stumble - The 1947 - Present Chevrolet & GMC Truck Message Board Network

76bonanza · 12-09-2005, 10:24 PM

At about 30-45 mph if I mash it I get a bad stumble from dead stop good if I slowly stomp it also good? What are the most obviose things?

Jimbotronics · 12-09-2005, 10:35 PM

my guess would be clogged fuel filter or carb jets or possibly timing a little off.

jhow66 · 12-10-2005, 12:18 PM

What kind of carb-what is time set at-start this all at once--how old is carb?

76bonanza · 12-10-2005, 12:50 PM

holley carb 3310 not sure how old it is not new not nasty old. I think timing is around 12intial I have no idea what total timing is tho. Also It seems like it only does it when it is cold or it is worse when it is cold. Could it just be the weather? Also the carb is on the rich side not super bad but enuf to notice.

jhow66 · 12-10-2005, 03:15 PM

Your biggest problem is then with your choke. Is it hooked up--what kind (electric or manuel)? 12* initial should be ok-total timing would not come to play here.

76bonanza · 12-10-2005, 03:31 PM

electric choke yes it is hooked up.

70 Bowtie · 12-10-2005, 11:04 PM

I had a simular problem with my 67 chevelle, It turned out to be a bad plug wire,and a vacuum (sp) leak around the bottom of the carb! Took care of the problem!!

Brett

jhow66 · 12-10-2005, 11:15 PM

Your choke is set to lean for cold weather. Have someone to set the choke pull-off so it does not open the choke as much when engine starts.

76bonanza · 12-10-2005, 11:28 PM

so should I rotate the choke toward front to make it come off sooner. Or to the rear to make it stay on longer?

jhow66 · 12-11-2005, 01:27 AM

Just set it richer a little at a time until it runs like you want it. Does it fast idle now when choke is on?

76bonanza · 12-11-2005, 01:46 AM

yes

Fatback · 12-11-2005, 10:01 AM

Did you just install the the carb? or have you been running it and this just start. It sounds like a lean condition as jhow66 suggested the choke.or maybe a lean condition cause by an accelerator pump issue. I had a similar stumble with a Holley and had to adjust the screw on the accelerator pump arm. Also, Holley makes an accelerator pump cam assortment that is almost essential in tuning a Holley for around $20 I think.

76bonanza · 12-11-2005, 11:23 AM

No I did not install the carb. I know the accelerator pump screw you speak of but never know how to adjust it shorter or longer. I also just today replaced a leaky brake booster?

jhow66 · 12-11-2005, 12:51 PM

Quote:

Originally Posted by jhow66

Just set it richer a little at a time until it runs like you want it. Does it fast idle now when choke is on?

Ok-just keep setting the choke a little richer until stumble stops. If it doe not stumble when hot the problem is with your choke.

Fatback · 12-11-2005, 04:52 PM

Quote:

Originally Posted by jhow66

Ok-just keep setting the choke a little richer until stumble stops. If it doe not stumble when hot the problem is with your choke.

Sorry....I didnt see the cold weather post.......nevermind.

76bonanza · 12-11-2005, 04:56 PM

hey fatback about adjusting the spring deal on the accelrator pump how does it work? If I make it longer or shorter what does it change.

jhow66 · 12-11-2005, 05:12 PM

Quote:

Originally Posted by 76bonanza

hey fatback about adjusting the spring deal on the accelrator pump how does it work? If I make it longer or shorter what does it change.

What you want to do is make sure that the pump arm moves at the EXACT same time as your throttle arm does. If it does not this will cause the throttle blades to open before the pump can delivered a charge of fuel from squirtors to cover the extra air that is flowing by the open blades--hence a lean stumble. Check it and if it does not just lengthen the spring by holding one end of bolt and turning nut until it touches lever.

76bonanza · 12-11-2005, 06:24 PM

ok there was some play in the spring thing made it a little longer, nice and tight now and moves with the throttle like a mirror . Question about those cams my friend brought so by to me how do you decide which one to use what is the thinking here looks like some make the pump deliver the whole shot faster and some make it slower? But not sure how to determine what each one will do?

