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Twin Rochester trouble
#1377302 Wed Sep 16 2020 04:40 PM
Joined: Apr 2010
Posts: 16
New Guy
I have a '58 Apache stepside 235 which has been fitted with an Offenhauser manifold and twin Rochesters. This has led to two problems. The first is that the linkage doesn't return properly when idling so it runs too fast but if a stronger accelerator spring is fitted the pedal won't go down. The second is that it runs too rich and the plugs are always black. I've tried carb kits, smaller jets (48s) and now new carbs but nothing seems to work. I've read many times that it should only have one carb and two never run properly. Would it be possible to blank off one carb or is there a way to fix both these problems, short of converting it back to one Rochester?

Re: Twin Rochester trouble
chevyfiftynine #1377304 Wed Sep 16 2020 05:02 PM
Joined: Nov 2002
Posts: 2,061
Carburetion specialist
There are many threads on this forum concerning dual carbs, and also Rochester type B's for your reading pleasure; searching should fine them.

(1) Make absolutely positively certainly sure that the power valves are functional, and not open all the time.
(2) Make certain the carbs are properly synchronized.
(3) "Would it be possible to blank off one carb?" : NO!
(4) We have found more often than not, if two stock carbs are used on the stock engine, LARGER jets are required because of lower venturii air velocity. Too rich is probably power valves (or a pertronix conversion, without an alternator).

Linkage can be difficult or easy to work with, depending on the type of linkage, and the experience of the adjuster. Make sure that, if either carb has a fast idle circuit, that the choke on that carburetor is not preventing the throttle(s) from closing.


Last edited by carbking; Wed Sep 16 2020 05:03 PM.

Good carburetion is fuelish hot air
The most expensive carburetor is the wrong one you attempt to modify
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Re: Twin Rochester trouble
chevyfiftynine #1377305 Wed Sep 16 2020 05:04 PM
Joined: Feb 2004
Posts: 20,803
You can block off one carb if you don't mind one end of the engine running a little leaner that the other. That problem can be minimized, but not totally eliminated with some jet size tinkering Use a piece of soft aluminum sheet metal instead of a base gasket and dimple the center of it down so the throttle plate on the dummy carburetor doesn't hang up on it. Also, block off the fuel line to the fake carb. The mouth-breathers at a "show and shine" will still marvel at how cool your ride is, and you'll have a lot better overall performance.

Overall, it's not a good idea to run a carb that far off center, particularly if you want the heat riser to work as designed. Tinkering with the way an engine was designed is very seldom successful, unless you're willing to do your homework first. It always involves a lot more work than just bolting a bunch of mismatched parts together.

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Re: Twin Rochester trouble
chevyfiftynine #1377315 Wed Sep 16 2020 06:08 PM
Joined: Dec 2008
Posts: 1,467
Shop Shark
it should only have one carb and two never run properly
Except for the Hudson and about 30 British L6 engines.

Re: Twin Rochester trouble
chevyfiftynine #1377373 Thu Sep 17 2020 01:33 AM
Joined: Dec 2017
Posts: 788
Shop Shark
Read the article by K. Patrick Smith on the subject. Pat was Dyson Racing’s long time crew chief, now retired, one of the best mechanical minds I know, former president of inliners international, and ran a pretty fast GMC powered race car a number of years ago. It’s a little bit of work to get them to run right.

On the other hand, and as an alternative, get a pair of adapters from tom Langdon over at stovebolt and install a pair of 1974 ford pinto Holley/Weber carbs. They are a progressive two bbl, small primaries and larger secondaries, threaded input for the fuel lines. They run really well right out of the box. You can also use the actual Weber carb, it’s the DGEV 32/36, essentially the same carb just no threaded input, uses a brass nipple.

Tom Langdon may still a carter/Weber carb, little smaller then the Holley Weber, that can also be used and will also run way better Right out of the box then the two 1 bbls.

Last edited by Dragsix; Thu Sep 17 2020 01:34 AM.


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