Technical Autolite 4100 4 barrel assistance please and thank you!

Hi guys!

1963 1\2 Galaxie 500 XL. 390 automatic. All stock except for glass packs. Autolite model F-4 four barrel carb which I recently rebuilt. This car hasn't been on the road since 2006 but has had regular "startup and run till hot" sessions over the years. Didn't find anything out of sorts when rebuilding the carb except a gas-filled secondary float which I replaced. It is hard starting, a condition which existed before the carb rebuild, requiring some gas down the carb after which it fires right up. It will only run with the choke almost fully closed and not smoothly with a slight up and down change in rpm's even under 1\2 to 3\4 throttle. I have had the carb apart several times and blown out every passage I can find. The float heights are set to spec. and gas levels in both seem fine. I've etched and sealed the tank, blown out the hard line to the fuel pump (which I replaced due to a cracked housing) and checked the hard line to the carb. What have I missed guys??? Thanks in advance for any words of wisdom! Regards, Dave.

 

Look for a vacuum leak

 

Sounds like blockage somewhere,,. Did you remove the passage plugs in the lower edge of the base and clear those passages ?

 

Thanks for your reply partssaloon! I did check a few things vacuum-wise but will do a more intense search. Many thanks!

 

Thanks for your input scrapiron! Where exactly are they located? Just ran out and had a look and the only plug I could see was one just behind the throttle shaft on the driver's side of the carb base. Looks like a baby frost plug. Only other passages are the idle mixture screw ones. Thanks again for your help!

 

Does this carb have a plate between it and the intake? If so I have seen them rot out and cause vacuum leaks.
There are some small plugs on the bottom of the throttle plate (or carb body) that can be blown out if not careful.
Do the mixture screws have any affect at all?

 

saltflats: Yes, it does have the plate that carries heater water. I checked it out during the carb rebuild as I replaced the hoses to and from it and it was in good shape. Will check out the plugs you mentioned and I did try screwing the left mixture screw in and the engine stalled out. Thanks for your reply! Regards, Dave.

 

From what I remember the plate uses different gaskets bottom verses the top. Are you sure you used the correct ones?

 

Yes, I recall them being different and will double check that I got them right as soon as we get a break in our current lousy weather! Thanks for your additional input!

 

I'll add this...check your ignition components as well.

I had a guy hire me to work on an O/T mower with a ford 4 cylinder car engine. He was certain that it was a carb issue and he was at his wits end dinking with the carb, only to find out that it was a burned set of points!

 

Will do! Thank you sir!

 

Make sure the secondaries are fully closed. I recommend using flammable brake clean with the straw to trickle at the gaskets to find a vacuum leak. Some gaskets lack a 1/16" of covering the base.

 

Aha! An excellent idea caton462! Many thanks!

 

UPDATE: Finally able to get back to this after dealing with a bunch of non-car stuff! Have checked all vacuum connections and hoses and carb p!ugs. All gaskets are in their correct places and seem to be sealing fine. I also ran a check on the ignition and found the distributor in need of some TLC ( points almost wore out and advance plate sticking due to corrosion). Also had coil tested which was fine. All other ignition components are up to snuff. Fired it up today and got it to idle half decent. Choke plate is not opening up as engine warms up and the minute I push it open, the engine dies. I took the carb off and am checking all settings. Many thanks to everyone for their advice so far! Regards, Dave.

 

2nd UPDATE: Checked all carb settings and other than the primary float level being set a tad too high, everything seemed fine. Bolted it back on, hooked everything up and fired it up. Started without having to pour some gas in it but sounded rough. Still dies when choke plate is opened manually (even a small amount) and plate still not opening as engine warms up. Checked all automatic choke components including bimetallic spring and heat tube from exhaust manifold. Rechecked distributor timing and cap wires in proper firing order. Wouldn't start at all on a final attempt so I packed it up and am having a cold one! Any further thoughts anyone? Thanks in advance! Regards, Dave.

