idling (440 six bbl)

[Bill Monk]

Still trying to dial the car in. 440 six bbl with a 4 speed. My timing is right, period. Mixture screws out 1 1/2 turns. The problem is that I can bring the car to temperature and set the idle, now when I take her for a spin, car runs good at part and full throttle but when you come to say a stop light, the idle want to fall off too low. Bring it back and reset, idling fine, take her back out and the same thing. I suspect an issue with the center carb but I'm not sure about that. Another detail is that it is idling a bit lean. With the choke disconnected and wide open it idles a little rough but opening the mixture screws any farther doesn't help. If I understand it right, the jets have nothing to do with idle quality right? In a manual trans car, I see no reason why the idle would fall off like that.

One thing at a time

 

[brian6pac]

How many turns is the idle screw off the bottom, as is count the turns out till the throttle plates bottom out.

 

[Bill Monk]

How many turns is the idle screw off the bottom, as is count the turns out till the throttle plates bottom out.

1 1/2 turns

 

[brian6pac]

1 1/2 turns is starting to get off the idle circuit and the port for your vacuum advance is open. try pluging your vacuum to the dist and see if it straightens out. you should be about 3/4 turns on the idle speed screw so the throttle plates are in the right place on the transfer ports.

 

[lewtot184]

the real problem is the idle jet in the center carb is way too small for the idle air bleed size. this is why people have to use the idle mixture screws in the end carbs to compensate for the problem. float level on the end carbs is critical. fuel level must be up to the bottom of the sight hole to reduce stalling. the real cure to all this is to richen the center carb idle jet (complicated) and drill and tap the idle air bleed hole for screw in air bleeds.

 

[66Satellite47]

Have you done anything with the end carb idle mixture screws? Very important to drivability.

 

[Bill Monk]

1 1/2 turns is starting to get off the idle circuit and the port for your vacuum advance is open. try pluging your vacuum to the dist and see if it straightens out. you should be about 3/4 turns on the idle speed screw so the throttle plates are in the right place on the transfer ports.

sorry, I misread your question. I was taliking about the air fuel mixture, I'm not sure how far on the idle screw but I'll check.

 

[Bill Monk]

Have you done anything with the end carb idle mixture screws? Very important to drivability.

the lead plugs are still there so no, however I get no change in idle when I put my finger over the air bleed hole on either outboard so I would assume that they are pretty close...no?

 

[lewtot184]

the lead plugs are still there so no, however I get no change in idle when I put my finger over the air bleed hole on either outboard so I would assume that they are pretty close...no?

the mix adjustment will have to be slightly rich. the mixture screws will need backed out at least 1/2 turn. somewhere between 3/4-7/8 turn always gave me the best idle. this adjustment makes a big difference in idle quality.

 

[Bill Monk]

the mix adjustment will have to be slightly rich. the mixture screws will need backed out at least 1/2 turn. somewhere between 3/4-7/8 turn always gave me the best idle. this adjustment makes a big difference in idle quality.

my mixture screws are out a full 1 1/2 turns and I have verified no vacuum leak using propane

 

[PurpleBeeper]

First, you have 3 carbs to set the idle mixture with & you're only adjusting one of them. Lewtot's explanation sounds reasonable, so your choices would be to remove the lead plugs & adjust the idle mixture on all 3 carbs OR drill/modify the center carb. I went the remove the lead plugs route.

Brian6pac makes another good point that has always frustrated me with 6-packs & bigger cams. If you have to turn the idle screw on the center carb more than just a little bit off of "completely closed", then the center carb's throttle blades expose the "transfer slots" and idle gets really, really hard to set right since the center carburetor isn't on the idle circuit anymore. I had this problem. When I "fattened up" the mixture on the end carbs I was able to close the center carb enough to cover the transfer slots & then everything was kosher. Before that, my idle mixture screws on the center carb didn't seem to do much at all.

