Bad Carb Or Timing Problem - The 1947 - Present Chevrolet & GMC Truck Message Board Network

djtlaz · 11-26-2005, 05:33 PM

How can you tell if you have a problem with the timing or the carb is bad. I have a 1995-00 generation 1 350. It seems that I have it timed at about 8 and at times when turning it off it will try to stay on. I have adjusted the carb and timing in many different combinations and have yet to find something that I am comfortable with. Any suggestions?

djtlaz · 11-26-2005, 07:21 PM

..

**truckdude239** · 11-26-2005, 08:22 PM

sounds like the carb isn't closing all the way when you cut it off

jhow66 · 11-26-2005, 08:29 PM

If it is a 1995-2000 it does not have a carb unless engine has been changed. These has TBI and computer controlled.

djtlaz · 11-26-2005, 08:32 PM

its just the block,,it was original for tbi, but a carb can be used. At least that is what the casting numbers say it is on mortec.com

djtlaz · 11-26-2005, 08:35 PM

This is actually what mortec.com says my motor is.

10243880...350...95-00...2 or 4...Vortec truck, Gen.I crate motors and "ZZ4", roller cam, one piece rear seal

DTerry · 11-26-2005, 08:51 PM

What type of distributor are you using? Sounds like an ignition thing to me.

(D)

jhow66 · 11-26-2005, 10:01 PM

What kind of carb & dist. are you using? What is the idle speed?

ChevLoRay · 11-26-2005, 10:16 PM

It sounds like a condition called "run on". The engine "diesels" when you try to shut it off. In the early-mid 70's, manufacturers were trying to comply with the emission laws and there was a good bit of it going on. So, the manufacturers went to an "anti-dieseling solenoid" that would put pressure on the throttle valve and hold it in the closed position. That was the intent, anyway.

A number of us, who had engines tuned for higher octane gas with lead in it, learned to leave an automatic in gear, when turning off the ignition. Timing that was too advanced for the low/no-lead gasoline, frequently saw this occur.

So, maybe to help, your timing may be a bit too advanced, although mine is set at 10 degrees BTDC. I'm running the original block ('69) with stock compression ratio, an Edelbrock Performer intake with an Edelbrock Q-Jet and headers. The Q-Jet leaned out my fuel mixture, compared to the Edelbrock 1405 that was on it. I didn't encounter any run-on when I changed carbs, but I did have some heat soak problems with the starter.

So, which carburetor are you running? Which intake? I assume you have an HEI distributor. What is your compression ratio? Does your vacuum advance work? I don't th ink you can say that the problem is "ignition" or "carburetor", per se. It is a combination of things that you will have to run through to find the answer. Which plugs are you running?

djtlaz · 11-26-2005, 11:08 PM

I have a 1904 edelbrock 750cfm carb which I think isn't the best for it. I plan on changing to a 1406 600cfm edelbrock. It has a edelbrock manifold I believe the performer series. It is HEI but don't know what kind or voltage. It needs new wires and plugs. I think it does need to be timed higher than the 8 degrees I have it at but I cant keep it from dieseling so I figured it was the carb. My throttle response isn't quite what I think it should be at right now. That's why I think it should be timed higher. I don't know how to test for compression. I am only some what of a weekend warrior in the garage. I try doing everything myself but this one thing has baffled me.

*screamin_c102* · 11-26-2005, 11:32 PM

Djtlaz, I would be surprised if had any throttle response with a 750 Quadrabog wannabe on a nearly bone stock 350. You probably are getting the run on from a comination of excess fuel, poor timing and carbon build-up on the plugs from age and the first two. You should be running a base timing of 10 degrees BDC.

Get yourself a cheap screw-in compression tester and thread it in in place of the cylinder's plug you are testing. DISABLE YOUR IGNITIONCrank your engine over three two four times and read the gauge, repeat the same steps for all the cylinders. Compare your reading and check to see if you have any really low or high cylinders. I would do a "wet" comp test next. You want to squirt a little oil into the cylinder and repeat the first procedure. Compare the "dry" and "wet" results.

Take it light....Bill

djtlaz · 11-26-2005, 11:45 PM

Yeah I know the carb sucks. Just got the truck and when you first get it you think about all the stuff you can do to it. I was trying to salvage a few things on it and I thought I could get the carb to work semi decent but I'm having to much problems so I'm just going to get a new one. A smaller one at that. I'm thinking about getting the performer series package from edelbrock(carb,intake,heads,and cam shaft). What do you guys think of that whole package and how much more horse power should it give me?

