Hello,

My 72 F-100 won't start. It was running alright as I talked in the church parking lot next to it for about 10 minutes. I left it running cause it usually has to turn over about 8 to 10 times with the pedal mashed to start, and sometimes just won't start. I've been working on it for a while, and re-built the carb, replaced fuel pump, plugs, wires, contacts, coil, points, condenser, cap, timing chain & gears, and I think that's it.

It runs with a miss on one or two cylinders at a rough idle and likes to die after reving when its not hot. She runs cool though. I timed it at 12 degrees before TDC, so if it's a tooth off, does that matter?

So she's running, and then idles down, and then dies. After that, I tried to start it back up, and I got an instant turnover like she was about to start, then nothing. I thought I wasn't on the gas fast enough, so I hit it again with the pedal mashed, and kaboom, a fireball out of the carb. Yes I had already removed the air cleaner, it's my favorite thing to do these days when I have my daily breakdown.

I have had all kinds of problems, but I thought I finally had them worked out. It starts, it doesn't start. It runs, then it dies warm and is harder to start back up, rather than the first start of the day which starts like it should usually. I don't think I have any leaks from the pump to the tank, as I found the last one I believe, and the cap isn't creating a vacumn. I have both screws on the front of the carb 4 turns out. The vac line on front of the carb is going to the vac advance. The one on the passenger side is capped off???? The big one on the base on the back of the carb is capped off. The tree over the #4 cylinder had the big fitting capped off and the small one I have going to the transmission vac. I am not sure I have all of the vac lines right.

One last thing, that crazy plate with the cooling water lines and the vent line off of the passenger valve cover that the carb sits on......I have it stacked up as so: Carb, Thick Gasket (1/4" or so) Crazy Mounting plate, Orange Permatex, Intake. I had a regular gasket under the plate, but it seemed to leak.

Tomorrow I have to beg for a ride to the next town where my church is, and then get this thing right the first try. I'm not sure what tools to take, and what part to buy, but I'm so broke it isn't even funny.

Can anyone put a finger on this problem? Thanks.--Nathan

 

Nathan, How about starting with what engine you are running, what carb, etc.

Sounds like a tuning issue. If you have a 4 barrel on an alum, intake you may need to add a 1" phenolic spacer under the carb to aid with the hot start issue.


A little more info please.



John

 

Well it sounds like you replaced most of the main items, but the rough idle, dieing issue sounds like carb issues. I'm guessing it's the stock 2bbl? Or what? If there is any vacuum leak, it will idle rough too, and by the sounds of your "permatex" it might still have one.

That cooling plate could be removed(plug/remove the lines). You need to get it sealed well witout using Permatex. I'm trying to picture that vent line? Should be a PCV in there, if not then you've got a real vacuum leak. Take a plug with you and cap that off and see how it responds.

It's really hard to diagnose problems over the internet, especially with minimal information and no pictures.

Timing sounds good, it can't be one tooth off and be at 12*. Once it's set, you're good.
I'd recheck your float level and make sure it's set properly. Sounds like it might be getting too much fuel.

Just a few things off the top of my head to look at.

 

I agree that it sounds like its getting too much fuel, especially at idle. Just exactly what screws on the carb are "4 turns out"?

 

OK, first Thank you for the replies.

I am running a 390 in a 1/2 ton 72. I am not positive it's a 390 but that's what the guy told me it was when I bought it.......

It is all stock, and has the stock 2bbl carb (aluminum) on it. It has the I'd say 1/4" phenolic gasket on it, and the problem is that if I put a thicker gasket on it I would run out of stud length as it is I already barely have enough.

What would be the result of chuncking that spacer out with the cooling water running through it? I hate that thing.

The two screws that are turned out are on the base at the front and I believe they are the gas and air screws but could you tell me which is which?

The automatic choke isn't in use. I have it twisted so that it barely holds the flapper open, or barely holds it a little closed rather. Its 7/8 open.

The float adjustment, I'm not sure how or how much to adjust it, could you give any advise on that please?

Does backfiring affect the Power Valve? What is that and what does it do? I think it adds gas when you push the pedal. Should I replace that one?

The vent line comes off of the valve cover on the back of the enging passenger side, it has an upside down tea cup sized cylindrical shape and has a 3/4" or 1/2" flexible rubber hose which goes up a couple inches, makes a u turn back down, and then over to the back of the base plate which mounts to the carb. I would like to chunk that too.

