The literature I have saved from Jon H’s tech tip suggests the application was for both the 230/250 6 cyl engines…in 1967. I think there are some folks here who have used a 250-sized carb on a 261.
Anyone have any additional info on calibration of this carb and whether that would work? My hunch is that it probably kinda splits the difference between 230/250 and might be a stretch on a 261.
Maybe I can help a little bit...but there is a gotcha or two. While it wasn't the 4376S, I got a 4145S a few years ago and after some work on the throttle rod connector (because of differences in the design of the 230/250 and the 235 it had to be re-worked---the first gotcha---image of it below) I learned it will perform okay on the 235. Slightly on the rich side, though. I ended up thinking it would have run rich on the 230 and fine on the 250 and GM probably didn't care. The 261? Don't know because I don't have one of those. But the 4145 will work and because it is on the rich side I believe it might be close to okay on the 261. Another gotcha? You have to use a center screw air cleaner or spend time making an adapter. But it does have a manual choke and throttle can be rigged up (throttles by 1966-67 were almost all gone from GM vehicles).
Here is what I learned about the 4373 and 4376 and some other newer ones I've come across that were also used in 155/194/230/250 (like the 4480s)...these have the same throttle diameter and the same venturi size as the YF models made for the 235, but some have pressed in jets and the ones I've seen are largely worn out by varying degrees. A few horribly worn out. The metering rods chatter in them and wear grooves and ruts. You may recall a month or two ago I showed how I was making replacement jets (that could essentially be made in any needed size). I think...but have not had the time to experiment because of some personal stuff...that tinkering with metering rod sizes, metering rod timing and jet size could produce carburetors from these that would work on the 235 or 261. It is another project.
If people here are committed to having a manual choke and throttle, it is becoming hard to find Carter YF carburetors that will work. And staggeringly expensive.
Last edited by Jon G; 09/03/20249:20 PM. Reason: mis-typed a word
~ Jon 1952 1/2 ton with 1959 235 | T5 with 3.07 rear end
Jon H’s website says application is 1967 GMC 230/250 with A/T (automatic transmission). Usually A/T engines have auto chokes. There may be a vacuum port for a choke diaphragm (divorced choke). The little info I have is that the YF-4376S has a 2-step metering rod (see attachment). Our beloved YF-2100S has a 3-step (economy, midrange, power) metering rod. Jon G nailed it about the center screw air cleaner requiring some type of adaption for older engines. In 1957 Chevy cars went to a low-profile air horn (Rochester) for hood clearance. Carter had to change the design as well. Truck carburetors followed shortly after. Some YF model throttle levers raise to open the throttle and some lower. You may have to cobble together appropriate linkage. Some YF models have a timing vacuum advance port above the throttle plate, some below and some both. Take this into consideration when setting the engine timing.
"Adding CFM to a truck will only help at engine speeds you don't want to use." "I found there was nothing to gain beyond 400 CFM."
