Tuning after carb rebuild

Hey all,

I have a Edelbrock 1406 - 600cfm 4bbl electric choke. I just rebuilt it last week and have gotten it running. My issue is the fine tuning. I don't want to be burning any richer than I need to be. I tried using my voltmeter tach and the edelbrock instructions for best lean idle. The issue is that the engine responds in spurts as opposed to evenly which makes it hard to see when the rpms stop going up. I need some instruction on how to tune one using a vacuum gauge if possible.

I have my initial timing set at ~14 BTDC (no vacuum advance) which seems to be ok. I checked it yesterday and it was up near 20 BTDC. I figured that some of my starting issues might be the engine loading the starter but the starting issues didn't seem to resolve when I retarded it. Regardless I know that 14 is pretty safe on a Cleveland at idle and I don't have pinging issues high up so I'm comfortable my total is at or less than 38 BTDC.

I need to figure out why it is having trouble starting, which is a fuel issue I believe. She'll crank and crank as strong as ever but she wont fire up without me working the gas pedal in a manner which I frankly haven't perfected (I think I've just been lucky because I don't even know if my starting issues are the fact that it is flooded or starved). Occasionally idling, at a light or what not, the engine will sputter and want to die unless I throw it in neutral (possibly transmission but don't tell me transmissions hurt my ability to start!) Seems like either the fuel pump is weak or the sending unit is clogged (or the tank vent is clogged even though it doesn't suck air when the cap is open). I'm going to be dropping the tank in a few weeks to see how bad it is. The car had been sitting for 15 years so if the tank looks like the carb then I have some work.

I have no idea what to do with the choke setting. Right now it is set at the middle base setting. Should I make it richer to help with starting?

Any recommendations on timing and carburetor tuning are welcome. Items I'd like to know: What should my idle speed be set at, how to tune a carb with a vacuum gauge, timing suggestions, everything else to do with my issues. Thanks again everyone.

Update: So I have been reading around and researching. I have found an instruction set for tuning with a vacuum gauge, but it doesn't specify what vacuum port to use. Am I using the ported or full-time vacuum port? They have 900rpm +/- 100 as the idle speed, this seems a little high to me. Thanks again for the help.

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This is ball back calibration and assumes it is an otherwise stock engine. Using a timing light, check initial advance. Vacuum line(s) at distributor disconnected and plugged, RPM at 600-700 in neutral. Initial should be 12-16 degrees. Slowly rev the engine until you see advance stop increasing, total should be 32-36 degrees. Reconnect vacuum hoses, re-verify total advance. Idle speed should be 750-850 RPM in neutral.

Choke setting: assuming 50 degrees temperature, loosen the choke housing screws enough to allow the choke bi-metal spring housing to rotate. Hold an 1/8 inch drill bit between the choke plate and the carb choke housing. Rotate the choke spring housing until it just touches the drill bit. Tighten the choke housing screws. Using your voltmeter, turn the key to the run position an verify you have voltage to the choke. Turn the key off to allow the choke to cool. when it is cool, apply 1/-1/3 gas pedal travel, and engage the starter. If it starts, note the cold idle speed (should be 1200- 1400 RPM). If cold idle is too low or too high, locate and adjust the fast idle speed screw. This is a rudimentary system and may require several cycles to get the exact results you want. It will change a bit with every 20 degree change in temperature.

Use direct manifold vacuum to set carburetor. Check to make sure there are no vacuum leaks and PCV is properly functioning. Set both AF mixture screws at 1 1/2- 2 turns CCW form closed. Start and allow the engine to come to operating temperature. This process will require several cycles alternating between setting the A/F screws and the curb idle screw. Basically you want the highest, reasonably steady vacuum while maintaining desired idle speed. If the most steady vacuum reading is still fluctuating +/- 2 to 4 inches of vacuum it may indicate valve sealing problems. When you are done, the L and R A/F mixture screws should be within 1/4-1/2 turn of each other. When you install the air cleaner assembly you may notice a slight decrease in idle speed due to the restriction of the air filter (slightly rich condition). 1/16-1/8 turn CW on A/F mixture screws usually corrects the idle speed and quality.

