The Stovebolt Site Forums The Shop Area Engine Shop Engine stalls on heavy throttle

I have been slowly working through getting the old girl running and am having some luck. This is my first time doing any of this aside from simple stuff like oil changes and rotating tires so am trying to learn all I can. When I got the truck, it wouldn't start without a fight. New plugs, checking the points gap and dist cap followed by resetting the A/F pin on the carb to 1 1/2 turns had it starting like a champ.

The next problem was that if I took off the choke at all the engine would die. I purchased a Rochester B rebuild kit and had at 'er, cleaned and rebuilt my first carb. I followed the instructions, set the float and as far as I know its assembled properly. The truck starts, warms up and I can close the choke. It was running rough so I hooked up a vacuum gauge and ran the screw out maybe 1/2 turn and was getting around 21-22 on the gauge. Its at least in the 'normal' range.

Since I rebuilt the carb (not sure if it did this before I rebuilt it as it was a chore just to keep it running) it stalls/chokes out when giving lots of throttle. If I feather the throttle and raise the RPM gently its fine but if I stomp on it it starts to die. I have to feather to get it back. I can gently increase throttle fine but at any point in the range if I step on it RPM's drop. I sprayed ether around the manifold and carb and did not detect any noticeable RPM increase.

I noticed a sound like a gorilla trying to suck air through a straw when pressing on the throttle aggressively. To me it sounded like it was coming from the oil fill cap, my wife thought it was coming from the air filter (Oil Bath). I tightened down the nut on the filter and that seemed to lessen the sound and its slightly more responsive. Is this normal or could this be part of my issue?

All of this is done on my driveway, I have only taken it around the block once, before the carb rebuild and it was a truly impressive experience, felt like I was on a horse trying to buck me off. Its much smoother now going back and forth to the garage and I hope to have a better experience going around the block soon... Does anyone have any ideas about the throttle response being to shutdown when I step down on the pedal?

Try loosening the exhaust pipe at the flange where it meets the manifold by about 1/2" or so. I's possible you've got some sort of restriction on the exhaust system that's preventing the engine from accelerating. That's a remote chance, but long-idle vehicles have been known to accumulate all sorts of debris in the exhaust system thanks to mice and other critters nesting in the tailpipe.
Jerry

Clean and reset the points. Then get a dwell meter and make sure the points are right.🛠

Along those lines; there's a thermostatic diverter in the heatriser on the exhaust manifold. If it's stuck in the "cold"
position (closed). That will also (obviously) cause exhaust restriction(s).
You didn't mention. But does it "cough" either out the carb, or the exhaust, when you stab the throttle?

HTH

--Chris

check to see if the accelerator pump is working. the ball may not be seating

I had to replace the accelerator pump one more time AFTER I rebuilt the carb, there was just too much varnish and debris in the old tank, lines, and fuel pump, now the whole fuel system is new or rebuilt and it starts and runs very well. The accelerator pump gives a shot of fuel down the carb throat each time you push the throttle, if it's not squirting fuel when you manually operate the throttle then you will get the symptoms your describing.

Low fuel pressure?

Check the advance on the dist.

I had the same issue with my truck and after going over everything two or three times with no improvement I finally figured it out. In my case the wire to the distributor had corroded and broken inside but maintained contact. When I stabbed the throttle the dizzy rotated causing the wire to momentarily separate. It would almost kill the engine until the dizzy relaxed to its normal position. I could accelerate slowly without a problem.

Just one more thing to check.

Wow, thanks for all the replies. I'll start going down the list you all have provided. I'm starting to think its with the rebuilt carb. When we were able to get the truck started before I bought it the PO was able to rev 'er up without this choking. Looking at your responses though I could see it being any one of those and will check each out.

To answer the questions:

Does it cough? Not that I noticed but I will listen for it. I did notice a couple backfires when the mixture was too lean.
Low fuel pressure? I honestly do not know, I will look into how to check that.

Thanks again guys. I'm looking forward to trying your suggestions.

Jay

At the risk of being "that guy", the heat riser does not restrict exhaust in any position. The flap simply allows exhaust to heat the intake manifold, or it redirects the exhaust directly out of the exhaust manifold, depending on what the bi-metallic spring dictates.
Having a malfunctioning heat riser can cause driveability issues.
1) During cold weather and a cold engine, with the flap in the "warmed up" position, the engine will fall on its face upon acceleration due to the accumulation of liquid fuel pooled up on the cold floor of the intake runner.
2) After the engine is thoroughly warmed up with the flap stuck in the "cold" position, the intake manifold will become too hot, causing the air/fuel mixture to be out of specifications and will not run well.
Carl
"That guy"

Coughing (backfiring out the exhaust) is often (but not exclusively) a distributor that is too
far retarded. That would also account for the "low growl" you indicated you were hearing.
Turn the distributor counterclockwise just a bit, and see if she doesn't respond a bit better.
In the end (all other things being correct). You might want to keep advancing the dist,
followed by stabbing the throttle, until she "coughs" out the carb. Then back it up to
*just* before she coughs. That should give you as much "response" as the ignition
will provide.

HTH

--Chris

@52Carl,
Ahem. Yep. Ya got me.
I'm afraid I was in too big a hurry, and didn't think it through. So yes, indeed.
The "flap" in the exhaust heat-riser, while still affecting the performance,
does NOT restrict the "flow". :O
Thanks for "keeping it real", Carl.
I wished I'd actually gone out to my rig, and confirmed it was in the location
I imagined it was.

