Stalling Issue (Slant Six w/Holley 1920 Carburetor)

-
66RedFish

66RedFish

Active Member
Joined
Apr 22, 2010
Messages
36
Reaction score
1
Location
SE Pennsylvania
I hoping someone can help diagnose the possible cause of a stalling issue I'm having.

The car ('66 Barracuda) starts fine and the choke seems to step down and operate as it should while warming up. However, if I step hard on the accelerator pedal before the car is fully warmed up, the car will sputter and stall. It can be started again right away without any problem. If I ease into the accelerator, it will run just fine and not stall. Once the car is fully warmed up, this problem goes away.

I rebuilt the carburetor a few years ago in the hope this would fix it, but no such luck.

Any clues what might be wrong?

Thanks.
 
Either the accelerator pump is faulty or the choke is opening too fast and you are getting a lean condition when cold.
 
I'll probably tic off some experts, but I'll say that is likely normal with many carburetors, especially a simple one like the Holley 1920. When you floor it, the choke is forced open, so you no longer get the idle enrichment. The accelerator pump is set for a warm engine, so probably doesn't squirt enough fuel when cold. Just drive slow when warm, which is smart anyway to not damage the engine, like say spin a main bearing. Sounds like you are lucky. I went thru 4 Holley 1920's in my 1969 Dart over 20 years. It always idled lean and would stumble and even die off the line. No mechanic could figure it out and I tried solving "a vacuum leak". When still a problem with a new long-block, I figured it must be the carburetor, tried the 4th and it ran like a dream. 1920's have a sealed metering block which gets clogged and most rebuilders don't touch, so many bad ones on the shelf.
 
Check for a vacuum leak at the throttle shaft in the base of the carb. The steel shaft wears the carb body and creates a vacuum leak there. I’ve been haunted by the same stumble and stalling, even with a freshly rebuilt and properly adjusted carb. Having a bushing installed cleared it right up.
 
The choke and pull off adjustments can be touchy on those. It sounds to me that you need a bit more choke tension so it stays on a bit longer. If you change that adjustment, you may need to readjust the pull off so it doesn't run too rich at start up. I've found that the factory manual adjustment specs will get you into the ballpark, but, it's usually necessary to tweak them a bit with today's gasoline.....especially our crappy Ca. fuel. It's bend some linkage time! :lol:
 
Have you looked into the carburetor throat to confirm a steady strong stream of fuel when the throttle is opened? If you have that, then refer back to posts #2 and #3.

How is the choke adjust exactly? In Pennsylvania, it's probably pretty cold in the mornings now. You should have the choke adjusted so that it snaps shut fairly well when you open the throttle first thing. The choke should have noticeable resistance when you open it with your finger. In other words, it should want to close "pretty good" when you remove your finger. It's simply something you're going to have to experiment with.

Another thing to check is the ignition timing. All too often carburetor issues are not carburetor issues, but timing issues. Where is your initial timing set? With today's crappy's gas, you're going to need more initial timing to help it run better. I have mine at about 12* BTDC and it runs great.

Referring back to post #3, you cannot hurry these old girls when they're cold. They don't have EFI. They must get some heat in the system before they run their best.
 
RustyRatRod said:
Another thing to check is the ignition timing. All too often carburetor issues are not carburetor issues, but timing issues. Where is your initial timing set? With today's crappy's gas, you're going to need more initial timing to help it run better. I have mine at about 12* BTDC and it runs great.
Click to expand...

I've seen references to advancing ignition timing, but this is the first time I've read why. Why does crappy gas = advanced timing? Is there an indicator for too much advance besides ping?

I thought too that someone that knows more than me (okay anyone) would have mentioned the exhaust heat flapper by now. No? :poke:
 
Duggie said:
I've seen references to advancing ignition timing, but this is the first time I've read why. Why does crappy gas = advanced timing? Is there an indicator for too much advance besides ping?

I thought too that someone that knows more than me (okay anyone) would have mentioned the exhaust heat flapper by now. No? :poke:
Click to expand...

I don't see the exhaust hot air valve causing a hesitation. There can be other indicators for timing too high such as running rough. It can cause a rough idle if it gets too high. I tried my 170 around 20 and it idled too rough. I never drove it so I don't know if spark knock was present, but I didn't like how it idled at 20 so I backed it down to 12 and it idles great and is zippy as can be.
 
Duggie said:
I've seen references to advancing ignition timing, but this is the first time I've read why. Why does crappy gas = advanced timing? Is there an indicator for too much advance besides ping?

I thought too that someone that knows more than me (okay anyone) would have mentioned the exhaust heat flapper by now. No? :poke:
Click to expand...
I made the poor assumption that ignition timing and a working heat riser were already something that had been set and in good shape. Yes, the heat riser can effect cold driveability to a certain extent, mainly in a cold climate. It has very little effect here in San Diego, so, that isn't something that immediately comes to mind.
 
RustyRatRod said:
I don't see the exhaust hot air valve causing a hesitation. There can be other indicators for timing too high such as running rough. It can cause a rough idle if it gets too high. I tried my 170 around 20 and it idled too rough. I never drove it so I don't know if spark knock was present, but I didn't like how it idled at 20 so I backed it down to 12 and it idles great and is zippy as can be.
Click to expand...

I thought I read here that a missing / frozen open exhaust flapper valve would leave the intake manifold cold and allow fuel to pool in the intake instead of vaporize, causing a cold - lean condition.
 
Duggie said:
I thought I read here that a missing / frozen open exhaust flapper valve would leave the intake manifold cold and allow fuel to pool in the intake instead of vaporize, causing a cold - lean condition.
Click to expand...

As mentioned, only in cold operation. Once warmed up it has no effect.
 
Soooo. I had the same problem on my 273 with a BBD carb. My float level was not high enough so at idle it was fine. Cruising around it was fine. The minute I went Wide Open Throttle (WOT) the car just stalled, like it wasn't even running.

I don't know if you can do this with a Holly, but, I pulled the top of the carburetor off and ran the car, when I went WOT I could see all the fuel leave the Power Valve Well and the car would stall, I nudged the floats just a bit and now it runs just fine.
 
You must log in or register to reply here.
-

Back
Top