I'll be glad to help if I can.

Chuck

Click to expand...

This is ball back calibration and assumes it is an otherwise stock engine. Using a timing light, check initial advance. Vacuum line(s) at distributor disconnected and plugged, RPM at 600-700 in neutral. Initial should be 12-16 degrees. Slowly rev the engine until you see advance stop increasing, total should be 32-36 degrees. Reconnect vacuum hoses, re-verify total advance. Idle speed should be 750-850 RPM in neutral.

Choke setting: assuming 50 degrees temperature, loosen the choke housing screws enough to allow the choke bi-metal spring housing to rotate. Hold an 1/8 inch drill bit between the choke plate and the carb choke housing. Rotate the choke spring housing until it just touches the drill bit. Tighten the choke housing screws. Using your voltmeter, turn the key to the run position an verify you have voltage to the choke. Turn the key off to allow the choke to cool. when it is cool, apply 1/-1/3 gas pedal travel, and engage the starter. If it starts, note the cold idle speed (should be 1200- 1400 RPM). If cold idle is too low or too high, locate and adjust the fast idle speed screw. This is a rudimentary system and may require several cycles to get the exact results you want. It will change a bit with every 20 degree change in temperature.

Use direct manifold vacuum to set carburetor. Check to make sure there are no vacuum leaks and PCV is properly functioning. Set both AF mixture screws at 1 1/2- 2 turns CCW form closed. Start and allow the engine to come to operating temperature. This process will require several cycles alternating between setting the A/F screws and the curb idle screw. Basically you want the highest, reasonably steady vacuum while maintaining desired idle speed. If the most steady vacuum reading is still fluctuating +/- 2 to 4 inches of vacuum it may indicate valve sealing problems. When you are done, the L and R A/F mixture screws should be within 1/4-1/2 turn of each other. When you install the air cleaner assembly you may notice a slight decrease in idle speed due to the restriction of the air filter (slightly rich condition). 1/16-1/8 turn CW on A/F mixture screws usually corrects the idle speed and quality.

I'll be glad to help if I can.

Chuck

Click to expand...

This is ball back calibration and assumes it is an otherwise stock engine. Using a timing light, check initial advance. Vacuum line(s) at distributor disconnected and plugged, RPM at 600-700 in neutral. Initial should be 12-16 degrees. Slowly rev the engine until you see advance stop increasing, total should be 32-36 degrees. Reconnect vacuum hoses, re-verify total advance. Idle speed should be 750-850 RPM in neutral.

Choke setting: assuming 50 degrees temperature, loosen the choke housing screws enough to allow the choke bi-metal spring housing to rotate. Hold an 1/8 inch drill bit between the choke plate and the carb choke housing. Rotate the choke spring housing until it just touches the drill bit. Tighten the choke housing screws. Using your voltmeter, turn the key to the run position an verify you have voltage to the choke. Turn the key off to allow the choke to cool. when it is cool, apply 1/-1/3 gas pedal travel, and engage the starter. If it starts, note the cold idle speed (should be 1200- 1400 RPM). If cold idle is too low or too high, locate and adjust the fast idle speed screw. This is a rudimentary system and may require several cycles to get the exact results you want. It will change a bit with every 20 degree change in temperature.

Use direct manifold vacuum to set carburetor. Check to make sure there are no vacuum leaks and PCV is properly functioning. Set both AF mixture screws at 1 1/2- 2 turns CCW form closed. Start and allow the engine to come to operating temperature. This process will require several cycles alternating between setting the A/F screws and the curb idle screw. Basically you want the highest, reasonably steady vacuum while maintaining desired idle speed. If the most steady vacuum reading is still fluctuating +/- 2 to 4 inches of vacuum it may indicate valve sealing problems. When you are done, the L and R A/F mixture screws should be within 1/4-1/2 turn of each other. When you install the air cleaner assembly you may notice a slight decrease in idle speed due to the restriction of the air filter (slightly rich condition). 1/16-1/8 turn CW on A/F mixture screws usually corrects the idle speed and quality.

I'll be glad to help if I can.

Chuck

Click to expand...