One last possibility..... after setting your idle, did you re-check & re-set the throttle return linkage to the outer carbs? One of the old tricks to get 6-packs to idle was to drill (or enlarge) the holes in the end carburetor throttle plates to allow for more air flow at idle. Some people would loosen the throttle return linkage to the outer carbs about 1 turn which does basically the same thing because when you take your foot off the gas the center carb doesn't pull the outer carbs 100% closed (leaves them cracked open slightly). I tried this approach myself, but found that my idle would do what you describe. "Sometimes" it would return to idle normally (end carbs still cracked open slightly) & other times the idle would drop a lot like you describe (carbs fully closed) & it seemed hit or miss. When you leave that little bit of slop in the throttle return linkage that last little bit of opening/closing of the end carbs is not controlled. The throttle return linkage should be "very slightly snug" in the end carbs & you have to re-adjust that linkage every time you adjust the idle screw on the center carb.

 

[Bill Monk]

First, you have 3 carbs to set the idle mixture with & you're only adjusting one of them. Lewtot's explanation sounds reasonable, so your choices would be to remove the lead plugs & adjust the idle mixture on all 3 carbs OR drill/modify the center carb. I went the remove the lead plugs route.

Brian6pac makes another good point that has always frustrated me with 6-packs & bigger cams. If you have to turn the idle screw on the center carb more than just a little bit off of "completely closed", then the center carb's throttle blades expose the "transfer slots" and idle gets really, really hard to set right since the center carburetor isn't on the idle circuit anymore. I had this problem. When I "fattened up" the mixture on the end carbs I was able to close the center carb enough to cover the transfer slots & then everything was kosher. Before that, my idle mixture screws on the center carb didn't seem to do much at all.

One last possibility..... after setting your idle, did you re-check & re-set the throttle return linkage to the outer carbs? One of the old tricks to get 6-packs to idle was to drill (or enlarge) the holes in the end carburetor throttle plates to allow for more air flow at idle. Some people would loosen the throttle return linkage to the outer carbs about 1 turn which does basically the same thing because when you take your foot off the gas the center carb doesn't pull the outer carbs 100% closed (leaves them cracked open slightly). I tried this approach myself, but found that my idle would do what you describe. "Sometimes" it would return to idle normally (end carbs still cracked open slightly) & other times the idle would drop a lot like you describe (carbs fully closed) & it seemed hit or miss. When you leave that little bit of slop in the throttle return linkage that last little bit of opening/closing of the end carbs is not controlled. The throttle return linkage should be "very slightly snug" in the end carbs & you have to re-adjust that linkage every time you adjust the idle screw on the center carb.

Seem snug to me but I'll double check it

 

[66Satellite47]

I'm sure you can improve drivability by pulling the lead plugs out of the end carb mixture screws and tuning them slightly, about 1/4 turn makes all the difference. If I recall mine wanted a 1/4 turn out (both on my '69 & my '70 end carbs). I'd avoid drilling the end carb holes bigger if you can (non reversible). I recall there's an idle adjusting screw under the end carb base plates that can be adjusted slightly to open the "closed" setting of the end carbs (instead of the hole in the blades), a small adjustment there will help when combined with the end carb idle mixture screw adjustment. FYI for some reason my '70 setup worked better than the '71 combination. My '69 end carbs were mated to an aftermarket 500 center carb.

 

[brian6pac]

I have drilled holes in the butterfly's on the center carb and leave the end carbs alone, the end carb mixture screws are very small brass screws and a slot cut in them, they brake off very easy. I have soaked them with wd40 and heated the base plate to get them loose and sometimes they still brake.

 

[6pktgo]

Would this car have power brakes by any chance?

 

[66Satellite47]

I have drilled holes in the butterfly's on the center carb and leave the end carbs alone, the end carb mixture screws are very small brass screws and a slot cut in them, they brake off very easy. I have soaked them with wd40 and heated the base plate to get them loose and sometimes they still brake.

I was lucky enough to get all of my end carb adustment screws to work, used WD, don't recall if I used a propane, but sure may have. Very careful use of force on them!

 

[Bill Monk]

Would this car have power brakes by any chance?

No Sir, manual drums on 4 corners, gotta love it!

 

[6pktgo]

I asked because I had the very same symptoms & we found too much vacuum being robbed by my brake booster .