cquisuila Posted December 17, 2021 Share Posted December 17, 2021 (edited) hello please how first to adjust a carburetor Rochester Quadrajet 4MC number 7026240 ? my enginE is a 425 the choke is located on the passenger side connected to the carburetor and draws hot air from the intake idle screws ? SEE PICTUREs THANK you for your help ! Edited June 14 by cquisuila (see edit history) Link to comment Share on other sites More sharing options...
plymouthcranbrook Posted December 17, 2021 Share Posted December 17, 2021 There are several vids on Youtube showing how to make adjustments on a Quadrajet. I was going to post a link but the IPad won’t let me. Just use search when you get there and you should find it without any problem. Link to comment Share on other sites More sharing options...
joe_padavano Posted December 17, 2021 Share Posted December 17, 2021 What "adjustment" are you asking about? The photo you posted shows the air horn removed from the carb. There are specific adjustments for the float level, choke vacuum break, secondary air valve wrap spring, and many other parts of this carb. These adjustments must be made while the carb is apart for rebuilding. Most rebuild kits come with instructions that list those adjustment specs and show you how to make the adjustments. Of course, the best option is to get the factory service manual for your car and follow the instructions printed in it. The idle mixture screws, fast idle speed, and curb idle speed are adjusted once the carb is back together and on the engine. At that point, ignition timing also effects carb adjustment, so it is even more important to follow the factory instructions and not the "Certified YouTube" mechanic. Link to comment Share on other sites More sharing options...
Frank DuVal Posted December 18, 2021 Share Posted December 18, 2021 The arrows point to idle mixture screws. If the car was running, I would say after the engine is warmed up to turn one screw CCW a half turn and see if it runs better. Then turn it CW until the RPM drops about 50 (slight drop in speed) back it out slightly and leave it there. Repeat for the other screw. This assumes everything else is in good tune. If turning these screws makes none or just slight difference, then you probably have an intake manifold leak or internal carburetor issues. Now that the carburetor is apart, follow directions in carburetor kit or shop manual, as Joe says. Awaiting others telling me I'm nuts.🤣 1 Link to comment Share on other sites More sharing options...
cquisuila Posted December 20, 2021 Author Share Posted December 20, 2021 ok for this information !! thank you !!!🙂 Link to comment Share on other sites More sharing options...
cquisuila Posted January 4, 2022 Author Share Posted January 4, 2022 I noticed when I was braking the car had a tendency to stall....:( Link to comment Share on other sites More sharing options...
joe_padavano Posted January 4, 2022 Share Posted January 4, 2022 1 hour ago, cquisuila said: I noticed when I was braking the car had a tendency to stall....:( That would imply a leak in the brake booster. The easy way to check this is to temporarily disconnect the vacuum hose to the booster and plug the port on the engine that feeds it. If you drive the car like this, be aware that you will not have power brakes, only unassisted braking. If the engine still stalls, it's not the booster. 2 Link to comment Share on other sites More sharing options...
cquisuila Posted January 4, 2022 Author Share Posted January 4, 2022 ok joe i will verify this point !! thanks Link to comment Share on other sites More sharing options...
cquisuila Posted January 24, 2022 Author Share Posted January 24, 2022 (edited) Unfortunately when i disconnect the booster from the port on the engine, the problem is always here :(. There is a problem with the gear box ? vaccum line ? PCV VALVE testing ? Other ? information : when i push gas pedal on P or N position the motor doesn't stall the stalling is on D or R position I HOPE that you can help me... philippe Edited January 24, 2022 by cquisuila (see edit history) Link to comment Share on other sites More sharing options...
Oldtech Posted January 25, 2022 Share Posted January 25, 2022 Problem sounds like carb but Do you know what transmission you have? Some of the GM's can get a torque converter clutch lockup and will stall the motor when you put it in D. Does the car lurch ahead when you put it in Drive? Link to comment Share on other sites More sharing options...
cquisuila Posted January 25, 2022 Author Share Posted January 25, 2022 my gear is super turbine 400 model BT > 3-element hydraulic torque converter and a compound planetary gear set > 3 multiple-disc clutches : 1 way clutch or sprag, and 2 bands provide the friction elemnts required to obtain the desired function of the compound planetary gera set > my problem is when i push the brake pedal when i am in R or D position (and the problem is the same if the vacuum power system is disconnected) Link to comment Share on other sites More sharing options...
carbking Posted January 25, 2022 Share Posted January 25, 2022 No offense meant, but did you plug the vacuum line from the carburetor after disconnecting from the booster? Otherwise, it would be a vacuum leak. Jon. Link to comment Share on other sites More sharing options...
cquisuila Posted January 25, 2022 Author Share Posted January 25, 2022 (edited) yes i make it I can screw this idle screw a little more ?! Edited January 25, 2022 by cquisuila (see edit history) Link to comment Share on other sites More sharing options...
