, and mixtures are right where they should be.
Your carb running on the test engine: Running cold with choke closed and cracked open by the pulloff:
Cold fast idle set to about 1270:
Cold fast idle air/fuel mixture right on the desired number in the mid 11’s:
Running hot with choke wide open:
Hot idle speed set to about 850:
Hot idle air/fuel mixture right on the numbers at 14.7:1
View from the top showing the Pontiac-style airvalves used to correct the air leak problems on the secondary side:
69 427 4bbl Idling Issue
