Erratic problem
 

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?

Re: Erratic problem
 

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.

Re: Erratic problem
 

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.

Re: Erratic problem
 

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?

Re: Erratic problem
 

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.

Re: Erratic problem
 

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.

Re: Erratic problem
 

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.

Re: Erratic problem
 

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.

Re: Erratic problem
 

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.:D

Re: Erratic problem
 

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

Re: Erratic problem
 

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.

Re: Erratic problem
 

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.

Re: Erratic problem
 

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.

Re: Erratic problem
 

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

Re: Erratic problem
 

Check your ignition switch.

Re: Erratic problem
 

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

Re: Erratic problem
 

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.

Re: Erratic problem
 

Spark plugs??? Brian

Re: Erratic problem
 

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

Re: Erratic problem
 

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

Re: Erratic problem
 

I apologize for dropping this thread and not reporting back as to whether or not I have fixed it. Just after my last post (7/14/10) I started a long hard battle with cancer. After chemo, cranial base surgery, and brain surgery I am pretty much recovered. No sign of live tumor at this point. I was able to start working again and playing with my '41 this July. I still have the same problem with it. It has run fine for the last couple weeks. But today it was bucking and snorting before I got out my driveway. Stopped and pulled the top off the carb - plenty of clean gas. Pulled the line off the carb and the fuel pump is pumping nicely when I turn it over. Started it and watched inside the carb and no fuel dripping in there. Pulled the plugs and they are all dark but not to the point where they are fouled. I am going to pull the ignition switch this weekend and check the connections. Also going to put a dial indicator in #1 cylinder, find TDC, and get a timing mark and pointer on the front pulley. Then I can check the timing with a light. Thanks for the previous answers and help with my problem. I will post more as I get to work on it.

Re: Erratic problem
 

Sorry, but you can't see the piston through the plug hole. Need to use something flexible, like a tywrap maybe to fish in the chamber to get over the piston.

Re: Erratic problem
 

set a volt meter in seat beside you and hook to hot wir from ign sw,to resister ,see if you lose voltage when it misses or bucks, use a analog meter so you can see it move.

Re: Erratic problem
 

I would check the gas cap to make sure it is vented correctly. You mentioned it seemed like it was running out of gas.

Re: Erratic problem
 

I'm glad you are doing well after all those treatments and surgery. These old cars loose their importance when health or family are at risk.

Re: Erratic problem
 

Red it sounds like sticky valves. There is a white residue that forms on the valve stems. Drop down to 10 or 12 MPH in high gear and step on the gas, as it picks up in speed you get the slight bucking. With the engine running drizzle MMO down both sides of the carb for a few minutes keeping it running then put the rest of the quart in the gas tank. Don't be skimpy on the MMO. I have seen this at least a 100 times and it works every time. When it pulls out smoothly in high gear the problem is gone. G.M.

Re: Erratic problem
 

Intermittent problems are usually related to intermittent discrepancies. Crap rolling around in the fuel tank or water for that matter will either occasionally block the fuel pick up tube in the tank or it will suck up a slug of dirty water. The sticky valve discrepancy is real. They will work fine for a while then start sticking just enough to slow the valve opening & closing which plays hell with the valve timing and can give you intermittent missing or after fire in the exhaust. Ignition intermittent problems can be due to leaky condensers or worn out spark plugs. An old worn distributor shaft can give intermittent problems with the rotor contact and breaker dwell. Carburetors and fuel pumps rarely have intermittent problems. Internal blockage, leakage, or bad accelerator pumps generally give trouble all the time.

Re: Erratic problem
 

Red glad you are doing well with your health!

I had the same problem with my 38pu. Hesitated/bucked under load only. Idled great. But once you take it for a run it would run poorly.

Switch out the condenser ($10), cleaned the points, and rotor contacts. Now it runs like it should.

Good luck!

Re: Erratic problem
 

Jeez, sorry to hear you've had such a rough time. Glad you have made a good recovery though.
Mart.

Re: Erratic problem
 

Anybody up there near Scranton that could help Reds drop his tank and flush it out so that that problem could be taken out of the loop? That's easy for me to suggest, since I'm 3000 miles away, but if there's something in the tank intermittently blocking the outlet, it won't go away by itself. Otherwise, I'd vote for a bad (new) condenser, or bad ignition switch, or bad wiring from the ignition switch to the coil. Might try bypassing the ignition switch by running a wire directly from the battery to the coil. Nothing worse than an intermittent problem to diagnose! And I don't discount GM's valve theory -- just have never experienced it myself.

Good luck to you Reds, and I admire your perseverance in the face of adversity. Been dealing with your health challenges in my family over the last few years, and it takes a lot of personal fortitude to pick yourself up and get on with your life in spite of it all.

Re: Erratic problem
 

Just dawned on me that you folks over there on the other side probably have a few other things to think about right now than Reds pickup. Hope you can all push Irene off into the deep end!

Re: Erratic problem
 

Hi Red. Just came across your thread while trying to sort a fuel problem I have. Thought I'd check in and see how you and car are doing. Sincerely hope your both sorted now.

Re: Erratic problem
 

KIWI, I just saw your post. My problem has still been coming and going. But I have narrowed down the cause, but not the fix. I was thinking that I had a fuel or electrical problem. But earlier this month it started running rough when idling too. The original problem was only when it was not idling. I hooked up a vacuum guage to the windshield wiper port on the carb base. The vacuum was at 12 and when I revved it up the vacuum dived down to about 2 and then started bouncing all over. I thought I would try my other vacuum guage for the hell of it. The truck was running and when I pulled the first vac guage off of the hose the engine started idling nice. So I have a vacuum problem but a strange one. When I create a huge vacuum leak by opening up the vacuum line to the outside air it ran nice, idle or revved up. Hook the vac line back up and it started running fine again. I have not had time to play with it this week, but will try to fiddle with it some more this weekend. I am going to try running a hose from vac. port at base of carb into the cab. I will start the truck and drive it with my finger over the hose. If it starts missing I will pull my finger off and see what happens. Maybe I will have my son work the finger in the hose thing while I drive. This is driving me nuts. But at least I know that I have a vacuum problem not a fuel problem or electrical problem. Thanks for asking about it. I just bought some MMO and Risoline - I'm going to drizzle the MMO down the carb while it's running.

Re: Erratic problem
 

It must be running too rich if creating an air leak makes it run better.

Maybe?????

Mart.

Re: Erratic problem
 

I had a problem that it similar to what you describe. The truck is is also a 41 and converted to 12V. It would start and run fine for a while. Then run like crap and quit. What I found was a bad wire and loose connection at the input side of the ballast resistor. This is with a Mallory breakerless ignition and a can type coil that needs the resistor. There were actually two problems going on at the same time. The bad connection and a dirty tank. It kept me hunting for a while.

Re: Erratic problem
 

I agree with gearhead. I had the same problem and found the wire inside the distributor was grounding out.

Re: Erratic problem
 

I don't believe there are any wires inside of the 1941 distributor. OOPs, just reread your original post and see you have a Mallory distributor.

Re: Erratic problem
 

My 36 does about the same things and I have tried most of the fixes listed here. I hope there is an answer.

Bill

Re: Erratic problem
 

I agree with Mart. If it runs better with an air leak, you are obviously too rich. Possibly a bad power valve? Float set too high? At idle can you look down the throttle barrels and see fuel dribbling from the boosters?

Re: Erratic problem
 

Flatjack beat me to it. Maybe a leaking power valve.