Ok, for the choke calibration: is that when the engine is cold and running, hot and running, cold or hot and off?

The PCV valve looks different than I remember from other engines. Is it the valve that pops out of the oil fill cap on the driver side vlave cover? How can I verify that it is working?

The overall tuning has greatly improved since I used the vacuum gauge to do the check and can see the drops while tuning. Thanks for the pointers.

This is ball back calibration and assumes it is an otherwise stock engine. Using a timing light, check initial advance. Vacuum line(s) at distributor disconnected and plugged, RPM at 600-700 in neutral. Initial should be 12-16 degrees. Slowly rev the engine until you see advance stop increasing, total should be 32-36 degrees. Reconnect vacuum hoses, re-verify total advance. Idle speed should be 750-850 RPM in neutral.

Choke setting: assuming 50 degrees temperature, loosen the choke housing screws enough to allow the choke bi-metal spring housing to rotate. Hold an 1/8 inch drill bit between the choke plate and the carb choke housing. Rotate the choke spring housing until it just touches the drill bit. Tighten the choke housing screws. Using your voltmeter, turn the key to the run position an verify you have voltage to the choke. Turn the key off to allow the choke to cool. when it is cool, apply 1/-1/3 gas pedal travel, and engage the starter. If it starts, note the cold idle speed (should be 1200- 1400 RPM). If cold idle is too low or too high, locate and adjust the fast idle speed screw. This is a rudimentary system and may require several cycles to get the exact results you want. It will change a bit with every 20 degree change in temperature.

Use direct manifold vacuum to set carburetor. Check to make sure there are no vacuum leaks and PCV is properly functioning. Set both AF mixture screws at 1 1/2- 2 turns CCW form closed. Start and allow the engine to come to operating temperature. This process will require several cycles alternating between setting the A/F screws and the curb idle screw. Basically you want the highest, reasonably steady vacuum while maintaining desired idle speed. If the most steady vacuum reading is still fluctuating +/- 2 to 4 inches of vacuum it may indicate valve sealing problems. When you are done, the L and R A/F mixture screws should be within 1/4-1/2 turn of each other. When you install the air cleaner assembly you may notice a slight decrease in idle speed due to the restriction of the air filter (slightly rich condition). 1/16-1/8 turn CW on A/F mixture screws usually corrects the idle speed and quality.

I'll be glad to help if I can.

Chuck

Click to expand...

Ok, for the choke calibration: is that when the engine is cold and running, hot and running, cold or hot and off?

The PCV valve looks different than I remember from other engines. Is it the valve that pops out of the oil fill cap on the driver side vlave cover? How can I verify that it is working?

The overall tuning has greatly improved since I used the vacuum gauge to do the check and can see the drops while tuning. Thanks for the pointers.

Click to expand...

Choke ballpark setting is engine cold, choke cold (key off). This my take several iterations and each time the cold conditions must be met.

PCV is in location you indicated. With engine off, remove PCV from oil fill cap. Shake it. If it rattles it is probably good. With engine running, remove from oil fill cap, leave the hose connected to the PCV. You should hear engine speed change a bit. Cover the inlet of the PCV with your thumb, should hear engine speed change more. If no engine speed change occurs, the PCV is bad (usually carbon/oil contamination).

Glad to help. Please let me know what results you get in the end.

Chuck

Click to expand...

Choke ballpark setting is engine cold, choke cold (key off). This my take several iterations and each time the cold conditions must be met.

PCV is in location you indicated. With engine off, remove PCV from oil fill cap. Shake it. If it rattles it is probably good. With engine running, remove from oil fill cap, leave the hose connected to the PCV. You should hear engine speed change a bit. Cover the inlet of the PCV with your thumb, should hear engine speed change more. If no engine speed change occurs, the PCV is bad (usually carbon/oil contamination).

Glad to help. Please let me know what results you get in the end.

Chuck

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Ok, I'll have to get on the choke when I get back to it. As far as the PCV goes, it works. I checked all of that and I'm confident it works. I had already gotten the engine hot by the time I started on your procedures so I haven't done anything with the choke, but the rest of the tuning went pretty nicely.

