Erratic problem

[Reds]

I have a 41 ford pickup, v8, converted to 12v. I have a problem with it bucking and missing. It always idles nice and smooth. But occasionally (every couple days) it will start bucking while I am accelerating. This goes on for a little while, then goes away. It's not overheating. When the problem started it acted like it was running out of gas - gulping air and sounding like it was running out of gas. So I checked the (electric) fuel pump and it pumps plenty of gas (fuel pressure set at 2lb). replaced rubber lines with fuel inj. hose. Then I got frustrated and bought a rebuilt carb. Still doing it. Then I pulled the Mallory dual point dist off, limited the total advance to 18 degrees, made sure the points were good, and changed the condensor and the coil (internal resistor coil). Also put on all new plug wires + new plugs. Still doing it. Then I sprayed the manifold and carb base with either to see if I had a vac leak - no. Then I timed it using a vac guage (adjusted to max vac then backed off 1 degree. final vac at 19). At this point it stopped acting like it was running out of gas and just started bucking when revved up. Any suggestions as to what to look for?

[Frank The Plumber]

2 lbs is not a lot of fuel pressure, you may be running your bowls dry, my carb float valves stick and or dont seat right due to gumming etc, you may be having a similar problem.

[jdl]

Do you have a mechanical pump? if so change the flexible fuel line, they can look and feel good ,but suck air... in line fuel filter dirty?..sticky valve?...try some MMO. good luck.

[Frank The Plumber]

Would this MMo help to lubricate the seats of the carb floats, I think it is gumming on mine, runs about 2 or 3 minutes and then gets all erratic and wants to die, either flooding or starving, can you use the MMO to lubricate the needle valves?

[jdl]

Frank, I think the Marvel Mystery Oil is a great product for our old Flatheads, will it solve your problem? maybe. add about 8oz. to your tank and give it a try, can't hurt. it's available at most parts stores or walmart.

[Reds]

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I took the mechanical pump out of the circuit to make sure that it was not part of this problem. I changed all the flexible lines (including the one coming out of my fuel tank) to fuel injection hose which is supposed to withstand the ethanol. I can blow thru the inline filters with no trouble. Will try some MMO today. Had this problem with "original" carb and pulled the top off to check the bowls - they had a good amount of clean fuel in them. Problem continued with new rebuilt carb. Also tried adjusting the fuel pressure up and down, with no luck. Next I am going to change the condensor & coil again just to make sure that I didn't get a new one that was defective too. I am grabbing at straws.

[G.M.]

MMO in the gas tank will clean the lines,pump and carb. On the first application drizzle some down both sides of the carb while running then put a 1/2 quart in the tank reguardless of how much fuel is in the tank. It will smoke but it will remove the hard white resin on the valve stems and free the rings. About a 1/2 pint every time you fill the tank after that. I drive 6 or 7 old Fords and if MMO is not added the valves slightly stick after the second tank without it. This sticking is very slight and most people if their engine is not running perfect will not notice it. The most noticable test is in high gear, drop down to 8 or 10 MPH in 3rd gear and step on the gas and as the speed increases you get a bucking, after treating with MMO in 10 miles it will pull out smoothly. Reds with the changes you made it sounds like dirt in the gas tank plugging the pick up tube. I just had the same problem and when it is intermittant it is had to detect the problem. I went 1150 miles, the 1st 125 it never skipped a beat. I could feel the carb bowl run out of fuel, if I let off a few seconds it would get enough fuel. On level ground ground it wasn't as bad as on hills. Sometimes it would go 50 to 100 mile and only miss a few times. I stopped about 10 times on the trip when it got real bad and blew back through the tank. A few times it stopped and wouldn't run until I blew back through the line. I did find some small black particials in the flex line and glass fuel filter bowl on the carb. I made the complete trip but was a pain when it was 100 to 110 the entire trip. I called the company that makes the gas tank sealant and they never had anyone who had the liner in over 25 years. I pulled the tank and it looked like the sealant was flakeing. I am soaking it with acytone to see if I can remove it. I may wind up putting in a new tank. G.M.

[Frank The Plumber]

When you turn on the fuel pump are you leaking down into the carb at all? It sounds like a problem with the advance on your distributor. You may want to search vacuum tuning on here and the hamb.

[Old Redneck]

I keep a good carb that works very well for a test carb and also a dist and coil.That works for me. So when I have a problem I start with a test carb and when that doesn't solve the problem I change the dist. and so on.It makes life easier for me.Let us know when you solve the problem if you will.

[Frank The Plumber]

Redneck, you need that set up, you have about 300 cars now by all accounts. lol thanks

[Reds]

When I turn on the fuel pump it does not leak down the throat of the carb, nor out the base. I did vacuum time it. It seems that timing helped but did not fix the problem. Tomorrow morning I will try the MMO and then drive it for a while. If that doesn't help I will just start playing with the timing. Thanks for the responses. I will let you know if I find the problem or not. The next thing I will try is to drain or pump some fuel out of the tank to see if there's any junk in it.

[G.M.]

Dirty gas tanks don't go away they keep causeing problems. I have had some I drained the fuel,strained it and kept putting it back, straining and draining. It may improve slightly but don't fix the problem. On the tank I have off now that has been soaking for several days with acetone and rolled into differant positions I drain the acetone through a paint filter today and got close to a cup of black particials out. Rinced it with water, dried it out and put the strained acetone back in. Will continue shaking, rolling and drain it again in a few days. It is starting to look good inside. I washed this tank with a very strong industrial detergent and flushed it several times before starting the acetone wash so whatever I'm getting out was not just loose dirt, it's a black carbon looking material. G.M.

[Reds]

MMO did not cure the problem. BUT, after all that I have done to try to fix this, the problem seems to have diminished. Once in while, while under power, it does a quick litle "buck" and then goes back to running normal. Sometimes it will buck 2 or 3 times over a 30 second period and then go back to running fine. Always starts and idles real nice. Never stops running. I am going to play with the ignition timing to see if it makes a difference.

[36 flathead]

did you try swapping out your condenser. I had the same problem on my 36 and that fixed it.

[4dFord/SC]

Check your ignition switch.

[Reds]

I did swap out the condensor and the coil. What am I checking for on the ignition switch ? Good connections?

[4dFord/SC]

Originally Posted by Reds

I did swap out the condensor and the coil. What am I checking for on the ignition switch ? Good connections?

Remove the body plate with the posts marked "Battery", "Coil", and "Gage." On the back side, check that the contacts for "Coil" and "Gage" are not pitted or burned, an indication that the switch is not making good contact with them. A new body costs about $14. I had similar intermittent problems with my '40, and that turned out to be the cause and cure.

[Brian]

Spark plugs??? Brian

[gearhead1952]

How about coil to distributor wire? Maybe shorting out inside the distributor?

[Reds]

I replaced all the wires with a new set. Ditto the plugs. Will look at ignition switch this weekend.