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Discussion Starter · #1 ·
I have a 56 Caddy w/ the 365 CID engine single 4 barrel carb. The car idles fine however dies when I accelerate. This happens both under load (ie. in drive) and not underload (ie. in Park). I have recently rebuilt the carb the engine has good compression and the heads were just probfessionally rebuilt. I have a feeling the problem is vacuum but I have no vaccum diagram or might it be something to do with my carb? Any thoughts would be appreciated!
 

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Since you have good idle a vacuum leak is probably not your problem. Does the accelerator pump give a good shot? Is the float level set too low? What about a clogged fuel filter? Is the vacuum advance working properly? When you reinstalled the distributor did you get the timing set right? Any of the above can cause your problem. Good luck :thumbup:
 

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Discussion Starter · #3 ·
I was careful to set the floats to factory specs, I can pull the throttle and see a good squirt of fuel. The entire fuel delivery system is new (tank, fuel line, pump, fuel filter). The engine Electrical system is new (Bat, wires plugs, points, condenser, Rotor & Cap, Coil). The distributor is the only original electrical peice, but I have timed the engine with a timing gun and it idles like a champ! It acts as if it is suffocating when I pull the throttle. The opposite of what I would expect. I am just baffled. There is however a small threaded tube extending down from my choke that I have tried giving vacuum to, plugging, and leaving open, but all with no success. Also I am getting about 15psi vacuum at the manifold.
 

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It's been a long time so this maybe off.

Have you been able to let it get to operating temperature? I know this sounds silly but if I remember right that little tube you are talking about is a heat senor of sorts.

What type of chock do you have manual or old style heat spring? This may have something to do with it also.

Pappy
 

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Discussion Starter · #5 ·
Yes I have let it idle for several minutes. The Choke is controlled by a Thermal Spring. The tube at the bottom of this housing almost seems like a drain spout, but it is threaded, which makes me wonder if I am missing somthing. I have the repair manual cd and I do not see any thing about this in the manual. ?? It has got me??
 

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Double check the Transition Circuit.It acts in between Idle Circuit and Main Circuit.Even if only one side is partially clogged the air/fuel will cause this blank condition.Also,15"Hg is too low for such an engine at idle.You might also have a small air leak.
 

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The tube supplies hot air to the choke. Most old engines had an exhaust passage in the intake manifold from one head to the other directly under the carb area. They then had a plate with a fitting that the tube attached to. This arrangement provided hot air to the bi metal spring in the carb choke and opened the choke as the spring heated up. After warm up, with the choke full open does it still run bad? What happens if you turn the idle screws in all the way shut? If it still runs you have a vacuum leak. Re torque the intake manifold bolts and check the carb base gasket and also the gasket between the top and base of the carb itself.:thumbup:
 

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Discussion Starter · #9 ·
Yes the problem exsits before and after warm-up. It sounds like I will have to do a detailed search for leaks. Hopefully the rain lets up for a bit to let me try your guys advise. I'll be sure to post what I find. Thanks!
 

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stalling engine

some of the older carbs. use a small check ball in the accel. pump well.. some just lay in a small recess and some are held in by a light weight snap ring. if you rebuilt the carb, re-check your carb diagram or exploaded view of the carb. just a thought!!
 

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One more thing to check if still using the stock exhaust manifolds, is the exhaust manifold heat riser valve. It is located between the manifold and header pipe, (only one on the left or right side) it's about three inches thick and has a shaft mounted butterfly valve in it and a spring somewhat like the choke spring and a counterweight on the outside. This is for engine warm up and choke heat. It must open and close freely. Use wd-40 or the like on it. Poor performance like you mentioned and engine damage can result if it doesn't work properly.

A little off subject, But. Cutty I used to work at Tracor Aviation at the airport years back and lived Up at El Capitan beach. Loved it there..
SedanD.. I ran a HD shop in Van Nuys Ca. back in the 70's and we had rebuilt Tillitson carb that just wouldn't stop running rich. HD has manuals with fuel flow schematics for their carbs and it turned out that the factory used a plastic check ball in the accelerator pump well and the carb cleaner had partially eaten the ball letting fuel by pass the check ball into the intake. We replaced it with a steel ball and the carb was all better. Some of the weird things you run into!!:thumbup:
 
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