part throttle issue, quick help please.

[BradyB]

Hello Gentlemen.
It's been two years since I pulled my sweet swepty out of the field and got her running. My truck is a 1970 383/727 with the stock Carter 2b.

Lately the truck has been missing at part throttle. Initially it started off idle but now it's up to about 2100 RPMs. For the last couple years the truck has ran very well after I added a rebuilt Carter, new point, rotor/cap, plugs, wires, etc...

It starts easy and runs well on the freeway at higher RPMs, at 40-45 mph it just kind of stumbles as you can feel the torque output decrease intermittently. It almost feels likes it running out of gas?

My guesses:
It shouldn't be the carb floats since the truck has ran well for a good year with the new carb.
I don't think it's the point, cap, rotor since they only have about 9,000 miles on them since new. Are those supposed to be replaced that often?
It shouldn't be the fuel filter, it's fairly new as well.
I redneck-tested the vacuum advance by sucking on the vacuum line and watching the plate rotate, it seemed to hold vacuum just fine. The blew through the vacuum line and it seemed to hold pressure. I may trim the vacuum line back a bit back to the non expanded portion.

Other ideas?

[BradyB]

I think it's just an ignition miss. So what would cause a part throttle, low load miss. It smooths out at higher RPMS. Is the vacuum advance not working all that well maybe, would that cause a studder?

[wally426ci]

Maybe its running lean?

[BradyB]

Check out the plugs, guess which plugs are the rear cylinders.

Feed back? These have about 8,000 miles on them, they are cheap Autolites.

[oklamopar]

I would 2nd that it sounds like an ignition misfire. Quit with the autolites and use champions. My big block runs best on the RJ14YC. I Change plugs about every 10K but my engine runs fat. Make sure you've got no water in the fuel,since it's been sitting. I would clean and re-set the point gap. Check the condensor. Make sure that you have the correct voltage to the coil. I had a similar problem and voltage at coil was too low. Total timing needs between 36-38 deg at 2500 RPM. Just the basics. Keep updated.

[BradyB]

I remembered the old high school auto shop trick and I checked for any arcing by letting the truck idle in the dark. I didn’t seen any problems. I replaced the ignition coil and the plugs last night, switched to the Champions this time. The coil seemed to be leaking a bit of oil at the plug so I figured it needed replacing.

The truck seems to be much happier running nice and smooth. I think the coil was the issue.

I love working on it, I took me twenty minutes to replace the plugs and coil. Total cost at checker was $40. :)

[JimE]

Do you still have a Checker Auto? All the ones in AZ are now O'Reilly. Jim

[oklamopar]

Glad it was somethin' somewhat simple.

[BradyB]

Do you still have a Checker Auto? All the ones in AZ are now O'Reilly. Jim

You're right, I still call it a checker rather than Checker O'Reily.

BTW, the truck is still not 100% happy. I figure that the current 10-15% ethanol blend at the pump isn't helping either. I turned out the carb screws a 1/4 turn to compensate and I will probably be adding fuel treatment to just about every tank. Winter gas sucks.

[JohnB]

Do you still have a Checker Auto? All the ones in AZ are now O'Reilly. Jim

You're right, I still call it a checker rather than Checker O'Reily.

BTW, the truck is still not 100% happy. I figure that the current 10-15% ethanol blend at the pump isn't helping either. I turned out the carb screws a 1/4 turn to compensate and I will probably be adding fuel treatment to just about every tank. Winter gas sucks.

Brady,
My truck runs much better on ethanol free gas....closest station to you with it is: Craigs Service. 904 S. 1300 East. Salt Lake City. They have 92 octane...try it