back fire seems to run lean

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birdacre
Posts: 411
Joined: October 8th, 2013, 2:37 pm
Body Type: AA express
Model Year: 1928

back fire seems to run lean

Post by birdacre » January 3rd, 2019, 10:10 am

any ideas why my AA would suddenly need the main jet knob turned out 3 turns to run well. points are good, it also works if choke is pulled 1/3 closed. i know it might be 25 degrees but i never had this before. i guess it could be a speck of dirt in carb? bad condensor. seems like fuel deliver? any ideas, i should start with carb disassemble first but thought i would ask any other members. never had this problem with model a or this aa until now. thank you, kevin

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1crosscut
Posts: 755
Joined: December 25th, 2010, 7:22 pm
Body Type: 82-A
Model Year: 1929
Location: Lincoln, NE

Re: back fire seems to run lean

Post by 1crosscut » January 3rd, 2019, 11:26 am

If choking it makes it run better then it is most likely that there is a chunk of crud in the carburetor. Pulling it apart and blowing it out is a good first step. If that doesn't help then a complete disassembly with a soak in carb cleaner is in order.
Be sure to check your fuel filter and check that you have good flow of gas to the carburetor.
See that the gas cap is venting.
Check for failed intake manifold gasket and that the carburetor is also tight to the intake manifold.
------------
Dave

KimVanOrder
Posts: 480
Joined: August 11th, 2013, 4:25 pm
Body Type: 82-A Platform
Model Year: 1928
Location: Hamilton, Mich.

Re: back fire seems to run lean

Post by KimVanOrder » January 3rd, 2019, 3:48 pm

1crosscut wrote:
January 3rd, 2019, 11:26 am
If choking it makes it run better then it is most likely that there is a chunk of crud in the carburetor. Pulling it apart and blowing it out is a good first step. If that doesn't help then a complete disassembly with a soak in carb cleaner is in order.
Be sure to check your fuel filter and check that you have good flow of gas to the carburetor.
See that the gas cap is venting.
Check for failed intake manifold gasket and that the carburetor is also tight to the intake manifold.
What e said !!
KVO
Dec. '28 AA

birdacre
Posts: 411
Joined: October 8th, 2013, 2:37 pm
Body Type: AA express
Model Year: 1928

Re: back fire seems to run lean

Post by birdacre » January 3rd, 2019, 9:17 pm

had a good rebuilt carb in cabinet. bolted on, like a new truck, i will soak the spare to have another spare. i think maybe an inline fuel filter. i have just the old sediment bowl in use although cleaned with new screen. most likely not as fine holes as an in line. thank you, kevin

User avatar
1crosscut
Posts: 755
Joined: December 25th, 2010, 7:22 pm
Body Type: 82-A
Model Year: 1929
Location: Lincoln, NE

Re: back fire seems to run lean

Post by 1crosscut » January 4th, 2019, 7:31 pm

Glad you found where the problem is. Be sure to test the carburetor out after you get it cleaned up before setting it aside as a spare.
I would be hesitant about adding in an inline filter. They can cause more issues than they solve. Check to see that you have a pencil filter in the tank fuel shut off valve. That will help keeping debris from getting into the fuel line in the first place.
------------
Dave

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