Won't idle
Drifting
Joined: Jan 2012
Posts: 1,908
Likes: 129
From: Fredericksburg Virginia
Perhaps the choke is keeping the throttle on a high idle and once the car is warmed up and you stab the throttle, the high-idle cam is released and the throttle screw that controls low idle is simple mis-adjusted.
I'd look at the low-idle throttle screw first. Then look for obvious vacuum leaks. Then check the idle mixture screws...perhaps those are way out of whack.
I'd look at the low-idle throttle screw first. Then look for obvious vacuum leaks. Then check the idle mixture screws...perhaps those are way out of whack.
Racer
Joined: May 2005
Posts: 399
Likes: 4
From: Suffield CT
Sounds like you have a some-what working choke as car runs until warmed up..?
1. double check the choke is setup properly for your setup, stock or not ?
2. check idle mix screws are set properly, it's a whole procedure to get idle speed correct.
3. you can test things like turning screws all the way in to see if motor dies ....
BUT : count number of turns in to fully seated and write that number down !!
you really need a manual if you don't know by heart how setup a stock one anyway....
GL and keep us posted ! 8-)
-ALF out...
1. double check the choke is setup properly for your setup, stock or not ?
2. check idle mix screws are set properly, it's a whole procedure to get idle speed correct.
3. you can test things like turning screws all the way in to see if motor dies ....
BUT : count number of turns in to fully seated and write that number down !!
you really need a manual if you don't know by heart how setup a stock one anyway....
GL and keep us posted ! 8-)
-ALF out...
Melting Slicks
Joined: Mar 2002
Posts: 2,164
Likes: 7
From: Beringen
There are a couple of things to check : vapor lock and fuel boiling in the carb first.
I finally solved my problem by pulling open the secondaries in the holley carb to equilize airflow and idle fuel distribution. Had to do that while the carb was on the engine which is, to say the least, a hassle.
Racer
Joined: May 2005
Posts: 399
Likes: 4
From: Suffield CT
Good luck with the rebuild, i just finished my first Q-jet rebuild that i started last August....
the car is running really well. I got tons of pics and vids if you see my thread.
that way you can see if you wanna do it your self or pay to have it done.
Have Fun !
-ALF out....
the car is running really well. I got tons of pics and vids if you see my thread.
that way you can see if you wanna do it your self or pay to have it done.
Have Fun !
-ALF out....
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Racer
Joined: May 2005
Posts: 399
Likes: 4
From: Suffield CT
yeah that's easy...
what your number ? also what is your 4 digit date code ?
mine is 7029207
Lars papers on the net should have it http://corvette.wikia.com/index.php?title=Intake
i can look it up for ya if want...?
-ALF out...
what your number ? also what is your 4 digit date code ?
mine is 7029207
Lars papers on the net should have it http://corvette.wikia.com/index.php?title=Intake
i can look it up for ya if want...?
-ALF out...
Pro
Joined: Feb 2008
Posts: 556
Likes: 13
From: C3 Forum, Colorado
The carburetor number should read 7040207 and will look like this. The 4 digit date code (0650 on mine) will vary depending on when your carburetor was manufactured.
Hope this picture will help.
Hope this picture will help.
Last edited by qtlow; May 1, 2013 at 02:29 PM.
Thread Starter
Advanced
Joined: Apr 2013
Posts: 65
Likes: 0
From: Morgan Hill Calif
Ok, sorry it took so long. on vacation. Anyhow. My numbers on the carb shows 704057. Is that the correct carb? This is for a L46
Last edited by Jethro Bodine; May 7, 2013 at 09:19 PM.
Thread Starter
Advanced
Joined: Apr 2013
Posts: 65
Likes: 0
From: Morgan Hill Calif
I did adjust the idle but not sure where it should be for a 11.01 Comp ratio. normally standard shifts are around 500rpm. but currently runs at around 900rpm. Is that where it should be?
Drifting
Joined: May 2012
Posts: 1,353
Likes: 44
From: Calgary Alberta
Factory spec is 750 RPM for an L-46 in 1970. I run mine at about 800 RPM. I would think at 900 RPM you might be experiencing some run-on and excessive fuel consumption. If your carb is a 7040507 it is a California carb, and is correct if the car was originally delivered there. These are good carbs, there's no need to switch to Holley, and they are very rare as well...so take care when you rebuild it, I've seen similar 7040207s sell for ~$1300 at the end of the day.
