The 1947 - Present Chevrolet & GMC Truck Message Board Network







Register or Log In To remove these advertisements.

Go Back   The 1947 - Present Chevrolet & GMC Truck Message Board Network > 47 - Current classic GM Trucks > The 1967 - 1972 Chevrolet & GMC Pickups Message Board

Web 67-72chevytrucks.com


Reply
 
Thread Tools Display Modes
Old 07-11-2018, 01:24 PM   #1
Jimjific
Registered User
 
Jimjific's Avatar
 
Join Date: Aug 2013
Location: Albany, NY
Posts: 137
1969 C10 Idle Issues

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
__________________
Thanks,

Jim - 69 Short Step CST 350 AC/PB/PS
- 69 Short Step 307 Man Column/PS
Jimjific is offline   Reply With Quote
Old 07-11-2018, 02:15 PM   #2
geezer#99
Registered User
 
geezer#99's Avatar
 
Join Date: Aug 2009
Location: Bowser
Posts: 9,561
Re: 1969 C10 Idle Issues

Have you checked your timing?
What’s your initial iming set at?
geezer#99 is offline   Reply With Quote
Old 07-11-2018, 02:42 PM   #3
Jimjific
Registered User
 
Jimjific's Avatar
 
Join Date: Aug 2013
Location: Albany, NY
Posts: 137
Re: 1969 C10 Idle Issues

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

Jim - 69 Short Step CST 350 AC/PB/PS
- 69 Short Step 307 Man Column/PS
Jimjific is offline   Reply With Quote
Old 07-11-2018, 08:06 PM   #4
dmjlambert
Senior Member
 
dmjlambert's Avatar
 
Join Date: Apr 2016
Location: Cypress, TX
Posts: 1,005
Re: 1969 C10 Idle Issues

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?
dmjlambert is offline   Reply With Quote
Old 07-11-2018, 08:32 PM   #5
GASoline71
"I ain't nobody, dork."
 
GASoline71's Avatar
 
Join Date: Sep 2007
Location: Whidbey Island, Washington
Posts: 8,355
Re: 1969 C10 Idle Issues

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
__________________
'cuz chicks dig scars...

My 1972 GMC 1500 Super Custom (Creeping Death) "long term" build thread.

The Rebuild of Creeping Death after the wreck

Quote:
Originally Posted by LONGHAIR View Post
I would never rebuild a 305.
Quote:
Originally Posted by prostreetC-10 View Post
I love using vacuum gauges as part of the carb tuning process. I hook the gauge to the inside of my garbage can and leave it there.
Quote:
Originally Posted by Marv D View Post
Remember Murphys 2nd law of mechanical relationships... "OPPOSING COMPONENTS ATTEMPTING TO OCCUPY THE SAME SPACE, AT THE SAME TIME, GENERALLY END UP OCCUPYING ADJOINING SPACE AT THE BOTTOM OF THE OIL PAN"
GASoline71 is offline   Reply With Quote
Old 07-11-2018, 10:26 PM   #6
SC1969c10
Registered User
 
Join Date: Jul 2018
Location: Little River, SC
Posts: 57
Re: 1969 C10 Idle Issues

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.
SC1969c10 is offline   Reply With Quote
Old 07-11-2018, 10:57 PM   #7
Steeveedee
Senior Member
 
Steeveedee's Avatar
 
Join Date: Jan 2013
Location: Simi Valley, CA
Posts: 1,938
Re: 1969 C10 Idle Issues

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.
__________________
'70 Chevy 3/4T Longhorn CST 400/400/3.54 Custom Camper

"Orange Acres"
Steeveedee is offline   Reply With Quote
Old 07-12-2018, 09:28 AM   #8
Jimjific
Registered User
 
Jimjific's Avatar
 
Join Date: Aug 2013
Location: Albany, NY
Posts: 137
Re: 1969 C10 Idle Issues

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
__________________
Thanks,

Jim - 69 Short Step CST 350 AC/PB/PS
- 69 Short Step 307 Man Column/PS
Jimjific is offline   Reply With Quote
Old 07-12-2018, 09:55 AM   #9
mr.precision
Registered User
 
mr.precision's Avatar
 
Join Date: Feb 2018
Location: Prescott, AZ
Posts: 37
Re: 1969 C10 Idle Issues

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.
mr.precision is offline   Reply With Quote
Old 07-12-2018, 10:00 AM   #10
geezer#99
Registered User
 
geezer#99's Avatar
 
Join Date: Aug 2009
Location: Bowser
Posts: 9,561
Re: 1969 C10 Idle Issues

And your timing is———?
geezer#99 is offline   Reply With Quote
Old 07-12-2018, 11:25 AM   #11
68 P.O.S.
Slow Member
 
