boggin at full throttle - The 1947 - Present Chevrolet & GMC Truck Message Board Network

crm318 · 06-30-2008, 03:21 PM

lastnight i was out gouging on by truck and i noticed that when i floor it, the engine would bog down very badly. this wasnt just a stumble. the truck would not overcome the bog at full throttle. it would bog as long as i had my foot down. what might cause this? i did just put a new vacuum advance on the distributor and set the timing to 12 degrees.

lowriden58 · 06-30-2008, 03:23 PM

sounds like your advance isnt opening or maybe you have a fuel issue

*Billla* · 06-30-2008, 03:34 PM

Timing, then carb.

Is the vacuum advance adjustable, and if so is it adjusted?
Have you set your mechanical advance?

If the timing is right, then we start looking at secondary opening - what kind of carb is it and what's it's condition (new, recently overhauled, never touched, etc.)?

crm318 · 06-30-2008, 03:51 PM

the carb is a rebuilt qjet. im not sure if the vacuum advance is adjustable. how could i tell? how would i set my mechanical advance?

**WorkinLonghorn** · 06-30-2008, 03:59 PM

I'd check the fuel filter as well. You can tell if the vac adv, is adjustable by looking at the area right next to where the hose attaches. If that area is smooth it's NOT adjustable. If it is five (or 6?)sided,it is adj.

crm318 · 06-30-2008, 04:40 PM

it is smooth and i assume non-adjustable. i have a clear fuel filter and there doesnt seem to be any debris in it, but ill check. the truck runs fine at all speeds accept full throttle.

d10s69c10 · 06-30-2008, 05:22 PM

a Quadrajet has a filter right in the carburator at the fuel line. i had the same thing happen to me i just removed it and the spring and my truck ran like a raped ape.

"i couldent blow thru it to save my life"
almost feels like vapor lock?

**Yukon Jack** · 06-30-2008, 05:32 PM

Was having a similar problem with my 70 K5 when I finally got it running with a rebuilt motor. I changed out the fuel filter in the quadrajet and it was a touch better but still having a bog at full throttle. It was also vapor locking pretty bad.

Replaced the mechanical fuel pump and the bog and vapor locking problems were gone!

haysonj · 06-30-2008, 07:18 PM

there should not be any vacuum advance at full throttle so I doubt the problem is in the vacuum unit. You could cap it off and it will only affect cruise and idle. I would tend to think it is fuel related. may have to large of secondaries or make sure that the secondaries are fully opening when you mash it from inside the truck. Have a friend look while the truck is not running.

*Billla* · 06-30-2008, 07:38 PM

Quote:

Originally Posted by crm318

the carb is a rebuilt qjet. im not sure if the vacuum advance is adjustable. how could i tell? how would i set my mechanical advance?

WorkinLonghorn nailed the adjustable vacuum advance question - the mechanical advance question is answered in my timing FAQ linked in my sig.

The vacuum advance for the Q-jet can be adjusted - it's called an Air Valve. Once the timing is right we can look at that.

Definitely agree making sure the in-carb filter is removed if you have an external filter!

crm318 · 07-01-2008, 04:23 PM

the filter in the carb is removed. probably about 2 weeks ago i got down on it and it roasted the tires off. i dont know how it could come out of adjustment in that amount of time. as far as the vapor lock issue, the truck acts like this reguardless of what temp the motor is or if i just started it or have been running it all day. i assume vapor lock is caused by heat. ill give the dist. and the carb a look over.

telly · 07-01-2008, 04:31 PM

I just finished fixing a similar problem with my Monojet and inline 6 250ci.

The things I did -

1) Replaced the fouled spark plugs
2) Rebuilt the carb (although it might not have been necessary - should have done this last)
3) Attached the vacuum advance to the proper port (PO had the vacuum advance port from the carb running to the charcoal cannister)
4) Reset the timing and idle speeds

Finally this morning the truck is accelerating like it should.

Hope this is helpful - don't know if there is carry-over from my truck ('70 C10) to yours.

Good luck. I'll be watching your progress.

crm318 · 07-01-2008, 06:06 PM

i just tore back in my distributor and i noticed that the new vac advance was very stiff. i took it off and sprayed some pb blaster lubricant in it ans now it moves more freely. we will see how that works.

welch_41 · 09-25-2008, 09:41 PM

I'm curious if spraying lub in the vac adv. cured your problem. I'm having a similar issue with my 66 C10/250. The carb has been rebuilt and timing set to 4 deg BTDC. When I first bought the truck it had a Holley carb on it but I couldn't find a rebuild kit for it so I picked up a reman Rochester Monojet. Thats when my problem started. From reading previous post, does an inline fuel filter make that much of a difference over the filter in the carb? Thanks for any help.

