Idle characteristics with a carb... Can it really be this bad??

[Jayru 17]

I've always been a fuel injection guy, i just think carbs are such antiquated technology. That being said... With so many other issues draining my Injection conversion budget, i decided to see how long i could stand this blasted toilet bowl on top of my motor (and how well i could learn about/tune it). This is not my first car with a carb, but definitely the first one I've modified heavily.

 

I'm running an Edelbrock 600 cfm carb (less than 1000 miles on it at this point). After much research, I finally got the electric choke dialed in pretty good, but the idle rpm and mixture is proving to be difficult. Not in the sense that i can't dial it in where i want, but that it will actually stay there on a day to day basis! It seems to change with the weather (literally).

 

I will set the idle and mix, go about my day using the car and everything will be fine. I park the car overnight, and if the next day has a slight weather change (temp/humidity/etc.), the idle/mix will be all out of whack. Sometimes it'll idle too high, sometimes too low, sometimes to rich, etc... If i readjust for the conditions of that day... It will be off the next time the weather changes.

 

Is this just how a carb works??

[69again 10]

My 302 is fairly well built with a 750cfm Edelbrock. Weather conditions seem to effect it until it gets warm and then it is perfect. I had mine dyno'd in chassi and haven't touched it since (18 months on it). I like old style though.

[danno 128]

Early carbs (before smog problems) were very simple. Only a couple moving parts and a couple of adjustments. Then things started getting fancy with automatic chokes, 4 barrels, etc. I have a simple 2 barrel in my vert for over 20 years with only one cleaning in that time. Starts fine every time, runs great. My point it carbs can be very good. There is a lot that goes into the equation, though, to get them to that point. You are in that position of getting it all tuned in. When you get that done, it should be good for 20 years. Good luck...

[tony 63C 14]

Reading this thread with interest. I recently purchased a concourse restored Autolite 4300 (original carb for the 1969 351W M code) from Pony Carbs. Fantastic looking restoration, but the looks haven't translated into how it actually performs. I've solved the fuel leak problem, but have yet to get it to hold the curb idle. It's been very frustrating, considering I paid a hefty premium to avoid exactly what I have been going through. Grrrrrrr.

 

T.

[1952 10]

welcome to the World of carbs

[Jurisd 10]

After much research, I finally got the electric choke dialed in pretty good...

 

Jayru, I think your experience is spot-on. You are used to a computer sensing the temp, humidity, and engine demands and adjusting things. Replace that with vacuum signals and mechanical linkage, and you can see why it's hard to get a steady result. If it worked well, nobody would have ever spent the money to invent fuel injection.:biggrin:

 

I'm in San Diego, and have the same set-up as you (Edlebrock 1406, I'm guessing?) It is hard to get a more consistent climate than SD, but I also have lots of trouble, at least until it warms up completely.

 

I was going to ask - what was the research on your choke, and how did you in the end determine how to adjust it? Mine will barely idle when cold at a stoplight, for example. I rotated the choke adjustment clockwise and counter, but noted no real difference...

 

On your

[LSG 15]

Jay, you may have a bad carb. Carbs are old tech, but they are reasonably well figured out. I would try a differant carb, and here is why. Edelbrock doesn't make carbs, they buy them from weber. The 'Edelbrock' carbs are a new version of the Carter AFB. The problem is that when Carter closed/was bought out, many of the Carter folks thought they had gottten a raw deal. In the last days of Carter manufacture, some of the tooling dissapeared, and some was damaged. Unfourtunately, 'brock didn't realize this and then built and sold hundreds of carbs with passages undrilled, half drilled, or the wrong size. There really isn't any fixing these turkeys.....try another carb and see if it is better. And ditch the electric choke. Chokes should be manual. Always, so they do what you tell them to, rather than what the choke thinks it should do. And why would you ever even need a choke in SD ? LSG

[Jurisd 10]

And why would you ever even need a choke in SD ? LSG

 

I'm in SD, not Jayru. And I asked the same question when I had to replace the POS that was on the car when I bought it (which had no choke). But, reality of living in paradise is that temps fluctuate between 45 and 105 if you don't live right by the water.

 

How difficult is it to convert an automatic choke to a manual?

[LoneWolf2U 136]

Converting a Holley is simple, Ed's not sure.

I run a Holley with electric choke, Once set it has worked perfectly.

[Jayru 17]

Jayru, I think your experience is spot-on. You are used to a computer sensing the temp, humidity, and engine demands and adjusting things. Replace that with vacuum signals and mechanical linkage, and you can see why it's hard to get a steady result. If it worked well, nobody would have ever spent the money to invent fuel injection.:biggrin:

 

I'm in San Diego, and have the same set-up as you (Edlebrock 1406, I'm guessing?) It is hard to get a more consistent climate than SD, but I also have lots of trouble, at least until it warms up completely.

 

I was going to ask - what was the research on your choke, and how did you in the end determine how to adjust it? Mine will barely idle when cold at a stoplight, for example. I rotated the choke adjustment clockwise and counter, but noted no real difference...

 

On your

 

I followed Edelbrock's instructions on how to set the choke itself. Let the car warm up and choke fully open, then dial the choke back (all the way lean), and slowly turn it rich till you see the choke move (closing) then back it off lean 1 step. This worked for me. But Edelbrock doesn't mention the fast idle screw.

 

The trick is to get the fast idle dialed in after the choke is set properly (trial and error). I also had a problem where the return spring for the linkage was rubbing/binding on the fast idle (choke) linkage. It was making the fast idle linkage/choke stick and stay closed. So look for that as well.

[Jurisd 10]

Thanks Jayru.

[MikeStang 247]

Wow the first edelbrock carb i owned had electric choke, and worked fine right out of the box, we set the idle and adjusted the mix screws and I drove the car for over a year with out messing with it...I find that the little edelbrocks like 1-1.25 turns from seated, much like a holley if I remember Correct.......Humm maby there is a way to put the most reliable and service free carburetor ever made on our fords......Yep just bolt on a Quadrajet. LOL

I actually prefer an Electric choke over a cable manual one, just less crap you gotta run to the pass compartment, and heck tap the gas once start the car waith 15 seconds and tap it again and your good to go LOL. Works like that when its warm anyhow hahah.

Mike

[70Mach03 12]

I’ve always used a regular vacuum gauge to set and adjust all my carburetors. I’m still kind of old school and it’s what my father taught me from over 40 years ago. I’ve used it on the stock Autolite 2-barrels, 4-barrels and Holley’s with good success over the years.

Some people like to use a tach to bring the idle to the highest rpm while setting the idle rpm and mixture. A vacuum gauge does basically the same thing as you’re going for the highest vacuum it can pull at idle. Depending on your mods and type camshaft, 15 to 19 inches of vacuum should be considered good.

This is for a street driven car. A race car that operates at high throttle settings would be different.

[link597 10]

you got a bad carb buy a holley my car has high compression race motor and my carb never goes out of tune because of the weather once it's tuned in it should not just randomly go out of tune every time you drive the car