304 W/ A Holley 4160 4-barrel Carburetor

So, still picking away at the 73 Bullnose. Been chasing a ghost for the past month, pulled the carburetor off twice now.

An earlier owner installed a Holley 4160 4-Barrel with a Mr. Gasket 2-to-4 Barrel adapter installed upside down so they could get a 4-barrel carb on the original 2-barrel intake manifold. I've rebuilt the carb, replaced the needles, installed a pressure regulator and filters, installed a phenolic spacer, and replaced the spark plugs, but she still has a Hot Flood problem. The engine will fire one the second key turn when she is cold, but if I let the engine warm up, then shut it down, I have to wait at least 15 minutes before I can start it again. I've even gone so far as to reroute the fuel line so it comes across just behind the front cross-member to the fuel pump, then jumps up to the pressure regulator/filter and into the carb.

I will note, the phenolic spacer did wonders for the earlier rough idle. I suspect the 4-barrels directly bolted to the adapter was resulting in impingement and bad fuel/air mixing.

I did notice this evening while reading Holley install instructions that the vacuum assist to the HEI distributer appears to be on the wrong port of the carb. That will be first tomorrow.

I've read that the Holley carbs don't like fuel pressures greater than 7-psig, I'm currently at 4.5-psig when the engine is running. If I go much lower, she'll starve.
I've installed a tach, she's idles at ~950 rpm.

BTW, what is the proper idle speed, my hood tag is faded?

The front bowl has a slight wetting when I open the sight screw while the engine is running, the rear bowl doesn't even wet. I've look down the throat of the carb at shut-down and don't see any fuel entering the intake. After I shut down the engine, the front bowl will have more fuel, enough for a slight dribble, but not enough to pour from the sight screw.

 

The 4-2 adapter is like taking a bath with your socks on...you either need a 4 bbl intake or a 2 bbl carb. Having said that, it's not the cause of your heat soak issue.
If you take the air cleaner off the carb when the engine is warm and not running, do you see fuel dripping in the venturis? Is there any vapor visible? Will it re-start if you hold the throttle all the way down?
One other thought...fuels with alcohol in them are more prone to this, if there's a station in your area that sells "pure" gas, give that a try.

 

4160 seems like a lot of carb for a 304. Do you know if the motor is stock?

 

4160 doesn't refer to a specific cfm, is simply a 4bbl carb with a rear metering plate.
Could be anywhere between a 390 and 750 cfm.

 

Right, but the factory MC2100 was probably closer to 250 CFM.

 

Yes, but a 4160 is a progressive (vacuum secondary) carb, so you really should compare 1/2 of it when talking about a 2 bbl carb. Most of the 4160 Holleys are 600 cfm, so the majority of the time you're operating on the 300 cfm primaries.

 

I have inspected, but cannot see fuel dripping from the venturies when I shut it down at operating temps. Light vapor will rise from the oil fill, but not from the carb. When I try to start it, without accelerator, the engine won't catch. If I floor the accelerator, it will chug/sputter, but not catch, and vapor will rise from the carb afterwards.

I check the site hole while running, no fuel from the carb. I've got the needle valve dialed down to where I don't get any fuel out when I shut it down when warm. Before the last round of adjustments, I would get fuel from the site hole when warm, though none when running. I have observed the fuel pressure will rise after shutdown to closer to 7 psig.

Did AMC include a foot valve in the fuel tank? I'm considering a solenoid with a timer to dump the fuel pressure back to the pump suction side on shut-down. I plan to upgrade to a 4-barrel intake at some point, but I want to allow my boys to learn stick before I replace the intake manifold. The engine has been "upgraded" from what the seller told me, but he didn't have the upgrade done, so not sure what has been done. She was meant to be a project for me and the boys to work on.

It does have a HEI distributor. I haven't found the valve cover tag on the engine, but the block is stamped as a 304. I can tell you the 304 is the only period correct part of the driveline. The transmission to the wheels appears to be from an early 80's CJ. (T176, D300, D30 w/ 5-bolt locking hubs, AMC Model 20). The 304 was removed at some point though, the motor mounts show evidence of replacement, the exhaust manifold is custom.

 

The only idea I have (besides trying the different gas) is to disconnect & plug the fuel line at the carb when hot...see if it still happens.

 

Not sure I could disconnect the fuel line that quick, even a minute is enough time for it to flood.

I'm going to rip out the hose that was installed and replace with stainless steel tubing, with just a couple of hose joints between the engine and the frame to manage the vibrations. I'm thinking the hose between the pump and carb is flexing enough to act like a balloon and hold just enough volume to cause the carb to flood. I will also install the solenoid valve to dump the pressure back to the suction on shutdown. I'm thinking the charge indicator that goes to the dash will be a good "run status" for the engine to trip the timer to open the solenoid.

Final question, anybody upgrade to an external fuel pump? If so, how much fuel rate should I need to a 4-barrel Holley?