Cuts Out When I Put Pedal to Floor - The 1947 - Present Chevrolet & GMC Truck Message Board Network

4tiresngas · 11-02-2005, 09:41 PM

Okay, I have a 69 SWB Step with a 87+ 350 with 350 auto. It has HEI. I have replaced the plugs...gapped .045, replaced the rotor, cap, wires, and vacuum advance. I set the timing to 8 degrees advanced. The idle is around 850. It cranks as soon as you touch the key and runs smooth. In park, I can floor it and the engine sounds fine. When I'm driving it and push the accelerator quickly, it bogs down. I can accelerator slow/smoothly with no problems. The carb is a 4-barrel quadrajet (rebuild)...less than 6 months old from AutoZone.

Do you think it is the vacuum going to the vacuum advance or something else?

llegos · 11-02-2005, 10:02 PM

i recently experienced a similar problem I have a rebuilt Q-jet. I can floor it like 97% and all will be fine. But, i floored it all the way, and it bogged down and kinda acted a lil wierd. All the rest runs fine. Just kind of wierd if u ask me

wink_tim · 11-02-2005, 10:02 PM

You might try a little more advance on you're timing, say 10-12 degrees. Its free to try.

**Boog** · 11-02-2005, 10:44 PM

It's possible the secondary air valve is opening too fast when you matt it. Even though it's a store bought rebuilt don't mean anything. If that air valve opens too fast it can cause it too sort of fall on it's face. A good shop manual will have pics and tell you in detail how to adjust the spring on the secondary air valve to help dial it in to your application. Most likely only 1 turn or less to tighten the spring will make a considerable change. Tightening the spring will delay the opening of the secondary air valve thereby taking some of the bog out of it. A quadrajets secondary bores are huge!

**69TowRig** · 11-02-2005, 11:16 PM

This might sound basic, but check the fuel filter.

shifty · 11-02-2005, 11:36 PM

**special-K** · 11-02-2005, 11:50 PM

Check filter first.Then,could be getting too much fuel,sticking float,rich adjustment...

jhow66 · 11-02-2005, 11:56 PM

Easy way to check if it is the secondarys opening to soon is to tie the air valves so they will not open.

llegos · 11-03-2005, 12:22 AM

its not the fuel filter/carb adjustments because last week i took it in to my mechanic(he tunes street/strip muscle) and he got it basically perfect. I may have to look into the seccondary air valve. Also, quick question, what is the CFM of a stock 4bbl q-jet?

**special-K** · 11-03-2005, 08:19 AM

780,iirc.

MrC1 · 11-03-2005, 10:54 AM

I saw a place that listed Q-jets for cars rated at 770 cfm and trucks at 800 cfm. Guess there were minor differences between the models.

If you're able to go 97% throttle w/o bog problems, I'd check to make sure your throttle cable isn't trying to rip the arm off the carb by pulling too far. You could be torquing it out of wack. Just a thought.

The tension spring on the secondaries only has one turn of total travel (at least mine does). A small adjustment might be all you need, but it sounds like you've already had an expert look at it.

truckster · 11-03-2005, 01:11 PM

I'd check the secondary adjustment as well. I had the same problem when I first installed my rebuild Quadrajet on my 455. It only takes a little bit of fine tuning to get it right where you want it.

4tiresngas · 11-03-2005, 07:09 PM

Okay, I was off the Net for a couple of days. I failed to mention that I did change the fuel filter also. I'm not familiar with the secondary adjustment. Anyone have pictures to show me. I know where the idle adjustment is and the two air/fuel adjustment screws and that's about the extent of my knowledge. Again. appreciate all the input.

jhow66 · 11-04-2005, 12:30 AM

this might help: (allen screw underneath-loosen this just enough so you can turn other slot head screw-tighten slot head screw about 1/4 turn-hold in this position and tighten allen screw. ) Try it out if not right tighten 1/8 turn each time. (P.S. there is no written warrenty on above advice

)

Cat Fuzz · 11-04-2005, 01:59 AM

No one has mentioned the accelerator pump dumping too much fuel?

