On Holley 94's sometimes the cam on the throttle shaft (which is peened onto the end of the shaft) gets loose and can cause the throttle idle set screw to go to the side of it, causing this.

 

That's along the lines of what i'm thinking Ross .
It could be something quite simple as not enough "slack" in the linkage or something similar to what you describe .

 

I just got back yesterday and since I will be on the road again, I was able to perform a little more troubleshooting so here's the latest. First, I confirmed the linkage was good and responsive. Since my float was set a bit low, I raised it up a bit, fired her up and let the motor get warm. Although I was having a nice steady idle, when I revved it up a few times by hand, and let it go back to idle, the engine would almost stall and then after 4 or 5 seconds, chug right back up to a good idle. Since I'm not a carb expert, could there be something going on in the idle circuit that would explain this delay? Although I had my 1904 rebuilt 6 years ago, it's beginning to look like it may need to be gone through again. Thoughts? Thanks!

 

Another rebuild would not be unreasonable depending on how often it is driven. I've had good luck, but I've read a lot of anecdotal stuff in the different forums that modern fuels really hork carburetors and they probably need disassembly and cleaning every few years with ethanol-laced fuels especially. Stale fuel in the tank and bowl turns to varnish/glue and tar and plugs up the passages and air bleeds &c

 

Update...got the carb rebuilt and back running good. With my vacuum gauge, the best idle vacuum reading I could get by adjusting the air/fuel and idle screws was 12 lbs. Although a little low, when I accelerated, the vacuum reading increased to 15-17 lbs them back to 12 when I let off. I thought about disconnecting the vac line from the distributor and turning it for a little more vac reading but since it idles and accelerates nicely, I think I may leave things alone for now.

 

Those vacuum readings are completely backwards from normal. Should be 17"+ at idle, and drop even into single-digits on acceleration. Stock Holley power valves open at 7.5". Where are you connecting the vacuum gauge?

 

Hello Ross. Just below the carb on the intake manifold. It was not in gear under a load rather I was moving the gas pedal linkage by hand. I would think it would decrease after I place in gear and drive. I took her out for a drive earlier today and she performed great. When I came to a stop, it returned to a nice idle and didn't want to cut out on me.

 

Hard to argue with good results. You're right, under a real load it might behave "normally". I used to run hose up thru the cowl area and tape the vac gauge to the windshield for road tests.

 

Appreciate all the feedback. Since I just got the carb back from a rebuild, I went ahead and opened the steel bowl and sure enough, the float was really set high which made me start thinking that maybe some of the fuel may be spilling over into the manifold when I come to a stop. So, I lowered the float to where the fuel line is just above the square on my glass bowl. Since my original glass bowl has a tiny chip on the top right corner, I went ahead and installed it. So far, no leaks. I will take it out tomorrow and see what happens. I know this is a real long shot but you never know till you try.

 

Float height will usually need at least a slight adjustment up or down to achieve the correct fuel height, at least it's easy to check.

 

Just keep plugging away and getting everything set back to factory spec. I'd adjust the valve lash, then check engine manifold vacuum again. That's one of those loadomatic deals right? Make sure vacuum gauge is connected to a source of constant manifold vacuum for measurement.

Then adjust initial ignition timing for highest steady vacuum on the gauge. Finally tweak the idle mixture screw for best lean idle drop. Re-Check fuel height in bowl when engine is thoroughly warmed up, fuel will expand. Those clear bowls make that easy. The manual should have the wet height spec in there somewhere.