--Chris

P.S. Please continue to be "That Guy".

I have an alternate heat riser version... I took off my manifolds and the heat channel on the intake was completely closed from carbon buildup... I guess the good news is that I also was missing the spri g that opens and closes that flap but it took lots of wire brushing, a foot or so of cable in a drill as a drain snake and some sandblasting and pressure washing to get it cleaned out... So it is possible for one position to be blocked 😄

I took the top of the carb off and was pumping the throttle linkage. I only saw gas squirt out every 10 pumps or so. Movement didn't seem restricted but admittedly I know next to nothing on how these should work properly. Should it be squirting out with each pump?

I haven't had much of a chance to try much with the snow we have been getting (don't want to get the cab wet as the windshield seal has a 2 inch gap and it has some rusty bits I don;t want to worsen) and it is stuffed into a 1 car garage.

It should squirt with each push of the accelerator.🛠

I seem to have a new development but not in a good way. I was unable to work on the truck at all last year so I started again this spring. This time I was unable to keep it running without throttle at all and after a few minutes it just quit. It didn't start up right away and the battery died so I had to enlist some help to push it back in the garage. I would be able to start it after letting it sit for a while but it would quickly die and after a couple tries, it gives me nothing.

I opened the carb up again to see if there was debris and noticed that I had the wrong checkball in the power piston bottom. It was pushed in and stuck but I was able to get it out by holding it with pliers and whacking it a few times. I though "This is it, problem solved!" after putting the right checkballs in the proper holes. Nope, it is doing the same where it will start, run rough for 30 seconds or so and shut down and give nothing after a couple tries. I tried screwing in the idle screw to help keep it running without my foot on the gas but it wouldn't stay running. I saw gas leaking out of the throttle plate and was thinking it must be a vacuum leak but after doing some research it sounds like this is most likely a flooding issue. I checked Mikes Carburetors where he had some info for these symptoms and from there started checking the floats. Oh, When I was putting the carb back when I found the checkball issue I also remeasured the float drop and it was off so I set it to the measurements for a 1958 which I am sure I did a year and a half previous.

I opened it back up to see what was going on inside (getting good at the removal process) and it had gas in the bowl and looked fine. I found my old float and tried it as it was at least able to idle with it but still, the same issue. Starts for a few seconds and thats it. I have some pictures here with the new and old float measurements, does anything look off on the new? There was plenty of gas in the bowl if that means anything.

I again opened it up and made sure the jets are clean and no debris in the inlet. I saw in the carb rebuild diagram that the inlet should have like 4 or 5 other parts in there including a screen but mine doesn't have anything inside, is this normal? I blew into the inlet and it seems like the needle valve is working. I also checked to see if the carb was squirting and honestly didn't see anything. I should see something down the hole in the "No Squirt" picture right? Would this be a bad pump? The one from the rebuild kit is what is installed but I had to order a new kit after tearing the gasket so do have another I can try. Does anything stand out to the experts here? I am getting very frustrated here!

Could this be a fuel delivery to the carb issue? I'm going to try the pump test tomorrow, taking the hose off the inlet and running the starter with the line in a bottle to see flow but is seems like it is getting fuel...

Jay, as a previous poster mentioned, I had a similar experience with my old 216 several years ago. The wire from the distributor to the coil was frayed and not making solid connection. As the distributor rotates hundreds and thousands of times, that wire can slowly deteriorate. Replaced the wire and started and ran much better. Definitely worth checking as part of your testing/diagnosis.

Also, you mentioned a few backfires. Have you had a timing light on it to confirm the timing is set correctly?

The ignition wires have all been replaced recently but I don't have a timing light. I lined up the white BB with #1 to get the base timing in but have not been able to keep it running long enough to set. It does have Pertronix instead of points if that would make any difference?

Do you have a ballast resistor?

What is your wiring between the ignition and the coil/distributor?

I bypassed the ballast resistor as per the instructions for the kit. I didn't remove it and could put it back in line if that may be part of the issue? I basically took the leads off the resistor and attached them as one.

Do Not Alter Pertronix Instructions! 🛠

I checked the fuel pump and it seems good, a good stream every 2'ish seconds. I tore the carb down again and cleaned everything I could while making sure there wasn't any blockages on the inlet, needle seat, anywhere I could see a hole that lead anywhere. It started up nicely and I was hopeful as it seemed like it was running longer but after a few seconds it started to die as usual.

I found this post where the OP had a similar issue although his ran longer than mine where polishing the needle valve helped. I noticed while mine does move smoothly it will slightly catch sometimes. Does this sound like something that may be causing my issue?

Well, I advanced the timing a hair on the dizzy and it ran quite a bit better. Advanced some more and with the idle screw turned in it will finally idle so I can get to setting the timing further and the a/f mixture. it does backfire a lot if i stab the throttle but will worry about that after i get the idle timing and mixture set. I just have to read some more on using the vacuum timing method as thats all I have available at the moment.

From what I see so far its set the dizzy at max vacuum then down 1", set idle as low as I can then set mixture to highest stable reading then repeat? How much does the order of the idle and mixture come in to play? Is one better to do first than the other or what is the most reliable order?