Oldtech Posted January 25, 2022 Share Posted January 25, 2022 Ok, no lockup then. Yes, try turning up idle sped a little. If it will idle at all IN DRIVE (make sure wheels are blocked) adjust the idle mixture screws - the 2 in the front for the smoothest running. best will be with a warm engine and turn out until no difference is noticed, then turn in until change is JUST noticeable. You will be pretty close. If it still stalls you have other problems. Such as a vacuum leak or carb rebuild. Link to comment Share on other sites More sharing options...
cquisuila Posted January 25, 2022 Author Share Posted January 25, 2022 2 hours ago, Oldtech said: Ok, no lockup then. euh....what's a lockup please ? Link to comment Share on other sites More sharing options...
Oldtech Posted January 26, 2022 Share Posted January 26, 2022 Lockup torque converters are used on cars starting late 70's? and it is possible for the clutches to fail to release causing stalling. Yours won't have that. I have had people insist that the engine was stalling when the transmission lockup was the problem. Link to comment Share on other sites More sharing options...
cquisuila Posted January 26, 2022 Author Share Posted January 26, 2022 4 hours ago, Oldtech said: Lockup torque converters are used on cars starting late 70's? and it is possible for the clutches to fail to release causing stalling. Yours won't have that. I have had people insist that the engine was stalling when the transmission lockup was the problem. Thank you for this precision !! Link to comment Share on other sites More sharing options...
cquisuila Posted July 6, 2023 Author Share Posted July 6, 2023 (edited) so the engine no longer stalls !!😃 it was my booster: it was all rusty inside and no longer had its effect !!! -on my carburetor rochester, normally the chock valve is closed when engine is cold. And the chock valve is opened when engine is hot. I have the feel that mine does not open until very late... fast idle cam is efficient and bend choke rod is efficient perhaps a bad setting... What do you think please ?😉 Philippe Edited July 17, 2023 by cquisuila (see edit history) Link to comment Share on other sites More sharing options...
EmTee Posted July 13, 2023 Share Posted July 13, 2023 There should be a vacuum line running from the back of the carburetor to the vacuum modulator on the right side of the transmission. If that line is not connected the transmission will shift late and hard. Link to comment Share on other sites More sharing options...
cquisuila Posted July 14, 2023 Author Share Posted July 14, 2023 18 hours ago, EmTee said: There should be a vacuum line running from the back of the carburetor to the vacuum modulator on the right side of the transmission. If that line is not connected the transmission will shift late and hard. Yes this is right and connected🙂 1 Link to comment Share on other sites More sharing options...
cquisuila Posted May 27 Author Share Posted May 27 here the complete notice to my carburetor rochester 4MC https://www.teambuick.com/reference/library/66_chassis/files/64-e.php Link to comment Share on other sites More sharing options...
cquisuila Posted June 14 Author Share Posted June 14 (edited) hello help for the experiment people please ! I need an explanation on how my carburetor works here the picture ! in blue the vaacum break with the adjusting screw in black the choke rod, choke shaft and lever in yellow the air valve lockout lever Questions : 1 - on vaacum break my adjusting screw screws in well but the screw support goes down on its own> is this normal? Isn't there anything broken above? when you screw, it doesn't works with the pin underneath (it does not move forward) DIAPHRAGM ? 2 - how it works the air valve lockout lever ? WHEN the choke rod is upstairs, the air valve lever must be positioned well above the choke rod ? What is the role of the air valvle lockout lever ? i think that the secondary baffle plates are open when it asks more power but what is the connection and position with the choke rod ? Thank you Philippe Edited June 17 by cquisuila (see edit history) Link to comment Share on other sites More sharing options...
carbking Posted June 14 Share Posted June 14 The purpose of the air valve lockout lever is to "lock out" or make non-functional the air valve UNTIL the engine is at normal operating temperature. When the choke butterfly is closed or partially open, the air valve lockout prevents the air valve from opening. The air valve lockout is attached to the choke linkage. When the choke butterfly is completely vertical (completely open), the air valve lockout will retract, allowing the air valve to open. Jon 1 Link to comment Share on other sites More sharing options...
EmTee Posted June 14 Share Posted June 14 The vacuum diaphragm ("choke pull-off") partially opens the choke valve once the car starts. The choke thermostat (bi-metal coil) will then open the choke gradually as the engine warms up until the choke is fully open. At that point, the secondary air valve lockout should allow the secondary air valve to open when the mechanical throttle opens the secondary throttle plates. If the secondary air valve is allowed to open too soon (before the engine is warm) the engine will stumble due to an overly lean condition. 1 Link to comment Share on other sites More sharing options...
cquisuila Posted June 17 Author Share Posted June 17 (edited) OK the retaining clip is interior and put after the shock shaft lever SO that the lever for secondary valve is on top of lever choke rod and can't go out... AS THE PICTURE Edited June 18 by cquisuila (see edit history) Link to comment Share on other sites More sharing options...
cquisuila Posted June 17 Author Share Posted June 17 and for the 1 point ? 1 - on vaacum break my adjusting screw screws in well but the screw support goes down on its own> is this normal? Isn't there anything broken above? when you screw, it doesn't works with the pin underneath (it does not move forward) DIAPHRAGM ? Link to comment Share on other sites More sharing options...
