Technical Tom Langdon Dual Carb First Run Issues

Here is a photo of my line set up at the carbs showing gentle curves in the fuel lines.
Fuel filter is not shown here & is down hear mechanical fuel pump.
Jimmie

 

Okay, thanks for the ideas everyone but I am going to officially close this post.

Again, the car runs fine when the pigtails to the automatic chokes are disconnected. When I connect the pigtails to the automatic chokes then the issue starts instantly. Unless i'm missing something how can it be a fuel delivery issue if it works fine when I don't have the automatic chokes hooked up?

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Try reading your voltage at the power side of coil with Chokes unhooked then hook them up look for a drop in volts.
The Wizzard

 

Now that is a good idea and will do when I get home.

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Seems like The Wizzard is on the right track. Besides checking the voltage as mentioned, you ought to trace out the wiring and find out where the power for the chokes is coming from, and what the connection there is between that source and the ignition coil.

 

Voltage draw is very possible, and if the wires are marginal, you may well have found your problem. You should see full battery voltage at the choke heating elements which I assume are 12 volt units.
Use a relay and pull full time power off the battery and activate the relay with an ignition source. This will apply more current to the chokes with out pulling power from the ignition, and if all goes right, the truck should work great hot or cold.

 

If disconnecting the wiring to the chokes is fixing the problem then it's time to take a very close look at ALL the wiring! If hooking that wire up causes the problem it could mean that you aren't getting good voltage (12 volts) to the coil. Who knows what kind of bird nest of wiring could cause that. I'd be disconnecting the battery when not troubleshooting until I found that short for sure!

 

Okay we may be on to something here. Why would I have a 6 volt coil going to a resistor In a 12-volt converted system??

Does this in any way make any sense?







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Yes it does. Ford did it for years and works just fine. In fact all Ford points style ign systems are 6V with a Ballast. Chevy did too. that's what post #2 on the starter is for,,,21V boost on start. Ford did it on the fender mounted sylonoid.
The Wizzard

 

No change...;(

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My chokes are wired to / the same resistor as the coil is. Would that be an issue?

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Yes. They are drawing power away from the coil and not allowing the coil to saturate properly when the points are closed.

And the distributor should not be turning when the engine speed increases. Set your timing and lock it down. Your problem screams ignition related to me.

 

Yes to what, sorry? I don't know what you're saying yes to. Also I was told that my distributor cap should be turning when I accelerate as it does now.

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Looks to me like your choke wire is going to the distributor side of the resistor unless that orange wire is the 12V wire, not the old frayed wire going into the harness. Any event, get the choke wires hooked to the ignition switch on the RUN side of it.

 

The orange wire is going to the coil and the red wire is going to the carb chokes.

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Yes to what, sorry? I don't know what you're saying yes to. Also I was told that my distributor cap should be turning when I accelerate as it does now.<br /><br />Sent from my Pixel using The H.A.M.B. mobile app

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Yes, your distributor should turn under acceleration. The 235 Chevy has a vacuum advance that is connected to the body of the distributor and runs off PORTED vacuum. The plate that holds the vacuum canister is bolted to the engine block with bolt thru a slot. The canister is clamped to the distributor body. When you open the throttle plates a vacuum signal is sent to the canister that TURNS THE WHOLE DISTRIBUTOR. This is entirely backward to the normal Chevy V-8 distributor where the connection is internal and you can't see anything moving from the outside, the plate that holds the points moves INSIDE the distributor. Additionally Chevy V-8 distributors ADVANCE the timing at IDLE using what is called manifold vacuum and opening the throttle plates removes the vacuum signal and actually retards the timing until the centrifugal weights under the rotor advances the timing by turning the rotor.

Listen to the guys that are pointing you towards wiring problems.

 

The choke wires should not be coming off the hot side of the coil. "Yes" was the answer to a question you asked.

 

Okay everyone, I have plenty to work on with all the suggestions. Maybe too much . I'm going to close this Post as I believe it has nothing to do with the carbs.

Thanks for the help everyone and will create a new post when I run into my next issue.

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Go ahead and close it, but I don't think you've got it handled yet. The chokes should NOT be powered off the ignition coil supply. What you can do is use that to trigger a relay, as a relay will have very little current draw, but the power going to the choke has to come from somewhere else.

 

Just going to close it as I originally thought it was the carbs and greet the post is now a little miss leading. I'm pretty confident from everyone's input that my issue has nothing to do with the carbs now. Will review the above hello from everyone and open new post/issues if I don't get this fixed.

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I dont see heat to the intake unless I missed it. You need hot manifold and cool carbs

 

It is water heated.

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Just keep your updates on this thread, so we can tell what fixed it. You are on the right track now, Gary

 

Offy intake???? Does it have a plate to the bottom? Cant see one

 

Yes, it's all there.

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Matt, you have quite a bit going on that needs attention or at least a closer inspection.

1) Wire going to coil, this should be good quality wire with solder ends, star washers, and clean connection. It should not come out of fuse box. It should be right off the ignition switch. The less joints/connections the better. 12-14 gauge would be fine, 10 gauge if going to HEI. Use factory resistor wire if available.
SIDE NOTE) Most all GM coils had two wires going to them, one was the resistor wire coming off the IGN 1 terminal on the key switch. The other wire came from the starter solenoid's " S " terminal. The " S " terminal sends full voltage to coil when starter was activated. The " S " terminal drops off and the IGN 1 terminal takes over when going to run mode. Foot activated starts may have same wiring.

2) The coil is 6 volts, assuming the truck is converted to 12 volts, someone added the resistor to reduce the voltage. Better option is to replace the coil with a 12 volt resistor type coil.

3) Find a 30/40 amp Bosch/Tyco relay to power the chokes. Pull straight ( fused ) battery voltage and run to the relay, then out to chokes. Use an ignition source to activate relay, a few micro amps is all that will be needed to activate the pull in coil in the relay.

4) Set timing when you are done. The distributor will rotate with vacuum advance, and it sounds like that is all working correctly. Ported vacuum is fine, no need to switch unless you are having idle issues that need more timing. Again, sounds like you are good there as well. Use vacuum gauge at manifold port and bump the time up a few degrees over factory setting, watch vacuum gauge for higher readings with advanced timing. More timing helps in cooling, emissions, and power.

Joe

 

This is awesome and thanks for taking the time to write this. Will be working on all of this during the coming weekend.

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I've been silently stalking this site for over a year and now I'm ready to contribute (finally!). I had so many issues after installing these carbs, as well as his "mini" HEI. After suffering with issues very similar to yours for nearly 2 months and replacing nearly everything, I swallowed my pride and called Tom.

"You've got dirt in your tank and it's clogging the carbs."

"Nope. New tank."

"In the lines then."

"Nope. I cleaned the hell out of them 3 times."

"Get a glass fuel filter."

I hung up, more pissed than when I called. Cleaned the carbs and the problem stopped. Then, a week later, it started again. Repeat.

After realizing that I MAY have overthought everything and that MAYBE he was right, I cleaned the carbs for the 3rd time and installed said fuel filter. Dammed if he wasn't right. A new tank, filler neck and lines may be the solution.

Just saying.

Keep us posted, please!
Chris

 

Check exhaust output. The older gm's used a double wall exhaust pipe off the engine. Sometimes the inner wall would collapse and cause this type of problem.