Join Date: Jan 2007
Location: University Place, WA
Posts: 706
Re: 1969 C10 Idle Issues

drumroll.....
__________________
72 C10 lwb fleetside -stock 350/350 combo
68 P.O.S. is offline   Reply With Quote
Old 07-12-2018, 12:01 PM   #12
davepl
Registered User
 
davepl's Avatar
 
Join Date: Aug 2006
Location: Redmond, WA
Posts: 6,001
Re: 1969 C10 Idle Issues

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.
__________________
1970 GMC Sierra Grande Custom Camper - Built, not Bought
1969 Pontiac 2+2 427/390 4-speed Coupe
1969 Pontiac 2+2 427/390 4-speed Convertible
davepl is offline   Reply With Quote
Old 07-12-2018, 03:19 PM   #13
Jimjific
Registered User
 
Jimjific's Avatar
 
Join Date: Aug 2013
Location: Albany, NY
Posts: 137
Re: 1969 C10 Idle Issues

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

Jim
__________________
Thanks,

Jim - 69 Short Step CST 350 AC/PB/PS
- 69 Short Step 307 Man Column/PS
Jimjific is offline   Reply With Quote
Old 07-12-2018, 09:40 PM   #14
Hank49
Registered User
 
Hank49's Avatar
 
Join Date: Jul 2018
Location: Kansas
Posts: 9
Re: 1969 C10 Idle Issues

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
Hank49 is offline   Reply With Quote
Old 07-12-2018, 10:06 PM   #15
dmjlambert
Senior Member
 
dmjlambert's Avatar
 
Join Date: Apr 2016
Location: Cypress, TX
Posts: 1,005
Re: 1969 C10 Idle Issues

Quote:
Originally Posted by Hank49 View Post
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
dmjlambert is offline   Reply With Quote
Old 07-13-2018, 09:06 AM   #16
Jimjific
Registered User
 
Jimjific's Avatar
 
Join Date: Aug 2013
Location: Albany, NY
Posts: 137
Re: 1969 C10 Idle Issues

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
__________________
Thanks,

Jim - 69 Short Step CST 350 AC/PB/PS
- 69 Short Step 307 Man Column/PS
Jimjific is offline   Reply With Quote
Old 07-13-2018, 06:30 PM   #17
demian5
Registered User
 
demian5's Avatar
 
Join Date: Aug 2016
Location: Lake Forest, CA
Posts: 1,507
Re: 1969 C10 Idle Issues

Quote:
Originally Posted by Jimjific View Post
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?
__________________
"Work hard, use your vacation days."
1970 C15 GMC Long Bed
1986 C20 Scottsdale (grandpa truck)
1964 Impala SS
1959 Austin Healey 100-6 BN6
Instagram: C10sofOC
demian5 is offline   Reply With Quote
Old 07-13-2018, 06:50 PM   #18
dmjlambert
Senior Member
 
dmjlambert's Avatar
 
Join Date: Apr 2016
Location: Cypress, TX
Posts: 1,005
Re: 1969 C10 Idle Issues

Quote:
Originally Posted by Jimjific View Post
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.
dmjlambert is offline   Reply With Quote
Old 07-24-2018, 03:33 PM   #19
Jimjific
Registered User
 
Jimjific's Avatar
 
Join Date: Aug 2013
Location: Albany, NY
Posts: 137
Re: 1969 C10 Idle Issues

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
__________________
Thanks,

Jim - 69 Short Step CST 350 AC/PB/PS
- 69 Short Step 307 Man Column/PS
Jimjific is offline   Reply With Quote
Old 07-24-2018, 03:50 PM   #20
paul blair
Senior Member
 
Join Date: Jan 2016
Location: massachusetts
Posts: 270
Re: 1969 C10 Idle Issues

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
paul blair is offline   Reply With Quote
Old 07-24-2018, 06:11 PM   #21
geezer#99
Registered User
 
geezer#99's Avatar
 
Join Date: Aug 2009
Location: Bowser
Posts: 9,561
Re: 1969 C10 Idle Issues

Quote:
Originally Posted by Jimjific View Post
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 itís 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.
geezer#99 is offline   Reply With Quote
Old 07-24-2018, 06:18 PM   #22
custom10nut
Registered User
 
custom10nut's Avatar
 
Join Date: Apr 2015
Location: Columbia SC (temp) East Tn (soon)
Posts: 1,068
Re: 1969 C10 Idle Issues

Put a Mallory, or Petronics Electronic Ignition Module in. You won’t be disappointed.
I put one in 20years ago, and never regretted it
custom10nut is offline   Reply With Quote
Old 07-25-2018, 01:17 PM   #23
Jimjific
Registered User
 
Jimjific's Avatar
 
Join Date: Aug 2013
Location: Albany, NY
Posts: 137
Re: 1969 C10 Idle Issues

Quote:
Originally Posted by custom10nut View Post
Put a Mallory, or Petronics Electronic Ignition Module in. You wonít 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.
__________________
Thanks,

Jim - 69 Short Step CST 350 AC/PB/PS
- 69 Short Step 307 Man Column/PS
Jimjific is offline   Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -4. The time now is 08:09 PM.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2018, vBulletin Solutions Inc.
Copyright 1997-2013 67-72chevytrucks.com