I have an Edelbrock 1406 carburetor for my 1968 350. After about 10 minutes of driving, the idle does not hold when I am in drive and stopped at stoplight, ie I have to keep my foot on both gas and brake to prevent killing the engine. When the car is in park it seems to idle just fine. Not sure how old the carburetor is, but the engine was rebuilt several years ago and has not had a lot of recent driving.
Do these symptoms seem to indicate that the carb needs to be rebuilt? If so, would I be better off just getting a new carb? Or is it possible the carb just needs to be adjusted? Does anyone have any directions/rule of thumb on how to adjust the 2 screws up front on the carb? Any help would be greatly appreciated. Thanks.
Check the curb idle speed screw. When cold, your engine will be running on the fast idle speed screw. You can test this by taking your car for a drive until it is warm, shutting off the engine, open the throttle and move the choke back to the closed position so the fast idle screw is on the cam, and then start it without touching the gas pedal. If it idles fine, press the gas pedal and release and see if you lose your idle. If so, adjust the curb idle speed screw.
Vikki 1969 Goldenrod Yellow / black 400 convertible numbers matching
The two screws on the front control the idle mixture. They should be set with the engine at operating temperature. Start by turning each screw in until it bottoms lightly (engine off), counting the number of turns for each and comparing. They should be within a 1/4 turn. Then set them back to where they were, averaging the number of turns so you have a baseline. Next, adjust the screws.
Two ways, one is to hook a vacuum gauge up and set the screws to give the highest vacuum at idle; the other is to adjust to give the smoothest sounding idle if you don't have a vacuum gauge. I turn one screw 1/4 turn in and listen for about 3-5 seconds to hear if the engine liked the change or not, then continue accordingly, same method 1/4 turn then listen (or read the vacuum gauge) until I like what I see or hear. As a quick rule of thumb, start with both screws out 2 turns then using the above method, turn the screw in until the engine starts to stumble. Back the screw out until it is smooth again. Now adjust the other screw using the same method. After getting both screws close, you can now fine tune by going back and forth between the screws moving both in the same direction 1/8 turn. Again look for the highest vacuum reading or listen for the smoothest idle. Once you and the engine are happy, shut off the engine and again count how many turns it takes to bottom the screws lightly. They should be very close to the same, and now you know where the screws should be set if some one plays with them.
If you don't get a response on one or both screws as you turn it in with the engine running, it's time for a good cleaning/rebuild. Also, a large difference in the number of turns would indicate the same thing.
Another issue can cause an unstable idle in gear. If your distributor's mechanical advance is already adjusting the timing at an idle, you can have a good idle with no load but when the engine is slowed down by shifting into drive, the timing will be retarded and will cause the idle to drop off enough to require the two foot method.
To test for this you'll need a timing light and an extra body. Pull the vacuum line to the distributor off and plug it with a golf tee. Set the idle speed screw to get a slow but steady idle, then turn the idle speed screw in a 1/2 turn to get a slightly higher idle. Check the timing with the car in neutral, then watch what happens to the timing when your helper puts the car in gear. Note: make sure they have their foot on the brake first, and don't stand in front of the car while doing this test! You may have to look fast to see what's happening before the car quits! If you have a good helper, they may be able to vary the idle speed while in gear using the two foot method so you can see if the timing is changing. If it is, that could be causing the unstable idle.
I was going to say , maybe bad gas... as a first easy check...as Jim says, gas could be weak, or you might have gotten some bad gas...run it almost empty ,fill up with gas from another station...run it thru , you should notice a difference before 1/2 tank used up...if still doing the same thing......start checking the other items...being lazy ,thats how I would start out , the "easy way"....lol
Happy reading That manual is general for all their Performer carbs. My guess is the electric choke is not setup correctly and has to be adjusted and/or the float is stuck or sunk or not adjusted properly.
The float on my Qjet would get stuck down every other month or so. The car would become undrivable...fuel leaking from the top of the carb...had to drive home with 2 feet. I had to disconnect and plug the fuel line, run the carb dry, then blow compressed air into the fuel inlet to clear out the resivoir. Worked everytime but, problem re-occured.
Of course fixing the problem will depend on - what the problem is. Fixing the ignition when the carb is messed up won't help either. Take it one step at a time and let us know what happens.
To me, the conservative approach starts with checking a few things before buying parts. By doing what Vikki suggested, then checking the things I mentioned, you can start eliminating possible problems without causing more - and maybe even fix it!
If you can't remember when the plugs and wires were changed last, by all means get your maintenace up to date - that also may fix your problem! Keep us posted!
Mentioned the ignition first because my carbs don't need attention nearly as much as my ignition parts. Am I just lucky or do carbs stay pretty well adjusted once you get them right?
Yes, I find that once they're set they stay that way until either dirt or somebody with a screwdriver gets into them! Really much more reliable than most people would think. The big trick is getting them adjusted in the first place. I was mostly responding to his request on how to do that, with a little extra based on what I've seen. Sorry for getting a little testy on that last reply, I didn't have a great day, and after rereading my post I see that some of that came through. :rolleyes:
Getting both the ignition and the fuel system set up properly really helps to keep that big grin on the driver's face! The worst mess I had to fix was an old Lotus Elan. The owner or his buddy adjusted every screw on the carbs (twin side drafts) and linkage, then tried to add more ignition timing to compensate. Took me two hours of incremental adjustments to the carbs and timing to get it back to normal. Took about half the time just to find out what they had played with ("No, have no idea what the problem is, just started acting funny all by itself!")! Wouldn't run at all below 3000 rpm when it came in, and chugged happily out at 600 rpm after. No parts replaced!
Sometimes, when I read a posted problem, I get a picture of when the same thing happened to me. I got a clear picture on this one. It's a 75 Monte Carlo back in 1987... That's the reason I keep coming back to a fouled plug. And then, I think about where I would be headed if I adjusted the carb when the problem was a fouled plug. Then it dawns on me why so many carbs are out of adjustment. I think the moral of the story came out really clear with the agreement that carbs usually don't need adjustment. Especially if you had your engine running good at some point.
That manual is general for all their Performer carbs. My guess is the electric choke is not setup correctly and has to be adjusted and/or the float is stuck or sunk or not adjusted properly.
