Re: 1968 GMC 250 Inline 6 4.1L Chugging
 

RICHARDJ

One question or yours that I forgot to answer. The Intake/Exhaust gaskets were replaced last year. Still look good. No black soot around this area.

Re: 1968 GMC 250 Inline 6 4.1L Chugging
 

RICHARDJ

One question of yours I forgot to answer. The Intake/Exhaust gaskets were replaced last year. They still look good and there is no black soot around that area. Thanks.

Re: 1968 GMC 250 Inline 6 4.1L Chugging
 

Sounds similar to my issue last year: Truck had an occasional backfire or load up when driving. It progressively got worse to where it would start OK, but would die when put into gear. It would idle and rev OK, but ran badly under a load, or when stopping at a stoplight. I had to put it in neutral a few times to keep it from dying at intersections. Later it would lean out and backfire after it warmed up and eventually would not restart when warm.
Fix: New coil and module. GM HEI was only a few years old, but as we know that doesn't matter. Upgraded to DUI coil and module and have been running great since.

Re: 1968 GMC 250 Inline 6 4.1L Chugging
 

UPDATE:

Carburetor came back from the shop and everything checks out ok.

I pulled the distributor and put new points and condensor in even though points looked good and condensor was a year old.

New issue. I marked the distributor and motor so I could just drop it back in. I also took a picture of which way the rotor was pointing. When I try to reinstall, the distributor will only seat with the rotor pointing another direction. Why? Should it not go back in the way it was? The truck was not moved and or cranked while distributor was out.

First pic is before I pulled it. Second pic is how it now seats... uuugh!

Help!

Re: 1968 GMC 250 Inline 6 4.1L Chugging
 

If the 6 cyl is like the V8, you use a long screwdriver after pulling the dizzy back out and turn the oil pump slightly. Looks like you want to turn it slightly to the right.

Sometimes when you pull the dizzy it turns the pump some so putting it back in same orientation the slot end of dizzy won't engage the pump unless it goes where the pump now is.

Re: 1968 GMC 250 Inline 6 4.1L Chugging
 

Looks like you are one tooth off. Do you have before and after pictures of the crank pulley and timing marks?

Re: 1968 GMC 250 Inline 6 4.1L Chugging
 

A gap setting is more of a starting point. Back in the day I use to wrench fullt ime and what I did was set peoples points with a match book cover to get it running. Faster to grab than a filler gauge and then find the one you need. Then hook up a dwell meter and dial them in better. The dwell setting is a more accurate setting. I even kept a match book in my glove box incase the points slipped on the car I drove. lol I dont think you will have crap clogging the sock in your tank as you said you have a new tank fuel lines and pump. If you do change gas stations. Another thing kind of related to crappy gas is water in the tank. The place you get gas from may have a lot of water in thier tanks or if you got gas while the fuel truck is filling the stations tanks. And in that case you can have crap in the new tank and water. If you dont find an issue have someone crank it over while you hold the fuel line hose in a jar. Get a good sample then let it sit. The sample that is. After a good while look at the fuel in the jar. If theres water in it you will see it on the bottom of the jar. Water is heavier than gas so it will settle to the bottom.

Re: 1968 GMC 250 Inline 6 4.1L Chugging
 

Well... The truck is now running like a champ. I changed the points, condensor and coil (again). Checked dwell and timing. Looks like it was ignition related after all.

I'd like to thank everyone for their help! I hope to be able all of you some day.

Thank you!

Re: 1968 GMC 250 Inline 6 4.1L Chugging
 

Nice! Glad to hear you got it going good. Now you can enjoy it.