Hey guys, I'm having a problem with a 63 DeVille. I just rebuilt the carb and now I'm having issues getting it to idle. There was a few different issues, so I'll start at the top. The car ran and drove fine, but didn't idle well on a cold start. Carb hadn't been rebuilt in a while, so I pulled it off and rebuilt it, no major issues found, just a bit dirty.
Sidenote- the carb kit came with updated needle/seat, so instead of your typical needle style, it uses a rubber bumper. Hard to explain on paper, but you may already know what I'm talking about. One of the new needles wasn't closing all the way, so I adjusted everything, and it seemed fine.
The exhaust passage through the carb spacer was completely plugged, so I cleaned that out also, even though I also just removed the butterfly valve in the exhaust. The choke also didn't work, so I cleaned and adjusted that, and it works well now.
So I go to start it up, and I have a few issues. It won't idle, backfires sometimes with throttle, hard start, etc.
I have set the timing to 5 degrees, and plugged the vacuum advance and brake booster lines.
I started with the 2 small air mixture screws at 2 turns out, and the middle vacuum bleed screw at 1/2 turn out (how it was before I took it apart).
The car starts with a little throttle, and will stay running with a little throttle. If I stab the throttle, it will usually backfire and definitely stumbles. I have a vacuum gauge hooked up and I cannot get anything to change on the vacuum gauge. It doesn't matter what I adjust on the carb, the car runs the same, and the vacuum doesn't change.
Now, I'm not completely new to carburetors, but I have only really dealt with boat/jetski and motorcycle carbs, and Edelbrock carbs. This is a bit different than what I'm used to. No carb idle adjustment, a TV rod, weird secondary valves, etc. I just feel like I am missing something or that I did something wrong when I rebuilt it, but how could I? All the same parts that were in it before and in it now (minus the updated needle/seat that I made sure was closing all the way). Another thing I found odd, but I guess this is normal, the vacuum advance gets full manifold vacuum all the time. I am used to the vacuum advance being on ported vacuum, so no vacuum at idle, and more vacuum with throttle. This is the opposite, so timing retards with throttle.... Is that correct?
Any ideas on what to do from here or what to check? I know there is a way to adjust the idle somewhere, but I don't think adjusting the idle is my solution. I think the carb is not working right. It ran great before, nice, crisp throttle response, no spiting or backfiring, and started right up when warm. I don't even know what to check now.
so the first thing is the stainless spacer shim. It may be missing from your carb. If your exhaust ports were completely plugged, it would have idled without it, but now that you have cleaned the exhaust channel, it won't.
If it is a Carter AFB you have to use the stainless steel shim under the carb. These carbs came with an idle spoil port that caused the carb not to idle correctly if left off. This was intentionally done to force mechanics to reinstall the shim which protected the aluminum base of the carb from the intense exhaust gas & heat that runs through the intake manifold center exhaust channel.
This was all covered in our Don’t Spoil Your Port … on that Carter AFB! article in the November 2010 newsletters which I have linked to here --> Carter AFB Shim and Idle Spoil Ports
If you have simply forgotten to put the shim back on, unbolt carb and install. If you no longer have one, I have the shim for $15.
if you have a point dist you cannot just reset the timing without installing new points first — and then set the timing
you have messed up your timing by resetting the timing with old worn points and now it is off —that is why you are backfiring
Install new points ( at a 28-32 dwell - I use 30 ) and set the timing to stock 5 degrees or try 8 degrees to see if you like that better ( ignition issues cause backfiring not the carb )
A good feeling that is your problem
Cleaning debri from the front channel of the carb —will be a big plus after a cold start to warm the carb and makes for a very smooth improved idle
Timing directly affects —-the cars idle speed
you need to be at 480 RPMs in drive e brake on —and wheels chocked and then set you timing
Set timing when at that Rpm
check the timing a second time after you snug the dist down to be sure no change
Use white out on the timing marks
plug the dist vacuum advance end of your hose to the carb connection when setting the timing
A tach and dwell meter—- is the tool to have to make this task an easy one
A good dist wrench made to easily designed to get to its bolt helps as well
If any of that is old news —- Oh Never mind —-LOL !
How many miles on the points and your last full tune up ?
Your timing was retarded if at 0-2 which is what happens as point wear out
3 degrees retarded from the stock 5 degrees is a lot of negative timing change
If your points are worn the engine will not perform well and changing the timing did not help that
These cars require a tune up every 6,000 miles
Changing timing with worn points never works to get the engine to perform as it should be doing
You back fire is a timing issue and putting your timing back is not going to improve performance but new points will and then resetting the timing
Best I can do to explain
If you do not have the correct gaskets and spacer under the stock carb that is important and necessary to have right also but I did assumed that those gaskets are stock and there
Clamp the PVC pipe going into the black spacer be sure it is not leaking air