Missing during cruising speed

T

Tubby

Senior Member
I have a 1939 all original Delux Tudor. Good compression, vacuum readings good, good fuel pressure. Car was running great. Sat for 2 weeks (don't know if this is relevant). Started and ran it today: idles great, and runs good when I hard accelerate; but in between car is missing badly. I am looking for suggestions for what this likely could be.
 
If it idles good it is running on the idle jets. If it accelerates good it is running on the power valve and accelerator pump. When cruising it is running on the main jets. So, I think you have some dirt in the main jets. Only takes some crud the size of fly ****. Take the main jets out and inspect and blow them out. Easy first check. So I think it is a fuel problem not ignition.
JMO
John
 
I had this exact same issue with my 38 pickup. Sticky valves.

GM suggested the MMO treatment and it worked.

Run the motor at idle and pour MMO down the carb till it smokes out. Add MMO to the gas and drive it 15-20 miles fairly hard.

After about 5-6 miles it stopped bucking for me. Now I'll do the MMO trick every once in awhile.

If that doesn't work, you're only out a jug of Marvel Mystery Oil. No harm can happen.
 
oldford2 said:
If it idles good it is running on the idle jets. If it accelerates good it is running on the power valve and accelerator pump. When cruising it is running on the main jets. So, I think you have some dirt in the main jets. Only takes some crud the size of fly ****. Take the main jets out and inspect and blow them out. Easy first check. So I think it is a fuel problem not ignition.
JMO
John
Click to expand...

John, good point.

Last August in Gettysburg I experienced a problem with a 59A engine running very poorly on my return to the hotel. When I pulled into the parking lot I noticed the engine running on 4 cylinders (at idle). A quick check by pulling plug wires indicated what barrel of the carburetor was not supplying fuel to the corresponding cylinders. Upon some consultation we decided to pull off the air cleaner, I revved the engine up full throttle and had a helper place his hand on top of the air horn of the carburetor. The small speck of dirt got sucked through the jet and the carburetor was then clear of the blockage and the engine was running smooth again.

So perhaps do check to see if you have dirt in the carburetor. That is the only time I ever had a fuel delivery problem.
 
Thanks to all who replied. I checked the easiest first; I opened up the carburetor and inspected the jets. Yep, one of them was clogged, cleaned 'em out, put it back together and the engine runs great. Really appreciative of the knowledge in this forum. Like plugging into a collective brain!
 
Tubby, there is no substitute for learning by experience. I'm glad you figured out the problem and followed up with the solution. Happy V8ing!
 
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