When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I have a 71 454 that i have been working on to get it back on the road. The car starts fine and idles at about 1500 RPMs, the down to about 1100 RPM. When I put it in gear it runs as long as I keep giving it a bit of gas. As soon as I take my foot off the gas it dies. I put some carb cleaner down the float vent and it feels pretty clogged. I put a small screw drive down ther and it is blocked except one spot.
Should this his be open or should it be blocked off? The engine sounds great when it's idling, this is the last problem before i can finally get it back on the road after 25 years. Any help would be appreciated.
If it is the bowl vent, it needs to be open. The carb works using pressure differentials and pressure above the fuel in the bowl needs to be atmospheric. With a clogged vent, it won't operate properly. A picture of where you are checking would be helpful...just to be sure that's what you are referencing.
If it is the bowl vent, it needs to be open. The carb works using pressure differentials and pressure above the fuel in the bowl needs to be atmospheric. With a clogged vent, it won't operate properly. A picture of where you are checking would be helpful...just to be sure that's what you are referencing.
7T1vette, thank you for the response. I have attached a picture albeit not a great one but it's the only one I have at work! The red circle marks the vent I am referring to.
The part you circled is where the stud that holds the air cleaner goes.
The vent tube is at the top right corner on your picture.
Peterbuilt, thank you for the response. It is not the best picture but the stud that holds the air vent is actually just below the red circle. That is where the stud was located when I got the car. Should the stud be moved to what is circled in the picture?
the vent in the upper right and the vent you stuck the screw driver in are for the float bowl. You cant use a screw drive to check the vent but before assuming anything what have you done with the idle mixture screws if anything?
the vent in the upper right and the vent you stuck the screw driver in are for the float bowl. You cant use a screw drive to check the vent but before assuming anything what have you done with the idle mixture screws if anything?
I have not done anything with the mixture screws. The car was in a barn for a long period of time. When it was parked, it was running perfect so I have not adjusted the mixtures, I just tested the vent with a thin screw driver to see if it was open but it hits something in the vent that is hard. I tried putting some carb cleaner in the vent after doing some reading and it sprays back. It could be that the float is stuck in the up position but I am not sure how to test for that.
The hole should not be plugged but the float is right below the hole and is easily damaged by sticking anything down it. You will probably have to take the top off the carb to see if it's really plugged or if you have damaged the float as it is quite fragile. If there is an obstruction plugging the hole and you stick something down there, you are going to have to take the carb apart either way to remove the obstruction from the hole or if it drops inside the float chamber.
Last edited by CanadaGrant; Aug 20, 2018 at 07:45 PM.
The hole should not be plugged but the float is right below the hole and is easily damaged by sticking anything down it. You will probably have to take the top off the carb to see if it's really plugged or if you have damaged the float as it is quite fragile. If there is an obstruction plugging the hole and you stick something down there, you are going to have to take the carb apart either way to remove the obstruction from the hole or if it drops inside the float chamber.
I'll try that Wednesday night when I get home. Both vents should be clear correct?
From: At my Bar drinking and wrenching in Lafayette Colorado
There is no way the vent is clogged. If you stuck a screwdriver down that hole, you just punched a screwdriver into your float. You had other problems - not a carb vent problem - before damaging the float.
There is no way the vent is clogged. If you stuck a screwdriver down that hole, you just punched a screwdriver into your float. You had other problems - not a carb vent problem - before damaging the float.
Lars
Then I guess it's time for a rebuild. My understanding was that the float is underneath the vent. The small screwdriver that I put down the vent didn't get far due to an obstruction. Does the part of the float sit inside the vent? Thanks in advance for the help.
I have had a carb with the bowl vent plugged. Surprised the heck out of me. Something I check every time, now. (sounds like a "no-brainer", but sometimes we can overlook the obvious)
You will still have to get the obstruction out and the only way is to remove the carb.
