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Old 02-08-2011, 08:46 AM
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RicardoJM RicardoJM is offline
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Join Date: Jul 2007
Location: Centennial, CO
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Quote:
Originally Posted by subzali View Post
Have you been tracking your gas mileage since you did the rebuild?
Yes, I keep a log book and calculate mileage with each fill up. After the rebuild, I average 12-14 mpg. Up until recently, I was not running vacuum advance. As soon as I started running vacuum advance, I had to deal with the cracked block and just after getting the rebuilt engine in my odometer stopped working. I got it fixed this past weekend.

I'm looking forward to seeing what my mileage is now. Then, I am going to increase my jet size.

Quote:
Originally Posted by subzali View Post
Also, I've been reading that there is a 38/38 and a 38/40. Is the 38/38 the 2 barrel carb for F engines while the 38/40 is the 2 barrel carb for 2F engines? Do you happen to know the venturi size difference between the two? I think on a 38/40 the venturis are 31/35. And from Ed Cook's writeup I think the 38/38 has 28/31 venturis. Do those numbers flange up? I think I'm going to tackle my carb at some point and figure out what I have. I know it's a '78 Federal spec, just don't know how it's jetted and if everything is working properly. How is your secondary actuated? Is it linkage actuated?

Sources:
http://forum.ih8mud.com/60-series-wa...ml#post3043800

http://www.ih8mud.com/tech/carbinfo.php
My research indicates the DD38 was used from 69 through 74. After that, I have not really paid much attention - but it would make sense that the carb specifications (jets, venturi size) would have changed with the "more powerful" 2F.

I'm not sure I understand your question about the "numbers flange up".

My secondary is mechanically actuated. I can tweak the linkage arm to get it to start opening earlier or later. I have not really worked with it to see how adjusting it would affect performance.

I am not a carb guru/expert but have come to understand through experience that the optimum setup (tuned for power or tuned for mileage) is something that will vary for each truck.
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1999 LX 470, 1971 FJ-40
TLCA #18941
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