Pop back through carb.

R

russcc

Well-known member
The original engine in the '40 is plenty tired, but starts right up, and runs pretty well. Have not been out on the road yet. with it. When sitting still, and you crack the throttle pretty good, it will pop back through the carb frequently. Is that an indication of a lean fuel condition ? Thank you Fordbrainers.
 
Yes it could be lean but could also be a bit retarded.
Try checking the timing first before you go to the trouble pulling the carb.
 
Poor some Marvel Mystery Oil down the carb with the engine running at idle. Continue until it starts smoking good and almost stalls. That should help loosen up those sticky valves. Always add about 1/4 pint of the MMO to every gas fill up.
 
Intake valve not sealing. Use Marvel Mystery Oil as 39topless said. Give it time, I had one go near a month of daily use 'til better.
 
Could be a stuck valve . . . but also check and see if the accelerator pump is squirting in the carb. Sometimes when you stab the throttle, with no pump squirting, the engine will go to a heavy lean state (temporarily), then when the rpm picks back up, it will run just fine. When I've had stuck valves, they tend to be stuck all the time and I have pop-back and other issues at any higher RPM - it doesn't usually go away.

You might also run a compression check on all cylinders - see if you have one or more that are leaking/low.
 
I had that happen once on a 351 Windsor and it turned out to be a bad spark plug wire, how are yours ? Let us know when you find out....................jhb
 
I had a cheap condenser go bad and it caused the coil to fire at the wrong time, the backfire through the carbs set the oil on the K&N air filters on my 97s on fire, burnt the paint off the hood of my avatar roadster 10 years ago. I would change the condenser and see if the problem goes away. No longer use K&N for anything.
 
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