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41 Special gets Dual Carb Equipment


Dave_B
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My 41 Special model 47 came to me with a single carburetor and a cracked exhaust manifold. I looked into just replacing the exhaust manifold but on closer inspection the valve body below the carb was cracked too so I decided to replace the whole mess with a dual carb set-up. I bought the parts out of the Bugle and got a reasonable deal. I used the carb that came with my car (Carter 663S) and found another one on eBay.

 

Shot of the engine with the original set-up. Side-bar: notice red engine paint on fuel lines.

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Dual carb manifold in place

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Ran out of file space, more to come.

 

Dave

 

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Here is a shot of the throttle linkage. I used original linkage parts that came with dual manifolds. I opted to have a direct link to rear carb. I made the rear link from the linkage that came from my original set-up.

In the bottom picture you can the linkage winding around the exhaust manifold.

 

 

 

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Edited by Dave_B
Clarity (see edit history)
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I'm having fun with the technology.  Can't seem to get the files in the right order. Oh well I'll just make multiple entries.

 

I got the plumbing done, below that is the trial fitting of the air filter.

Bottom pic shows the extension piece between the rear carburetor and air filter.

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I drove the car to the muffler shop with open exhaust. It was loud. I didn't get pulled over for excessive noise. Ha! They fitted the Y pipe and connected it to existing exhaust pipe. The muffler shop also made the extension piece for the air filter.

 

All painted and looking good. Went for a test drive and she runs really well. Nice bottom end torque for backing up hill slowly to get out of my driveway and on the interstate there is plenty of power. Next, I'll be checking the gas mileage.

 

Dave

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Edited by Dave_B
correcting typos (see edit history)
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22 hours ago, valk said:

Nice work. Looks like you made a sleeve for the rear carb so the air cleaner would sit right?  What do you intend to do with the rear carb choke and heat tube? 

Peter

Thanks Peter. Thanks Morgan.

 

Yes, I added the the sleeve to the air filter to make up the difference for the missing "damper valve assembly."  I saw your problems with the choke interference with air filter body and I don't trust my metal shaping skills, this was easier. You blazed the trail for me.

As for the choke, I have been running it without a choke on the rear carb and it starts right up. The car had a hand choke when I got it, so for now, I put the hand choke on the rear carb and use as needed which, so far, has been never. Go figure.

 

One thing that's bugging me though is the chevy orange valve cover. Gotta paint that thing! Ha!

 

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My car stumbles a bit on take off when cold but runs great once fully warmed up. I attributed this to the chokes being out of sync but there is no good solution since there isn't a choke tube "port" on the rear exhaust manifold as there is on the front. I have rigged the rear heat tube to just rest against the manifold but since the front is a "ram-air" set-up, ie., exhaust gas goes through the tube to heat the choke  vs. just conductive heat thru the steel tube,  it doesn't work as well as the front choke.  I suppose a "Y" fitting could be fashioned for the single port, but the heat tube lengths would be very different and thus the chokes would still not be the same.  Maybe bagging the rear choke altogether - like the original set-up - would work best. Not a big deal so it's down on the priority list...and, err, I agree painting the valve cover would do wonders for your engine bay since everything else looks good.  Let us know if you perceive any difference with 2 carbs. 

Peter

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Looks great! I have two functioning chokes on my car and when it's very cold (like below 45 degrees) it becomes VERY hard to start because it seems to be flooding. I believe I will also disable the rear choke and see what happens. I am now of the opinion that two carburetors don't each need a choke on an engine designed to be started and operated on one and may, in fact, lead to the very problem I'm having where it's getting too much gas. It started and ran on one choke when it was new, the dual carb cars only had one carb with a functioning choke, I realized there's no need for twice as much choke with two carburetors operating in sync.

 

Nice work!

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One choke and one accelerator pump would be for progressive linkage. I can't imagine how that could ever work well with the carbs tied together by a solid linkage.

 

For one thing, the accelerator pump exists because gas is heavier than air, and takes longer to accelerate than air. On tip in, the squirt of the accelerator pump covers the time that it takes to get fuel moving through the regular fuel circuits. Without it, you would just get a big ball of unmixed air, and probably a backfire.

 

With only one choke, and the carbs tied together, one carb would just let pure air in when the car should be on choke. That can't be good. Also the throttle would be open while cranking on an autostart Buick. There is no reason for the single choke to even work, let alone work right, because the other carb has the manifold open to the atmosphere.

 

There are 3 states of the choke(s) to pay attention to. 1) Closed cold (this is the thermostat coil setting). On most carbs this is almost closed or maybe just barely closed at room temperature. If you do need less for starting with 2 carbs (I doubt it), then set less. 2) What happens immediately after startup. This will often be called "choke pull off" in the setup tables for carburetors. If the engine is too rich after it starts on choke, then you need more pulloff, in other words a wider opening of the choke when the pulloff pulls. It is probably a vacuum piston on these carbs. 3) Choke unloader. This pops the choke partly open at full throttle, and you might never clear a flooded engine without it. Car wont un-flood? Set this more aggressive (more open).

 

If the carbs are tied together, the choke settings should match on both carbs.

 

Fast idle will need to be set less with 2 carbs to achieve the same fast idle speed. Slow idle screws and idle mixture screws also will need to be set less. It may not even want to idle as slow before, due to the extra air leakage of a second carb.

 

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Bloo, I hear what you're saying and it makes sense but so far my experience has been that it starts right up with only the front carb choked. The front carburetor is the same one that was I was running solo and it never used to start so well. It wasn't hard starting but you had to crank it for a few seconds. Now it's just, boom, started. Like I said, go figure? I will admit that now it will start right up but cough once and then all is good. This morning when is was about 45* I started it with the rear carb half choked and it started right up with no cough. Friday morning it will be in the low 20s and I'll try it then and see what happens.

As to the fast idle: the two are tied together so when the front carb is on the fast idle cam it pulls open the rear throttle an equal amount, so they are in sinc.

 

Best,

Dave

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