The Stovebolt Site Forums The Shop Area Engine Shop DUAL CARB SET UP

Thinking about installing offy dual single carb on my 235.already have fenton header/splint exhaust, trucks runs real good, question would I gain that much more performance with the dual carb set up. I know that it would look neater,I have heard that dual carbs can sometimes be a pain
to adjust. thanks for any comments----redryder

howziit guy!

JMO, you could also try a 4-barrel intake, with 390cfm Holley, 500cfm edelbrock, or whatever.

much easier throttle linkage hook-up, no synchronization problems, larger air cleaners available, as are jets/rods/gaskets,etc.

Thats true, run one 4 barrel and its easier to set up...... however, everyone else does that and it's not that exciting anymore
Personally, its all in what you want. Im a hot rodder, so I'm planning to use 3 Dellorto side draft carbs for good atomization and to look cool!

I figure by the time I ebay my intake and 390cfm Holley........ it'll break even for me $$$$ for the intake and linkage

If you are going with dual rochesters, go to inliners.org and go to their tech tips. They have a good article on the modifications needed to the carbs.

Dual carbs will provide about a 10 hp increase mostly in the top of the RPM range. They help the 235 breathe a little better, which it sorely needs.

As much as I like the single 4-barrel, it's pretty boring as far as the "Open hood impact" factor. Speaking of side-draft carbs - I've located an old McGurk triple side-draft intake for my GMC. The owner was not anxious to sell it, but admits it's likely to just gather another 40 years of dust. The S&S Harley carbs seem to be able to flow enough for a 100" V-twin, so thats going to be my winter project...like I needed another one.

Sixpack - We'll have to hold a party and worship you when you get that one done.

Joker:
I installed 2x2bbl Holley Webers on an Offenhauser manifold using adaptors from Tom Langdon on my 57 Chev pickup. Works great: started right up and tuned very easily. Also, two carbs always look better than one.

You guys are weenies, I have a 4 cylinder motorcycle with 4 sidedraft carbs on it, one for each cylinder. It's not that hard to keep tuned, you just need a vacuum gauge (it doesn't have balance tubes). With a 2x carb set up you need a flow meter to synch it right but you can get very close by listening to the venturi whistling and matching the pitch between the two. The idea is to match the air flow between all the carbs at two points- 2000 rpm and idle, in that order. Then just set the idle screws at the same point for good idle mixture and you are good to go. When you first install the carbs you need to change the power valve so it opens at half the vacuum than the original one did so you get a rich enough mixture.

4ontheFloor, Just how does one go about changing the power valve for half the vacuum? Can you explain? I'm working on dual rochesters. Thanks
George

You can order differant (lighter) springs for the power valve. I'm not sure where to get them, though. Some people just cut them, but that's not a good idea. I am going to put dual Holley 94's on my 261 when I get it done and it's easier with those, you just put a differant cartridge valve in. I get my parts from www.vintagespeed.com, a multi-carb specialist.

The secret to getting your DUAL CARBS to march in lock-step is LINKAGE, (assuming you have two IDENTICAL carbs, which may be the biggest hurdle these days). I know, I learned the hard way, linkage must be fully adjustable and not junk. As you crack the throttle, the throttles must open exactly together, look down the throats and make sure. Think inside the CARB! Once this is achieved, you then can use the Unisyn or what ever trick you want to check out flow of air/fuel and adjust away. I believe if I didn't have a collection of BXOV-2 Strombergs I'd go with Langdons dual Holley-Webber set up.
Enjoy!

Thanks for the response on my dual carb for 235 question,I appreciate all of the input,I will have to ponder on it for awhile, redryder