Technical Tom Langdon Dual Carb First Run Issues

You know those carbs have sort of a double step to open both barrels, right?

 

Yes, but I can't even get it to go fast enough to kick in the double Jets.

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On your distributor, pop the cap off, take the vacuum line off the carb to the vacuum advance and **** hard on the end and see if the points plate starts moving. If it does then you know that the advance is working. If you **** hard and nothing moves then the plate is probably stuck. If you can **** thru it easily and nothing moves then you have a leak in the vacuum advance.

I agree though it sounds likes lack of fuel. I had a motor do that to me once and it was the sock filter in the gas tank. It got ****ed up into the pick up tube. I took the fuel line loose off the tank and the gas cap off and with a air compressor and air blower blew backwards into the tank, it blew the sock filter out of the fuel pick up tube and ran great for 2 weeks, started doing it again, pull the sending unit and cut the sock off. Ran great for 2 yrs until I sold it.

 

How much pedal do you have in the cab? One inch from the floor? Two inches? It sounds like you have good idle; is there full range of motion from idle to WOT? If full, uninterrupted range of motion, I'm going back to bits of Teflon in the carb(s).

 

Okay everyone Huge update. I decided to take the electronic choke wires off..... when I do that the truck is driving really good...... It backfires little bit when getting off the pedal but it's running 80% better. What is going on??

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Did you have those wires on constant hot or switched hot?

 

Let me check, I think it's a constant hot......

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Nope, it is connected to a ignition on....

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The electric choke has a + and - mark for wires. Do you have it wired accordingly?

 

I don't think that is correct on those carburetors. There is only one place to put a hot wire on those carbs too.

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Pasted below is a reply I made to another post about these carbs. Make no mistake I love the carbs and Tom was super accessible and helpful. In fact I bought his HEI for my '54. This problem may have been an isolated incident but my car ran the same way yours is running.


A word of caution, after about a year and a half of running these carbs my cars performance went to hell. Chased it for over a month. Finally removed carb tops and looked in the bowl and found metal turnings from a drill stuck in the bowl outlet. They had been hung up in a high spot in the bowl and finally got flushed out of their little hiding spot into the bowl outlet. I think a hole is drilled into these tops for use in our application and the drill shavings never got removed from the bowl following that operation. I never ran the vehicle without the stainless fuel filter recommended by Langdon either. Not that these pieces could have ever made it through a fuel pump or lines.

 

Wow.... And thanks! My truck seems to be running really good now tonight that I have disconnected both automatic choke wires. Do you run your with the electric chokes hooked up?

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I was just going to say something about the metal shavings folks have found in those carbs. Scott is not the first one to post about it. I would pull the tops and have a look.
I would suspect ignition problems due to your statements about pre-dual carb running. Double check timing, vacuum advance, coil, and capacitor. Even poorly running carbs will get up in rpm if you baby them, sounds like yours won't.

 

Another issue that was similar to yours was driving home from a friends house one cold november afternoon. Started running like ****. Wouldnt gain rpm, stumbled sputtered and stalled. This was before i switched to hei. Eventually nursed it the last ten miles home and it died for good in the driveway. The condenser had gone bad. Replaced condenser and it felt like a new Corvette.(sort of?) hahaha

 

But seems to be running really good now that I have disconnected both choke wires.....[emoji43]


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So a HEI distributor fixed your issue? Thanks for the info!

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No, the hei came awhile later. A new condenser fixed that particular issue. For the $3-$4 I kept a spare in the glovebox after that.

 

Ahhhhhh... Thanks for clarifying!

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What condenser are you talking about? This is my first project car sorry....[emoji15]

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I had the same experience. I wondered if less fuel flow due to blockage was helped by keeping the chokes closed??? Maybe???

 

But even with the wires off the choke ****erflies are wide open. So they are not closing....

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When I have the choke wires on or off the carb.... The ****erfly choke flaps are both wide open and not closing after the motor warms up.

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Gotcha. So the condenser is the cylindrical thing on the left. . It's found under the distributor cap.

 

Excellent and thanks....I was thinking I don't have AC in this truck....ha!

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Thanks for all the help everyone. I've got to get some sleep for the night. Will work on more tomorrow.

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They shoRuldn't close when the engine warm. The electric elements just heat the coil spring up so it opens the choke plate quicker than just and automatic choke would . Sometimes a little too quick in cold weather.
There is a possibility that the way or where you had the choke wires hooked up may have caused a draw that took power away from the coil. I'd make sure that they were hooked up per the instructions and not just connected to the easiest place to get to.
Scott F mentioned a restriction in the fuel line. I had that on a 327 with a dual Corvette intake and carbs that came with a 57 Chevy panel I bought in Texas in the mid 70's. Thing would leave a stop light like Jack the bear and then fall on it's face, let up off the gas for a second and hit it again and it would go for a few seconds and fall flat again. I finally decided to figure out what the deal was and took the lines off the carbs from carbs to the end of the line at the frame rail. Took it all apart and one of the br*** fittings was a natural gas fitting with an orifice of about 1/8 inch. Redid the whole setup and it pulled hard until you decided that was fast enough or the tank ran dry.
I'd go over the whole fuel system from the end of the pickup tube in the tank to the fittings going into the carbs and make sure there were no restrictions . I've found a lot of shop rags in gas tanks in the last 55 years on rigs that stalled out at road speed or stalled out at intermittent times. I've also found a lot of twisted fuel lines where the line went into something. Last and maybe the most important here I have found a number of fuel pumps and carbs plugged up with Teflon tape. Unless you are using a pipe thread you should never need the Teflon tape. There is no need for it except on pipe threads if the fittings and flairs are done right to use it.

 

If it is truly a fuel restriction issue why does the truck seen too run like it should *** soon as I disconnect the ignition on wires? Put the wires back on the carbs and the issue starts back up right away. I appreciate your thoughts and help.


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Does anyone know what kind of volts I should be reading on the pigtail wires that connect to the electric chokes?

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RMonty gave you some good advice early back. Do some basic checks. Being you think you may have had this issue prior. Were it me I'd go clear back to doing a compresion test. Prior to that I'd run the valves even if they are Hyd. Then by all means use a Dwell meter to know for sure your point gap is dead on. Last once running again I'd test for Vac leak at the head. Does that manifold still use the metal rings between the Head and Intake? If so did you re install them?
Reason I say run the valves is you have a Flat Tappet motor. Todays oils in that motor can and will Kill a camshaft. First sign of one going away is Backfire then loss of acceleration.
The Wizzard

 

Hi. In thinking fuel issue I see you have a very sharp U bend in the line between the filter & the Carb. You say you get plenty when you put fuel line in a jar. Are you straightning out that sharp U bend when you do that test? Could the line be closing inside due to that sharp bend. My thoughts are that you filter is in a real bad location requiring that sharp bend. Perhaps shorten steel outline from fuel pump and mount it in an upright position somewhere above pump.
Also you should have a flex line from fuel tank to steel line along frame. Could that line be bad? Have you replaced it? If that is a very old line it could be ****ing shut from pump suction if you have a strong fuel pump.
I have similar setup in my 46 coupe but I am using the Clifford heated intake with the 2 bbl Weber carbs. Instead of Teeing the fuel line at first carb the Weber's have both an inlet & outlet fuel access on opposite sides of the carbs. I just ran fuel line to first carb and came out other side of first carb and put a short line to inlet on second carb. No tee choking down flow. These carbs do require heavy spring return tension.
Good luck, Jim