Post by
Davezilla »
https://forums.nicoclub.com/davezilla-u195464.html
Thu Nov 15, 2012 6:22 am
For the Holley that's the exact same as the Weber you'd want to look up the 5200 series, but these were not all created equal since some of them will have the smaller 23mm venturi on the primary side. On the side of the Weber and the Holley's main body you'll see some numbers cast in the side of each barrel. The numbers you'll want to see are 26 on the primary and 27 on the secondary, this is the venturi sizze in milimeters. The best match to the Weber that's commonly sold for these trucks comes off a '72 Ford Pinto, it'll have the water activated choke where you can either run your heater hoses thru, or you can swap this out for an electric choke which I opted to do.
There's also the issue about the linkage and the throttle shaft rotates opposite to the Weber, I fixed this problem by making a taller throttle cable bracket, and took off the throttle cable horn off the original Hitachi carb and installed it on the Holley, problem solved there.. Then I needed to make a return spring bracket that mounts to the carb base bolt. These were the only issues I had to overcome to make this carb fit and work on my truck.
The other Holley choice would be the high performance carbs like the 350 cfm 2 barrel, it works great on these trucks and will perform as good as if not better than the 38/38 Weber plus you can buy all the jets etc locally if you need to tune it since these parts are common in almost every auto parts store, and you have a huge choice for air filters as well.
The drawback for this one is that you'll need to get the bigger adapter plate since this one's base is considerably bigger than the Weber/Holley 5200 base size, and you may need to buy a universal fit throttle cable as well as making a few brackets etc, not that hard to do tho...
For the 500 cfm Holley 2 barrel, this is too much carb for these engines which will make it difficult to tune if even possible, the problem is that the venturis are too big so they get a weak booster signal meaning you'll need to use larger jets but what works at cruising won't work under full throttle and vise versa... just stick with the 350 2 barrel if going this route.
Yes, you can put a 4 barrel on these too, the Holley 390 cfm vacuum secondary is right at home on these engines, but again, it'll have to go thru an adapter plate and some manifold porting may be necessary. From the people who I talked to who used this carb, they love it but some of them wished they would have used the 350 2 barrel since it's the easiest to tune and so trouble free. The benefits of the 390 4 barrel is that it has very small venturis so the boster signal is nice and strong at all rpm's, and it'll run off the primaries most the time saving you gas, but the power is definitely there when you step into it.
For me, I've gathered up all the parts to put a Holley 350 on mine and as soon as I got a free weekend I'll do the swap, I'm going to use a universal throttle cable and some pre fab brackets for the throttle and return spring to speed up the installation... When I do this I'll take lots of pics and do a write up as well as a full report on tuning and performance.