Constant Miss-Fire

[LTZ C20]

Okay guys here is the scoop. I set the timing back to 16° and I switch vaccum ports like Rich said. I pulled the metering rods out of the cylinders and they were pretty dirty, they were covered in this blackish gray stuff that has this really foul smell that guessing is the carbon buildup. So I got the metering rods and the springs and the cylinders and those little metal parts and they're all clean and back again, I fired it up and let it run for a couple minutes while I put my tools away and then I power braked the truck and it didn't feel like it was missing it just felt like it was being held back by the brakes. So I haven't driven it yet but I will after work on my way home and I'm hoping that all is well and it should be running pretty good it sounded better when it was idling.

[rich weyand]

Sounds promising.  Dirty rods together with retarded timing will screw up a lot.  Surprised it ran as well as it did!

[LTZ C20]

Yea! Well now I'm getting really irritated. It power braked pretty good at lunch earlier, but when I drove it home it was still doin it not as bad. Then I drove to my friends and it's getting pretty noticeable. I checked the timing again, yesterday set it at 16 like Rich said, today it was at 14, the. I revved it, and back at idle it was back at 16 then moved to 18 and then to 17. It's like something is forcing the distributor over or pulling it out of time. My timing clamp bolt it tight and it seems to be holding so I don't get it. It sits at a number then if you rev it and let it go back to idle it resets at a different number. After all this work I'm getting pretty aggravated at this.

[74 C-10 Shorty]

Sounds like the advance is sticking, pop the cap and check the weights they could be crudded up, make sure they're clean and moving freely.

[454Man]

Sounds like the advance is sticking, pop the cap and check the weights they could be crudded up, make sure they're clean and moving freely.

X2, when was the last time you adjusted the valves? Prob bout time
I'd pull the valve covers off and inspect for flat cam lobes. Or push rods not spinning

[LTZ C20]

Ok so, I pull the cap off, then what I'm I checking??

[74 C-10 Shorty]

Under the rotor you'll see two weights and springs, take them off and clean everything and put a film of grease on the little round pad the weights rest/slide on, make sure they move freely their full travel.

[Irish_Alley]

isnt there supposed to be little plastic bushings also?

[74 C-10 Shorty]

Hmmm, I think the newer ones have the plastic bushings?, I got a bunch of them and none have them but they are all early 80's on back.. But if it does have the bushings they probably need to be replaced by now..

[rich weyand]

See the third picture in this article.
http://www.chevyhiperformance.com/howto/97438/

[74 C-10 Shorty]

That one don't have the bushings on the weights, only bushings used on those are on the limiting pins to shorten the curve.

[LTZ C20]

Hey, I was wondering if maybe a video of the truck idling or driving would be of any use? So you guys can hear it? Also, an old hot rodder at my work said I should check the timing chain variance. Pull the cap off, set the motor at TDC and then rotate the crank with a wrench. He said if there's more than 2* I could have valves not opening fully or at the right time? How's that sound to you guys?

[74 C-10 Shorty]

As long as the lobes on the cam aren't flat the valves has to open, only thing a stretched chain does is retard cam timing and if anything will give a little more top end and won't cause eratical behavior.

[LTZ C20]

Ok I just tried to clean those, the had a little crud on them. I cleaned em best I could, I didn't realize they came off without pulling the distributor. So tonight I'll try again. I did try and push the apart but they seemed to not expand very far, maybe a 1/4 or 3/8 inch?? They seemed like they were moving a little bit then stopping against something underneath them, is that normal? I thought they didn't go that far but if there supposed to go further then I'll try and pull them off completely tonight. The cleaning I did just now didn't seem to do anything.

[454Man]

There is a little c clip that hold them on. Just slide it off, pick them up clean them and the base they sit on. This may not b the issue. Take the valve covers off . Turn the engine on let it idle then see if all valves and rockers are moving the same distance. Also check for pushrods that aren't spinning. If you have a close to or all the way flat exhaust lobe on the cam that will b the miss you are having as the engine will inhale but not b able to exhale...