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quadrajet bog

Babaganoosh

Babaganoosh

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No matter what I do this thing has a nasty bog when it comes off idle like it has no gas or to much gas.

I will try to explain my symptoms

1. It will idle and start like a dream... flick of the key and it roars to life.
2. One you give it any throttle in gear D or R it will bog and if I don't let up off the pedal it will completely die.
3. I have tried adjusting the APT through the air horn and nothing seems to change it.
4. Fresh plugs, wires, cap, rotor and fresh bran new rebuilt carb from a Chevy Tech who has been around for ever.

Before I had the carb rebuilt it was doing the same thing.




sigh, maybe I should just get rid of 20 years of family heritage... :frown1:
 
sounds like the accelerator pump is heading south or leaking... with the truck off, go out and manually operate the plunger, or actuate it with the seesaw style actuator... it's the plunger on the top, ds forward...

you should see 2 nice heavy streams shoot into the primaries... also check for fuel around the top of it, indicating a bad top seal... but if the squirts are weak, it's not uncommon for the pump wiper to have deteriorated... it's the umbrella shaped seal at the bottom of the accelerator pump.. inside the carb...

it's an easy rebuild if you need to...
 
doh, missed the fresh rebuilt part.... if the above checks out... how's the ignition timing? vacuum advance working, etc?
 
check the simple stuff- is your timing off? did you check for vacuum leaks? getting enough fuel?
 
Fresh rebuild or not I'd be checking the accel pump too. That's the most common cause for bog/falling on it's face.

Rene
 
The vacuum advance on the distributor is working I checked when I did the cap and rotor yesterday by moving it and allowing it to snap back.

It has a bit of unhooked vacuum lines and you can hear a little hiss with the engine running. Timing could have jumped a tooth or so, but I have no way of check because it has the wrong balancer / timing tab combo to set it with a light. :doah:


When I open the choke plate and turn the throttle linkage it squirts 2 heavy streams in. Truck has a bran new fuel pump to.

The truck ran good yesterday no problems. today I set the idle mixture screws with a vacuum gauge and acquired a max of 18inches of vacuum. Took it for a spin and bam runs like crap once again.... maybe its destiny is sitting in my driveway for another few years...
 
Use the vac gauge to set your timing too. Turn the idle down to 550 or so and adjust timing for best vac/highest idle speed. Test drive and if you hear any pinging back it off a little.

Timing too retarded will also cause it to bog.

Oh, fix the damn vac leaks too. No sense trying to diagnose a problem if you haven't removed all the variables first. Bad vac leaks won't help it run better.

Rene
 
I'm trying to get my Dad to look over the vacuum lines, it's a rats nest and I get confused/pissed off and slam the hood. Problem is he is disabled and bending over looking at them hurts to much.

I was mainly looking for other advice to check possibility's.
 
i had that problem recently on my 76 k5 400CI SB w/ a quadrajet, in neutral i could rev it up and down all day but in gear it would struggle bad. I limped it to my dads house blipping the gas to get some momentum then cruising off it over and over. My max speed of the trip was 20mph and ppl behind me were pissed :haha: . Turned out that the fuel adjustment screws were all the way open and the mixture was way too rich. Turned em back down and played with it for a few minutes and it ran fine again.
 
Same with mine in park and neutral it will rev up but have a slight hesitance at about 1200 then shoot up normal.

Maybe my carb doesn't like a smooth as silk idle? :dunno:


some specs probably wont hurt either

78 or 79 bone stock 350, quadrajet, accel super coil, ac delco plugs, and autozone brand plug wires. only thing not new is the engine and the coil in that list.
 
For now, if it leaks...plug it. You're not gonna hurt anything and you'll be able to confirm or deny that that is part of the problem of not.

Same with timing, adjusting it by ear for now isn't gonna hurt anything. Just make small changes. Lower the idle and see if advancing it brings up the idle speed any. If it does advance it a bit more. Then drive it and see if it pings and how the response is. I don't think I've ever owned anything with the timing 100% on spec. Every engine has it's very own personal sweet spot for timing, and you can find it with a little trial and error, and a good ear.

My buddy had a '76 Grand Prix that would barely run at all timed to factory specs. We kept messing with it until it ran liked a scalded cat, idled perfectly etc. It ran hard enough to starve for fuel at the top end. Out of morbid curiosity we checked it with a light and it was 13 degrees more advanced than factory specs. W/E, that's where it ran best.