 

Have you checked the fuel pressure and volume and have fresh fuel
Do you see the accelerator pump squirt in the carb when you pump it
How far out are the mixture screws
Show us what the plugs look like
May need to start by checking the health of the engine like a compression test
Maybe a stuck lifter

 

As I remember "that's scary", there is a red rubber part in the accelerator pump. Was that replaced? As to not running without the choke on, in my exp. that almost always means that there are plugged passage ways or the float settings are off. One of my friends whose old like me always recommends another st of eyes to look at the problem. Is there someone that can double check your work? I ran these carbs all the time when I was young and never had any of the symptoms you describe. Unless the throttle shafts and the body is ruined, they are about as simple as it gets. Good luck!

 

Did you check all the gas hoses? Sometimes they dry out and suck in air and little fuel. They also can collapse internally.

 

Did the jets get swapped front to back
You may need to turn the mixture screws out some more

 

Recent new pump and fresh fuel as I redid the tank last month. Will check volume and"squirt". Mixture screws out a turn and half. Plugs are textbook "coffee with cream". Engine has only 29,000 on it since full rebuild back in '91. Did comp. test a while back and all cylinders up to snuff. Wouldn't rule out a stuck lifter as car has been off road since 2006. Thanks for your further input saltflats!

 

There are many good suggestions posted above. The Autolite 4100 carbs were built by the thousands....why don't you go down to Lordco get a rebuilt one and give it a try. If it doesn't work out for you, Lordco should take it back without question. Just my .02.... good luck.

 

Thanks for replying wfo guy! I don't recall a "red" part, but will check it out. Float levels have been checked and have blown out every passage I could find. Don't have anyone knowledgeable enough in my circle of car guys to check my work. Yes, these carbs are so damn simple for a four barrel that even a carb dummy like me shouldn't be able to screw one up!

 

Hey bobss396! Yes, I replaced the ones at the tank when I etched and sealed it and also checked the one just before the fuel pump when I blew out the hard line from the tank. Thanks for the suggestion!

 

Don't believe they got swapped. I did have the primary ones plug up once which prompted the tank clean due to bad gas. Yes, will have a go at the mixture screws. Thanks again saltflats!

 

Thanks Zapper68! It may very well come to trying another carb. I deal at Lordco all the time so will check them out if it comes down to that. Regards, Dave.

 

So your primary injector diaphragm is squirting gas when you pump it? I just rebuilt the same carb and my primary and secondary diaphragms were shot. Anyway you could have forgotten to put the springs back in. I'm thinking if you have gas in the bowls why's it not getting sprayed into the engine that's just my 2


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The "red part" mentioned is a check valve located behind the accelerator pump diaphram. Don't recall what year they changed but the early ones had a check ball that sat in a little cavitie. Sometimes the check ball would wear a bit and cause a hesitation on accell. When they went to the rubber check valve it eliminated that problem. That said, I don't think that area is your problem. Carb sound lean or engine has a vacuum leak to me. When the choke plate won't open fully it's usually not enough heat to the choke from broken tube, frozen piston in choke or a bad spring in the cap.
Does the car have a pcv valve system? If it does maybe the valve is stuck open.
One "backyard" thing you can try is reving the engine up to about 3k then hand choking the carb to try and suck through and contaminates stuck in the passages. Easy to do, costs nothing. Might get lucky.

 

Yes, when you manually push the choke open it decreases the vacuum in the carb above the throttle plates, so partially plugged jets, mixture set lean, or a vacuum leak will all cause it to stall.

I've never heard of doing this before, but it's a damn fine idea!

 

Those old 390 intakes would occasionally burn out through the heat crossover passage causing an internal vacuum leak. I read through the posts but I didn't see anywhere posted an actual vacuum reading. Have you checked it with a vacuum gauge?

 

I've done the hand over the carb thing too and had it work. I had a 2GC on a '65 Chevy that probably had a crapped up gas tank. An old Holley canister fuel filter was the permanent fix.

Those Autolite carbs are pretty simple to rebuild. I've done a few. I used to drop off the bare casting pieces to a local rebuilder and he'd clean them for a few bucks. After that they always worked well.