1969 C10 Idle Issues

[Jimjific]

Hello All,

So I have a 69 C10 short bed step side that I recently got on the road. It has a 307 with a stock two barrel, three on the tree. The truck starts great every time. Once it warms up, and gets off of the choke, it stalls or barely runs.

Here's the facts:
- Gas tank, not sure what condition is inside.
- Power Steering
- Manual brakes.
- Stock distributor.
- Stock sintered fuel filter.
- New fuel pump. Old one diaphragm was toast.
- Rebuilt the carb. (first time with just usual carb cleaner). Didn't help.
- No vacuum leaks that I can find.
- Rebuilt the carb. using an ultrasonic cleaner. Success!
- Set the idle around 700-800 adjusted idle screws with vacuum gauge. Ran well for a while.

But now it is doing the same thing again.

I work only 2 miles from home, so I can usually make it there and back without too much problem. Could there crap in the tank getting past the filter plugging the idle circuit? The carb is pretty simple and can't understand why it's giving me such trouble.

Any thoughts?

Thanks,
Jim

[geezer#99]

Have you checked your timing?
What’s your initial iming set at?

[Jimjific]

I have not checked the timing. I will do that and post the results.
Jim

[dmjlambert]

That is an interesting condition, runs fine cold but worse as it warms up. Has it done that for a long time or recently started it? Do you know if you have a hot slot intake manifold that heats up the carburetor? Since you have a lot of stock setup I just wonder if the problem could be related to boiling gasohol. Do you have the ability to try no ethanol gasoline on next fill up? I'm just throwing the idea out there, don't know how scientific it is. When you say ran fine for a while, do you mean until it warmed up, or for a few days?

[GASoline71]

Improper timing can make an engine do a lot of wonky things.

Also, are you sure the choke is opening all the way once warmed up?

Gary

[SC1969c10]

funny timing on this post. my 69 all same everything is doing the same exact thing. If I don't sit in the truck and gas it a little every once in a while, the truck will stall out after a few minutes.

[Steeveedee]

I'm in the crowd that says ignition is 99% of the problem when something doesn't run right, but it's important to get the wheat and chaff sorted. Look around carefully for vacuum leaks. Look everywhere. Plug off nonessential vacuum lines and see what helps. Spray around the carburetor with carb cleaner or even WD-40 to see if the idle changes. If the thing has good acceleration when cold, it's because the choke is covering up a vacuum leak, a lot of times, and not the timing or points. That is, ONLY if it changes when the choke is open. Points and timing will affect a cold engine in pretty much the same way as a warm engine.

[Jimjific]

Thanks for all the feedback.

Here are answers to questions.

Engine pulls good and starts with no problem when cold. It does give me trouble restarting after it is hot and it stalls though.

This truck is pretty basic. It only has PCV and distributor vacuum lines. I have plugged both of those and I still have the same problem once it is warmed up.

Yes, the choke is off. In fact, if I use my hand to partially cover the carb inlet, it stays running. The choke coil is in the manifold and is free and seems to work properly.

It ran for well over a week with no problems after the second ultrasonic cleaning rebuild.

I got the idea for the ultrasonic cleaning from a Jeep forum. They use the same carb and a guy had the exact same issue as me. He cured it after ultrasonic cleaning. I did the same and thought I had it conquered.

On a side note, if I put an inline filter in, where should I put it? The fuel line from the pump to carb is all nice stock tubing and I hate to cut it. I could put it before the pump but that always seems weird to me.

Thanks,
Jim

[mr.precision]

Is your gas cap vented? Might be creating a vacuum inside the tank. Seen it happen on older chevys.
My 1967 C10 283 is timed 10 deg advance at idle with the vacuum advance disconnected and plugged. Seems to work well on the stock motor.
Agree try some non ethanol gas. Even my truck is a little hard to restart when hot.

[geezer#99]

And your timing is———?

[68 P.O.S.]

drumroll.....

[davepl]

I'll assume the timing is off, but if it comes back as correct, here's a theory:

You've got a vacuum leak. This causes two problems, a lean mixture from and a weak vacuum signal to the carb.

When the engine is cold, the choke is on. This makes the mixture MUCH richer, hiding the vacuum leak. It also "sucks" on the jets harder with the choke door closed, so those internal vacuum systems get a stronger signal.

