I am wondering how to adjust my carb. I don't want to get it wrong and burn up my engine or something. If you know how to do it or know of a good resource i would like to know. I have an edelbrock on a 1976 f250

 

I realize this is not answering your question, but based on what I've been reading in your other posts, I think it would really help for you to pick up a Chilton's manual for your truck, just to get a basic understanding of the principles behind everything.

That being said, I'm taking a wild guess that you started this thread because I asked in your other thread if you've tried adjusting the idle speed and mixture. Can you confirm that your issues are happening once the engine is completely warmed up? 1-2 minutes of running with the choke on does not necessarily mean it's a warm idle issue.

If it is, then the two items that affect curb idle (which takes effect with the choke completely disengaged) are the idle speed and the idle mixture. The idle speed controls how far the throttle plates are held open when your foot isn't on the gas. If you have a valve cover sticker, set the idle speed (measured in RPMs) according to the valve cover sticker. A tachometer is a handy tool for this until you can do it by ear.

Once you have that dialed in, adjust the idle mixture. Shut the truck off, gently turn both idle mixture screws all the way in, then both back out 2 full turns each. That generally gets you in the ballpark - but you really should use a vacuum gauge for this adjustment. Connect the gauge (under $30 at most parts stores) to a manifold vacuum source, start the truck up, then slowly adjust both mixture screws simultaneously until you maximize the reading on the gauge. You're looking for a steady reading between 19 and 21 inches of Hg.

Maximizing the idle mixture will make the idle speed go up, so as a last step you'll have to bring the idle speed back down to what you set it to before you tuned the mixture. You don't have to worry about burning the engine up from idle adjustments - at worst the engine just won't run. The only way for the carburetor to really "burn up an engine" is if the jets are so lean that they lead to detonation (pinging at cruise), but that usually requires the timing to be over-advanced as well.

 

It doesn't want to idle after driving it for about 15 minutes. Before that it will idle just fine. Then there are two in the front of the carb which are both mixture screws is one air and the other gas? Can you just hook it to a vaccum source right on the carb or does it need to be on the manifold because if you were to take any of the other vaccum tubes off the engine would run different which would screw with your tuning.

 

On an Edelbrock, the only screws on the passenger side of the carburetor should be the three that hold the choke cap. If you had an automatic choke, you'd loosen these to adjust the choke, then tighten them back up. Since you have a manual choke, you don't have to worry about that. In your case there are no settings for you to adjust on the passenger side of the carburetor, so I'm not sure what screw you're looking at.

On the driver side of the carburetor, there are two screws. One screw is for the curb idle speed. The other screw should be underneath and it's part of a linkage that you have to pull up to access.

The idle mixture screws are on the front of the carburetor. One isn't for air and the other gas - each controls the air/fuel ratio. The one on the driver side controls the driver side primary throttle bore mixture, and likewise, the one on the passenger side controls the passenger side primary throttle bore mixture.

Also, here is the Edelbrock owner's manual, made available by Edelbrock on their website. Give this a read; it will be a wealth of information for you:

http://www.edelbrock.com/automotive_...ers_manual.pdf

 

The whole not idling when warm, does it try to idle then die, or does it just die when you let off the gas. Also, if you keep your foot on it, just barely, will it run or do you have to keep playing with it to keep it running.

A good way to set the air/fuel without a vac. gauge is like said above set both screws at 1.5 or 2 turns out and that will get you close enough that it should run assuming those are the issue. Set idle. Once there turn each in 1/4 turn at a time until the engine starts to "labor" at idle. Back both screws out 1/2 turn and your good to go. A quick sniff of the exhaust pipe will let you know if youre close. If youre too rich it will make your nose burn. All of this is assuming there are no other problems present.

Next step i would try would be removing the top of the carb. and check for dirt /debris inside the carb. If you have a plugged idle circuit it will mimic the symptoms you mentioned. The reason is while the choke is on it raises the idle and chokes the air coming in, this creates a vacuum in the fuel bowl drawing in extra fuel masking the problem of a plugged idle circuit. This is the reason for my questions above. If it will only idle by pumping the throttle then i suspect idle circuit. This is because pumping it actuates the accelerator pump which is dumping in extra fuel. If it will idle by just keeping your foot on it a little, i would lean towards it being an adjustment issue on the carb or at the least not a problem in the idle circuit.

To be safe i wouldnt put the engine under any load while its acting like this. It seems obvious its a lack of fuel problem, in which case the engine is running lean. This can lead to backfiring, burnt valves, or in extremem cases torched pistons. Although this is rather unlikely given the timing and compression on these engines.

 

jjurva

The base line carburetor adjustments, idle speed and mixture, must be done on a fully warmed up engine with the choke off. If it just won't idle then get it hot, shut down, turn the idle screw up a turn or so. Restart and repeat till it does idle hot. Then adjust the speed down to where you want it. Then adjust your mixtures.

From the Edelbrock instruction manual: Quote:

" Start engine and check for fuel or vacuum leaks. With engine at
normal operating temperature and the choke fully open, set idle
speed and mixture screws "

And from the manual:

IDLE MIXTURE
The Edelbrock Performer Series carburetor has conventional Idle Mixture Screws (IMS) that provide a leaner A/F when turned clockwise and richer A/F when turned counter clockwise. The idle air flow is controlled by a conventional screw that opens the Primary Throttles. The following procedure should
be used to set the idle mixture and speeds.
1. Fully warm engine and ensure choke is fully open.
2. Air cleaner in place.
3. Set desired speed with the air screw.
4. Adjust the IMS on ONE side to get the maximum possible RPM. Do not go rich beyond the maximum speed point.
5. If the above changed the idle speed more than 40 RPM, then readjust the speed.
6. Adjust the side OPPOSITE of that in Step 4 to get maximum RPM.
7. Reset the speed.
8. Carefully trim each IMS to again get the maximum idle RPM.
9. Go leaner just enough to get a 20 RPM drop in speed.
10. Reset the speed to the desired RPM.
11. This is a Lean-Best Idle Set. Setting richer than this will not improve idle quality or performance, but could tend to foul plugs.

Here is the link to the installation manual:

http://www.edelbrock.com/automotive_.../1000/1407.pdf

Here is the link to the owners manual:

http://www.edelbrock.com/automotive_...407_manual.pdf

 

Here you go this might help depending on your carb.

Edelbrock.com - Tech Center - Tech Videos

 

Is there only the two mixture screws and the idle speed screw or is there one more for idle air. Do the two mixture screws need to be set the same or does that matter. So as long as I maximize the reading on the vaccum gauge there is no threat of going too lean and harming the engine?

 

There are the two mixture screws on the front, to control the ratio. No such thing as a separate air control or fuel control. This is stuff that I have already told you. Typically you want both idle mixture screws at the same position (equal number of turns out), but you may find that they each need to be tweaked slightly to peg the vacuum gauge.

One screw controls curb idle speed (choke disengaged), a separate screw controls fast idle (choke engaged). Four screws total. Did you look at the manuals we provided you?

You can't burn up the engine by setting the idle mixture too lean. Lean jets and advanced timing are what do this, and the problem happens at cruise, not idle. I already explained that.

Not trying to sling you out, but do you actually read the answers people give you? I feel like I'm just repeating myself.

 

Im an extremely novice mechanic. I like to run stuff by people twice to reassure myself before i just jump into things. I don't mean to inconvenience you but then again you do not need to answer my questions. Im not saying im not thankful for your help because I really am. I set the idle mixture screws at 2 turns each and the truck is running much better. Im going to get a vaccum gauge to get it perfect but just changing it helped alot.