Backfire issues

Bobant

Bobant

Member
First off, I'm a new owner. Car sat for 10 years and original owner died so I don't have him as a resource. 1930 car. I replaced the plugs, distributor cap,points, and condenser . Also rebuilt the carb. Car is now idling and running great up to about 30 miles per hour. If I go out on the highway at 40 and above it may or may not backfire when I leave off the gas. It gets ugly but does not stall, straightens out by itself and I continue to run. If I open the GAV valve while running 30 or more it seems to backfire less but I have not eliminated it altogether . When idling, it is about 1/8 open. When running 30 or more I open it about 1 1/2 turns. What exactly is the GAV valve, what does it do, and am I messing with the right thing?

I am at the end of my abilities to do much more and may need to get educated help.

PS. -- timing seems good as I did it by the book and used test light and it seems perfect. I also put an extra washer on gas valve in bowl to lower level of gas in bowl. Like I said , seems to run great at 30 and below.

Any suggestions. Help greatly appreciated.

Sounds like fireworks in Chattanooga.
 
Could be that the carb. is running lean, maybe jets need size. The GAV adjusts gas , rich is counter clockwise, lean is clockwise.
JD
 
The carburetor, by design, runs a little lean so it can handle perform at higher altitudes. The GAV allows you to adjust a little more fuel in IF it is needed, such as when cold or low RPM. I generally find that once I am at highway speeds I can close mine and gain about 3mpg.

Question - where are you setting you spark advance?
 
You have a high speed lean misfire, your running out of gas. Check the filters... Pencil filter in the tank would be my guess. Pull the line at the carb... Should have a strong stream of gas straight out of the line... If not that's your prob... If good stream... Float or needle and seat.
 
Bobant said:
First off, I'm a new owner. Car sat for 10 years and original owner died so I don't have him as a resource. 1930 car. I replaced the plugs, distributor cap,points, and condenser . Also rebuilt the carb. Car is now idling and running great up to about 30 miles per hour. If I go out on the highway at 40 and above it may or may not backfire when I leave off the gas. It gets ugly but does not stall, straightens out by itself and I continue to run. If I open the GAV valve while running 30 or more it seems to backfire less but I have not eliminated it altogether . When idling, it is about 1/8 open. When running 30 or more I open it about 1 1/2 turns. What exactly is the GAV valve, what does it do, and am I messing with the right thing?

I am at the end of my abilities to do much more and may need to get educated help.

PS. -- timing seems good as I did it by the book and used test light and it seems perfect. I also put an extra washer on gas valve in bowl to lower level of gas in bowl. Like I said , seems to run great at 30 and below.

Any suggestions. Help greatly appreciated.

Sounds like fireworks in Chattanooga.
Click to expand...
If the main jet is to large(flow test jets),It will make the mixture rich,give low mileage,sooty plugs,smell of gas, and irregular running. If the Main Jet is to small,it will make the mixture lean, the car won't go very fast,and might even Backfire at high speed. open at 1 1/2 turns is to much as I see it. !/8-1/4 is good if all jets are of proper size,gaskets and float level set to specs.
 
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