Rene
 
mine had this same prob recently. rebuilt holley, new distributor,wires, plugs, cap, rotor and coil. got it to start n run fine but would die as soon as i touched the gas. got pi$$ed one day when it was half in the road and couldnt get it in the garage. climbed under the hood and cranked the dist. a full inch advanced and it drove right in the garage. a little more advance and it was runnin good all through the range. dont know if this was right but it runs now:dunno:
 
Hey Trusty, what is your opinion on vac advance, port or manifold? Also if its manifold do you leave it connected for tuning timing by ear? TIA
 
i like va to be unported... even if setting timing by ear (which is exceptionally rare for em anymore), i always set final timing by total timing..... it's safer imo, motors not gonna nuke at idle, but it will above 3 g's......
 
Hey Ryoken, thanks for the quick reply. I am going to check total timing when I am through. Heres my situation. Truck ran great until I sucked an intake end seal. Redid that but didnt confirm timing before taking manifold off. I did mark dist. pretty well and dist. dropped in and motor fired up. Came to realize that timing tab/mark dont align so I did thought I was way off. The mark was at about 9:30 looking in and designed for about 12:00. I think they adjusted timing to compensate for a bad vac. advance which I just replaced. Found TDC #1 thru spark plug hole and remarked balancer. I set initial at about 8 and reconnected vac. to manifold. Reset idle and took for a test drive. It falls on its face just like OP's and I am pretty sure acc. pump is great, shoots fuel out.
Sorry for the novel--P.S. Motor is unknown but I rebuilt the carb after I got the truck six months ago
 
A bog is probably the hardest thing to get rid of ,and a hundred things can cause one.--vacuum leaks,worn accelerator pump cup (or the bore it rides in is all scored up,a common dilema in high mileage carbs)--or the discharge check ball inside the carbs accelerator pump passages isn't sealing properly,all those things will reduce the amount of gas squirted out of the nozzles...there is an adjustment on the accelerator pump lever too,you can swap the lever into the outer hole to increase the amount of pump travel,and also bend that lever if need be,to increase it..

I'd look for vacuum leaks first--use carb cleaner whith the engine running and douse any suspected hoses & fittings on the carb & intake ,the engine will either race or die if carb cleaner is inhaled thru a vacuum leak--do not overlook the power brake booster and charcoal canister as possible sources of leakage,and the PVC vale and its hoses too...(and make sure its working,I've seen plugged PVC passages throw off the fuel/air mix enough to cause this kind of problem)...check the carb base gasket too,and ensure the EGR isn't sticking open or opening too soon (if you still have it hooked up!)...

Ignition timing can be a factor too,as already suggested..ensure the mechanical advance weights are free and not sticking or rusted,and the weights aren't hogged out where they ride on the pins...I'd adjust the timing like Rene said too,"by ear" and see if that improves it any...

Weak spark can cause a bog under a load,a bad cap or rotor,or even an HEI module that has a bad dwell advance circuit can do it..a dying coil can too--I see you have a "Super Coil"--be sure its the correct one for your particular distributor & module,they make 2 styles,that have different polarity (and the wires must match the ones on the pick up coil)--it'll run with the "wrong" coil,but lack power under a load and cause driveability problems...(Gm even had a recall back in the 80's when some coils got installed in the "wrong" vehicles!)...
It might not hurt to take a fuel sample "piss test and see if any water or diesel,or dirt is mixed in with the gas...maybe thats the first thing to check?...

Good luck,and let us know if you find out what caused it...
 
I did take a little fuel sample before I put the carn on. It came up a little dirty but not to bad and still smelled like gas. Once I got it running I put 15.3 gallons in the tank (16 gallon tank)

Im having it towed to the dealer I work at. Really im tired of the problems and im willing to assist someone to fix it.
 
Well turns out the tank was nastier then I thought and the fuel filter was completely plugged up and when taken out would hold fuel. :eek1:


It will live to see another day... :D to bad a FURD pulled me in. :doah:

fail.jpg
 
I am glad the problem has been found, I tracked mine as well. My timing curve is way off and I cant believe the PO had it running so decent until I monkeyed with it. Oh well Highjack off:D
 
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