EmTee Posted June 19 Share Posted June 19 On 6/17/2024 at 5:56 AM, cquisuila said: the retaining clip is interior and put after the shock shaft lever SO that the lever for secondary valve is on top of lever choke rod and can't go out... I don't understand your question, but I had replaced the accelerator plunger in my Quadrajet last week, so I took these pictures which may be helpful to you. Link to comment Share on other sites More sharing options...
cquisuila Posted June 19 Author Share Posted June 19 It is the clip on the chose rod Link to comment Share on other sites More sharing options...
EmTee Posted June 20 Share Posted June 20 Are you missing the 'hairpin' clip? 1 Link to comment Share on other sites More sharing options...
cquisuila Posted June 20 Author Share Posted June 20 (edited) 5 hours ago, EmTee said: Are you missing the 'hairpin' clip? Yes ! I ordered a 0,078 inch clip Edited June 20 by cquisuila (see edit history) 1 Link to comment Share on other sites More sharing options...
EmTee Posted June 20 Share Posted June 20 Here's a close-up picture of the one on my Q-jet. Link to comment Share on other sites More sharing options...
cquisuila Posted June 20 Author Share Posted June 20 my clip is different of your clip but it makes the job ! 1 Link to comment Share on other sites More sharing options...
cquisuila Posted September 16 Author Share Posted September 16 hello - clip is good now and the rod is ok - now my carburetor seems to working cold engine : choke valve closed>>>>>>>>>>>> ok ? cold engine< before to start engine, i have to push gas pedal once and the fast idle cam returns to its initial position as picture : then I have to wait a little before I can ride... I THINK TO find the right setting of the CHOKE SYSTEM Link to comment Share on other sites More sharing options...
Oldtech Posted September 16 Share Posted September 16 Yes, the standard procedure with a cold engine is to depress the gas pedal once which sets the choke. then start the car and it will idle too fast. blip the gas pedal once and it should slow downto something reasonable. Up here in the cold north where a choke is important, in the 70's, the carb companies relied too much on the choke for mixture management. we all got pretty good at setting / modifying things to work. 2 Link to comment Share on other sites More sharing options...
carbking Posted September 16 Share Posted September 16 Not that it matters, as both clips will work, but both are incorrect for the Rochester. EmTee's clip is normally referred to as a "spring clip". Cquisuila's clip is a "C-clip"; Holley used a lot of these. Both are easier to use than the Rochester, as the Rochester clip was a piece of flat metal with a slot. Once the groove of the rod was in the slot, a pair of needle nose pliers was used to crimp the end of the slot, preventing the clip from falling off. Jon 2 Link to comment Share on other sites More sharing options...
EmTee Posted September 17 Share Posted September 17 20 hours ago, carbking said: ...the Rochester clip was a piece of flat metal with a slot. Ah, I remember those -- and they definitely are not user-friendly! Link to comment Share on other sites More sharing options...
carbking Posted September 17 Share Posted September 17 The best thing about those Rochester clips was................................. As far as the spring clip and the C-clip, Snap-On used to (maybe still does) make a spring-loaded install/uninstall tool, which could be manipulated with one hand. Jon Link to comment Share on other sites More sharing options...
Frank DuVal Posted September 19 Share Posted September 19 (edited) Just on case someone needs reminding what these Rochester clips look like: The only place I like them is on the choke pull off link on a Rochester HV, as once on, they NEVER need to come off, as the link slides out the other way when one needs to disassemble the carburetor.😉 Everywhere else gets the spring (hairpin) style clip. 😁 Edited September 19 by Frank DuVal (see edit history) Link to comment Share on other sites More sharing options...
Larry Schramm Posted Friday at 10:14 PM Share Posted Friday at 10:14 PM On 9/19/2024 at 11:18 AM, Frank DuVal said: Just on case someone needs reminding what these Rochester clips look like: The only place I like them is on the choke pull off link on a Rochester HV, as once on, they NEVER need to come off, as the link slides out the other way when one needs to disassemble the carburetor.😉 Everywhere else gets the spring (hairpin) style clip. 😁 Those clips look exactly like the retainers for the trucks to the frame for Lionel Trains box cars. 1 Link to comment Share on other sites More sharing options...
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