Then the engine warms up and the choke comes off and the vacuum leak manifests itself.

Can I prove it? Nope, but it's my best guess from across the Internet.

[Jimjific]

Thanks again everyone. I will check the timing either tonight or over the weekend. I will also check for vacuum leaks again.

Jim

[Hank49]

I had the same issues with my truck that you are having. After checking everything like timing, points, plugs and wires, I hooked a vacuum gauge up to the carb and found that I had a big vacuum leak...I replaced the carb base gasket with several gaskets and it still would not stop leaking, long story short I ended up replacing the intake manifold and it ran like a top. Good luck

[dmjlambert]

Originally Posted by Hank49

I had the same issues with my truck that you are having. After checking everything like timing, points, plugs and wires, I hooked a vacuum gauge up to the carb and found that I had a big vacuum leak...I replaced the carb base gasket with several gaskets and it still would not stop leaking, long story short I ended up replacing the intake manifold and it ran like a top. Good luck

That is why I was asking Jimjific about whether the engine has a hot slot manifold. Potential for vacuum leak if gasket is wrong, just like the vacuum leak I had. http://67-72chevytrucks.com/vboard/s...d.php?t=762751

[Jimjific]

I looked at your links about the "Hot Slot" manifolds. Mine is a two barrel and I'm not sure if they did that for those and I can't remember what it looked like when I had the carb off..

Jim

[demian5]

Originally Posted by Jimjific

if I use my hand to partially cover the carb inlet, it stays running

Vacuum leak. Probably from throttle shaft. Use a propane torch (unlit) to find leak, or you can use brake cleaner or cab spray.

Is the vacuum canister for the advance on the distributor ruptured and leaking (as it should be on manifold vacuum at idle)?

How about pictures of your setup with the air cleaner off?

[dmjlambert]

Originally Posted by Jimjific

I looked at your links about the "Hot Slot" manifolds. Mine is a two barrel and I'm not sure if they did that for those and I can't remember what it looked like when I had the carb off..

Jim

It is a long shot anyway. If you have a hot slot AND you also have the wrong carburetor gasket, you have the potential for a vacuum leak on the driver's side of the carb toward the front of the engine. You can look for the edge of the smiley sticking out from under the gasket like I show in the photos of that thread.

[Jimjific]

Sorry for the delayed response or update. I finally had some time to look at the truck.

Well, this is strange. IT seems like the truck has decided to fix itself. The only thing that I did was to put an inline filter in. I put it in the frame before the pump. Not a lot of room there but I was able to do it without having a kink in the rubber tubing. Not sure how a filter would have cured my issue. but I'll take it. It has been running well for a week now.

One weird thing about these two barrel carbs though. There seems to be no adjusting the high idle (Choke on) like I see on every other carb.

Thanks,
Jim

[paul blair]

Jim, You can bend the choke linkage rod to make the choke open quicker! All depends if the intake heat riser cross over is not clogged and the bi metal spring is ok

[geezer#99]

Originally Posted by Jimjific

Sorry for the delayed response or update. I finally had some time to look at the truck.

Well, this is strange. IT seems like the truck has decided to fix itself. The only thing that I did was to put an inline filter in. I put it in the frame before the pump. Not a lot of room there but I was able to do it without having a kink in the rubber tubing. Not sure how a filter would have cured my issue. but I'll take it. It has been running well for a week now.

One weird thing about these two barrel carbs though. There seems to be no adjusting the high idle (Choke on) like I see on every other carb.

Thanks,
Jim

The 2bbl carbs have only one screw that sets the normal idle speed and also sets the high idle speed. The screw adjusts on the choke cam. Sometimes it’s a
compromise to set the low idle and still have enough highidle. make sure the idle screw drops off the cam completely. You might need to bend the linkage rod slightly.

[custom10nut]

Put a Mallory, or Petronics Electronic Ignition Module in. You won’t be disappointed.
I put one in 20years ago, and never regretted it

[Jimjific]

Originally Posted by custom10nut

Put a Mallory, or Petronics Electronic Ignition Module in. You won’t be disappointed.
I put one in 20years ago, and never regretted it

Yes, I have put them in all my old vehicles. Hacen't done it for this truck yet, but will.