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Discussion Starter · #1 ·
Hi everyone, hope I'm in the right forum because I also have a '56 gasser I'm working on but this question is about my '57 Belair. In this car I have a 406 sbc engine with a BDS 671 blower. Mounted on top are 2 600 cfm Edelbrocks. Almost from day one (about 4 years) I have had what I call a problem with the motor stumbling/missing. This seems to occur at lower rpm's and especially after sitting while waiting for a traffic light. It doesn't happen all the time but once is too much for me. The engine feels like its actually missing when I take off and not even under alot of throttle. My fuel pressure is a constant 6 lbs. and after a few seconds, the motor will straighten itself out. At higher speeds/rpm's, it performs quite well. Never a problem. I'm running a mechanical fuel pump. The gas line runs close to one of the mufflers but I have it wrapped with an insulation material (thought maybe the gas was boiling in the line). Previously, I had 2 750 Edelbrocks and experienced the same problem. Via Edelbrock, I've tried every combo of jets, metering rods, etc. to no avail. The plugs/wires are almost new. I went to a car show today and it acted out again. Embarrassing. I'm approaching a new level of total disgust with this car. I would appreciate any ideas/suggestions that anyone could share. Many thanx, Carmine.
 

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Trifive Automotive Electrical Wiring Expert
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This seems to occur at lower rpm's and especially after sitting while waiting for a traffic light. It doesn't happen all the time but once is too much for me. The engine feels like its actually missing when I take off and not even under alot of throttle.
Do you have power brakes? I don't know how it would affect an engine with a blower, but a leaking booster when you push the pedal will cause low vacumn.
 

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I had a VERY similar problem with my tunnelram and it took me almost all summer to get it. The problem was a combination of intake gaskets and I also replaced 1 carb. That fixed it but only after killing the season chasing the problem and replacing everything else and takin the dist. out several times, changing plugs, wires, testing voltages all over, adding grounds etc.
 

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I run a blower and 2- 750 carbs (carter comp), and I had that problem too. My engine builder suggested that I "lock out" the distributor @ 34 deg., and do away with the advance mechanism. So it starts and idles at 34 degrees, and never changes, problem solved.
PS: I have to spin the motor with the ignition switch off, then flip it on, when it is spinning ,on a hot day if the engine is hot, to start. Same procedure as a magneto.al
 

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"Previously, I had 2 750 Edelbrocks and experienced the same problem."

If these carbs were on this same vehicle and set up, it's likely the problem isn't the carbs. Check out the ignition. The coil might be getting too hot, then breaking down. Put an MSD 6BTM ignition box on it if you don't already. Use a new style Blaster SS coil and ditch the round canister coil if that's what you have. Coil technology has improved dramatically over the last 50 years! This set up will fire just about anything and the box is made for blown cars.
Also check the linkage to be sure both carbs are syncronized EXACTLY the same. The throttle on the front carb needs to be opening at the same exact time the rear is. No progressive linkages on blown cars. If one carb is open farther than the other, then weird things can happen. This might sound simple, but it's an easy mistake to make or overlook. Make adjustments to the curb idle screws on both carbs to set the idle, not just one also. What RPM does the car idle? Without knowing the cam size, I'd try it around 900 -1000 RPM. If you have the engine set up so it does the "blower surge" this plays havoc on the vacuum signal to the carbs and they can act up.
If the car has issues when it idles too long, then starts its fussing, consider carefully adjusting the idle mixture screws.
With the motor OFF, turn the screws in until they just stop (don't crank 'em in tight!). Then, turn each one out 2 full turns and start from there. This way you'll know both carbs are the same when you start your tuning. Start the car and see how it runs. Set the idle RPM if you adjusted and corrected the linkage, then let it idle and warm up, maybe drive it around a bit to get it warmed up where it would have had a prob. If you still need to adjust it, make only 1/4 turn at a time to the mixture screws. Turn one in 1/4 turn, let the engine receover 15-20 seconds, then go to the next one and so on. You don't have to adjust all the mixture screws the same. If you are able to turn 3 of the four and it cures the problem, then leave the fourth one alone. Turning the screws out might be what it needs too. It 's a bit of a game to figure out what setting works the best. Just use 1/4 turns at a time though. Make sure you do all of this on a flat area. Don't have the car on an angle.
Keep in mind whether they are Edelbrock's or Holley's, they are universal carbs and don't know what they are going on when they leave the factory; they need to be tuned to your car's engine combination.
This could take you a couple hours, but take your time, be thorough and it will be worth it.
I know this was lengthy, but I hope it helps.
Now, what are you doing sitting there?! Get out to the garage and start tuning so you can do BURNOUTS!! What car guy doesn't like doing burnouts once in a while?? :driver:
 

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ive had the same problem and after many hours wreaking my head and checking this and that and checking thing other suggested . it was as simple as running a hotter plug and opening the gaps 5 thousands more . i barely was able to pull it into the garage becase of the hessitation and spiting ans spuddering. the day before i installed new plug and ran the same. after installing the hotter plugs it ran great no load up yet at stop lights . just my thoughts and what ive run into
 

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Discussion Starter · #9 ·
"Previously, I had 2 750 Edelbrocks and experienced the same problem."

If these carbs were on this same vehicle and set up, it's likely the problem isn't the carbs. Check out the ignition. The coil might be getting too hot, then breaking down. Put an MSD 6BTM ignition box on it if you don't already. Use a new style Blaster SS coil and ditch the round canister coil if that's what you have. Coil technology has improved dramatically over the last 50 years! This set up will fire just about anything and the box is made for blown cars.
Also check the linkage to be sure both carbs are syncronized EXACTLY the same. The throttle on the front carb needs to be opening at the same exact time the rear is. No progressive linkages on blown cars. If one carb is open farther than the other, then weird things can happen. This might sound simple, but it's an easy mistake to make or overlook. Make adjustments to the curb idle screws on both carbs to set the idle, not just one also. What RPM does the car idle? Without knowing the cam size, I'd try it around 900 -1000 RPM. If you have the engine set up so it does the "blower surge" this plays havoc on the vacuum signal to the carbs and they can act up.
If the car has issues when it idles too long, then starts its fussing, consider carefully adjusting the idle mixture screws.
With the motor OFF, turn the screws in until they just stop (don't crank 'em in tight!). Then, turn each one out 2 full turns and start from there. This way you'll know both carbs are the same when you start your tuning. Start the car and see how it runs. Set the idle RPM if you adjusted and corrected the linkage, then let it idle and warm up, maybe drive it around a bit to get it warmed up where it would have had a prob. If you still need to adjust it, make only 1/4 turn at a time to the mixture screws. Turn one in 1/4 turn, let the engine receover 15-20 seconds, then go to the next one and so on. You don't have to adjust all the mixture screws the same. If you are able to turn 3 of the four and it cures the problem, then leave the fourth one alone. Turning the screws out might be what it needs too. It 's a bit of a game to figure out what setting works the best. Just use 1/4 turns at a time though. Make sure you do all of this on a flat area. Don't have the car on an angle.
Keep in mind whether they are Edelbrock's or Holley's, they are universal carbs and don't know what they are going on when they leave the factory; they need to be tuned to your car's engine combination.
This could take you a couple hours, but take your time, be thorough and it will be worth it.
I know this was lengthy, but I hope it helps.
Now, what are you doing sitting there?! Get out to the garage and start tuning so you can do BURNOUTS!! What car guy doesn't like doing burnouts once in a while?? :driver:
 
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