4 barrel carb help please!
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From: Pulaski, TN
4 barrel carb help please!
i have a holly 4 barrel bolted to a performer intake on my 351w everything seems to be in tact i have just rebuilt everything but the 4 barrel will not engage unless i manually open it with my finger. so what makes it open? is it a cable i need to make it work or does it just work on vaccum?
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You must have a vacuum secondary type carb... You will notice on the right side (passengers) a bell thing next to them, and a rod sticking down. Vacuum opens them, you can carefully take it apart, change the rubber boot and switch spring tension for vacum adjustment.
In other words lighter spring meens less vacuum opens it. That is a good setup for Automatic street cars, It eliminates the dreded bog on the punch. Some people put a screw on the lower side slide to make it manual, I dont advise it, and it defeats the purpose. If you rebuilt the carb, those parts came with the rebuild kit. If the diaphram is old and torn, it will caus a vacuum leak
In other words lighter spring meens less vacuum opens it. That is a good setup for Automatic street cars, It eliminates the dreded bog on the punch. Some people put a screw on the lower side slide to make it manual, I dont advise it, and it defeats the purpose. If you rebuilt the carb, those parts came with the rebuild kit. If the diaphram is old and torn, it will caus a vacuum leak
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From: Pulaski, TN
i had it it rebuilt about a year ago. by a family friend that builds drag cars (a chevy guy). so couldnt i just put a brand nw diaphram on to fix it? or are you saying i dont have enough vaccum to open it?
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Did the carb sit for a lenght of time, and now you are going to use it again?? It almost sounds like it wasnt stored properly, and you might have some passsages plugged as the gas in the passages turned to shelac, or mayonaise.
Vacuum secondary carbs eliminate the bog because it creates a higher vacuum in the manifold. When you punch a manual secondary typr (double pumper ect) the vacuum drop is so fast that the accelerator has to fill the void as far as engine demand for fuel. Vacuum avoids that issue partially.
Take the air cleaner off, with the engine turned off, look down the throat of the carb, and slowly open the venturies. you should see gas squirting. If you dont, your accelerator pump is either bad, or the passages that feed it are plugged.
Its one or the other.
Vacuum secondary carbs eliminate the bog because it creates a higher vacuum in the manifold. When you punch a manual secondary typr (double pumper ect) the vacuum drop is so fast that the accelerator has to fill the void as far as engine demand for fuel. Vacuum avoids that issue partially.
Take the air cleaner off, with the engine turned off, look down the throat of the carb, and slowly open the venturies. you should see gas squirting. If you dont, your accelerator pump is either bad, or the passages that feed it are plugged.
Its one or the other.
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I am assumeing your ignition is OK... right?
Ignition failures and carb or fuel issues sometimes have the same symptoms.
Ignition failures and carb or fuel issues sometimes have the same symptoms.
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From: Pulaski, TN
yes all that is ok, what about a non vented fuel tank? when i got my new gas tank it was not vented and it causes the tank to pressurize, so i keep the gas cap loosened to prevent this until i can get another tank that is vented like my old one was. i have not yet punced it while i was driving it with the cap loosened.
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Ya but Your tank will not be a vacuum right away. It will cause this issue, but when the bog is happening, you should open the cap and get a big air rushing sound, kinda like opening a bottle of pop, except it would suck in not fizz out.
Put it this way, (I had that issue) My vent on my fuel tank got crmped between the frame and the tank... (750hp Mustang) OK I did my burnout, staged at the light, then tree came down, I went. Threw 2 gears into the third, I bogged at 6500 rpms high end of the track. When I got back to the pit I went to put gass in it cus it felt like I was out, when I opend the cap. the sucking sound. My point is, you fuel is at the float bowl. The bowls are full of fuel. You have to use that up then pump enough fuel to cause the tank to vacuum, and use the float bowls up from what was pumped. Could it happem? maybe, Ideal conditions, Weak fuel pump, collapsing fuel intake line?? So many scenario's. I guess? does it bog woth the cap loose?
Put it this way, (I had that issue) My vent on my fuel tank got crmped between the frame and the tank... (750hp Mustang) OK I did my burnout, staged at the light, then tree came down, I went. Threw 2 gears into the third, I bogged at 6500 rpms high end of the track. When I got back to the pit I went to put gass in it cus it felt like I was out, when I opend the cap. the sucking sound. My point is, you fuel is at the float bowl. The bowls are full of fuel. You have to use that up then pump enough fuel to cause the tank to vacuum, and use the float bowls up from what was pumped. Could it happem? maybe, Ideal conditions, Weak fuel pump, collapsing fuel intake line?? So many scenario's. I guess? does it bog woth the cap loose?
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From: Pulaski, TN
i havnt tryd it yet with the cap off. but as long as i ease into it the truck runs great. it does have a cuction to the tank cause when i go to get gas or just check it after a little while you can hear the air release when you pull the cap off, it actually flooded my entire engine with gas all the way up to the end of the dipstick tube, but im past that now.
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If you have access to a hand vacuum pump you can check the diaphragm with that. If it's ok you can get a spring pack for it and find the right one for your application. I would buy a quick change top for the pot though, changing springs without one is a real pain and you can end up tearing the diaphragm without one.
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From: Pulaski, TN
thanks guys, all that really helped out, so far its running good, its not bogging anymore. 4 barrel is opening up, this has been my first build and so far its goin good thanks to all the help i got on fte.
