How many 25's came from the factory with a Vaporizer Carburetor? Would these blocks have also been drilled for the throttle rods used on earlier carburetors?
First the easy one – all the blocks had an opening for the throttle rod up until Ford switched to using only the Holley Vaporizer and the more limited Kingston Regenerator during 1927. So a 1925 would definitely have the hole between the cylinders for the throttle rod to pass through. Note Terry Horlick at: http://www.mtfca.com/discus/messages/257047/292998.html?1338506739 mentions that the hole in the block is just punched out and not drilled.
Not asked for but you probably would like to know, “When did the hole for the throttle rod in the valve cover go away?” At: http://www.mtfca.com/encyclo/doc26.htm
OCT 2, 1926 Acc. 94, Box 169, Ford Archives
The one-piece valve chamber cover without the hole for the throttle rod was adopted on October 2, 1926.
Remember there would have been some overlap when the cover with the hole was still used on some of the engines assembled at some of the branch plants.
As far as using the Holley Vaporizer being used on a 1925, at http://www.mtfca.com/encyclo/C-D.htm#Carb1 it mentions Holley Vaporizer (Limited number of cars in 1925). And in the MTFCI Sixth Edition of the Model T Ford Judging Guidelines it mentions “Holley vaporizer used very late (1925 model year). So an early 1925 car would not normally have a vaporizer on it. So how many were used? We don’t know. But if you take the last three months of 1925 production May – Jul 1925 they produced approximately 550,000 engines. Some but not all of them would have had the Holley Vaporizer. (ref page 532 & 533 of Bruce’s book for the engine production numbers.) So I would estimate less than 500,000 and probably way less than that number as they were testing them to see if they worked well or not. Ref http://www.mtfca.com/encyclo/doc26.htm
JUL 24, 1926 Letter to dealers from Fargo branch
"After extensive tests we have adopted the Holley Vaporizer for Ford cars and trucks.
I believe if they had done a large test during the last part of 1925, they would have adopted the Vaporizer sooner as it was they continued testing them through Jul 1926 before they replaced the older NH carbs.
Hap l9l5 cut off
Hap is right on the vaporizer as it was common in the 27s but not really used in the 26 models. My Jan 1926 parts book doesn't have them. Also don't forget that the 1927 model year would start in August of 1926. This would be inline with what Bruce found.
Just to throw another wrench in the research, my 26 Tudor (engine made in early December 1925) has a factory installed Holley Vaporizer set-up on it. Since the car sat for over 50 years, and by the look of the crud on the engine, I have no doubt it is an original engine.
I'm familiar with the "use it up" Ford mentality. I had a '27 Tudor that had a vaporizer. It had the hole in the valve cover metal plate and no (oval) hole in the gasket. I don't recall the block # or if the eng. was original but it had the block/linkage passage hole too. Early '27?
Don't forget that the throttle arm lever (P/N 3531B) for the vaporizer is a different length and in a different place on the throttle control rod than the one (P/N 3531) for the NH.