Also re: your idle...the first thing I'd do is check your timing. Timing can affect carb, but carb cannot affect timing. Then look at your choke and idle speed and mixture...you should get yourself a GM shop manual.
Good luck.
Also re: your idle...the first thing I'd do is check your timing. Timing can affect carb, but carb cannot affect timing. Then look at your choke and idle speed and mixture...you should get yourself a GM shop manual.
Good luck.
Racer
Joined: May 2005
Posts: 399
Likes: 4
From: Suffield CT
Jethro,
you are getting great advice here...
I'm no expert but this stuff is kinda fresh in my head so PM me if you wanna chat via phone.
My car is '69 but also a L-46 350/350 with 380 ft/lb torque and 11:1
1. check timing if needed
2. get choke working (hard to do but not difficult to understand)
3. turn mix screws in all way and out 3 turns (per the manual)
4. start car and let warm up (assuming choke works)
5. turn IDLE screw to get car run at 750-800 RPM (or close as you can without stalling) (IDLE screw is on drivers side of carb)
6. car running warmed up adjust one mixture screw to get highest vacuum reading you can (need to get vacuum gauge & hook to carb)
7. repeat step #6 for the other mixture screw
8. adjust the IDLE screw one last time to get car idling where you want it.
this is all by memory so do your own homework, but this should get you very close. Assuming carb is fine, bolted to car and just needs typical rebuild... If carb is due for a rebuild these steps may not work until AFTER the rebuild.
Good Luck !
-ALF out...
you are getting great advice here...
I'm no expert but this stuff is kinda fresh in my head so PM me if you wanna chat via phone.
My car is '69 but also a L-46 350/350 with 380 ft/lb torque and 11:1
1. check timing if needed
2. get choke working (hard to do but not difficult to understand)
3. turn mix screws in all way and out 3 turns (per the manual)
4. start car and let warm up (assuming choke works)
5. turn IDLE screw to get car run at 750-800 RPM (or close as you can without stalling) (IDLE screw is on drivers side of carb)
6. car running warmed up adjust one mixture screw to get highest vacuum reading you can (need to get vacuum gauge & hook to carb)
7. repeat step #6 for the other mixture screw
8. adjust the IDLE screw one last time to get car idling where you want it.
this is all by memory so do your own homework, but this should get you very close. Assuming carb is fine, bolted to car and just needs typical rebuild... If carb is due for a rebuild these steps may not work until AFTER the rebuild.
Good Luck !
-ALF out...
Race Director
Joined: May 2006
Posts: 18,666
Likes: 2,564
Before you start digging into the carburetor and you dont know the maintenance history of the car. Start with the ignition system. Pull the plugs, check their gap, replace them if the center electrode looks worn. Remove the cap and rotor and check if the points are burnt, if they are replace them. Look inside the cap and at the rotor for signs of burning or carbon tracking, replace if necessary. Use an ohm meter on the wires, no more than 1K ohms per foot of wire, if it is exceeded or they look like they have cracks replace them. With the engine running set the dwell angle to 30 degrees and then set the timing with the vacuum advance disconnected. Adjust the carburetor idle speed screw and mixture screws. If all of this doesnt improve the problem than you can start looking at the carb.
Last edited by MelWff; May 8, 2013 at 02:53 PM.
Thread Starter
Advanced
Joined: Apr 2013
Posts: 65
Likes: 0
From: Morgan Hill Calif
Ok so yes i have adjusted idle . did check plugs and they look bad. Checked points and they look ok. Want to send carb for rebuild. could do myself but would like a pro to do it. Been checking things out and found previous owner not much of a grease monkey. Thanks for all your guys help. Well send more info as i fix stuff. Thanks again
Thread Starter
Advanced
Joined: Apr 2013
Posts: 65
Likes: 0
From: Morgan Hill Calif
Ok, so yes, spark plugs were garbage so replaced. idle is good but still want to rebuild carb. Now i have rebuilt many carbs in my day but have a secondary bar missing on carb and just being a *****. who does the best rebuilds in Nor cal?