Erratic Stumble

Capt Kirk

Capt Kirk

Well-known member
I took the car out for a little Sunday drive to the dairy to get an ice cream. It's about 85 out. The car fired up immediately cold and ran fine. Stopped at a friends house on the way and shut it off. Stayed probably 15 minutes and when I went to leave, the car cranked hard for a second and once it got past the first revolution, it eased up and started. When I did the Dream Cruise a few weeks ago and today, there is an erratic stumble. Go a few miles at 40 mph or so and it stumbles. Some of the stumbles are barely perceptible and some are larger, more noticeable.
I have a skips coil and I rebuilt the distributor last year. Resistor is new. The engine has less than 200 miles since professional rebuild. The only thing that hasn't been touched is the carb. The car (and carb) sat in the barn for probably 25 years and it sat around for several more years at my house waiting to be restored. Once I finished the car, I threw the carb on to see how it would do and it seemed like the car ran fine so I left it. Now that I'm in the lower 48 and taking longer drives on hotter days, this stumble is showing up. I'm also not sure about the gas we're using here in Michigan. Any thoughts about what's causing this? Capt
 
Here's the carb in question
 

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If it's been sitting for that many years I would certainly go through the carb. Gaskets and accelerator pumps dry out and can cause the issues your describing.
Which carb does it have?
 
Oops, we must have been posting at the same time.
I'm no expert on strombergs, but I know there are several here on the barn. I
Rebuild 94's all day long but I sent my last 97 to uncle Max. It came back looking as new.
I've yet to start the engine it's going on, but I have no doubt it will fire right up.
 
Not too much, but it does require special tools, it uses emulsion tubes that should be cleaned or replaced, it's just more specialized than the 94, and I am not used to doing them. I've rebuilt holleys, edelbrocks, carters but not quadrajets or strombergs. Although I did do a cast iron carb on a 1931 Knight engine once, may have been a stromberg. I also did a 2GC on my sons Chevy truck, what a linkage nightmare that was.
A twisted mind designed this one.
 

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RalphM said:
Not too much, but it does require special tools, it uses emulsion tubes that should be cleaned or replaced, it's just more specialized than the 94, and I am not used to doing them. I've rebuilt holleys, edelbrocks, carters but not quadrajets or strombergs. Although I did do a cast iron carb on a 1931 Knight engine once, may have been a stromberg. I also did a 2GC on my sons Chevy truck, what a linkage nightmare that was.
A twisted mind designed this one.
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LOL...that is a nightmare!!! Must have been designed my MC Escher!
 
Do you have a ball park as to what Uncle Max would charge to rebuild mine? I've rebuilt plenty of carbs but don't have any specialized tools.
 
Capt.
In my opinion the Stromberg is a more basic carb, it does not trouble itself with a vac power circuit. You will need a jet wrench, proper kit, and be ready and patient enough to remove the emulsion tubes. Uncle Max has the goods and I'm sure the willingness to guide you thru the tubeilagation. One little sicky item is the mechanical power valve in the Stromberg, it is at the bottom of the acc pump well and in my opinion it must be removed and checked for leak down. If the PV is leaky you may get that great Stromberg gas smell.
Charlie ny
Charlie ny
 
Try some Marvel Mystery oil you may have stick valves. Get a quart, drizzle
some down the carb when it's running for about a minute then dump the
rest in the fuel tank. Drive it about 20 miles and see if it clears up. G.M.
 
Thanks Charlie. Tubeliagation sounds scary...I don't have to pull my pants down do I? I'd like to get a ball park on price for Uncle Max...if it's something I can swing, I'll have him do it. If I can't swing the price, I'll give it a shot...and then send him the box of parts when it turns out I screwed it up :)
 
G.M. said:
Try some Marvel Mystery oil you may have stick valves. Get a quart, drizzle
some down the carb when it's running for about a minute then dump the
rest in the fuel tank. Drive it about 20 miles and see if it clears up. G.M.
Click to expand...

It's not popping out of either the intake or exhaust at all. It's a stumble, an instantaneous loss and return of power...no other associated anomalies. When I was driving, the temp gauge was a fuzz over center but after I stopped for that 15 minutes, the temp gauge was reading just a fuzz below the upper line. I'm wondering if fuel is boiling out of the carb and running into a few of the cylinders making it hard cranking on restart?
 
Kirk ,So its stumbling ? you mean the engine cuts out then comes back in ,run a jump wire to coil sound like lose of ING ..the power valve cannot leak down because it feeds higher so it has to go up hill I would ignore the PV for the moment ,You say its hard starting possibly a unrelated problem .Ted
 
FlatheadTed said:
Kirk ,So its stumbling ? you mean the engine cuts out then comes back in ,run a jump wire to coil sound like lose of ING ..the power valve cannot leak down because it feeds higher so it has to go up hill I would ignore the PV for the moment ,You say its hard starting possibly a unrelated problem .Ted
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FlatfheadTed. Yes, an instantaneous cut out-cut in. All wiring are new harneses purchased during restoration. Not hard starting when hot but rather a hard crank for a couple seconds and then normal crank and start.
With the engine increasing in temp after shutdown, can fuel leak into the manifold and cause a couple flooded cylinders resulting in a hard crank during hot startup? I have an optima battery that's a year old and the generator is charging fine...10 amps going down the road.
 
fuel can drip down but only if the float is not working or leaks so the fuel level increases but with a Stromberg not as prevalent as a Holly Ford for leak down ..You would get some blue smoke and a bit of hunting from the motor on start up then clear running .The system of hard initial crank can be timing to far advanced ,it can be other thinks as well like bad earths ,a instant cut out sounds a bit like electrical so a jump wire to coil might be worth trying ,does it have a resister .? Ted.

Capt Kirk said:
FlatfheadTed. Yes, an instantaneous cut out-cut in. All wiring are new harneses purchased during restoration. Not hard starting when hot but rather a hard crank for a couple seconds and then normal crank and start.
With the engine increasing in temp after shutdown, can fuel leak into the manifold and cause a couple flooded cylinders resulting in a hard crank during hot startup? I have an optima battery that's a year old and the generator is charging fine...10 amps going down the road.
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The use of MMO on a fresh rebuild is good - I have had to do that. Also check the condition of the contacts in the ignition switch and add dielectric grease. I realize that the ballast resistor is new, but consider soldering the nichrome wire to the terminals. Best wishes
 
Flathead...you're theory might be right...I'll need to think about that. I know that when it's time for a cold start, I could drive up and down the street on the starter. This is temperature related. I had skip do my coil and it made a world of difference but I rebuilt the distributor myself (my first time). Set the points to the proper gap and put the slide to the first notch. Nothing scientific. The car never smokes...even when it does this hard cranking thing. This may be unrelated but I've read some threads. My spark plug wires (which came with the car when my dad sent it) are Belden...soft and flexible and in good shape. Not sure if they're the resistance wires but I would bet. There's also champion plugs. Just checked the plugs (which came with the car) and they're RHIOC. Could this be the problem?
 
Check the ignition wires with an ohmmeter - should not have resistance. I would not use resistor plugs on a 6v system, use H10C. Consider the fact that the engine has only 200 miles and still tooooo tight.
 
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