C10 won't idle

[Scott_williams2]

So I have a 68 c10 with a 250 I6. It ran fine for 125 miles then it started buckin and stealing doin down the road. So I cleaned all the lines, replaced the fuel pump, cleaned the carb, and cleaned out the tank. It ran like a sewing machine the rest of the day. I woke up the next day and it hard started which had never happened. Then it wouldn't idle unless I gave it gas. I drove it another 25-30 miles until it go to where it would die without gas and it was missing terribly and really hard starting. So I replaced the gas tank and just got a new carb, new plug wires, new plugs, new dist cap, new rotor, new coil, new points, set the gap to .19 and set the timing to 8 degrees BTDC. I replaced the carb yesterday and adjusted it to where it now idles for 30 seconds but the rpm rises really high randomly and it dies. I'm stumped. Any help would be appreciated

[davepl]

Why does the RPM raise up randomly? That'd be the first thing I'd chase. Might be as easy as a vacuum leak, and if you're running rich, introducing extra air speeds up the engine.

You could wait until it does the high idle again and spray carb cleaner around the carb base gasket to see if it changes anything. If there's a leak it'll suck in the spray and run "different", but if there's no leak it'll change nothing.

[Marine-58]

Originally Posted by davepl

Why does the RPM raise up randomly? That'd be the first thing I'd chase. Might be as easy as a vacuum leak, and if you're running rich, introducing extra air speeds up the engine.

You could wait until it does the high idle again and spray carb cleaner around the carb base gasket to see if it changes anything. If there's a leak it'll suck in the spray and run "different", but if there's no leak it'll change nothing.

Exactly what I would check though it would be WD40 to spray for a leak...

[Scott_williams2]

Ok guys thanks I'll try it out. I forgot to mention that I put a rag on it and it ran really good but as soon as I took it off the rpms surge and it dies

[Marine-58]

Originally Posted by Scott_williams2

Ok guys thanks I'll try it out. I forgot to mention that I put a rag on it and it ran really good but as soon as I took it off the rpms surge and it dies

Rag over the top of the card? Almost 100% sure it is a vacuum leak, but in saying that it will probably be something else... That damn Murphy...

[Scott_williams2]

So I did like y'all said and the rpms didn't raise up when I sprayed the carb. I sprayed all around it except in the top. All around the gaskets and such. I did notice that the truck idles a bit longer when I run the vac advanced to the front inlet instead of the side one or if they're Both plugged. But the problem still persists. Really high idle, hard starting, and missing. I believe it isn't firing right on all cylinders. I took the dist cap off and I did notice that there was a black smudge on the #1. Other than that all cylinders showed equal signs of spark

[Grumpy old man]

check the pcv hose connection on the intake to see if it's loose or the hose cracked ?

[Scott_williams2]

It's all good. Not loose or cracked @grumpy

[Scott_williams2]

SO I examined what I believe to be the PCV hose ( it runs from the top of the valve cover to the intake )and I found that it was rotten where it was clameped to the intake. So i cut the hoseoff and it was clogged with black debris that looks like tar. can anybody shed light on this?

[Grumpy old man]

put a new hose on it also a new pcv valve and using a stiff wire make sure the fitting in the intake manifold is not clogged and the fitting itself is not loose , Also if that hose is clogged with debris you can bet the passages in between the intake manifold and exhaust manifold are clogged with carbon .

[Scott_williams2]

Ok thanks grumpy. It just started pouring but When it stops I'll try it out. I hope it will fix it

[skinnan]

almost sounds like a timing issue....just a thought

[Marine-58]

Originally Posted by Grumpy old man

put a new hose on it also a new pcv valve and using a stiff wire make sure the fitting in the intake manifold is not clogged and the fitting itself is not loose , Also if that hose is clogged with debris you can bet the passages in between the intake manifold and exhaust manifold are clogged with carbon .

Grumpy... learn me something please. I don't remember any passages between te exhaust and intake. What are they for? I haven't worked on one of these I6's in many years...

[Grumpy old man]

Originally Posted by Marine-58

Grumpy... learn me something please. I don't remember any passages between te exhaust and intake. What are they for? I haven't worked on one of these I6's in many years...

Carb heat passages , I've got one apart in the shop I'll post a picture. L6's don't run right without heat to the bottom of the intake passage for fuel atomization thats why they are bolted together with a tinned gasket

when cold the flapper in the exhaust manifold on the right is open and allows hot exhaust to go into the intake passages on the bottom of the intake manifold on the left , once warm the spring on the exhaust flapper get hot and allows the flapper to close many times these passages get filled with carbon from the exhaust and prevent fast warm up of the intake manifold slowing the heat to the runners and making the truck "cold blooded" until fully warmed up.

http://

[Marine-58]

Thanks. . Sure makes sense. I would appreciate a picture. Having trouble visualizing it for some reason.

[Scott_williams2]

Quick question grumpy. How do I change the PCV valve? Do I have to take the intake off? And are u sure it's a PCV valve or a egr

[Grumpy old man]

it depends on what carb you have ,but there should be a pcv valve in the top of your valve cover like this one on the left

http://

[Grumpy old man]

Originally Posted by Scott_williams2

Quick question grumpy. How do I change the PCV valve? Do I have to take the intake off? And are u sure it's a PCV valve or a egr

post a couple pictures of the top of your engine

[Scott_williams2]

Ok I will. And my pcv valve is fine. I need to know about the fitting that the hose runs to from the PCV to on the intake

[Scott_williams2]

Man I'm new to the forums and i can't figure out how to send a pic out of my photo gallery. I'm on a iPhone 5s

[Scott_williams2]

I have a monojet. And I want to know about the fitting to the left of the carb. It is completely clogged with crud. Where does it go to? And how do u get it off to replace it? And do I have to take the intake off?

[Grumpy old man]

you don't replace it you clean it out . its pressed into the manifold . Look thru my parts thread you'll see a broken one and what it looks like inside the intake manifold ' Clean it out using carb cleaner and a wire coat hanger you won't hurt anything .

http://67-72chevytrucks.com/vboard/s...d.php?t=737893

post # 32on the second page

[Scott_williams2]

Ok thanks grumpy i appreciate it. The tube just ends inside the intake so all I would have to do is just push it through and burn it out right?

[Grumpy old man]

Originally Posted by Scott_williams2

Ok thanks grumpy i appreciate it. The tube just ends inside the intake so all I would have to do is just push it through and burn it out right?

yeah , that fitting uses a hose back to the pcv valve on the top back of your valve cover .

[Marine-58]

Originally Posted by Grumpy old man

Carb heat passages , I've got one apart in the shop I'll post a picture. L6's don't run right without heat to the bottom of the intake passage for fuel atomization thats why they are bolted together with a tinned gasket

when cold the flapper in the exhaust manifold on the right is open and allows hot exhaust to go into the intake passages on the bottom of the intake manifold on the left , once warm the spring on the exhaust flapper get hot and allows the flapper to close many times these passages get filled with carbon from the exhaust and prevent fast warm up of the intake manifold slowing the heat to the runners and making the truck "cold blooded" until fully warmed up.

http://

Now that I'm back at the computer can see the pictures. They didn't show up on the cell. As soon as I saw them, it all came back... One thing I hate about getting older is not remembering or misremembering things... Thanks again for posting these!!