10 minutes fun, then misfires, finally dirt nap

'46 stovebolt. Cranks up, runs, idles great. 'Bout ten minutes on the road she seems to misfire, then just dies. Wait ten to twenty minutes and she may or may not crank up and run, only to do it again. I changed the fuel filter and lines today. Has about 5 gals new gas. Any suggestions? Could it be some sort of vapor lock (I am in Florida and it is very humid)? Something else? Help!

 

It very well could be vapor locking, try throwing a bottle of HEET or something similar in with your fuel and see if that helps at all.

 

Check for Spark @ Coil, if yes... Check for Fuel @ the Carb(air cleaner off, look inside and pump throttle to see if accelerator pump is squirting anything, or prime with a couple of ounces of gas and crank over) Don't look into carb while cranking!!!

 

sounds like fuel to me, my truck had hayseed in the tank when i got it and would plug the line, take some gass with you on your next drive and when it dies pour a little into the carb and see if it starts.

 

If it's repeatable like you mention, look for electrical stuff failing when it gets to hot. I think either the coil or the condenser perhaps.

 

I would also have to go with coil

 

Same thing happened to me w/a 60 el-camino.I took ithe tank out & shook it,sounded fine but as soon as I put gas in it,a bunch of crud fell off the sides and it would run for a few minutes then quit.I had to have the tank re-lined.

 

Thanks everyone.. I will go with the tank and then move to the other items. Not sure where I can get a condenser for it...

Big T

 

Parts?: National Chevy Assoc, Filling Station (I've used them alot and had great luck wiht parts & customer service). You could probably get coil, points & condensor at a local NAPA. Does it have the phenolic carb spacer between the carb & intake? Does it still have the original steel fuel lines and are they running clear of the exhaust manifold? I would strongly suggest getting the tank boiled & blow the lines clean while the tank is out if it was sitting for any length of time. You may also want to check out the Chevytalk forum as there are some SUPER knowledgable folks over there..... BItchen looking truck by the way!

 

Parts?: National Chevy Assoc, Filling Station (I've used them alot and had great luck wiht parts & customer service). You could probably get coil, points & condensor at a local NAPA. Does it have the phenolic carb spacer between the carb & intake? Does it still have the original steel fuel lines and are they running clear of the exhaust manifold? I would strongly suggest getting the tank boiled & blow the lines clean while the tank is out if it was sitting for any length of time. You may also want to check out the Chevytalk forum as there are some SUPER knowledgable folks over there..... BItchen looking truck by the way!

What is the website for National Chevy Assoc, Filling Station? Also the chevytalk forum?

Not sure about the spacer... I will take a look tomorrow in the light. Good deal on NAPA, I will give them a shout as well. Original steel lines far as I know... I think I'm gonna take your advice on the tank regarding the boil.

Thanks again!

Big T

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try here:

http://www.chevytalk.org/fusionbb/index.php

Parts:

http://www.fillingstation.com/

http://www.nationalchevyassoc.com/

 

Thanks for the websites bro... I will check them out.

Big T

 

Why would't you go with the easy stuff first before pulling the gas tank out? The coil and condenser are right in front of you and they are cheap. I guess I am just lazy. Good luck on your quest, Keith

 

I agree, go with the easy first...
Did you check for spark when it quits?
Don't start throwing parts at it unless you're sure you know what's wrong... If you think there's a fuel problem, pour a few ounces into the carb first... The engine won't care where the gas comes from, you can also run a hose from the fuel pump to a can of gas and bypass the tank and line completely too...

 

I'd have to guess coil or condenser if it runs again after it cools down. Gas is a possibility but clogged fuel lines are less likely to unclog after a giving period of time while electric components are commonly affected by heat.Take some gas or starting fluid along with a spark plug for a ride. When the truck stops running poor a little gas down the carb and see if it starts back up. If it doesn't pull a plug wire and install the extra spark plug in the end. Ground the metal part of the plug to a good ground and jump the starter. While the engines turning over you should see spark. If there is no spark start with points and condenser, they're cheap and replacing them is normal tune up procedure.