Fatback · 12-11-2005, 09:16 PM

http://aolsearch.aol.com/aol/redir?s...t+a+carburetor
Here is some info......It's important not to push the pump lever too far. You should be able to move the arm.015-.020 at WOT.The reason is the pump arm can rupture the diaphram. Also a little adjustment on the pump lever can go a long way...so loosen it about 1/4 turn then test drive it. As far as the cams....it was trial and error for me.

Frizzle Fry · 12-11-2005, 09:53 PM

Each pump cam is two sided. Before you buy a cam kit, you can flip the one that's on it now and see how that does (given the other side is bigger). They wear out and chances are the side you're using now is worn.

Also, the 3310 is a vacuum secondary carb. You might consider getting a Holley vacuum secondary spring kit (PN 20-13) and adjusting the secondary opening rate by replacing springs. Go heavier until the quick open WOT bog condition goes away.

Why did this show up in colder weather? Maybe you were marginal to begin with and the denser air makes it worse? Just my two pesos.

12-09-2005, 10:24 PM	#1
76bonanza Senior Member Join Date: Mar 2003 Location: St robert Mo Posts: 2,001	stumble At about 30-45 mph if I mash it I get a bad stumble from dead stop good if I slowly stomp it also good? What are the most obviose things? __________________ 1968 c10 lowered 3" 4" 355/Th400 built by Hatfield racing in joplin MO

12-09-2005, 10:35 PM	#2
Jimbotronics YA YA Join Date: Aug 2004 Location: Rockledge, Fl Posts: 1,273	Re: stumble my guess would be clogged fuel filter or carb jets or possibly timing a little off. __________________ Jimbo '72 SWB - 350 (frame-off resto in progress - donations accepted) '04 Chevy Avalanche '03 Cadillac CTS (wife's ride) Restoration progress - http://67-72chevytrucks.com/vboard/s...d.php?t=335707

12-10-2005, 12:18 PM	#3
jhow66 Registered User Join Date: Jun 2002 Location: Knoxville Tenn. Posts: 3,058	Re: stumble What kind of carb-what is time set at-start this all at once--how old is carb? __________________ 56 Chevy Bel-Air 2dr. HT (purchased new) 71 Chevy Cheyenne SWB PU (502HO) 65 GMC short bed step--work in progress and my gofer

12-10-2005, 12:50 PM	#4
76bonanza Senior Member Join Date: Mar 2003 Location: St robert Mo Posts: 2,001	Re: stumble holley carb 3310 not sure how old it is not new not nasty old. I think timing is around 12intial I have no idea what total timing is tho. Also It seems like it only does it when it is cold or it is worse when it is cold. Could it just be the weather? Also the carb is on the rich side not super bad but enuf to notice. __________________ 1968 c10 lowered 3" 4" 355/Th400 built by Hatfield racing in joplin MO

12-10-2005, 03:15 PM	#5
jhow66 Registered User Join Date: Jun 2002 Location: Knoxville Tenn. Posts: 3,058	Re: stumble Your biggest problem is then with your choke. Is it hooked up--what kind (electric or manuel)? 12* initial should be ok-total timing would not come to play here. __________________ 56 Chevy Bel-Air 2dr. HT (purchased new) 71 Chevy Cheyenne SWB PU (502HO) 65 GMC short bed step--work in progress and my gofer

12-10-2005, 03:31 PM	#6
76bonanza Senior Member Join Date: Mar 2003 Location: St robert Mo Posts: 2,001	Re: stumble electric choke yes it is hooked up. __________________ 1968 c10 lowered 3" 4" 355/Th400 built by Hatfield racing in joplin MO

12-10-2005, 11:04 PM	#7
70 Bowtie Registered User Join Date: Jul 2005 Location: South Dakota Posts: 70	Re: stumble I had a simular problem with my 67 chevelle, It turned out to be a bad plug wire,and a vacuum (sp) leak around the bottom of the carb! Took care of the problem!! Brett

12-10-2005, 11:15 PM	#8
jhow66 Registered User Join Date: Jun 2002 Location: Knoxville Tenn. Posts: 3,058	Re: stumble Your choke is set to lean for cold weather. Have someone to set the choke pull-off so it does not open the choke as much when engine starts. __________________ 56 Chevy Bel-Air 2dr. HT (purchased new) 71 Chevy Cheyenne SWB PU (502HO) 65 GMC short bed step--work in progress and my gofer