I'm still having issues every time I start the engine when its been sitting more than 20 minutes. I know that it is a lack of fuel because I have to pump the pedal like a wild man to get it enough to fire up.

I forgot to check voltage at the coil. I'm currently researching how to bypass the resistance wire since I have the Pertronix III and the flamethrower coil. I still need to drop the tank and check the state of it and the sending unit.

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This may have been already asked. Have you checked to see if the accelerator pump is working?

Chuck

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This may have been already asked. Have you checked to see if the accelerator pump is working?

Chuck

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I'm really glad you asked because with the kind of pumping I have to do to the pedal to get it started thats what I wanted to learn about. Any methods to do this testing? I'm pretty sure after the last few weeks I have all the basic tools I need to get to work on it.

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With the engine off, remove the air cleaner assembly, hold choke plate open, while looking into the carb (primary/front side), manually open the throttle about 15 degrees (not critical). You should see gasoline being discharged from two small ports at the center front of the primary side. If you do the accelerator pump is probably good. If not it is probably bad. Changing the pump requires at least partial disassembly of the carb. When you drive the car does it hesitate when you apply light throttle?

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Choke setting: assuming 50 degrees temperature, loosen the choke housing screws enough to allow the choke bi-metal spring housing to rotate. Hold an 1/8 inch drill bit between the choke plate and the carb choke housing. Rotate the choke spring housing until it just touches the drill bit. Tighten the choke housing screws. Using your voltmeter, turn the key to the run position an verify you have voltage to the choke. Turn the key off to allow the choke to cool. when it is cool, apply 1/-1/3 gas pedal travel, and engage the starter. If it starts, note the cold idle speed (should be 1200- 1400 RPM). If cold idle is too low or too high, locate and adjust the fast idle speed screw. This is a rudimentary system and may require several cycles to get the exact results you want. It will change a bit with every 20 degree change in temperature.

Chuck

Click to expand...

Choke setting: assuming 50 degrees temperature, loosen the choke housing screws enough to allow the choke bi-metal spring housing to rotate. Hold an 1/8 inch drill bit between the choke plate and the carb choke housing. Rotate the choke spring housing until it just touches the drill bit. Tighten the choke housing screws. Using your voltmeter, turn the key to the run position an verify you have voltage to the choke. Turn the key off to allow the choke to cool. when it is cool, apply 1/-1/3 gas pedal travel, and engage the starter. If it starts, note the cold idle speed (should be 1200- 1400 RPM). If cold idle is too low or too high, locate and adjust the fast idle speed screw. This is a rudimentary system and may require several cycles to get the exact results you want. It will change a bit with every 20 degree change in temperature.

Chuck

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Ok, I tried to actually get this right today. Issue: When the housing is loose and I rotate it, tightening the spring and thereby applying more pressure to the choke plate, the plate will not move past a certain point. The issue is a linkage on the opposite side of the carb that is limited by the throttle assembly. Applying a small amount of throttle allows for the choke to move to the closed position. This is all engine cold and off. The linkage looks like it is designed to do this but it really puts a hurt on the instructions you gave me. \

1. Behind this plate there is a set screw limiting the travel of number 2

2. This plate has an indentation which seems like it is to control the travel of the choke plate.

3. This linkage connects to the choke plate.

In post #4 I ask you to depress the throttle about 1/4- 1/3. This allows the throttle linkage to move out of the way so the pressure of the choke bi-metal spring can close the choke plate and engage the fast idle (stepped cam and screw). If you do this does the choke close?

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In post #4 I ask you to depress the throttle about 1/4- 1/3. This allows the throttle linkage to move out of the way so the pressure of the choke bi-metal spring can close the choke plate and engage the fast idle (stepped cam and screw). If you do this does the choke close?

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In post #4 I ask you to depress the throttle about 1/4- 1/3. This allows the throttle linkage to move out of the way so the pressure of the choke bi-metal spring can close the choke plate and engage the fast idle (stepped cam and screw). If you do this does the choke close?

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Yes. Then I should be depressing the accelerator as I set the choke plate then as well. Not a problem. I need to get more familiar with the carb. I like to understand what I am doing.

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I'm on the right track with the choke! Thanks for all the help

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