1951 JD B

Hi People
Just wanna pick your brains , My B starts fine and will Idle fast or slow Perfectly.. but as soon as ya apply the slighttest load, it misses ,coughs and backfires, put new points, condenser ,cap and rotor on, still no change ,tried openin up the carb load needle a few clicks , still no change, I am a little bit baffled as this seems to have started all of a sudden. I havent taken the valve cover off yet to see if a broken valve spring maybe? i guess better do a compression check too first.. any one have any ideas?

Thanks in Advance

Does choking it hurt of help?? If it helps you may have some junk in the main jet circuit of the carb. If it hurts then how long has it been since you serviced the air cleaner and dumped the mud and water out of it and fill with fresh oil

What old said, or some obstruction to fuel flow between the tank and carb.

You might consider removing the oil cup from the bottom of the air cleaner.

If the tractor runs better with the oil cup removed, then there could be blockage in the air stack.

We use a "[i:654c4848f0]flexible pre-cleaner[/i:654c4848f0]" on the air stacks of our tractors to deter dirt/mud daubers.



Hope this helps.

Weak coil

Sounds like varnish on the metering needles to me, might also explain why you saw no improvement when adjusting them. It takes time for a fresh load of gasoline to dissolve that blood clot out of the way. If you gave it neither some extensive run time or a fresh load of new gasoline you can't expect much in return.

This blood clot effect is exactly why I never leave any gas in the tank or carburetor. Although one can develop out in techniques on both needles before starting to allow fuel to pass around the clot, the mixture is off for a good long while. Without fuel in there to form the clot there is no adjustment nor re-adjustment needed - it just runs.

For final metering adjustment I flick the throttle lever full open with my thumb, if it backfires or stumbles it needs more open on the load needle - much more. One or two clicks is not going to get it, half a turn should show at least some improvement. If your spark plug wires are over ten years old they should be changed for new.

I just got done with a 67 for a customer with same complaint. He showed a video of his and when opened up quickly, it fell flat on it's face until you backed the throttle back off. It had been re-built not too long ago. He sent to me and I tore down . As a standard procedure, I drilled it all , (all were open but not quite to size) I pushed the shaft bushings in where they belonged and ground them to bore contour and replaced worn throttle disc. All this would affect idle and fast idle more than load/acceleration but needed done. Absolutely nothing wrong in load circuit. Tested perfectly on my '50 "B" test tractor. Made a video and sent to him. I have to believe it's electrical and/or this "B" has a distributor as apposed to mag , and the advance mechanism is gummed up or rusted. I'll know more when he gets it back and puts it back on his B and still acts same way which I bet it does. Will let ya know what and if he finds the problem with his tractor. Yes, it acts just like it will if you close the load needle and try to open throttle. Difference is...it doesn't spit & pop when closing the load needle. This is telling me that it is spark / timing or bad plugs etc.