Problem with my rebuilt carb. - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Tynee · 03-25-2003, 03:33 PM

Ok, rebuilt my little 2 barrel last weekend. Dramatic improvement in idle, take-off, and fuel mileage. Best $11 I've spent in a long time. The only problem I'm having now is that before the engine warms up, if I try to accelerate from around 30 mph, I get back-fires and hesitation. I have to let off the gas, and ease back into, sometimes 2 or 3 times to get it to go ahead and burn some fuel instead of just swallowing it.

Any suggestions?

Tynee · 03-26-2003, 08:54 AM

Nobody? hm. Surely I'm not the first to screw up a carb rebuild.

JimKshortstep4x4 · 03-26-2003, 09:53 AM

Make sure your timing is set right and the engine tune is good. Check the accelerator pump. The other thing that could affect cold performance is the thermactor setup.

Jim

oleblue72 · 03-26-2003, 09:58 AM

Could be any number of things. My first guess would be the fuel filter, maybe somewhat stopped up or blocked? That would surely cause the hesitation.

Tynee · 03-26-2003, 09:59 AM

What's the thermacter setup? Why would I have developed this problem after the I put the carb kit in when it didn't do this before?

Tynee

Tynee · 03-26-2003, 10:01 AM

Oleblue, I went to get a new fuel filter the other day and the parts house was out of them, and I haven't made it back to get one yet. How likely is it that the filter is the problem?

Thanks for the suggestions all.

68speedalert · 03-26-2003, 02:20 PM

accel pump, accel pump, accel pump...........

Look down the throat of carb, engine off, and grab the throttle linkage and stroke it. Slow down guys, the throttle. You should see 2 streams of gas shoot from the front center of the barrels down thru the venturi on each stroke. It should be steady. I bet you don't see any spray or it is intermitant. You could have gotten a bad new pump diaphram or didn't get the check balls back inthe right place.

Steve

JimKshortstep4x4 · 03-26-2003, 07:43 PM

From your description, my first assumption was that you probably put the carburetor together correctly, so I was ticking off items that can affect cold performance. You said that it runs good when warm.

The thermactor setup is a sheet metal shrouding around your exhaust manifold with a duct going up to your air cleaner which provides warmed air to the carburetor when the engine is cold.

One thing I did not mention is the float level, if it is low can cause cold running problems. Accelerator pump as I mentioned can be a problem but you replaced that.

Jim

LudwigTheMad · 03-29-2003, 03:04 AM

we seemed to have missed the possible easy one.....

Check your choke......

Tynee · 03-31-2003, 08:41 AM

Thanks for all the help guys. Jim, I'm with you now on what a thermactor is. Do some call it a heat stove?

Huck · 03-31-2003, 09:33 AM

Tynee, choke that chicken~~~~if it runs great when warm, what is your choke set up?? When cold, the choke plate should be closed on the top of your carb and full open when it's warm. If you are not running any choke or the plate is full open when cold, it will run like you described.
Electric chokes are great when set up correctly as they eliminate the cable, manually pulling it closed. opening it up as you drive etc.

JimKshortstep4x4 · 03-31-2003, 10:11 AM

Tynee,

Yes it is called that too!

I hope you let us know what you find out on the cold running problem.

Jim

O'l Buck · 03-31-2003, 10:45 AM

Good timing. I just had the same problem with the 2G on my boat. I put a kit in it real quick because all I figured it needed was the needle and seat. I started it, it ran if I pumped the accelerator, but would not idle. I figured it was dirty jets, so I pulled it apart again, took a flashlight and looked down the bore for the accelerator pump. It had a big chunk of the old pump in it. cleaned it out. Cleaned the jets with air and carb cleaner, now it runs like a dream. (note to me.....this thing has a brass float.....DON'T BLOW AIR IN THE CARB!!!!!).....Yes, I collapsed my float.......Whoops!

03-25-2003, 03:33 PM	#1
Tynee I miss this truck. Join Date: Dec 2001 Location: Lexington, KY U.S.A. Posts: 2,863	Problem with my rebuilt carb. Ok, rebuilt my little 2 barrel last weekend. Dramatic improvement in idle, take-off, and fuel mileage. Best $11 I've spent in a long time. The only problem I'm having now is that before the engine warms up, if I try to accelerate from around 30 mph, I get back-fires and hesitation. I have to let off the gas, and ease back into, sometimes 2 or 3 times to get it to go ahead and burn some fuel instead of just swallowing it. Any suggestions? __________________ '07 GMC Acadia SLT. Sweet ride. '08 Crew Cab Z-71 short bed. Really like this truck A LOT.

03-26-2003, 08:54 AM	#2
Tynee I miss this truck. Join Date: Dec 2001 Location: Lexington, KY U.S.A. Posts: 2,863	Nobody? hm. Surely I'm not the first to screw up a carb rebuild. __________________ '07 GMC Acadia SLT. Sweet ride. '08 Crew Cab Z-71 short bed. Really like this truck A LOT.