With a flashlight at night, I can see smoke coming from that and from the other side vent which feeds into the air cleaner. It looks like allot of blow-by, but I am not sure how much is too much. Its about as much as if you took a short drag off a cigarette and a deep breath of fresh air, and then blew out, if that helps any. I don't smoke but I used to when I was a kid. lol

The engine makes a faint sound that sounds like two horses running down the road, at night, one horse has only 3 legs and is carrying a box of nitro glycerin. I can hear some kind of tap, some kind of slight knocks, its hard to identify over the exaust leaks which seem to be just enough to ignore, just enough to say, this guy can't afford gaskets.

Thanks again, Nathan

 

Oh yeah, the intake is stock, I guess that's cast iron. Thanks Jowilker. Thank you Freighttrain, thank you Argess.

 

Where to even start? First, maybe get the nitro unloaded from that 3 legged horse! OK.....maybe try these:

1/ Buy a manual for your vehicle. $15 for a Haynes guide, would be worth it. Or even try the library and do some photo-copying.

2/ Fix or remove the choke. One way or another, you need some consistentcy even if you remove it and have to pump the gas pedal a lot to get it to start. But fixing it would be better. Choke adj can be tricky. Another reason to get a book on your vehicle.

3/ I'm not that familiar with that carb, and I gave away the one I had, so nothing to look at. But those air-mixture needles sound way too far out. I suspect 2 turns each or so.....once you get it started and warmed up, turn each in ...a little bit, alternating back and forth between them. Try to get the highest idle speed with those mixture screws. Then turn the idle back down with the single screw that stops the carb from closing too far. If you get a book, it will tell you how ot do it with a vacuum guage, whihc is a better method, but the "ear" works fairly close.

4/ I think Power Valves are only in Holley carbs, so that shouldn't be a worry for you.

5/ Those "other" noises arn't encouraging. I't try not to spend too much money until you get the tuning right. If the noises are still there, the engine may be on borrowed time.

6/ Some of the noises may be misfires. Do the midnight-test and look for leaking sparks (arcing) and/or blue corona around the plug wires. Also check the plugs, dist cap and rotor visually.

 

Wow...okay.

Yes, you can chunk that heater plate under the carb. It is meant to get the carb heated up in the winter, but it's pretty much useless otherwise. Plug the hoses off and remove it.

The vent tube you speak of sounds like only a breather from the valve cover to the air cleaner. This is NOT a PCV valve, it just uses the air flow in the air cleaner to draw fumes from the motor into the motor to be burnt. The smoke you see coming from the tube is BLOWBY from the rings being worn. This is a tell tale sign the motor is WEAK. Don't waste a bunch of money on it.

You mentioned you rebuilt the carb, so I figured you had the details for float setting. It's not difficult. Removed the lid from carb(screws around the top) and you then measure the from the top edge of carb body to top of float. The paperwork you got with rebuild kit should have a dimension and a paper scale to use. If, when you get the top off the float is basically level on top(not pointing up or down) then likely it's pretty close. You can lift the float body out of the carb and see the needle is hanging on the end of a tab. That tab you bend slightly to adjust the height of float. This is not for the faint of heart, so if it looks straight, leave it alone for now.

I too would also crank the choke so it doesn't close at all. If it's weak and can fall closed for no reason, it will make it hard to run/start/etc. Loosen the three little screws on the passenger side of the carb(black round piece) and turn the black part til it pulls the choke plate fully open(tight). This might make it a bit harder to start in the morning, but not a big deal if it actually RUNS afterwards.

The mixtures screws in the front of carb, should both be about the same number of turns out. FOUR turns is probably a bit much, as you should start at about 1 1/2 turns and play with it from there. They adjust the idle mixture ONLY!! One for each venturi in carb.

Hopefully we can get you down to a good starting point to eliminate any problems and get it reliable.

 

Timing Chain. I'll betcha.

Pull the distributor cap off. See if the rotor turns when cranking. If not you've found your problem. Try using a 15/16 wrench to turn the motor in one direction and then back the other way while watching to see how much the rotor turns - or doesn't. Lots of rotation without rotor movement shows slack in the timing chain..