 

I have the exact same symptoms you are describing, on a '40 Chevy more-door, with a 235 and a 4 speed
Only thing is, we seem to have completely different equipment- this car has an Offy intake and two Rochesters, Fentons, and a coil-in-cap HEI.

I'll be watching this thread, I need to go out and do the same tests. I'll post if I figure anything out.

 

I had a car do this once. It was a clogged vent hole on the gas cap. Is your tank vented well?

 

My gut feeling is the coil too. Gets hot and shorts out cools off then it runs. ( Like an old 9N Tractor) next time it dies check for spark at the coil. If it still sparks then move on to fuel. Also check for large pieces of old rubber hose in the fuel line getting sucked flat after a while running. I have seen it happen.

 

My little truck did something close to this

after complete redo ..
I hid all the wires on the truck ..Ran dist wires under carb thru intake

(air gap for those that don't know)

And I got on "pinched" some how ?

when motor would warm up ..bloop, shut off ..sit for a little
and vroooommmm ..


I found it, when the truck was idling ..started wiggling wires

and it stumbled ..simple problem

 

a friend had the same problem on a car once - driving it 900 miles home was an adventure. Turns out the coil was getting super hot and stopped working every 15 minutes. Replaced that and it ran like a dream ever after..

 

Couple of questions...

When the truck dies, can you get it to start back up and idle? Or is it completely dead until it cools? If it starts back up and idles, it's probably a clogged line that's not letting enough fuel get to the carb.

When you're trying to get it restarted, does it backfire? This would indicate that fuel is making it into the carb but no spark.

You may want to take the air filter off and while it's idling have someone give it gas and look to see if the spray in the carb increases. (I'd suggest using a mirror as to not burn your face off)

Also, are you're brakes locking up?

 

No, once it dies, thats it. It might restart once in a while but only for a few seconds.

Yes, the brakes are locking up in the back. Is this a heat related issue? I look forward to seeing your response as you are the only one who has mentioned the brakes locking and I'm wondering what the correlation is.

 

Just wondering cause I had a 46 that looked like yours and had similar problems with it. I got frustrated and ended up selling it to my neighbor for $6k. He's actually got quite a collection.

 

I've had a similar thing happen caused by a faulty condenser.

 

I remember back in the 60s a friend of my Dads didn't know if the 55 gal drum of alachol was empty so he struck a match to look inside. There were only fumes and needless to say he has no hair left above the shoulders (eyebrows, eyelashes, mustache and hair) second degree burns. Knowing my day and the bunch of racers he ran with I am sure beer was involved. Keith

 

Quicky coil/condenser test:
Get jumper wire with alligator clips.
Car cold, remove small wire to distrib, install jumper on its coil terminal, ground/release repeatedly while watching spark from big wire jump to ground.
Probably big, fat blue spark.
Run car to failure point--repeat same test.
Big, happy spark, coil/condenser good.
No spark or thin, scrawny yellow spark--one of them is bad. Throw on new condenser or ANY leftover condenser from garge floor and retest--condenser dirt cheap. This will implicate one or the other...

 

I'd check the coil & condenser, had the same kind of problem on my roadster run great till the old coil would get hot then it would break up bad. Good luck

 

condensor. Mine made me walk 2 miles home. I replaced it and a week later went with Pertonix. That was years ago.

 

Has it been changed over to 12 volts? If so was a resistor installed between the Ignition switch and the coil? If not the coil will get too hot. Even if a 12 volt coil has been installed the resister is necessary. Also Ive seen steel fuel lines plugged up with rust and crud where fuel wouldn't go through them at all. Yours could be restricted but not plugged yet. My Grandpa was having the same problem with his 66 ford pickup many years ago and I pulled it off and rinsed a handfull of elm leaves out of it. He had a habit of forgetting to put the cap back on and always parked it in the shade of a big elm tree.

 

If you find it's not electronics, then I'd consider today's gas. It's pretty much formulated for closed injection systems, under 45psi. It boils incredibly easy in an open unpressurized fuel bowl, due to the alcohol used to provide octane in place of the older, more toxic additives. I had problems such as you describe in extremely hot weather. Mixing in a little 110 octane race gas cured it