1953 ford NAA backfires under load

[Johnyt1776]

I inherited my great grand daddies ‘53 naa, for as long as I remember it ran well and even growing up would use it occasionally and never had issues. I do the maintenance as necessary, but it started bogging down this season while bush hogging, so I replaced plugs, wires, cap, rotor, button, and point. Also rebuilt the carb. Runs great! Idles @ 450rpms as it should be, But the moment it gets under power it backfires and struggles to stay running. Any thoughts? Does changing all of the ignition components change where the distributor need to be clocked at?

 

[Janicholson]

Welcome to YT forums and ASAP parts. The replacement makes no difference if the point gap is correct. If it is not correct, that needs to be fixed, not the distributor rotation. The most likely issue is fuel supply. with a clean container open the carb bowl drain and see if fuel can flow at 1 pint in 2 minutes. (don't count the first rush of fuel as good evidence. Jim

 

[old]

I inherited my great grand daddies ‘53 naa, for as long as I remember it ran well and even growing up would use it occasionally and never had issues. I do the maintenance as necessary, but it started bogging down this season while bush hogging, so I replaced plugs, wires, cap, rotor, button, and point. Also rebuilt the carb. Runs great! Idles @ 450rpms as it should be, But the moment it gets under power it backfires and struggles to stay running. Any thoughts? Does changing all of the ignition components change where the distributor need to be clocked at?

Did you set the point to the correct 0.025 gap?? Do you have a good blue/white spark that jumps a 1/4 inch gap from the center wire of the cap and at all the plugs?? If you pull the carb drain plug do you get a good steady flow of gas that will fill a pint jar in less then 2 minutes.

 

[Johnyt1776]

Welcome to YT forums and ASAP parts. The replacement makes no difference if the point gap is correct. If it is not correct, that needs to be fixed, not the distributor rotation. The most likely issue is fuel supply. with a clean container open the carb bowl drain and see if fuel can flow at 1 pint in 2 minutes. (don't count the first rush of fuel as good evidence. Jim

Thank you for that, I did see it on a previous post and checked that earlier and I am getting 1p in 2 mins. And for clarification, the original fuel line finally gave out last season and I replaced it and the fuel bowl sediment trap as well as flushing out the fuel tank. So I’m fairly confident my fuel supply and cleanliness is good.

 

[Frankmn]

Did you set the point to the correct 0.025 gap?? Do you have a good blue/white spark that jumps a 1/4 inch gap from the center wire of the cap and at all the plugs?? If you pull the carb drain plug do you get a good steady flow of gas that will fill a pint jar in less then 2 minutes.

That's how an old Harley runs with a bad condenser. Maybe you got a bad one. Your list of parts doesn't include that.

 

[Russ from MN]

That's how an old Harley runs with a bad condenser. Maybe you got a bad one. Your list of parts doesn't include that.

Yes, and even a new condenser can do that! Best to just leave the old one in, they don't wear out. If it's not broken, don't fix it!

 

[used red MN]

Hello Johny, welcome to YT! What was your method of cleaning the carb. Should have been poke wire or torch tip cleaner through passage, spray in carb cleaner then blast with compressed air. And it the passage can’t be seen directly through to day light repeat the poke, spray and air blast TWO MORE TIMES! Do this to any and all passages. What did you set the main jet at should be 1 1/2 turns open from lightly seated. ADJUST FROM THERE! Did you try opening the main jet a 1/2 turn more to see if that helps. And again if it still doesn’t work. Do that until your 4 turns out. If no change turn it back to 1 1/2 or wherever it seemed to respond best to opening the throttle quickly. Check the mechanical spark advance. The point lobe can should spin forward in the the distributor turns slightly against spring tension and return back to nearly where it was before. May need to put cereal box card board on the point cam and grasp it with a pliers to twist it for the check. Just a light twist the spring tension is not real strong. When spinning weights spin below the points and the centrifugal force advances the spark as speed increase. If it locks up this doesn’t work.