1985 chevy c10 rough running

[Dead Parrot]

One possible vacuum leak cause is the intake gaskets between the heads and intake manifold. PITA to replace but if everything else checks good, might be worth installing new. Would let you pull the lifters and put eyes on the cam lobes.

Another thing to check is your exhaust riser flapper if you still have one. If stuck shut or part shut can force too much exhaust through the intake that both causes a lot of back pressure and overheats the carb and causes it to go bad.

2nd to franken's suggestion. Look at the engine in the dark after your eyes have adjusted. Looking for sparks from the plug wires to nearby metal parts and for blue fire playing over the distributor cap.

If you haven't replaced the distributor cap, probably worth doing it and checking the ground strap connection for the coil. They sometimes get corroded. Make sure the little button in the center of the cap is in good shape.

[Jake Wade]

Almost sounds like a cam lobe(s) going flat.

[geezer#99]

Originally Posted by Chevyman1987

Thanks geezer for the info. I advance timing to 16 and did a little more adjusting on my carb as much as I could do and we went down the road there is very slights poping at idel. And can't give it all it's got it will bog down after about 3/4 peddel down. But for the most part it's back running like it use to hell it's better then it use to run. Got it non running lol and when you say manifold vac where is that located. I'm not very incline on this kinda stuff but love monkeying with it.
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Manifold vacuum is usually any port below the primary throttle shaft on your carb.
Now it sounds like you might be flooding a little due to the popping inside the carb.
Look inside while it's idling. You shouldn't see any raw fuel.

[andyh1956]

You need a vacuum gauge plumbed into manifold vacuum on the intake.
The pistons draw against the closed plates of the carb at idle & create a negative pressure, called Vacuum. This reading is very important.

[Chevyman1987]

I didn't see any raw fuel. And will check the vac today been raining here for the past 3 days lol
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[geezer#99]

Does it start good when it's hot?
If so, bump the timing up a bit more.

[Chevyman1987]

It starts will a little drag. But not to bad but I tried that I bumped it up just a tad. And won't start starter would drag so bad it couldn't catch up. It's so close where it wants to run like it should. It cranks up fine now and very little backfire out the tailpipe and goes down the road pretty well. Just if you gotta kick it to get on the freeway you gonna get ran over. It bogs down when you gotta kick it's round 3/4 pedal
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[geezer#99]

Next!!!!

Might be your secondary air valve opening too quick.
To test just tap the door with your finger. It should pop open and then snap shut.
If not you might need to adjust it.
Look here.
http://www.73-87.com/7387garage/drivetrain/myqjet.htm

[Chevyman1987]

It pop open and shut right back
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[geezer#99]

And on we go!! LOL!!

Check your metering rods aren't stuck down.
Look in the vent tube at the top of the carb.
You'll see the top of the metering rod hanger.
With the motor off, reach in with a small pencil and you should be able to push the rods down and feel them pop up.

[Chevyman1987]

Just checked them and they are free and pop back up too. Lol I'm just happy it's up and driving somewhat lol before I couldn't even make it to the mailbox with it lol. Now I can make it to the mom and pop store right down the road 1 mile. Just still sucks trying to climb a hill. I checked all my hoses all are hooked up and most are fairly new around year old. I advance the distributor as far as I could go. Which did help. I have adjust the carb. May can adjust a little more. Checked for arcing at dis. Wires. And plugs all where good. Checked around carb for air leaks with carb spray nothing changed. Checked the fly weights in the dis. And are free not stuck. Checked the pushrods all where good. Now I'm banging my head against the motor trying to understand what I'm doing wrong
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[geezer#99]

And another thought!
Could be a plugged emulsion tube.

On each side of the vent tube you'll see some holes. These are the emulsion tubes. They can sometimes get plugged and your secondaries will run lean and sputter. You can check them by running a welding tip or pipe cleaner thru them. A steel guitar string works too.
Here's a link with some other possible cures.
http://www.digitalcorvettes.com/foru...ad.php?t=88376

[truckin 79]

I am going to go with Jake and say it sounds like a flat cam lobe. What made you change timing chain out in the first place? Are you sure you lined up dots correctly on cam and crank gears, did you advance or retard on chain install

[Chevyman1987]

Yes I lined the dots up right. Was told it might could have jumped time and already had the water pump off so just a few more bolts and down to timing so I thought why not. Geezer I cleaned them. No change
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[Chevyman1987]

And if i do have a flat cam lobe couldn't you take the valve covers off crank it up and look at the rocker arms. And see if 1 or few are not going as fast as the others?
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[geezer#99]

Originally Posted by Chevyman1987

And if i do have a flat cam lobe couldn't you take the valve covers off crank it up and look at the rocker arms. And see if 1 or few are not going as fast as the others?
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That's the way to check!

I had one more thought on your secondaries.
Tie the air door so it can't open at all and then do your test.

[cadillac_al]

What happens when you climb a hill? Is it dying or backfiring? If the firing order is right I would be suspecting the plug wires. If it is popping through the carb then your cam is bad.

[Chevyman1987]

When climbing a hill just lose at power not total lose like it use to but a lot more than it sould be and no backfiring when climbing. I'm pulling vavle covers now to look at the rocker arms.
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[Chevyman1987]

All the rocker arms are all going the same speed.
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[geezer#99]

Have you tried the 'tie the secondary door shut' test.

[Chevyman1987]

Yes I tried it and no change.
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[cadillac_al]

Sounds fuel related to me or a clogged catalytic.

[Chevyman1987]

The cat was one problem when I first got it. Got it fixed. I have another carb like the one that's on it I'm going to be rebuilding to see if that helps. I can still smell a good amount of fuel when sitting.
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[mMad Dawg]

One thing no one mentioned. Did you check the inside of the distributor cap for cracks or tracking from one contact to the other. Also when you say you screwed the screws in it still ran ,sounds like a vacuum leak to me. Also if you rebuilt the carb and put the old plastic float back out and put a new one in or better yet a brass float. Good luck

[Chevyman1987]

Yea I already replaced the cap and all the wires and plugs. And the kit comes with new float. And when I screwed them in it ran but that was it couldn't hit the gas or would die
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