shew01
Well-known member
Seasoned Model A mechanics probably wouldn’t have had a problem with this, but I’m posting in case a newbie experiences a similar issue and runs across this post.
My old carburetor started leaking worse over the last several weeks, and my fuel shutoff valve was leaking too, which means that, overnight, the carburetor would start dripping on the garage floor (and create a fire hazard). So, I bit the bullet, and I replaced the shutoff valve, the inside gas line, the sediment bowl filter and screen, the outside gas line, and I installed a rebuilt carburetor. Somewhere along the line, I reset the points and lubed the cam.
When I put the car back together, it would idle fine with the new parts, but the car developed a bad miss under load (going up hills), and the car would backfire sometimes. I swapped out the coil and condenser with known good parts and test drove the car after each part swap to see if I could find the issue. The miss was still there.
I swapped out the carburetor, coil, and condenser back to the old parts. The miss was still there.
I cleaned the spark plugs, and spark plug #4 was very sooty. However, the other three spark plugs were nice and tan. So, I changed out the Motorcraft TT10 spark plugs for Champion W18 plugs (because they were in stock at the NAPA store). That fixed some of the miss. However, the miss was still there.
Today, I decided to check the point gap again to make sure it was correct. I use this tool because it takes the guess work out of setting the gap.
https://www.snydersantiqueauto.com/searchm.htm?type=merged&sterm=ModelA&searcht=point+tool
Despite using an "idiot proof" tool, I somehow managed to set the point gap too wide, probably by holding the tool at an angle that I didn't notice. Today, I closed the point gap a quarter turn on the set screw and took the car for a test drive. The miss was gone, and I now have good power under load. I wouldn’t have thought that a quarter turn of the point set screw would make such a dramatic difference in engine performance.
My old carburetor started leaking worse over the last several weeks, and my fuel shutoff valve was leaking too, which means that, overnight, the carburetor would start dripping on the garage floor (and create a fire hazard). So, I bit the bullet, and I replaced the shutoff valve, the inside gas line, the sediment bowl filter and screen, the outside gas line, and I installed a rebuilt carburetor. Somewhere along the line, I reset the points and lubed the cam.
When I put the car back together, it would idle fine with the new parts, but the car developed a bad miss under load (going up hills), and the car would backfire sometimes. I swapped out the coil and condenser with known good parts and test drove the car after each part swap to see if I could find the issue. The miss was still there.
I swapped out the carburetor, coil, and condenser back to the old parts. The miss was still there.
I cleaned the spark plugs, and spark plug #4 was very sooty. However, the other three spark plugs were nice and tan. So, I changed out the Motorcraft TT10 spark plugs for Champion W18 plugs (because they were in stock at the NAPA store). That fixed some of the miss. However, the miss was still there.
Today, I decided to check the point gap again to make sure it was correct. I use this tool because it takes the guess work out of setting the gap.
https://www.snydersantiqueauto.com/searchm.htm?type=merged&sterm=ModelA&searcht=point+tool
Despite using an "idiot proof" tool, I somehow managed to set the point gap too wide, probably by holding the tool at an angle that I didn't notice. Today, I closed the point gap a quarter turn on the set screw and took the car for a test drive. The miss was gone, and I now have good power under load. I wouldn’t have thought that a quarter turn of the point set screw would make such a dramatic difference in engine performance.