*screamin_c102* · 11-27-2005, 12:04 AM

depends....

djtlaz · 11-27-2005, 12:10 AM

Thanks screamin c10. That would be nice horsepower to match up to the 700r4 being put in right now

jhow66 · 11-27-2005, 12:53 AM

100,000s of stock 350's, 305's, 327's 400sb's. 396's. 402's. 427's,454's etc. have Q-jets. I have rebuilt 100's of these for all kinds of engines. No better stock carb for your street & strip car. Just my 2 1/2 cents worth.

jhow66 · 11-27-2005, 12:59 AM

Just a thought--does your HEI have a vacumn advance--does it have more wires coming out of it then the 3 in front-what year truck do you have?

djtlaz · 11-27-2005, 01:16 AM

This is my engine per mortec.com
10243880...350...95-00...2 or 4...Vortec truck, Gen.I crate motors and "ZZ4", roller cam, one piece rear seal, I feel a 750cfm is to big for a stock 350

*screamin_c102* · 11-27-2005, 06:23 PM

I just checked the specs on the 1904 you are running. It flows 795 CFM

Regardless of the style, or manufacturer, that is waaayyyy too much carb for a bone stock small block. You might as well mount a toilet on your intake.

I have had better luck with Qjets off road, and in marine applications (they practically run upside down), as well as my GN turboed S10 (don't ask) but for a daily driver I prefer the edelbrocks, if properly tuned.

Jhow66, I didn't mean to insult, You have far more experience than I with Qjets, I don't have the patience to screw with 1 of 'em let alone 100

Everbody has their preference, I just think he is severely over-carbed

jhow66 · 11-27-2005, 11:44 PM

No insult taken. Just was pointing out that they can be made to work on many engines.

ChevLoRay · 11-28-2005, 12:25 PM

I have the 1901 Edelbrock Q-Jet, rated at 750CFM. I, too, am running the stock block and stock compression ratio. Q-Jets are misunderstood by many people. It's not a bad carburetor. Carburetors, in general, have been fingered as the culprit in many cases in which they were not to blame. I have made money rebuilding them because someone else said it needed to be overhauled.

One problem that they have, is leaking fuel from the float bowl, via the plugs in the bottom of the body of the carb, but visible after you remove the throttle plate off of the bottom of the carb. If those plugs are leaking, you'll be getting fuel in the intake, via the leak. That fuel, combined with a lean condition in the engine AND with a "hot spot" in the combustion chamber, COULD cause the run-on condition. This problem will also be shown to cause bad gas mileage and flooding. There are repair parts available that don't require a rebuild.

11-26-2005, 05:33 PM	#1
djtlaz Registered User Join Date: Sep 2005 Location: Tempe,AZ Posts: 38	Bad Carb Or Timing Problem How can you tell if you have a problem with the timing or the carb is bad. I have a 1995-00 generation 1 350. It seems that I have it timed at about 8 and at times when turning it off it will try to stay on. I have adjusted the carb and timing in many different combinations and have yet to find something that I am comfortable with. Any suggestions?

11-26-2005, 07:21 PM	#2
djtlaz Registered User Join Date: Sep 2005 Location: Tempe,AZ Posts: 38	Re: Bad Carb Or Timing Problem ..

11-26-2005, 08:22 PM	#3
truckdude239 Senior Member Join Date: Sep 2005 Location: Lewisville, Nc Posts: 10,237	Re: Bad Carb Or Timing Problem sounds like the carb isn't closing all the way when you cut it off __________________ David fuller Ase Certified Mechanic Click here to help support our board!! 1971 Chevy c-10 under going a 4.8l LSx swap Build Thread http://67-72chevytrucks.com/vboard/s...d.php?t=421305 2007 Honda Accord my daily 145kmiles 2002 Honda Accord 4 door With 330k(sisters car) 2005 toyota Avalon 228k( brothers car) 2002 Sububran 5.3 245k 2000 Tahoe 5.3l 378 General manager for Marco's Carwash & lube

11-26-2005, 08:29 PM	#4
jhow66 Registered User Join Date: Jun 2002 Location: Knoxville Tenn. Posts: 3,058	Re: Bad Carb Or Timing Problem If it is a 1995-2000 it does not have a carb unless engine has been changed. These has TBI and computer controlled. __________________ 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

11-26-2005, 08:32 PM	#5
djtlaz Registered User Join Date: Sep 2005 Location: Tempe,AZ Posts: 38	Re: Bad Carb Or Timing Problem its just the block,,it was original for tbi, but a carb can be used. At least that is what the casting numbers say it is on mortec.com