OrangeCrush1970 · 09-26-2008, 03:37 PM

Quote:

Originally Posted by d10s69c10

a Quadrajet has a filter right in the carburator at the fuel line. i had the same thing happen to me i just removed it and the spring and my truck ran like a raped ape.

"i couldent blow thru it to save my life"
almost feels like vapor lock?

raped ape is good, I might have to try that one

06-30-2008, 03:21 PM	#1
crm318 Alright Alright Alright Join Date: Mar 2004 Location: Midland, Texas Posts: 1,672	boggin at full throttle lastnight i was out gouging on by truck and i noticed that when i floor it, the engine would bog down very badly. this wasnt just a stumble. the truck would not overcome the bog at full throttle. it would bog as long as i had my foot down. what might cause this? i did just put a new vacuum advance on the distributor and set the timing to 12 degrees. __________________ 1972 Cheyenne Chevrolet red and white 357ci, Vortec heads, GM Performance high rise intake, Comp 268H .454/.454 218/218 110 LSA Quadrajet carb, Flowtech headers, 2.25 40 series HEI, Curve kit, TH 350, 3.07 gears 275/60/15s on 15x8 rallies

06-30-2008, 03:23 PM	#2
lowriden58 Registered User Join Date: Jan 2008 Location: Chesapeake Beach, MD Posts: 812	Re: boggin at full throttle sounds like your advance isnt opening or maybe you have a fuel issue __________________ 71 cheyenne lwb 300rwhp best 1/4 time so far 12.8 @103 http://i195.photobucket.com/albums/z...en58/001-2.jpg

06-30-2008, 03:34 PM	#3
Billla Account Suspended Join Date: Sep 2005 Location: Monroe, WA Posts: 3,815	Re: boggin at full throttle Timing, then carb. Is the vacuum advance adjustable, and if so is it adjusted? Have you set your mechanical advance? If the timing is right, then we start looking at secondary opening - what kind of carb is it and what's it's condition (new, recently overhauled, never touched, etc.)?

06-30-2008, 03:51 PM	#4
crm318 Alright Alright Alright Join Date: Mar 2004 Location: Midland, Texas Posts: 1,672	Re: boggin at full throttle the carb is a rebuilt qjet. im not sure if the vacuum advance is adjustable. how could i tell? how would i set my mechanical advance? __________________ 1972 Cheyenne Chevrolet red and white 357ci, Vortec heads, GM Performance high rise intake, Comp 268H .454/.454 218/218 110 LSA Quadrajet carb, Flowtech headers, 2.25 40 series HEI, Curve kit, TH 350, 3.07 gears 275/60/15s on 15x8 rallies Last edited by crm318; 06-30-2008 at 03:52 PM.

06-30-2008, 03:59 PM	#5
WorkinLonghorn Senior Member Join Date: Dec 2006 Location: Studio City, Calif. Posts: 2,883	Re: boggin at full throttle I'd check the fuel filter as well. You can tell if the vac adv, is adjustable by looking at the area right next to where the hose attaches. If that area is smooth it's NOT adjustable. If it is five (or 6?)sided,it is adj. __________________ '69 GMC C2500 Custom Camper, 8 1/2' bed, New GM 350, NP 435 Close Ratio 4spd. Trans., 3.73 Dana-60 open.Camper and Trailer wiring, PS, PB, AC, tach , three gas tanks, stereo speakers, 2nd owner, Work-Truck supreme.

06-30-2008, 04:40 PM	#6
crm318 Alright Alright Alright Join Date: Mar 2004 Location: Midland, Texas Posts: 1,672	Re: boggin at full throttle it is smooth and i assume non-adjustable. i have a clear fuel filter and there doesnt seem to be any debris in it, but ill check. the truck runs fine at all speeds accept full throttle. __________________ 1972 Cheyenne Chevrolet red and white 357ci, Vortec heads, GM Performance high rise intake, Comp 268H .454/.454 218/218 110 LSA Quadrajet carb, Flowtech headers, 2.25 40 series HEI, Curve kit, TH 350, 3.07 gears 275/60/15s on 15x8 rallies