MrC1 · 11-04-2005, 11:24 AM

Quote:

Originally Posted by Cat Fuzz

No one has mentioned the accelerator pump dumping too much fuel?

Not likely if it runs okay at all but WOT.

11-02-2005, 09:41 PM	#1
4tiresngas An American Soldier Join Date: Feb 2005 Location: Grumolo D' Abadessee, Italy Posts: 503	Cuts Out When I Put Pedal to Floor Okay, I have a 69 SWB Step with a 87+ 350 with 350 auto. It has HEI. I have replaced the plugs...gapped .045, replaced the rotor, cap, wires, and vacuum advance. I set the timing to 8 degrees advanced. The idle is around 850. It cranks as soon as you touch the key and runs smooth. In park, I can floor it and the engine sounds fine. When I'm driving it and push the accelerator quickly, it bogs down. I can accelerator slow/smoothly with no problems. The carb is a 4-barrel quadrajet (rebuild)...less than 6 months old from AutoZone. Do you think it is the vacuum going to the vacuum advance or something else? __________________ Dan dan.brue@us.army.mil

11-02-2005, 10:02 PM	#2
llegos Registered User Join Date: Aug 2005 Location: pleasanton, CA Posts: 570	Re: Cuts Out When I Put Pedal to Floor i recently experienced a similar problem I have a rebuilt Q-jet. I can floor it like 97% and all will be fine. But, i floored it all the way, and it bogged down and kinda acted a lil wierd. All the rest runs fine. Just kind of wierd if u ask me __________________ -Steve

11-02-2005, 10:02 PM	#3
wink_tim Registered User Join Date: Jun 2003 Location: Rowlett, TX Posts: 120	Re: Cuts Out When I Put Pedal to Floor You might try a little more advance on you're timing, say 10-12 degrees. Its free to try. __________________ 67 SWB

11-02-2005, 10:44 PM	#4
Boog laying low Join Date: Mar 2001 Location: Searcy, Ark. USA Posts: 13,666	Re: Cuts Out When I Put Pedal to Floor It's possible the secondary air valve is opening too fast when you matt it. Even though it's a store bought rebuilt don't mean anything. If that air valve opens too fast it can cause it too sort of fall on it's face. A good shop manual will have pics and tell you in detail how to adjust the spring on the secondary air valve to help dial it in to your application. Most likely only 1 turn or less to tighten the spring will make a considerable change. Tightening the spring will delay the opening of the secondary air valve thereby taking some of the bog out of it. A quadrajets secondary bores are huge! __________________ Boog 69 Chevy stepside, 358/T350, 4.11 posi, 4.5/4 drop, rallys, poboy driver primer is finer 91 Chevy sportside, Tahoe, Yukon & GMC Crewcab All GM..'nuff said. I stand for the flag and kneel at the cross

11-02-2005, 11:16 PM	#5
69TowRig Senior Member Join Date: Jan 2005 Location: Raleigh, NC Posts: 897	Re: Cuts Out When I Put Pedal to Floor This might sound basic, but check the fuel filter. __________________ -Chris Building a stripper, one part at a time: 1969 K5, 307, 3spd, 3 seats, hard top. Added Pwr Discs, Pwr Steering, Aux Battery, T-case Skid, Lighted Sidemarkers, HEI, Lock-Right Diff, ECE Class IV Hitch, 32" MT/Rs. Parts to Install: Hand Throttle, Console, Tow Hooks, Dual Horns, AM-FM, Dealer Swing-Away Tire Carrier, Gas Tank Skid. Also building a 1950 Willys CJ-3A and off-roading a 2001 Nissan Frontier on 1-Ton Portals...

11-02-2005, 11:36 PM	#6
shifty Questionable Join Date: Mar 2005 Location: Atlanta Posts: 13,373	Re: Cuts Out When I Put Pedal to Floor __________________ If I've got anything up for grabs, it'll be here: 7-hole gauge cluster for a 67-72 p/u FREE (link) I can't check the forum daily. If I don't reply to you within 24 hours, drop me a PM! I'm (hopefully) still alive and will reply faster to a PM.

