When adjusting a holley carb, what does "stumbling" mean?

Many of the instructions say to turn in your idle mixture screws until the engine begins to "stumble", then turn out until steady and add another 1/8 turn.

What exactly does "stumble" mean?

Is it where the rpms start to drop, or where it is about to stall and is struggling to stay running, or what?

 

Use a vacuum gauge connected to intake vacuum source and adjust mixture screws for highest vacuum while also adjusting idle speed screw (on the throttle) to maintain correct idle speed for your car.

 

OK, well I went the vacuum gauge route and I was able to get 14, but when I put in gear it stumbled.

I riched up 1/8 turn on all 4 corners, and it dropped to around 11, but holds idle speed better when I put in gear. Idling smooth at 800, then drops to 650 in gear but smooth.

Also, amazingly, it started this morning cold, first try, and I did not have to hold the throttle down to keep it alive until it warmed up (no choke). It started right up, held steady at 800, I immediately backed out of the driveway and is stayed alive!

So THAT is an improvement right there.

I used to have to hold it above 1000 to keep it alive for a minute or two, sometimes at 1500 if it was really cold.

 

I need to swap the power valve.

The one that was in it originally was 4.5 (half of 10), but in the rebuild kit I got two 6.5s and two 3.5s.

Which would be better?

Running 3.5 now.

 

Whats the engine vacuum?, that's how you determine the power valve.

 

10, but that was in neutral. This says to do it in gear.

Need a friend right about now.

 

That's why you get married..

 

I am married, but she is working in the garden.

 

Of the power valves you have I would choose the 6.5. Adjust your carb for highest vacuum with the car in gear, sorry I should have said that before.

 

My cousin and nephew came over so I had one of them put it in gear while I checked the vacuum, and it was 12". So technically I should be using a 5.5

3.5 that I have in there is definitely too small.

I can easily obtain a 5.5, so I might just do the right thing and put one of those in.

 

I still think you would be fine with the 6.5. It will come in a little quicker for better throttle response.

 

Well, I have 2 of the 6.5s, and can quickly swap it out. The 3.5 doesn't seem to be responding the way I want it to.

Too tired to do it today.

I ended up out in the yard with the wife pulling tree roots and old bushes off the foundation of our house...2 feet deep.

I can barely move now.

 

Trust me here.. you want that 14 inches of vacuum back. The engine will respond faster to throttle inputs and be much more efficient.

What is the initial advance setting?

full manifold vacuum running to the disty.. or ported vacuum from the carb?

 

I guess you call it "ported"...only pulls a vacuum to the dizzy when I rev it. No vacuum at idle. IIRC...10 degrees.

If I can get my cousin or nephew back over, or my wife in the car, I might tweak it a little more and see if I can pull a little more vacuum at idle in gear. I did no adjustments when my cousin was in it, just measured it. All adjustments were made in Park.

But I will be swapping in that 6.5 power valve ASAP.

It is running very well, so that 11-12 might be as good as it gets. And it has a little bit of gassy smell at idle again, which I have not had for a long time. But it also has never started so easily and stayed running when cold, so i will live with the smell if I don't have to hold the gas down to keep it alive when cold.

 

Timing is a very important part of the tune. I'm sure this is why groberts101 was asking. You can experiment with that also. To an extent the more initial advance you have the better it will run. If you're at 10 then I would try 14. Make sure it doesn't ping and it's not hard to start. If it likes it at 14 then try 15 or 16.