06-30-2008, 05:22 PM	#7
d10s69c10 Built 4 Speed Join Date: May 2008 Location: Geneva FL Posts: 619	Re: boggin at full throttle a Quadrajet has a filter right in the carburator at the fuel line. i had the same thing happen to me i just removed it and the spring and my truck ran like a raped ape. "i couldent blow thru it to save my life" almost feels like vapor lock? __________________ 1969 C/10 Short Box: 496/T-56 in worx. "To Be Old And Wise, First You Must Be Young And Stupid"

06-30-2008, 05:32 PM	#8
Yukon Jack Post Whore Join Date: Feb 2000 Location: Rose Hill, KS, USA Posts: 12,684	Re: boggin at full throttle Was having a similar problem with my 70 K5 when I finally got it running with a rebuilt motor. I changed out the fuel filter in the quadrajet and it was a touch better but still having a bog at full throttle. It was also vapor locking pretty bad. Replaced the mechanical fuel pump and the bog and vapor locking problems were gone! __________________ 1970 Blazer with a 400 sbc and 4" lift 1980 Pontiac Trans Am, 455 Oldsmobile 2012 Kawasaki Concours 14

06-30-2008, 07:18 PM	#9
haysonj Registered User Join Date: Dec 2007 Location: Santa Maria, Ca. Posts: 1,423	Re: boggin at full throttle there should not be any vacuum advance at full throttle so I doubt the problem is in the vacuum unit. You could cap it off and it will only affect cruise and idle. I would tend to think it is fuel related. may have to large of secondaries or make sure that the secondaries are fully opening when you mash it from inside the truck. Have a friend look while the truck is not running. __________________ 69 Chevy 4x4 383 Power

07-01-2008, 04:23 PM	#11
crm318 Alright Alright Alright Join Date: Mar 2004 Location: Midland, Texas Posts: 1,672	Re: boggin at full throttle the filter in the carb is removed. probably about 2 weeks ago i got down on it and it roasted the tires off. i dont know how it could come out of adjustment in that amount of time. as far as the vapor lock issue, the truck acts like this reguardless of what temp the motor is or if i just started it or have been running it all day. i assume vapor lock is caused by heat. ill give the dist. and the carb a look over. __________________ 1972 Cheyenne Chevrolet red and white 357ci, Vortec heads, GM Performance high rise intake, Comp 268H .454/.454 218/218 110 LSA Quadrajet carb, Flowtech headers, 2.25 40 series HEI, Curve kit, TH 350, 3.07 gears 275/60/15s on 15x8 rallies

07-01-2008, 04:31 PM	#12
telly Registered User Join Date: Jun 2008 Location: Stanwood, WA, 98292 Posts: 151	Re: boggin at full throttle I just finished fixing a similar problem with my Monojet and inline 6 250ci. The things I did - 1) Replaced the fouled spark plugs 2) Rebuilt the carb (although it might not have been necessary - should have done this last) 3) Attached the vacuum advance to the proper port (PO had the vacuum advance port from the carb running to the charcoal cannister) 4) Reset the timing and idle speeds Finally this morning the truck is accelerating like it should. Hope this is helpful - don't know if there is carry-over from my truck ('70 C10) to yours. Good luck. I'll be watching your progress. Last edited by telly; 07-01-2008 at 05:44 PM.

07-01-2008, 06:06 PM	#13
crm318 Alright Alright Alright Join Date: Mar 2004 Location: Midland, Texas Posts: 1,672	Re: boggin at full throttle i just tore back in my distributor and i noticed that the new vac advance was very stiff. i took it off and sprayed some pb blaster lubricant in it ans now it moves more freely. we will see how that works. __________________ 1972 Cheyenne Chevrolet red and white 357ci, Vortec heads, GM Performance high rise intake, Comp 268H .454/.454 218/218 110 LSA Quadrajet carb, Flowtech headers, 2.25 40 series HEI, Curve kit, TH 350, 3.07 gears 275/60/15s on 15x8 rallies Last edited by crm318; 07-01-2008 at 06:17 PM.

09-25-2008, 09:41 PM	#14
welch_41 Registered User Join Date: Jul 2008 Location: Conway, AR Posts: 11	Re: boggin at full throttle I'm curious if spraying lub in the vac adv. cured your problem. I'm having a similar issue with my 66 C10/250. The carb has been rebuilt and timing set to 4 deg BTDC. When I first bought the truck it had a Holley carb on it but I couldn't find a rebuild kit for it so I picked up a reman Rochester Monojet. Thats when my problem started. From reading previous post, does an inline fuel filter make that much of a difference over the filter in the carb? Thanks for any help.



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