Has anyone used progressive linkage on a dual Carter inline six? 1936 inline 207 engine with split exhaust.

Hi bowtiejoe . . .

Your '36 project sounds like fun.

Progressive linkage isn't typically used on a dual. The carb placements favor the front and the back of the engine respectively. Choosing one as primary and the other as secondary could lead to lean conditions on the other end of the engine.

Carb placement is the primary benefit of a dual over the single. The stock single setup has a tendency to run the cylinders #1&2 and #5&6 leaner then the #3&4 which are closest to the carb.

Buick used a progressive 2 deuce setup in the early 40's called 'compound carburetion'. The manifold had a split log and a baffle that blocked off the rear carb using the front carb for most driving conditions. But when the throttle position was sufficiently 'open' the baffle would open and the rear carb would join the party.

Buick Compound Carburetion

regards,
stock49

Thanks for the info. The pic is great, I never new about the Buick set up. What I am about to post ought to spark some controversy. Don't shoot the messenger!
In conversation with someone in the carb business for 30 plus years told me the following:
"When the fuel is atomized in the intake the vapor is sucked into the cylinders in a sequence as the valves open. Because it occurs at different times for each cylinder it does not matter where the carb is located, the fuel/air will be distributed evenly. Unless there is a vacuum issue.
If there is an over carbing risk then progressive is advised.
I never heard this theory before. I agree with you. Admittedly it does make me think.
I did install dual Carters on a modified Fenton to fit my monster 74HP inline. I am waiting over a week for a fuel log from The Hot Rod Company. It looks great! I don't know how to post a pic on this site.

There are a lot of variables to consider when evaluating fuel distribution in a log/plenum manifold fed by a carburetor. Size of the plenum and it's ratio to the displacement of the cylinder(s) it feeds. Air speed which affects the 'size' of fuel droplets being pulled from the carb. At lower speed the droplets will be bigger leading to a richer mixture - at higher speeds the mixture will lean as the droplet size decreases. Temperature of the plenum can cause the fuel to drop out of suspension perhaps even pooling in the floor of the manifold (in the coldest spots) - especially at lower speeds.

Also, the 'atomization' of fuel and air into a 'charge' doesn't actually happen until the compression stroke in the cylinder. The stoichiometry of the charge depends on how much fuel managed to get included in what was drawn from the plenum. If distribution is poor enough one could have certain cylinders running rich while others are pinging from detonation.

Open a gas can on a hot day and watch the vapors play in the air like the tongues of many snakes. The environment in an intake plenum is similar.

This is why multiple side draft carbs were eventually fitted to inline engines - especially for racing. Many configurations eliminated the plenum entirely with a carb dedicated to single cylinder or pair of cylinders (depending on head configuration).

Ultimately, carbs were replaced by fuel injection which meters fuel directly to the intake valve leading to the most even fuel distribution possible.

Hilborn Tech Paper

Classic Inlines

regards,
stock49

Great reading and info. A little confusing to the novice. If you were to install a 235 Fenton intake modified to fit a 207 engine with split exhaust. 2 Carters with metering rods to reduce flow. Straight linkage. What would you do with it? A wall ornament is not out of question.

Hi bowtiejoe . . .

A wall ornament is last thing I would choose. This stuff was meant to be installed and driven! The important thing is two identical carburetors. The metering rods won't likely need to be changed because the air flow will effectively be cut in half as it is now flowing through the two equally sized venturi - so the fuel drawn from each will be halved.

You should be prepared to tinker and tune to get a dual setup to behave. Synchronization is important:
Dual One Barrels
and using carbs from a smaller engine (lower CFM rating) is also typically recommended. But you are fitting to a 207 so I am not sure that there are any Carter OEM carbs out there from a smaller engine.

Also, dual carbs are typically fitted in conjunction with a compression ratio increase and extended cam duration. Absent these changes the increased carburetor capacity is likely to reduce fuel efficiency with only modest improvement in performance.

With the parts in hand I would build it.

regards,
stock49

Not sure if Carter W1 or WA1 were fitted to a smaller engine then a Nash 184. But you could use a pair of Carter W-O carbs. The Model 513s was fitted to the Nash 172. The Model 507s was fitted to the little Wllys 134 (4 cylinder).

I have a pair of Ball & Ball carbs that Came on a 413 Dodge flat head 6. They have tiny throats. I am going to run a pair of Zenith down drafts on my 153(175) 4 cylinder. Those are nice because they have changeable venturies and an outside adjustable main jet. I'd like to find a source for venturies.

Sorry, I have been off line. The Carters are up and running great! Went with straight linkage. I had to add a regulator as they both were dripping. It seems
2-1/2 lbs pressure is good. Thanks for all the advise.

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Great news. Glad to hear that things are working out. Are you running an electric fuel pump?