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Need your help- here's the background - I've got a 4 barrel holley carb, model 80457-1. I rebuilt this with a kit of quality parts. I've set the idle to ~750 (or slightly higher), checked the float bowls when not running and a gentle giggle leads to fuel spilling out thru the 2 sight screws. I started the air-fuel adjustment screws and they both are around 2-3/4 turn out. This truck has a new fuel pump and that's putting out nicely. The whole carb was cleaned when I installed the rebuild kit. it has a 1" spacer on the intake, gaskets on either side. I've double checked and there are no vacuum lines I've missed. The trans has the correct amount of fluid.
When the truck is shifted into gear, it stalls. I've tried adjusting the idle up, adjusted the air-fuel screws in/out, just about every adjustment I can think of. This truck drove ok when I first got it so I'm at a bit of a loss.
If you need to have the screws turned out 2 and a half turns that's quite a bit. Most of the time with a Holley carburetor that's about right the screws end up being about 1 and 1/4 to 1 and 1/2 turns out. With the curb idle adjusted if you take the carburetor off of the engine and look at the bottom side of the primary throttle plates you should see the idle discharge hole as well as the bottom of the transition slot exposed. The amount of slot that should show should be about as tall as it is wide, it should look like a little square. The slot and the idle discharge are both fed fuel from the idle well and that is fed by the idle feed restriction in the metering block. It is blended with air from the idle air bleed and then it splits off to either feed the slot or the idle discharge which you can control using the screw. The screw does not make the mixture richer or leaner it just controls how much of the mixture that is given to the engine. Fuel should flow from both sources at idle, screw and slot if it can't do that it can't always respond adequately to slight changes in engine load.
Thanks for this excellent write-up. I stepped away from this to have a break and it has occurred to me that the PCV valve and other lines have changed. As we added power brakes, I believe there are some engine vacuum things going on that need to be sorted out. I appreciate your confirming about the adjustment screws. I initially had them both just under 1.5 turns out and it seemed to run quite well so I'm glad my initial setup was reasonable.
I'm going to correct the PCV and vacuum line and rest the carb where I started. I appreciate your help!
Is your vacuum advance hooked to ported or manifold? if it's on manifold it can drop out when the idle slows and then it drops even more killing the engine.
yea so I'd like to connect the pcv to the spacer under the carb but the spacer does not have a vacuum nipple. I'm going to check all vacuum lines and make sure they're tight. I also found laying behind the motor (just dangling on a rubber line) a valve that looks like this valve assembly. It was not connected but appears to go between the carb and the distributor. I don't know what this does?
yea so I'd like to connect the pcv to the spacer under the carb but the spacer does not have a vacuum nipple. I'm going to check all vacuum lines and make sure they're tight. I also found laying behind the motor (just dangling on a rubber line) a valve that looks like this valve assembly. It was not connected but appears to go between the carb and the distributor. I don't know what this does?
Drill and tap that spacer for a PCV vacuum port. I had to do that on the phenolic spacer I bought after the aluminum one was heating up so much you could fry an egg on it.
Do you have a vacuum advance line running to your distributor? That's what that check valve is for.
Can someone school me on this? The coolant temp sensor I've pictured below has 2 vacuum ports. Both these rubber lines were cracked as were the metal tubes which attach to this sensor. What is this sensor called and where should the 2 lines run to? What does this thing do? warm the carb on cool days? Not too sure about this. here's where the sensor came out of here's the body of the sensor with the broken attachment tubes product code
That's your ported vacuum switch. It turns ported vacuum on or off depending on temperature. Your distributor vacuum line should connect to that unless you have modified the setup.
ah ok! Now my switch only has 2 ports on it, not 3 like in your diagram. "E" port on the top, "S" port on the bottom. So intake vacuum should go into this switch and then the other end leads to the distributor?
You don't need that thing. Looks like someone before you already figured that out and crimped the lines. Apparently they didn't do a very good job based on the look of the thing. Plug the hole in the manifold with the appropriately sized pipe plug (coated with some pipe thread sealant) and run the vacuum advance hose from your distributor to the ported vacuum fitting on your carb.
yea so I'd like to connect the pcv to the spacer under the carb but the spacer does not have a vacuum nipple.
Used a double ended hose barb like one uses for hooking two hoses end to end, drilled hole just big enough for easy insertion, J B Weled in place, then for extra safety after JBW cured, drilled a hole from top into spacer and brass inserted, inserted small nail.
Done.
You can ignor the yellow and red parts, is a pair of tubes insert to keep velocity up from carburetor primaries leading into the intake below (I only did the primary side). My PCV uses 3/8" hose.
ah ok - thanks for the info about the ported switch and adding the nipple to the spacer. I had considered doing this but thought I'd ask here.. perfect!
Hey fellas
so last nite I installed a 3/8” nipple into the base of the carb spacer which I connected to the pcv valve. I found a torn vacuum line to the transmission which I replaced. I ran full vacuum from the bottom of the carb to the distributor (not the vac line from the side of the carb which is for timing advance - that port I plugged). Had to rebalance the float valves in the carb. It also turns out I had the electric choke installed incorrectly as the plastic clip was under the metal rod to the butterfly valve. Fixing all these things and starting it runs like a champ! Beer tasted extra good! I now need to figure out if the alternator is putting out enough as after 20 or so min running it didn’t have enough CCA to start the truck. Anyway- thx for all the help with this!
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