The only other thing I can think of is that some re-builders press a small flat piece of metal lengthwise into the vent to prevent people from trying to install the filter stud in the wrong hole and damaging the carb. See if you can look down the vent with a penlight and if you see what looks like the tip of a flat blade screwdriver looking up at you just down in the vent, that would be it. Anything I have seen is even with the top of the vent and visible but who knows....
Last edited by CanadaGrant; Aug 21, 2018 at 12:24 AM.
Have some video of the issue. Car idles fine a little high but you will see when I punch the gas the rpm's drop and then it stalls. Choke stays wide open afterwards. I have ordered a rebuild kit as well as a new fuel filter and gasket (I had replaced it once already). Any guidance would be great. Also, carburetor number is 7042220, not original to the car. It looks like it was manufactured in 1972 and was for an automatic, I have a manual 454. Not sure if that matters This is the last issue before I can start driving it.
From: At my Bar drinking and wrenching in Lafayette Colorado
You can put a cork in the vent with no ill effect. There are multiple other sources for vent air on a Q-Jet float bowl: Take a look at all the slop and space around the secondary metering rods where they go through the airhorn: Those big sloppy holes go right into the float bowl. There are several other vent sources, too. This photo shows all the air vent penetrations into the Q-Jet bowl, not counting the air vent slop around the accel pump hole. You can plug that forward main vent and it won't cause the problems you are having:
You can put a cork in the vent with no ill effect. There are multiple other sources for vent air on a Q-Jet float bowl: Take a look at all the slop and space around the secondary metering rods where they go through the airhorn: Those big sloppy holes go right into the float bowl. There are several other vent sources, too. This photo shows all the air vent penetrations into the Q-Jet bowl, not counting the air vent slop around the accel pump hole. You can plug that forward main vent and it won't cause the problems you are having:
Thanks Lars, could it be as simple as adjusting the idle and swapping out the fuel filter? The car was sitting in a barn for about 25 years, I suspect a rebuild may not hurt.
From: At my Bar drinking and wrenching in Lafayette Colorado
Originally Posted by clrayjr
Thanks Lars, could it be as simple as adjusting the idle and swapping out the fuel filter? The car was sitting in a barn for about 25 years, I suspect a rebuild may not hurt.
Oh, goodness... A carb will not survive sitting for 25 years without ill effect - all your smaller fuel metering passages are plugged from evaporated fuel sediment, and no amount of "Sea Foam" or other crap is going to fix it. Yes, it needs to come off and be rebuilt. The fuel lines should probably be blown out, and I'll bet your distributor has a ruptured or seized vacuum advance along with a stuck centrifugal advance system. It all needs to be rebuilt and fixed - it is all contributing to your issues.
Oh, goodness... A carb will not survive sitting for 25 years without ill effect - all your smaller fuel metering passages are plugged from evaporated fuel sediment, and no amount of "Sea Foam" or other crap is going to fix it. Yes, it needs to come off and be rebuilt. The fuel lines should probably be blown out, and I'll bet your distributor has a ruptured or seized vacuum advance along with a stuck centrifugal advance system. It all needs to be rebuilt and fixed - it is all contributing to your issues.
Lars
Thanks Lars, I will get started on the rebuild this week. I have blown out the fuel lines and replaced the tank and sending unit etc. I have also replaced most of the parts around the distributor as well. On the bright side, it is running again!
There is no way the vent is clogged. If you stuck a screwdriver down that hole, you just punched a screwdriver into your float. You had other problems - not a carb vent problem - before damaging the float.
Lars
Lars, I just wanted to follow up on this. You were absolutely correct about the float. I rebuilt the carburetor and the float was damaged. I replaced the float during the rebuild and once I got it mounted the car turned over and is running smoothly with no stalling. It is idling around 600 RPM. Prior to the rebuild, it was idling at 1500 RPM on start up and once the gas was pushed, it came down to 1000 RPM then stalled out. I think some fine tuning may be needed but this issue is resolved. Actually got to take for a couple spins around town. Thanks for the help and thank you for sending your papers along, much appreciated!
Clogged float vent? Rochester Quadrajet