11-26-2005, 08:35 PM	#6
djtlaz Registered User Join Date: Sep 2005 Location: Tempe,AZ Posts: 38	Re: Bad Carb Or Timing Problem This is actually what mortec.com says my motor is. 10243880...350...95-00...2 or 4...Vortec truck, Gen.I crate motors and "ZZ4", roller cam, one piece rear seal

11-26-2005, 08:51 PM	#7
DTerry '70 GMC C-25 LWB Join Date: Oct 2004 Location: Binghamton, N.Y. Posts: 273	Re: Bad Carb Or Timing Problem What type of distributor are you using? Sounds like an ignition thing to me. (D) __________________ 1970 GMC C-25 LWB (middle of frame up) 5-7 drop with 3in drop spindles, flip kit with blocks and still keeping the 3/4 ton. Shaved drip rails and marker lights, rear roll pan, cowl induction hood. 1987 Camaro z28 350, vortec 305 heads. 10:1 comp, t5 trans. Street terrrorizer. 1988 Monte Carlo (Super Stock ashpalt race car) My Truck

11-26-2005, 10:01 PM	#8
jhow66 Registered User Join Date: Jun 2002 Location: Knoxville Tenn. Posts: 3,058	Re: Bad Carb Or Timing Problem What kind of carb & dist. are you using? What is the idle speed? __________________ 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

11-26-2005, 10:16 PM	#9
ChevLoRay Old Skool Club Join Date: Jun 2001 Location: Benton, AR "The Heart of Arkansas" Posts: 10,880	Re: Bad Carb Or Timing Problem It sounds like a condition called "run on". The engine "diesels" when you try to shut it off. In the early-mid 70's, manufacturers were trying to comply with the emission laws and there was a good bit of it going on. So, the manufacturers went to an "anti-dieseling solenoid" that would put pressure on the throttle valve and hold it in the closed position. That was the intent, anyway. A number of us, who had engines tuned for higher octane gas with lead in it, learned to leave an automatic in gear, when turning off the ignition. Timing that was too advanced for the low/no-lead gasoline, frequently saw this occur. So, maybe to help, your timing may be a bit too advanced, although mine is set at 10 degrees BTDC. I'm running the original block ('69) with stock compression ratio, an Edelbrock Performer intake with an Edelbrock Q-Jet and headers. The Q-Jet leaned out my fuel mixture, compared to the Edelbrock 1405 that was on it. I didn't encounter any run-on when I changed carbs, but I did have some heat soak problems with the starter. So, which carburetor are you running? Which intake? I assume you have an HEI distributor. What is your compression ratio? Does your vacuum advance work? I don't th ink you can say that the problem is "ignition" or "carburetor", per se. It is a combination of things that you will have to run through to find the answer. Which plugs are you running? __________________ Member Nr. 2770 '96 GMC Sportside; 4.3/SLT - Daily driven....constantly needs washed. '69 C-10 SWB; 350/TH400 - in limbo The older I get, the better I was.

11-26-2005, 11:08 PM	#10
djtlaz Registered User Join Date: Sep 2005 Location: Tempe,AZ Posts: 38	Re: Bad Carb Or Timing Problem I have a 1904 edelbrock 750cfm carb which I think isn't the best for it. I plan on changing to a 1406 600cfm edelbrock. It has a edelbrock manifold I believe the performer series. It is HEI but don't know what kind or voltage. It needs new wires and plugs. I think it does need to be timed higher than the 8 degrees I have it at but I cant keep it from dieseling so I figured it was the carb. My throttle response isn't quite what I think it should be at right now. That's why I think it should be timed higher. I don't know how to test for compression. I am only some what of a weekend warrior in the garage. I try doing everything myself but this one thing has baffled me.

11-26-2005, 11:32 PM	#11
screamin_c102 Account Suspended Join Date: Feb 2005 Location: Yoncalla Oregon Posts: 775	Re: Bad Carb Or Timing Problem Djtlaz, I would be surprised if had any throttle response with a 750 Quadrabog wannabe on a nearly bone stock 350. You probably are getting the run on from a comination of excess fuel, poor timing and carbon build-up on the plugs from age and the first two. You should be running a base timing of 10 degrees BDC. Get yourself a cheap screw-in compression tester and thread it in in place of the cylinder's plug you are testing. *DISABLE YOUR IGNITION*Crank your engine over three two four times and read the gauge, repeat the same steps for all the cylinders. Compare your reading and check to see if you have any really low or high cylinders. I would do a "wet" comp test next. You want to squirt a little oil into the cylinder and repeat the first procedure. Compare the "dry" and "wet" results. Take it light....Bill

