Technical Tom Langdon Dual Carb First Run Issues

Okay fellow Hamb'rs! I need some help with a little troubleshooting....



I just finished installing my complete Tom Langdon kit on my 1951 - 3100, 261 Chevy truck. Idles fine, electric chokes work with no issues and dampers open up after it warms up but I can't get this truck to go over about 1500 RPMs.

Please see the video..

I thought maybe I had a clogged up carburator but when I just run the vehicle off of one carburetor it acts the same way on each of them. They are both new carbs so I don't think the issue is there. Also, truck has new gas tank and inline filter. I am at a complete loss and any help would be greatly appreciated!!

So what do I need to check next guys?

https://goo.gl/photos/xovs2gSbGYupatLL9



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Are the carbs opening all the way up? I bought the same setup and haven't gotten it installed but I know the spring pressure on the linkage of the carbs is hella tight! Almost need two hands to overcome the spring pressure. Maybe the ****erflies aren't cranking open all the way?

 

Good thinking, but I already removed one spring from each carb based on exactly what you are talking about as I ran into the same issue. . Tom talks about what spring to remove in his directions.

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I have no experience with the Langdon set up, but from what little I know, he does good stuff. I was not able to run the video on my old computer, so I am at a loss there. Just some basic troubleshooting.
Are the ****erflies actually opening to wide open throttle ?
Did you change anything else at the same time ?
Was anything done to ignition at same time ?
What is fuel pressure and volume vs. what these style carbs need according to Langdon specs ?
Is there some electrical issue that may actually be causing electric chokes to partially close while driving ?
Any exhaust changes ? restrictions ?
Possible timing issues ?
Vacuum advance issues from vacuum hose routing/changes with carb/manifold installation ?
Hook up vacuum gauge readable in cab during road test......how does it act ?

Parking brake partially on.......just kidding.

Keep us posted.

 

Wow you just threw me a laundry list. I think it will help a lot when people watch the video. Hopefully it will narrow it down to a few things to first check.

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The video sound is hard to tell much from. It almost sounds like when you step off in it that she is bogging... hard to say without being right there tho

 

Just to let everybody know the ****erflies do stay open after warming up and stay in that position when running.

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It's the opposite, she starts bogging down when you step down on the gas.

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Yes....when you "step off IN it" is a Texas term for accelerating. Lol!

 

Did the engine run good pre-Langdon?

 

Woops!!! Sorry.

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Actually, if I remember right it did something like this before I put it in the garage and doing the Tom duals.

Just figured maybe I had a bad Carter carburetor, but it drove fine for a day and then I had this issue and barely got it into the garage and started working on it..... That was 6 months ago....ha! So actually I cannot say definitively if there was a big issue or not before I started working on it.

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Do you have the stock distributor and is the vacuum advance working? Does the distributor twist when you rev the engine?

 

Yes, I can turn the distributor by hand so I think it does turn when I rev up the engine. I do have the vacuum advance connected to one of the carburetors... Now if it's working I can't tell you for sure.

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Thinking and knowing are different. You need to visually see it twist when you have the hood open and operating the throttle by hand. If you haven't already, I would make sure the points are clean and adjusted to the proper gap. Has it popped or backfired any at all? Are you sure the plug wires are all correct? Meaning is the firing order correct? Start with the basics is the best advice!

 

They are new spark plugs, I have checked that they're all in the right positions on the distributor. And yes if you listen to the video it backfires and Pops alot when you let off the gas.

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I would reset the timing and clean and set the points....and see where you are after that.

 

I don't see a Heat Plate in the photo.

 

Are you talking about these?



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If you get Teflon tape in those carbs you are going to block fuel flow, looks messy from here. You need heat to the bottom of that intake to prevent icing. Tom Langdon wrote the book on the necessity of heat to the intake plenum.

Just from the sound the problem seems to be fuel delivery.

 

The intake manifold is water heated, I am confused.

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It is a heated manifold by water. So I don't need to use teflon tape at those connections going into the carbs? And if this is the issue would I not be able to run okay on one of the carbs unless by some freak of nature they are both clogged by Teflon tape?

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I didn't say you didn't need it, use it judiciously. Those are pipe/compression fittings and a little tape or liquid Teflon, or gas resistant Permatex is all you need. BTW I have over 80K miles on those two carbs, dual intake.

 

Sure sounds like a fuel delivery problem. By chance do u have a fuel filter somewhere else that may b clogged up? Like maybe on the frame rail.

 

Let me look...

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Only fuel filter that I have is here and it's brand new. When I crank the engine I get plenty of fuel coming out into a gl*** jar.



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The mechanical fuel pump looks fairly new also compared to the rest of the motor......



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What happens when you just very slowly advance the throttle? Same thing?

 

Yes, until I get to I figure about 12 - 1300 RPMs

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Also, to answer your earlier question the distributor does rotate when you rev the engine.

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