03-26-2003, 09:58 AM	#4
oleblue72 No, U Da Man! Join Date: Mar 2001 Location: Southaven, MS Posts: 284	Could be any number of things. My first guess would be the fuel filter, maybe somewhat stopped up or blocked? That would surely cause the hesitation. __________________ (sold ole blue 1972) 1997 Dodge 1500 5.9L 1996 Saturn SL2 1.9L 2002 Mitsubishi Montero 3.0L 2005 Ford Escape 3.0L *1967 Olds Vista Cruiser 330-320HP*

03-26-2003, 09:59 AM	#5
Tynee I miss this truck. Join Date: Dec 2001 Location: Lexington, KY U.S.A. Posts: 2,863	What's the thermacter setup? Why would I have developed this problem after the I put the carb kit in when it didn't do this before? Tynee __________________ '07 GMC Acadia SLT. Sweet ride. '08 Crew Cab Z-71 short bed. Really like this truck A LOT.

03-26-2003, 10:01 AM	#6
Tynee I miss this truck. Join Date: Dec 2001 Location: Lexington, KY U.S.A. Posts: 2,863	Oleblue, I went to get a new fuel filter the other day and the parts house was out of them, and I haven't made it back to get one yet. How likely is it that the filter is the problem? Thanks for the suggestions all. __________________ '07 GMC Acadia SLT. Sweet ride. '08 Crew Cab Z-71 short bed. Really like this truck A LOT.

03-26-2003, 09:53 AM	#3
JimKshortstep4x4 Senior Member Join Date: Jul 2001 Location: Muskegon,MI,USA Posts: 6,026	Make sure your timing is set right and the engine tune is good. Check the accelerator pump. The other thing that could affect cold performance is the thermactor setup. Jim

03-26-2003, 02:20 PM	#7
68speedalert Semi-Senior Member Join Date: Feb 2003 Location: Washington, MO Posts: 390	accel pump, accel pump, accel pump........... Look down the throat of carb, engine off, and grab the throttle linkage and stroke it. Slow down guys, the throttle. You should see 2 streams of gas shoot from the front center of the barrels down thru the venturi on each stroke. It should be steady. I bet you don't see any spray or it is intermitant. You could have gotten a bad new pump diaphram or didn't get the check balls back inthe right place. Steve __________________ '68 50th Anniversery LWB Custom Fleetside, '77 305 v-8, turbo 350, factory speed alert (still works), '71 drivetrain w/front discs. Some call it ugly yellow, others call it Ochre '83 Jeep CJ-7, <80,000 miles, original owner '04 Chevy Suburban, 4x4, 2500, 6.0 ltr, Predator Diablo programmer '95 GMC K1500 Extended cab

03-26-2003, 07:43 PM	#8
JimKshortstep4x4 Senior Member Join Date: Jul 2001 Location: Muskegon,MI,USA Posts: 6,026	From your description, my first assumption was that you probably put the carburetor together correctly, so I was ticking off items that can affect cold performance. You said that it runs good when warm. The thermactor setup is a sheet metal shrouding around your exhaust manifold with a duct going up to your air cleaner which provides warmed air to the carburetor when the engine is cold. One thing I did not mention is the float level, if it is low can cause cold running problems. Accelerator pump as I mentioned can be a problem but you replaced that. Jim

03-29-2003, 03:04 AM	#9
LudwigTheMad Registered User Join Date: May 2000 Location: Ramona, CA Posts: 2,033	we seemed to have missed the possible easy one..... Check your choke...... __________________ That's right, I'm back in the game again. No it's not pink..... 1972 Blue and White Suburban.

03-31-2003, 08:41 AM	#10
Tynee I miss this truck. Join Date: Dec 2001 Location: Lexington, KY U.S.A. Posts: 2,863	Thanks for all the help guys. Jim, I'm with you now on what a thermactor is. Do some call it a heat stove? __________________ '07 GMC Acadia SLT. Sweet ride. '08 Crew Cab Z-71 short bed. Really like this truck A LOT.

03-31-2003, 09:33 AM	#11
Huck Senior Member Join Date: Jun 2001 Location: Shelbyville, KY Posts: 3,269	Tynee, choke that chicken~~~~if it runs great when warm, what is your choke set up?? When cold, the choke plate should be closed on the top of your carb and full open when it's warm. If you are not running any choke or the plate is full open when cold, it will run like you described. Electric chokes are great when set up correctly as they eliminate the cable, manually pulling it closed. opening it up as you drive etc.

03-31-2003, 10:11 AM	#12
JimKshortstep4x4 Senior Member Join Date: Jul 2001 Location: Muskegon,MI,USA Posts: 6,026	Tynee, Yes it is called that too! I hope you let us know what you find out on the cold running problem. Jim

03-31-2003, 10:45 AM	#13
O'l Buck Recovering Truck Driver Join Date: Mar 2002 Location: Orleans, NE USA Posts: 1,883	Good timing. I just had the same problem with the 2G on my boat. I put a kit in it real quick because all I figured it needed was the needle and seat. I started it, it ran if I pumped the accelerator, but would not idle. I figured it was dirty jets, so I pulled it apart again, took a flashlight and looked down the bore for the accelerator pump. It had a big chunk of the old pump in it. cleaned it out. Cleaned the jets with air and carb cleaner, now it runs like a dream. (note to me.....this thing has a brass float.....DON'T BLOW AIR IN THE CARB!!!!!).....Yes, I collapsed my float.......Whoops! __________________ 67 K-20 350, SM465, Eaton rear, 4.56 no spin option 00 Dodge 2500 4x4, 24V cummins, 5 speed Chad South Central Nebraska

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