12-10-2005, 11:28 PM	#9
76bonanza Senior Member Join Date: Mar 2003 Location: St robert Mo Posts: 2,001	Re: stumble so should I rotate the choke toward front to make it come off sooner. Or to the rear to make it stay on longer? __________________ 1968 c10 lowered 3" 4" 355/Th400 built by Hatfield racing in joplin MO

12-11-2005, 01:27 AM	#10
jhow66 Registered User Join Date: Jun 2002 Location: Knoxville Tenn. Posts: 3,058	Re: stumble Just set it richer a little at a time until it runs like you want it. Does it fast idle now when choke is on? __________________ 56 Chevy Bel-Air 2dr. HT (purchased new) 71 Chevy Cheyenne SWB PU (502HO) 65 GMC short bed step--work in progress and my gofer

12-11-2005, 01:46 AM	#11
76bonanza Senior Member Join Date: Mar 2003 Location: St robert Mo Posts: 2,001	Re: stumble yes __________________ 1968 c10 lowered 3" 4" 355/Th400 built by Hatfield racing in joplin MO

12-11-2005, 10:01 AM	#12
Fatback Registered User Join Date: Dec 2003 Location: North Central FL Posts: 126	Re: stumble Did you just install the the carb? or have you been running it and this just start. It sounds like a lean condition as jhow66 suggested the choke.or maybe a lean condition cause by an accelerator pump issue. I had a similar stumble with a Holley and had to adjust the screw on the accelerator pump arm. Also, Holley makes an accelerator pump cam assortment that is almost essential in tuning a Holley for around $20 I think. __________________ 70 C/10 LWB 69 Cougar 68 Mustang 68 GMC 4X4 SWB

12-11-2005, 11:23 AM	#13
76bonanza Senior Member Join Date: Mar 2003 Location: St robert Mo Posts: 2,001	Re: stumble No I did not install the carb. I know the accelerator pump screw you speak of but never know how to adjust it shorter or longer. I also just today replaced a leaky brake booster? __________________ 1968 c10 lowered 3" 4" 355/Th400 built by Hatfield racing in joplin MO

12-11-2005, 04:56 PM	#16
76bonanza Senior Member Join Date: Mar 2003 Location: St robert Mo Posts: 2,001	Re: stumble hey fatback about adjusting the spring deal on the accelrator pump how does it work? If I make it longer or shorter what does it change. __________________ 1968 c10 lowered 3" 4" 355/Th400 built by Hatfield racing in joplin MO

12-11-2005, 06:24 PM	#18
76bonanza Senior Member Join Date: Mar 2003 Location: St robert Mo Posts: 2,001	Re: stumble ok there was some play in the spring thing made it a little longer, nice and tight now and moves with the throttle like a mirror . Question about those cams my friend brought so by to me how do you decide which one to use what is the thinking here looks like some make the pump deliver the whole shot faster and some make it slower? But not sure how to determine what each one will do? __________________ 1968 c10 lowered 3" 4" 355/Th400 built by Hatfield racing in joplin MO



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12-11-2005, 09:16 PM	#19
Fatback Registered User Join Date: Dec 2003 Location: North Central FL Posts: 126	Re: stumble http://aolsearch.aol.com/aol/redir?s...t+a+carburetor Here is some info......It's important not to push the pump lever too far. You should be able to move the arm.015-.020 at WOT.The reason is the pump arm can rupture the diaphram. Also a little adjustment on the pump lever can go a long way...so loosen it about 1/4 turn then test drive it. As far as the cams....it was trial and error for me. __________________ 70 C/10 LWB 69 Cougar 68 Mustang 68 GMC 4X4 SWB

12-11-2005, 09:53 PM	#20
Frizzle Fry Registered User Join Date: Aug 2005 Location: Hillsboro Oregon Posts: 6,449	Re: stumble Each pump cam is two sided. Before you buy a cam kit, you can flip the one that's on it now and see how that does (given the other side is bigger). They wear out and chances are the side you're using now is worn. Also, the 3310 is a vacuum secondary carb. You might consider getting a Holley vacuum secondary spring kit (PN 20-13) and adjusting the secondary opening rate by replacing springs. Go heavier until the quick open WOT bog condition goes away. Why did this show up in colder weather? Maybe you were marginal to begin with and the denser air makes it worse? Just my two pesos.

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