High idle

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VonCramp

VonCramp

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I will start from the beginning to make sure no details are left out. my 'Cuda broke the rocker shaft on driver's side on my 340. Frustrated, I let the car sit for two months. So, the ethanol did a number on the pro comp carb. I got a kit and rebuilt it. I installed the carb and started the 340. It runs but starts out idling at 1100 rpm and soon dies out. I can feverishly work the throttle to make it run, but it isn't close to running right. Adjusting the timing has no affect on how it idles it seems. I have adjustable 1.6 rockers on aluminum heads and a solid roller cam. I am running a Mopar performance distributor and orange box and resistor. Manual 18 spline trans. About to give up and shoot the motor and crush the big block body because all this thing does is let me down. Figuratively speaking of course. Thanks for the helpful advice I always get from the awesome members here.
 
When it's at 1100 is that on the fast idle cam?
Or is that on the curb-idle screw?
Did you do anything else besides replace the shaft and rebuild the carb?
Did you figure out why the shaft broke?
 
Sounds like a vacuum leak to me pal. Make sure all rubber hose are in good shape and making a good sealing connection. Do you have power brakes? Did you match up the replacement gaskets you used? Sometimes you can use your idle enrichment screws, turn them counterclockwise 3 to 4 turns to richen things up(compensating for the air leak) to get it to run while you listen for the leak. Still can't find it? Take a squirt bottle with water or wd-40 and squirt around the intake and carb. Some guys use a propane torch (unlit) and pass the propane around the top of the engine, and listen for the rpm to change. Still can't find it? It maybe internal. You may have used the wrong gasket or it didn't quite seat right.
 
VonCramp said:
I will start from the beginning to make sure no details are left out. my 'Cuda broke the rocker shaft on driver's side on my 340. Frustrated, I let the car sit for two months. So, the ethanol did a number on the pro comp carb. I got a kit and rebuilt it. I installed the carb and started the 340. It runs but starts out idling at 1100 rpm and soon dies out. I can feverishly work the throttle to make it run, but it isn't close to running right. Adjusting the timing has no affect on how it idles it seems. I have adjustable 1.6 rockers on aluminum heads and a solid roller cam. I am running a Mopar performance distributor and orange box and resistor. Manual 18 spline trans. About to give up and shoot the motor and crush the big block body because all this thing does is let me down. Figuratively speaking of course. Thanks for the helpful advice I always get from the awesome members here.
Click to expand...


What carb is it? Pro Comp or Pro Form? Do the accelerator pumps work? Did you blow out all,the emulsion holes and air bleeds?
 
I run ethanol fuel most of the time in my proform 950 and it hasn't afftected the carb. I had the carb apart once because my car was running screwy.

The base plate was loose from the main body.
 
AJ/FormS said:
When it's at 1100 is that on the fast idle cam?
Or is that on the curb-idle screw?
Did you do anything else besides replace the shaft and rebuild the carb?
Did you figure out why the shaft broke?
Click to expand...
Shaft broke due to one of the hold down bolts coming loose and since shaft is hardened steal, it broke instead of flexing. The carb is a Pro Comp with idle screw turned to where there is no opening of butterflies.
 
yellow rose said:
What carb is it? Pro Comp or Pro Form? Do the accelerator pumps work? Did you blow out all,the emulsion holes and air bleeds?
Click to expand...
I did not blow out the emulsion or air bleeds. It is a Pro Comp. Accelerator pumps are new.
 
Dana said:
Sounds like a vacuum leak to me pal. Make sure all rubber hose are in good shape and making a good sealing connection. Do you have power brakes? Did you match up the replacement gaskets you used? Sometimes you can use your idle enrichment screws, turn them counterclockwise 3 to 4 turns to richen things up(compensating for the air leak) to get it to run while you listen for the leak. Still can't find it? Take a squirt bottle with water or wd-40 and squirt around the intake and carb. Some guys use a propane torch (unlit) and pass the propane around the top of the engine, and listen for the rpm to change. Still can't find it? It maybe internal. You may have used the wrong gasket or it didn't quite seat right.
Click to expand...
I will follow your advice and let you know what I find. Thank you for the help! I am running a thinner gasket at carb base.
 
VonCramp said:
Shaft broke due to one of the hold down bolts coming loose and since shaft is hardened steal, it broke instead of flexing.Ok I see The carb is a Pro Comp with idle screw turned to where there is no opening of butterflies.
Click to expand...
Well if the curb-idle screw is fully backed out, and the primary butterflys are fully closed........you have to ask yourself where is the engine getting the A/F charge to run at 1100,even if only briefly. It then becomes apparent why it takes pumping the pedal to keep it running.
If I had to guess, I'd think the secondaries are hung open.Get them closed up, then crank the primaries open until the lowest part of the transfer ports look like a little square from the under side of the butterflies. Then set the mixture screws to 1 turn out. Then make sure the float level is bang-on. While the carb is off, check the base gasket, and the PCV hose for cracks or splits.
 
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I can almost guarantee that you used a wrong gasket on the metering block. Did you save the old ones? Kits come with several different ones. You need to make sure you use the right ones.
 
I can only find one pro comp carb and it doesn't have a choke. If it don't have a choke it won't have a fast idle cam.
 
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