Your Diagnostic Wisdom Please

[bluec10]

I'm frustrated with trying to troubleshoot a problem with my truck.

My '69 has a 250 with a three speed manual. Its a low mileage truck and I enjoy driving a truck with the powertrain of the trucks we drove when I was a kid.'

So...I rebuilt the factory carb two years ago and it made a big difference. The truck also has a new fuel pump and a new alternator. Up until the end of last summer the truck was running great. Smooth acceleration, lots of power, and it cruised right along at highway speeds.

The problem started suddenly. The truck would accelerate relatively well to about 45 or 50 mph then start stumbling. It was like the truck wasn't getting enough fuel. The funny thing was that after sitting for a few minutes I could restart the truck and it would run better...for a while..

I checked and blew out the fuel filter. I sent some compressed air through the fuel lines to make sure there wasn't a blockage. Since that time I've run some Sea Foam through the system and refilled the tank with fresh gas.

Any ideas? I'm baffled - especially since it went from running like a top to its present state almost overnight.

[TBONE1964]

Check all of the rubber hose from the tank to the carb.

I had the same problem about a month ago on my 72. It was the short piece of rubber hose where the steel line comes through the floor and hooks up to the steel line that runs up the frame to the fuel pump. If it is soft, it will collapse and make the engine starve for fuel.

My truck did the same exact thing. Ran perfect, I made a left tun and gave it a little juice and bam, falls on it's face, sput ant spitter and for what ever reason when I would shut it off for a while, it would be OK for another 10 miles or so,

I hope you have a steel line from the fuel pump to the carb. The less rubber you have the better., You do need a little for flex but not any more than that.

Also, what ignition do you have? Is it original points or upgraded to HEI.

[bluec10]

The ignition hasn't been upgraded but I've installed all new parts.

Your suggestion to check the fuel line is a good one and I'm going to get to it ASAP. Another thing I'm going to check is the line going from the fuel pump to the carb. I used new rubber fuel line to temporarily replace the damaged metal line. The line looks like its in good shape but I wonder if it could soften when it gets hot and partially collapse.

[Mr Chevorlet]

blue c10, i am having the same issue right now also, drive for about 10 miles and start spitting and sputtering, get it home let it set and starts right up and idles smooth all day long. May i will figure it out this weekend and let you know what i find. If you find out first let me know! thanks

[geezer#99]

Originally Posted by Mr Chevorlet

blue c10, i am having the same issue right now also, drive for about 10 miles and start spitting and sputtering, get it home let it set and starts right up and idles smooth all day long. May i will figure it out this weekend and let you know what i find. If you find out first let me know! thanks

You got a vented gas cap?
Take the cap off, go for a drive.

[cdowns]

me i'd replace that rubber fuel line from your pump to carb the sooner the better or you could just wait till your truck burns to the ground

[motorcritter]

I second CDowns advice! A rubber hose on the most critical part of the fuel system- with all the heat, vibration and other potentials for mayhem, is not a good idea. I repaired a square-body for a guy- it 'ran bad'- the Q-Jet was leaky, the filter was ugly, the pump was weak (original w/ a bazillion miles), and, a rubber line from the pump to the carb. Someone had cut the steel line at either end and put hose in, probably make it easier to hook all that up, with the smog pump and etc. in the way. Got done- ran great, the carb overhaul probably helped, but the pump and line were a big factor, too. The hose had spots of wear and fretting on it, a real time bomb of misery.

[PanelDeland]

My six used to do the same things.I rebuilt the carb and replaced the fuel lines,and pump.It was much better but still a little rougher than I wanted.I did a tune up but it jut wouldn't run with it timed.I started looking for a problem and found that the vacuum advance was leaking thru the diaphragm.I replaced that and had to retune the carb(basically a vac leak).That made it run much better.A few months later I did an HEI upgrade. I haven't touched the ign in several years except for the yearly,put the light on it and check timing and I have swapped to new plugs once.
If that's all the maintainence I have to do in 10 years,I'll take it.

[bluec10]

Good advice from all. The vacuum advance is something I'm going to check - another rubber line to replace at the very least. The fuel cap is an interesting question too. Still looking for a cause.