11-26-2005, 11:45 PM	#12
djtlaz Registered User Join Date: Sep 2005 Location: Tempe,AZ Posts: 38	Re: Bad Carb Or Timing Problem Yeah I know the carb sucks. Just got the truck and when you first get it you think about all the stuff you can do to it. I was trying to salvage a few things on it and I thought I could get the carb to work semi decent but I'm having to much problems so I'm just going to get a new one. A smaller one at that. I'm thinking about getting the performer series package from edelbrock(carb,intake,heads,and cam shaft). What do you guys think of that whole package and how much more horse power should it give me?

11-27-2005, 12:10 AM	#14
djtlaz Registered User Join Date: Sep 2005 Location: Tempe,AZ Posts: 38	Re: Bad Carb Or Timing Problem Thanks screamin c10. That would be nice horsepower to match up to the 700r4 being put in right now

11-27-2005, 12:53 AM	#15
jhow66 Registered User Join Date: Jun 2002 Location: Knoxville Tenn. Posts: 3,058	Re: Bad Carb Or Timing Problem 100,000s of stock 350's, 305's, 327's 400sb's. 396's. 402's. 427's,454's etc. have Q-jets. I have rebuilt 100's of these for all kinds of engines. No better stock carb for your street & strip car. Just my 2 1/2 cents worth. __________________ 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

11-27-2005, 12:59 AM	#16
jhow66 Registered User Join Date: Jun 2002 Location: Knoxville Tenn. Posts: 3,058	Re: Bad Carb Or Timing Problem Just a thought--does your HEI have a vacumn advance--does it have more wires coming out of it then the 3 in front-what year truck do you have? __________________ 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



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11-27-2005, 01:16 AM	#17
djtlaz Registered User Join Date: Sep 2005 Location: Tempe,AZ Posts: 38	Re: Bad Carb Or Timing Problem This is my engine per mortec.com 10243880...350...95-00...2 or 4...Vortec truck, Gen.I crate motors and "ZZ4", roller cam, one piece rear seal, I feel a 750cfm is to big for a stock 350

11-27-2005, 06:23 PM	#18
screamin_c102 Account Suspended Join Date: Feb 2005 Location: Yoncalla Oregon Posts: 775	Re: Bad Carb Or Timing Problem I just checked the specs on the 1904 you are running. It flows 795 CFM Regardless of the style, or manufacturer, that is waaayyyy too much carb for a bone stock small block. You might as well mount a toilet on your intake. I have had better luck with Qjets off road, and in marine applications (they practically run upside down), as well as my GN turboed S10 (don't ask) but for a daily driver I prefer the edelbrocks, if properly tuned. Jhow66, I didn't mean to insult, You have far more experience than I with Qjets, I don't have the patience to screw with 1 of 'em let alone 100 Everbody has their preference, I just think he is severely over-carbed Last edited by screamin_c102; 11-27-2005 at 06:29 PM.

11-27-2005, 11:44 PM	#19
jhow66 Registered User Join Date: Jun 2002 Location: Knoxville Tenn. Posts: 3,058	Re: Bad Carb Or Timing Problem No insult taken. Just was pointing out that they can be made to work on many engines. __________________ 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

11-28-2005, 12:25 PM	#20
ChevLoRay Old Skool Club Join Date: Jun 2001 Location: Benton, AR "The Heart of Arkansas" Posts: 10,880	Re: Bad Carb Or Timing Problem I have the 1901 Edelbrock Q-Jet, rated at 750CFM. I, too, am running the stock block and stock compression ratio. Q-Jets are misunderstood by many people. It's not a bad carburetor. Carburetors, in general, have been fingered as the culprit in many cases in which they were not to blame. I have made money rebuilding them because someone else said it needed to be overhauled. One problem that they have, is leaking fuel from the float bowl, via the plugs in the bottom of the body of the carb, but visible after you remove the throttle plate off of the bottom of the carb. If those plugs are leaking, you'll be getting fuel in the intake, via the leak. That fuel, combined with a lean condition in the engine AND with a "hot spot" in the combustion chamber, COULD cause the run-on condition. This problem will also be shown to cause bad gas mileage and flooding. There are repair parts available that don't require a rebuild. __________________ Member Nr. 2770 '96 GMC Sportside; 4.3/SLT - Daily driven....constantly needs washed. '69 C-10 SWB; 350/TH400 - in limbo The older I get, the better I was.

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