Idle Mixtures screws do nothing - Can't tune my car!
 

Maybe you all can help me out here.

My car has been sitting for a month and a half or so because of exhaust leaks at the manifolds. I replaced the donut gaskets and they seal up nice now, but for some reason I thought I should re-tune my car after this.

When I first hooked up my vacuum gauge it read at about 16, but when I started to adjust the idle mix screws and the idle itself everything fell out of tune. Now I can screw the mixture screws all the way in and nothing happens, all the way out, nothing happens. So obviously it is not running on the idle circuit anymore, how do I fix this?

The carburator is a Edelbrock 650 cfm with an electric choke. Here are my thoughts on possible problems:

• Choke is messed up
• idle mixture screws damaged
• the ports for both idle mixture screws are completely clogged
• vacuum leak

I don't think it is a vacuum leak, I just rebuilt my carburetor a few months ago so all the gaskets are new and the vacuum lines seem fine. This is why I'm also not sure if the ports are clogged, since I just rebuilt it.

Can I remove the two mixture screws and spray carb cleaner directly in there to try and clear a clog? Is there simply a way to adjust when the idle circuit begins and ends?

Any suggestions are welcome, I've spent the last hour trying to tune it so I can drive it again and now luck. Car is my 1969 Mach 1 with a 351w

Think I may have found a problem, my adjustment screws/needles have flattened out. I looked them up on google images and they should come to a point. Obviously this is a result of over-tightening somewhere in the past, but can this cause my idle circuit to not work? Did it damage anything inside the carb that it screwed into?

Here's my screws:

http://i18.photobucket.com/albums/b143/4reboy/photo.jpg

last time I spent hours on my carb I ended up giving up and buying a new one after 2 rebuilds. Just not worth the head ache. Problem free and shiny out of the box works wonders on frail nerves

Try replacing the screws...The car has to be running on the idle circuit I dont think there is another choice...it either runs on the idle circuit or it doesn't idle (it dies)

So blunt screws would be unable to lean the mix past a certain point because they cant get down into their seats..I think you're on to something.

-Gun

Thanks for the advice. My understanding was that if the idle screw was cranked up high enough the carb could idle on the cruise circuit, not sure if that's true or not though. I'll definitely buy some new screws, do I have to buy them online or can I buy them from an autoparts store?

With these screws being bottomed out have damaged anything in the carb? Or are the seats they go into pretty tough? I imagine they would be fine if they did that so easily to the screws.

Any other advice?

It could have damaged the seats...

I suppose it could run on the primary main im not a 100% sure...I think idle circuit delivers a 100% of idle fuel and most of part idle acceleration and an increasingly less amount as speed increases.

Your local O'Really? auto parts should be able to get them screws for you.

-Gun

It probably did damage the seats, but new needles may just be able to function.

Also check your secondary stop screw to make sure the secondary is fully closed. If not, you won't be able to idle it down far enough when you do get new screws.

If by whatever chance the new needles don't fix the problem because the seats are too damaged, are these replaceable? I rebuilt my carb myself, but I don't remember having to do anything to this part of the carb. I definitely don't have money for a new carb so hopefully the new needles will be enough and/or the seats are easily replaceable.

the fact that both screws are the same 'blunt' and that there is a taper makes me wonder if the edlelbrock ones are like that stock.
You'd have to be really brutal in closing them, and in this case both to get them from pointed to that. there is no burr at the top or taper indicating that either.
I'd say your idle circuit is clogged or you are spilling so much fuel into the carb that you don't need the idle circuit anymore.

This is the most likely cause as otherwise it wouldn't idle ...

I still say there's something up with the screws mine are very pointy (but thats a performer series 600) but yes I agree that they were either built like that or modified for some reason. I wouldn't give up trying to hunt down new screws yet.

SO what do the faces of those screws look like...are they polished like the sides or rough like the tips both broke off at the same place and are stuck in the carb still?