11-02-2005, 11:50 PM	#7
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,851	Re: Cuts Out When I Put Pedal to Floor Check filter first.Then,could be getting too much fuel,sticking float,rich adjustment... __________________ "BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~

11-02-2005, 11:56 PM	#8
jhow66 Registered User Join Date: Jun 2002 Location: Knoxville Tenn. Posts: 3,058	Re: Cuts Out When I Put Pedal to Floor Easy way to check if it is the secondarys opening to soon is to tie the air valves so they will not open. __________________ 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

11-03-2005, 12:22 AM	#9
llegos Registered User Join Date: Aug 2005 Location: pleasanton, CA Posts: 570	Re: Cuts Out When I Put Pedal to Floor its not the fuel filter/carb adjustments because last week i took it in to my mechanic(he tunes street/strip muscle) and he got it basically perfect. I may have to look into the seccondary air valve. Also, quick question, what is the CFM of a stock 4bbl q-jet? __________________ -Steve

11-03-2005, 08:19 AM	#10
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,851	Re: Cuts Out When I Put Pedal to Floor 780,iirc. __________________ "BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~

11-03-2005, 10:54 AM	#11
MrC1 Dork For Days Join Date: Aug 2005 Location: Dallas Posts: 407	Re: Cuts Out When I Put Pedal to Floor I saw a place that listed Q-jets for cars rated at 770 cfm and trucks at 800 cfm. Guess there were minor differences between the models. If you're able to go 97% throttle w/o bog problems, I'd check to make sure your throttle cable isn't trying to rip the arm off the carb by pulling too far. You could be torquing it out of wack. Just a thought. The tension spring on the secondaries only has one turn of total travel (at least mine does). A small adjustment might be all you need, but it sounds like you've already had an expert look at it. __________________ 1972 C20, 402/700R4 - My first classic truck, bought in September 2005. 85% transformed from "Farm" to "Cool" status! 1970 Dodge Challenger 440, 4sp (my other toy) 12.67 @ 117 MPH, with a pathetic 2.022 60' 2007 Dodge Charger SRT-8 2008 Cadillac CTS All-American garage, baby!

11-03-2005, 01:11 PM	#12
truckster Registered User Join Date: Jan 2001 Location: Orem, Utah Posts: 8,021	Re: Cuts Out When I Put Pedal to Floor I'd check the secondary adjustment as well. I had the same problem when I first installed my rebuild Quadrajet on my 455. It only takes a little bit of fine tuning to get it right where you want it. __________________ I have sworn upon the altar of God, eternal hostility against every form of tyranny over the mind of man. - Thomas Jefferson

11-03-2005, 07:09 PM	#13
4tiresngas An American Soldier Join Date: Feb 2005 Location: Grumolo D' Abadessee, Italy Posts: 503	Re: Cuts Out When I Put Pedal to Floor Okay, I was off the Net for a couple of days. I failed to mention that I did change the fuel filter also. I'm not familiar with the secondary adjustment. Anyone have pictures to show me. I know where the idle adjustment is and the two air/fuel adjustment screws and that's about the extent of my knowledge. Again. appreciate all the input. __________________ Dan dan.brue@us.army.mil

11-04-2005, 12:30 AM	#14
jhow66 Registered User Join Date: Jun 2002 Location: Knoxville Tenn. Posts: 3,058	Re: Cuts Out When I Put Pedal to Floor this might help: (allen screw underneath-loosen this just enough so you can turn other slot head screw-tighten slot head screw about 1/4 turn-hold in this position and tighten allen screw. ) Try it out if not right tighten 1/8 turn each time. (P.S. there is no written warrenty on above advice ) Attached Images __________________ 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

11-04-2005, 01:59 AM	#15
Cat Fuzz My son, my joy. Join Date: Sep 2003 Location: Spokane WA Posts: 463	Re: Cuts Out When I Put Pedal to Floor No one has mentioned the accelerator pump dumping too much fuel? __________________ '69 Chevy 3/4 ton, 327cid, Carter AFB, Edelbrock intake, HEI, TH400. Founding member of the No Money To Spend On My Truck Club. When your at Home Depot, you WISH you had gotten an 8 foot bed!



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