Need some ideas. My truck is barely running (FIXED)

[jayoldschool]

Since putting my 65 C10 230 back on the road, it has operated just about flawlessly in all weather, hauling everything from house moves, engines, to loads of hardwood. However, it is currently stranded in a driveway :-(

After taking it out of winter storage, it ran fine, as usual. While driving last week, it "coughed" once while in top gear (manual 3 sp). Felt like a brief misfire. Then, next time I took it out of my place, it was running rough within a block of my place. Second gear, no power. I thought it was running out of gas, so I coasted in for fuel. Added ten gallons, and set back out. No luck. I managed to limp it along by pushing in the clutch, revving enough and letting the clutch out enough to get some momentum. Was en route to mom's place, so once I got the truck there, it stayed.

I can start it with no issue, and the idle speed lopes. It will stall unless I add some choke and/or the manual throttle. I've played with the mixture, the idle speed and the idle vent valve (to no avail). It's getting fuel. I rebuilt the carb a few years ago and has seen a couple thousand miles since with no problems. It's not making enough power to get out of its own way.

I changed plug wires (was STUNNED to see April 1964 date codes on all!!), and put in fresh 44XL Delcos (had XLSs in it, and they were BLACK, but all the same, no oil/carbon build up).

Pulled the cap, cleaned the points and the rotor tip. No difference.

It SEEMS like a dead lean condition. If I blip the throttle, it makes a gasping noise before revving and catching up. If I open throttle slowly, it revs with a normal noise. It reminds me of what happened with my 65 Impala when there was rust between the carb and intake making a big vacuum leak.

My plan this weekend:
- check spark strength
- compression test on all cylinders (starting to worry this is a stuck valve/bad lifter/flat cam lobe
- check timing, dwell, idle speed (but tough with it running rough)

If the compression test passes, I'll start throwing more parts at it. Points/condenser. A fresh fuel pump. I did a NOS carter on it when I was rebuilding the truck, but it had been on a shelf for a couple decades. It fills the clear Fram filter, though. Maybe pull the carb off and look inside to check the float.

I'm open to ideas, thoughts, speculation... motivation...

[Steeveedee]

Did you look down the carb when it was running to see if maybe it's spilling fuel into the venturi? That would explain the sooty plugs.

[jayoldschool]

Nope, not straight down. I was avoiding backfire eyebrow delete. Good idea. Keep them coming!

[theastronaut]

Sounds like weak spark if the plugs are sooty. Start with points and condenser and new plug wires. Check the coil too.

Make sure the accelerator pump is working, if it stumbles when revving but will pick up with slow application of the throttle its a sign that the pump isn't working or is delayed. I had to go through three pump seals/umbrellas in my Monojet before I got one that fit and worked correctly.

[AcampoDave]

When that happened to me i found crap in a main jet. I thought the fuel filter could handle its job but there was a surprising anount of sediment in my float bowl too. I was on the gas full throttle when it happened

[Steeveedee]

Originally Posted by jayoldschool

Nope, not straight down. I was avoiding backfire eyebrow delete. Good idea. Keep them coming!

I wasn't asking you to blip the throttle. I went to an antique vehicle meet last Saturday, and my truck started running crappy on the way home. I looked down the primary bores and saw fuel dripping. Rebuilt the carb yesterday; it's running better now. I have a friend who got his hair styled back in about '72. They put lacquer in his hair. He was working on his '62 Grand Prix, and it backfired. I told him that his hair was on fire, and he wouldn't believe me, at first! He had to go back for another style job.

[65truckowner]

I would check the timing. I had one jump time a long time ago.

[jayoldschool]

Originally Posted by theastronaut

Sounds like weak spark if the plugs are sooty. Start with points and condenser and new plug wires. Check the coil too.

Make sure the accelerator pump is working, if it stumbles when revving but will pick up with slow application of the throttle its a sign that the pump isn't working or is delayed. I had to go through three pump seals/umbrellas in my Monojet before I got one that fit and worked correctly.

Ding ding ding, we have the winner. Just got back from diagnostics. Accel pump is good, nice strong shot when I open the throttle. No pooling/spilling of fuel.

Put the dwell/tach on, dwell is 25-30 depending on how much I was on the choke (to keep it running). No issue. Put the timing light on, and boom, there's the problem. Hit the trigger, it was like morse code. Like SOS. Not kidding. Random fast normal flashes, about three to five, then dark, then one or two, then dark, then normal... repeat. Checked #1, 2, and 5. No need to check the other three, the flash pattern was the same.

I'll guess bad coil? Goes dark while trying to build up the charge again? Probably original like the plugs. Truck only has 80k on it. I'll throw coil, points, and condenser at it. Then re-time, and re-adjust carb. Then neglect it for a few more years, lol. Plugs should look better, and I'll have a lot more power!

[Steeveedee]

6 cylinder dwell should be 31º-34º. Also, dwell bouncing that much could mean the shaft is wobbling or the spring on the points is toast.

[jayoldschool]

I'll see if I can get points local in the morning.

[oem4me]

Originally Posted by jayoldschool

I'll see if I can get points local in the morning.

Do not forget the condenser. Many years ago I was tormented with an intermittent problem that would cause erratic ignition and backfires. Blew out some mental fuses and a couple mufflers before landing on the idea that it was the damn condenser. $3 later, no more troubles.

[Steeveedee]

Dwell bouncing like I mentioned above can also be caused by a varying vacuum signal. The 4- and 6-cylinder breaker plates vary the dwell as the vacuum changes (and the mechanical weights move). My comment above should be taken with a grain of salt if you were checking the timing with the vacuum advance connected, or if the engine speed was varying too much. Sorry if there is any confusion.

[1971 GMC SHORTY]

Did you Put a Vacuum Gage And see What She’s Doing ?

[jayoldschool]

Had the vacuum gauge with me yesterday, but didn't need it. Parts place call in the morning, new condenser, points, and coil installed before lunch. Nice steady idle at 800 (for now) and 32ish degrees on the dwell. Running better than ever. Steady pulse on the timing light now. Time to get it back to work, it was great on the test drive in 90F heat.

Coil supplied was a Standard UC12 (Delco wasn't in stock), clearly marked "for use with external resistor". Makes sense, truck is still on points with the resistance wire. Interestingly, the coil that I removed is a 27270, marked "USE WITHOUT EXTERNAL RESISTOR". Hmm. Wonder if that caused the problem? Despite having the factory spark plug wires, it did have the coil swapped and the coil wire as well. Coil removed is exact same as this one.

[forestb]

Could your gas have gone bad?

[jayoldschool]

No, gas was fresh. Truck got a new tank/sender/lines as well when I rebuilt it.

Swept out the bed today, ready for activities.

LMK if you guys have thoughts on that coil.