I'm running an original AVS carb on my 340 with original style choke. Idle is set and it runs pretty good. However, when it's first started up and cold I have to keep the RPMs up for a minute or so to warm the engine before it will stay running at idle.

How do I set the fast idle cam properly to remedy this? The engine has to be cold to do this, correct?

No if you look up the specs in a manual you usually set it with the eng at opperating temp. I forget on the AVS without looking at the specs myself but many call for the rpm setting for the fast idle cam on the second highest step of the cam or the next to highest step of the fast idle cam. But look in a service manual or motors manual and it will give you the spec and the right step of the cam to be on to set the fast idle rpm. Ron

Are you starting it with the throttle partway open? If so try pumping the throttle half way twice and then take your foot completly off the gas pedal and start it, that will, should, allow the carb linkage to set up on the fast idle cam. The choke pull off will make the fast idle linkage not work after the motor is started unless it has the throttle already closed

When starting from cold, I usually give the accelerator pedal a few pumps before cranking. I do notice that the choke plate is always in the full closed position when cold, and nothing seems to change the position of it when pumping unless I hold my foot on the pedal. The horizontal rod that the fast idle cam is on has a lot of side to side play, and I'm wondering if that is allowing the set screw not to engage on the cam?

Does what I am saying make any sense? Still learning about carbs...

Sure it makes sense. You are right as with a carb and choke you should always press the gas pedal at least halfway down when starting and it can be more or a few times depending on the engines temp when you start it. You have to push the gas at least halfway down so the choke and fast idle cam will set as they wont if you dont push the gas pedal down some since the fast idle cam will be pushing against its lowest step until you open the throttle some. And yes after you do that make sure the fast idle screw stays resting on the cam. Normally when the choke is fully closed and you push the gas pedal down the fast idle screw should go to the highest step of the cam. After the eng starts and the choke blade opens some from the choke pull-off or piston then you hit the gas a little and the fast idle cam screw should drop down to the second highest step of the fast idle cam or a lower step depending on the eng temp. But yes make sure the fast idle screw lays against the cam. Ron

OK- this makes sense! After looking at my carb, it seems that the set screw tab (attached to throttle) does not line up with the fast idle cam. It looks like either the set screw tab needs to be bent out, or the cam needs to be shimmed in. Not sure if the latter is possible. Is it a bad idea to try and bend the set screw tab out?

I'd be leery of bending it. How far off is it? not sure why yours ain't lining up. I will eyeball mine on the bench & holler back

There is your first problem , it's in the FULL CLOSED POSITION , that means there is no air getting thru and why you need to keep your foot in it to keep it running till it warms up a little and the choke thermo relaxes . You want roughly an 1/8" gap between the choke plate and the carb horn, to start , when it's STONE COLD, do one pump of the gas pedal to set the choke before cranking, get it running and then adjust the idle speed.

You can do this when the engine it warm by manually setting the choke to the 1/8" choke open, or whatever you decide on at stone cold closed position.

Why not do it by the book ?

Note: location of fast idle screw/ adjustment

I think I have it adjusted properly now. The only thing different from the book is that my carb has a different looking cam. On mine there are only two steps, and one notch in between. I have my screw set about 3/4 of the way up on the highest step. It's in a similar position to where the 2nd highest step is per the book, except it's not really a step on mine. Seems to work OK though.

Now that this issue is solved, two more have cropped up. First, I noticed that the throttle tab has some (wiggle) play on the (butterfly) shaft where it is peened over on the throttle tab. Is it possible that the tab could loosen up and break free under stress from throttle cable and return springs, or does that seem unlikely?

Also noticed that the car seems to run rich all of a sudden, when it didn't do it before. I can just smell it, and I didn't even fool with the mixture screws since it was originally tuned...

Hasn't been the best week out in the garage...

John I was guessing he just ment when he looked at the choke without the eng running it was closed after he hit the gas pedal. The choke will be fully closed with the eng cold and off it you push the gas pedal down some and of course it should open some when running by the choke pull-off diaphram or piston. Ron

This is to set the fast idle cam posistion so it is on the right step when started and running. There is also a procedure for the fast idle cam rpm in the book. Of course to do it all right you need to set everything on the choke including the choke pull-off , choke unloader and the choke lockout specs. I would set and check all of the settings when rebuilding a carb which you can check and set to make sure all aspects of the choke system are working right. You can just follow the manual but from the question I assumed he just wanted to know the specs and how to set the fast idle speed. Course its always best to check and set all of the choke/carb settings. Ron

I don't need no stinkin' book ...

plus not everyone has the special tool to bend the rod ...

Bill posting picture of special tool in 3 ... 2 ... 1 ...

Ron , if the carb is set as shown above by Bill the choke blade Should never be fully closed , the choke thermo is what sets the choke blade and the hit of the throttle when the engine is cold will allow it to go to the almost closed position and have the throttle on the fast idle cam ...

But you knew that ...

John,you have those tools,you just forgot !!

I am guessing Bill is 62 Maxwgn ? I was not referring to that as thats where you would set the linkage of course to adjust the cam posistion. I thought you were talking about the OP very first post that when he looks at the choke on the cold eng after hitting the gas pedal with the eng off as the hit of the throttle with a cold eng will let the choke be fully closed on the highest step of the cam until the eng starts. Thats when I meant the choke will be fully closed and should be until he starts the eng. Ron

340clone you may be past this by now but I checked mine today for you & the stepped/notched cam bolted onto the side of the body with the big screw (the notches) are inline with the fast idle speed screw. If yours ain't see which one is bent & that'd be the one I would bend back (happens alot to the throttle linkage part when carbs are tossed around). Otherwise FYI it looks like it would be pretty hard to bend the flat stepped cam piece (not much area there to work with and you dont want to end up with an angled contact) but on the throttle tang it sure looks like you could take out the screw & with some vice grips bend its tang (if needed obviously) then return the screw

Thanks! I finally got it working somewhat. I did tweak the tang and got it lined up properly. Now just trying to get the fast idle speed right. When fooling with these old cars, it makes me wonder how they could have possibly been built on an assembly line in the numbers that they were. So many damn adjustments and fit problems!

it is a challenging hobby at times. I take it piece by piece & the best thing I learned from my mechanical mentor decades ago (a WW2 aircraft master sergent mechanic) was to learn to NEVER get emotional/frustrated/angered when difficulties arrive. the slightest bit of emotion skews the logical intellect process. Took decades to put that into practice (took a day or two off many many times till that was cemented in place)