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Hi Forum, I have a '58 Apache 235 which has been fitted with twin Rochesters and an Offenhauser manifold. Since I've had it it has always run too rich with sooty plugs. I've tried carb kits, new jets and eventually two new carbs. I've read many times it should only have one carb, so is it possible to ever get it running properly with the dual set-up? Can one carb be decommissioned so it only runs on one? The second problem is that the Offenhauser linkage which operates both carbs won't shut down properly when idling so it always runs too fast. I suspect the accelerator rod isn't able to pull down the mechanism for both carbs. Fit a stronger spring and the throttle pedal can't be depressed. This twin set-up is so common that surely it must be able to be adjusted properly. Anybody got any ideas? Thanks.

I ran two Mono-jets on a 250, everything was set right on the money, even the linkage was set with indicators so I knew they were even. I got about 5 miles per gallon with that set-up. It was so bad I could almost see the fuel gauge moving as I drove. The problem I had and what you have, is the air velocity through the carburetors. The carburetor bores are to big for the amount of air required to run the engine. You need two carburetors off a 216, both identically set and metered. The bores are smaller so the air speed is quicker which makes the signals closer to what the carburetor is calibrated for.
A lot of guys are running twin Pinto carburetor, a progressive two barrel with each half having very small bores. I will bet yours runs pretty good at full throttle, peak rpm, and even half decent just driving, both due to air velocity being higher.

So, to cure your problem, you need smaller carburetors, nothing else you can do. If you block one, you will lean out the far cylinders. If you run progressive linkage, same thing, the farthest away cylinders will run lean till the second carburetor is opened. No amount of jetting will lean it out.

I run dual Carter W-1's from a 216 on my 250, It took quite a bit of tuning to get it right, but it was worth the trouble to me. It runs much better then even the stock set-up the engine came with.

Joe

This website is full of examples and information on this subject. Here is one that some others have posted:
https://www.stovebolt.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=84514

With time and money, certain dual carbs can be made to run well on your engine. There may not be that much improvement in performance. It's usually more for aesthetics. It's a personal choice. I like low maintenance, "runs well" and minimum aggravation. For me it's a working stock intake and a Carter YF 2100S carburetor with a new ethanol resistant rebuild kit.

Find a set of matched Carter W-O carbs for a CJ-2 Jeep, the flathead 4 cylinder used in WW II. There are usually several of them available on Ebay. Stay FAR away from the new offshore-made substitutes that are advertised as replacements. Rebuild them to be as close to identical as you can. They will only be slightly overcarbureted on a 235, not massively too much.
Jerry

Which Rochesters (bolt pattern 2-11/16" or 2-15/16", or throttle disc diameter)?
What # manifold?
Your rich condition is probably your power valve open at part throttle due to reduced engine vacuum.

If you don't have a Uni-Syn tool then get one. Under fifty bucks and is the only way for the home enthusiast to set multi carbs. I don't know what base size or bolt pattern the Holley 1904 carb for a 144ci Falcon has but it would be another one to check out and is available from Rock Auto. Two of these would not be completely out of range for what you need. I do know over carbed (or over cammed) engines run like crap.

I have found the Uni-sync tools doesn't work for setting my carburetors. At idle, the amount of air each carb is pulling is not enough to activate the float ball in the uni-sync tool. If I close the tool down enough to activate to ball, the calibration is off in the carb due to high restriction.

My tool of choice is dial indicator on the throttle lever. I set both for the same ( X-amount of ) opening, then adjust both for proper idle rpm. It's not hard to get them the same once you are close, just keep adjusting while watching a tachometer, you will see the rpm raise with even the slightest adjustment.

Or, you you can just go buy you a nice trailer. Everyone needs a trailer anyway. I need a trailer.

When all the other shops stopped working on Corvairs we specialized in them. It bought me two houses and a four time shop upgrade. Enough prelude, if a 140 cubic inch engine works with a Uni-Syn then a 235 should. The way ours worked was the tool completely covered one carb to measure how the OTHER carb was being tuned. The 4 carb 145hp Corvair engines were a bit more involved but doable.

I'am not sure my gauge works right, it has to be almost complete shut for the float ball to raise. It may have been banged around before I got ahold of it. It did work on my Corvair carburetors at one time.

I have been running twin Rochester b s for more than 15 years with no problems. Yes I know I have posted problems but they were of my own making. At first, I had mismatched carbs one was a manual choke and the other had the auto choke and I blocked off the ports and use it until I could get a matching one.

Getting Rochesters set up correctly takes time, some amount of bravery, a lot of patience. Read this article.

https://www.inliners.org/tech/tech4.html

Pat was Dyson Racing’s head crew chief for many years and one of the smartest tuners I have ever known.

As for the Unisyn, get a new one. You defiantly need to have both carbs taking in the same amount of air at idle and the unisyn or the fancy unit used on Weber carbs is the way to do it. Otherwise, you end up with the carbs taking in differing amounts of air at idle. So much so that one carb goes into off idle circuit, leads the other carb into the off idle circuit, then cycles back to idle and starts all over again.

As an alternative, the carter carbs, especially the smaller carbs like the YF for the 216 motors run pretty well in dual single form.

Another alternative, get a pair of adapters from tom Langdon over at stovebolt engine company and install a pair of 74 Ford pinto Holley/Weber 5200 carbs. Nice progressive two bbl carbs that run great in dual form. Tom also sells the Weber variant, the 32/36 if you want factory new carbs.