How Much Gas Should a 1927 Model T Use? (UPDATE)

[BLB27]

My 12-04-23 post is getting long so I am starting a new post to provide an update.

I recently drove the coupe 20 more miles. I don't have a speedometer so I verified the miles by driving my F150 the distance. As mentioned in the original post, I had previously checked the mpg after a 12 mile run and found it was 7mpg. After that check, I removed the spark plugs and found what is shown in the attached photos. Surprised to see the difference between plugs 1,2 and 3,4.

On the 20 mile run, I adjusted the carburetor to a leaner setting by turning it down until the engine started to hesitate and then backed it of a little. I carefully checked the gas used using Lang's dip stick and found I had used just over 1 gallon so that's about 18mpg. Before making the 20 mile run, I cleaned the plugs and after the run they were still clean and all the same condition.

I plan on making another 20 mile check. I now have about 60 miles on the coupe.

[TXGOAT2]

It looks like you have made a big improvement. The two front cylinders were evidently running very rich, and the rear two probably OK. The plugs staying clean and being closer to matched after the second run is encouraging. You may have had an air leak at the rear manifold-to-block joint that sealed off from the heat of running, thus improving the mixture balance across all 4 cylinders. I'd check the torque on the manifold fasteners to be sure they have not loosened. Checking the head bolt torque might be a good idea too. Don't overtighten, just make sure they are all even and up to the proper torque as shown by a good torque wrench. Keep an eye on the oil and water and look out for any sign of bands dragging or the rear axle binding.

[Jerry VanOoteghem]

Progress!

What did you ever do about the hot differential? Has it settled in and gotten cooler?

[BLB27]

Jerry, I have taken temperature measurements. I will provide an update post.

Bruce

[Moxie26]

Freshly rebuilt engines need some time to wear in. .... at least 1000 miles ....Why don't you change your oil, re-torque the head, check for tightness on the manifold bolts and carburetor bolts. Since you're still experimenting, why don't you clean up those plugs and regap them to 25 thousands..... And use the Ford hot air pipe on the carburetor. I had a similar problem and those steps did help a lot to have those plugs of modest gray when checked .... and the engine ran better.