The Stovebolt Site Forums The Shop Area Engine Shop Carb replace,

I have 2 Rochester bs on my 1954 235. If it was yours would you replace them with Rochester's or switch to other brands and what would that brand be? One of the carbs is original to the truck and the other was an aftermarket purchase.

235 carbs are WAAAAAYYYYYY too big for a dual carb setup to handle if you're feeding that same engine with two of them. There's no way to turn that 235 into a 470 cubic inch engine, no matter how much boring and stroking you do. 216 carbs would be better, but not by much- - - -they're still capable of feeding a 432 cubic inch engine. Dual Rochesters of any size are double trouble. Get a couple of Carter YF's, the 951S series. They're made for a 140 cubic inch Jeep F-head engine. You'll only be a little over-carbureted, like for a 280 cube engine!
Jerry

If it were me, I'd get a stock intake manifold and replace with one model BC properly rebuilt and jetted correctly. Make certain it is rebuilt with ethanol resistant parts and make certain the airhorn either wasn't warped or has been fixed correctly. Please note: I'm not as negative about the Rochesters as some, and while I could be wrong I believe I can come up with ways to solve some of their problems and basically I don't believe they are bad carburetors. I say BC because long ago I decided a working auto choke was much better at its job than I'd be.

Or get a Carter if you prefer, but if you drive your truck infrequently enough that your carb becomes dry I believe there is a neoprene part in there you'll become handy at replacing every year or two and if it gets dry enough it is possible you might have to replace more often than that. But hey...once you've done that a couple of times it will give you a reason to never let that carburetor become dry. If you want an example of what neoprene does when it dries out, ask any plumber or tilesetter...even an apprentice. It is one of the first things he/she learned about toilets and the reason any tilesetter worth hiring figures out what toilet bowl seals will be needed at the end of the job.

The only problem with the advice on the carbs is, that I have been driving with them for over 12 years with no issues. What I am trying to do is eliminate what could have caused the drastic gas mileage drop. Jerry thinks it is the carbs and I respect his opinion but the issue raised it's ugly head after I came back from HQ a year ago April and I averaged 20 mpg then, when I went to KC in Sept. it had dropped to 15mpg. The carbs were not touched at that time. I did have electrical problems. First, it stopped and would not start, I fiddled with it and finally got it started and drove 5 miles home, the next morning it would not start, no power to the coil, so the mechanic thought it was the HEI coil so he replaced the internal parts and still no start. I thought maybe it was the ignition switch so to see what type it was, I reached behind the dash to check the connector then I tried to start it and it did, it was just a loose pin type connector. I tried to find someone to check the dwell but nowadays shops don't bother with that, everything is electronic. I live in a small town. I did think of 2 places that may be able to check it. The search goes on.

There is no point in checking the dwell in an HEI system because the ignition module keeps adjusting it with RPM. The HEI will either work or it won't and it seems to be working.

If your fuel economy dropped but the fuel and ignition systems seem to be working fine, I would check other things like timing advance. Have you checked your vacuum advance canister for leaks?

If it was mine, I would replace the intake manifold with a three-carb manifold (for either side-draft or down-draft carbs).

If it were side-draft, I would use three Carter type YH carbs number 2618s from a Dearborn marine engine (most common of the YH series) and recalibrate for the Chevy.

If it were down-draft, I would use three Carter type W-1 carbs from a 1939 Chevrolet, part number 420s.

In the meantime, I will remain happy with my off-topic shop truck (brand name same as an old country singer from Tennessee) with a 390 and two 625 CFM genuine Carter AFB's running solid linkage that gets 22 MPG at 70 MPH (it doesn't do this well in town with my foot in the rear carburetor ).

And they have been on the truck for 18 years, without being touched!

Jon.

Ditto on the three carbs- - - -but put a piece of solid aluminum sheet metal under the two outer ones.

Jerry - they need to run straight linkage, NOT progressive.

Jon.

If they block off the two outer carbs and make them eye candy like they should be, linkage style is irrelevant.
Jerry

fraso, what you advised follows my suspicions. The distributor was the thing messed with the most just before the mileage drop. It also reinforces what I experienced last Saturday coming back from a 300-mile trip. The truck seemed to top out on the slightest rise. On my trips to KC, 8, there are some hills that are long and even with cruise set it does not slow down and has extra if it needs help. Will have it checked and maybe replaced. I went online and watched checking and adjusting.

Didn't you find a problem with the speedo being off in another related thread????

One of the worst things to do is fix some thing that ain't broke.....

Pontiac Sprint OHC L6: 230", 750 CFM QuadraJet = 3.26 CFM per cubic inch.

Did you check your odometer accuracy as per your thread in the "Spoon?"

Yes. I am installing a new vacuum advance later this week and having everything check.

You're losing 5-8 degrees or more of timing advance at light throttle cruise speed. That will definitely have an adverse impact on gas mileage. It's like the ignition is set for a hard uphill pull all the time.
Jerry

Dave, I should have left things alone but of course, I did not. I assumed the odometer was off and I attempted to reprogram it. In this convoluted process, you have to push and hold a button for so many seconds to calibrate the rear end ratio then by driving a measured mile and I assumed that mile roads here in Indiana are a mile, not. So then I got out the trusty Gps on my phone and measured a mile but just as you are ready to set a car comes along and you have to move and start all over. This a backcountry rural road in the middle of the day. Then I had the electrical problem. I still think it is the problem and I picked up a new vacuum advance today and will have the timing set per specs. I know HRL only got 5 mpg on his trip in the fire engine/truck but when you have been getting 20 mpg on a long trip and it drops to 15 mpg something is off. Also, the in-town mpg is down from 14-15 and now 10-12