Hey guys...quick question before I start ripping things apart. Experienced an odd issue today. Everything is new and rebuild top to bottom on my truck. I haven't driven the truck but periodically run the 292 engine and its been running great with no issues. I let it run yesterday for a few minutes, no problems. Tried it today and it wouldn't start. All of a sudden I'm not getting any fuel spraying out the venturis of my 2 barrel holley carb. One venturi just kinda drips and the other doesn't put out any fuel. When I press the lever though, fuel does come out of both secondary sprayers. What could have caused this sudden change? A clog or maybe the fuel pump died? Just seems weird that it would go from perfectly running to DOA overnight. I've got a fuel filter in line (pre fuel pump) and have never had ethanol fuel in the tank. Maybe a quick change on the fuel filter is where I should start? Thanks!

 

If it's a 2 barrel carb there are no secondary's to speak of, only primaries. If there is fuel in the float bowl it should run for a few minutes. What type of Holley carb is it?

Can you clarify the fuel issue not spraying from the venturis ( main discharge nozzle)? It's not clear what is occurring because it is very rare to ever see fuel coming out of the main discharge nozzles when revving the motor in park or neutral. Especially on a Holley carb. Under those conditions the idle and transfer circuit are being used and not the main circuit. If it's dribbling fuel through the main nozzles with the engine off and during cranking, the float has sunk or the needle and seat are not sealing. The result would be a flooded motor.

 

Not sure the exact model. Found the marking List 1772 on it. See pic. Once before I’ve had the air cleaner off and witnessed fuel spraying out of the two venturis while revving the motor. Not so much anymore. When I press on the lever I get another a shot of fuel to each side from what I think is a secondary. It comes out of the cylinder where the Phillips head is in the 2nd pic.

 

Looks like a common Holley 2300 from here. The phillip screw is the pump nozzles.
Venturies likely plugged up. We hold throttle wide open and shoot shop air in each
venturie you should see a fine mist of fuel.

 

Where exactly would I shoot the air?

 

That spray of fuel you are seeing when you actuate the throttle is from the accelerator pump discharge nozzle, which is normal and good. You should see two good streams of fuel from the accel pump discharge nozzle when actuating the throttle. You are correct in that's the part in your bottom photo, in the middle with the philips head screw holding it in place. With the engine running when you rev the motor that spray of fuel will hit the air stream and booster venturis and atomize . Sometimes looking like it's coming from the booster venturis.

But with that said, that looks like a fairly small carb, so you might see some fuel from the booster venturis when revving the motor. Is the float bowl full? If you remove the fuel level inspection screw on the side of the bowl and shake the truck a little, fuel should dribble out. If the float bowl is empty, there is something wrong with the fuel pump, filter, etc. or it leaked out overnight. I have seen them leak into the motor through poor sealing metering blocks. If the float bowl is empty you can fill it from the vent tube, then see if the motor will run okay for a few minutes. If the float bowl is full and it won't start and there is spark at the spark plugs, one or both idle fuel restrictors in the metering block might have gotten plugged with some debris. They are very small orifices, usually 0.025" to 0.035" depending on the carb model.

Does it have spark at the spark at the spark plugs?

 

Bowl was full. Will check spark but everything is brand new so doubtful it’s spark but ya never know. My money is on a clog somewhere.

 

Spark plugs are looking pretty nasty....

 

Clean or replace the spark plugs and see if it will start or try to start. Although it seems cleaning spark plugs never works as good as replacing them. I'm starting to think it was running too rich and fouled the spark plugs. Merely prolonged idling with the choke closed can do that as well.

If something is plugged internally in the carb, it would still try to start or start momentarily from the fuel out of the accelerator pump nozzles from actuating the throttle.

 

Yeah definitely gonna get a new set of plugs. These are toast. Yesterday when it ran nice and smooth I did let it idle about 8 or so mins because I was fixing the temp gauge. Choke was off. The motor ran so nice I’ve actually never had to choke it to start it. Given how smooth it ran at idle I never suspected it to run rich enough to fowl the plugs.

 

After you get it running again, it might be worth double checking the adjustment on the idle A/F mixture screws. Could be something that simple. Plus, stock ignition systems are not as capable of keeping a spark plug clean if the mixture is a little too rich.

Another last simple thing to do just as an occasional precaution is clean the air bleeds on the carb. If you look at the bottom picture of your previous post you will see 4 small brass plugs, two on each side of the accelerator pump discharge nozzle. The outer most two are for the idle and transfer circuits, and the inner most two are for the main circuit. There is a very small air bleed hole in each one. These allow air to enter the fuel stream in the passages inside the carb and emulsify (aerate) the fuel mixture. When they plug the mixture will get rich. Take a can of carb cleaner and with the straw on it and spray it through those bleeds to be certain they are clean.

 

Thanks for all the help! My air/fuel screws were both about 1 to 1-1/8 turn out from closed. Will definitely clean the bleeds as well.

 

well....new set of plugs and same result. What's next?

 

As was suggested previously, instill a few ounces of gas into the carb via the vent. You should see the accelerator pump discharge when operating the throttle. If you don't see the accelerator jets squirt, then the carb may be dirty.
If you see fuel but still no vroom, then start checking for spark.

 

Hmmm....poured two oz of fuel down the vent and no improvement. I also checked spark and it’s there at every plug.