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Old 05-30-2021, 07:11 AM
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Default Another bogging post

Ok, so I posted about 5 years ago when I first took this car the strip about it bogging and life took over and I never had a chance to look further into the issue and it never bogged after that.

Fast forward to now, and the car is bogging way more. I checked the secondary air valve and the tension was quite low as I could push open the flaps easily and they would not snap back shut. I tested by putting some more tension on them by loosening the allen head screw and turning the screw just enough so they snap back. Test drive and no change.

The bogging was first noticed going from 2nd to 3rd but it does not matter, as long as it is WOT. It has occasionally done it at part throttle too but that is intermittent.

I warmed the car up and took it for a drive and then removed the shaker and air cleaner assembly. I then checked the flaps on the secondary's and they were closed (by vacuum). I pulled the throttle cable wide open and the flaps on the secondary's only opened a few cm's and I never got that "quad bog" sound. I also never notice that sound when driving WOT.

I checked the choke vacuum diaphragm on the front passenger side of the carb and it appears to be ok (as far as I can tell) but when it is running, the vacuum from that seems pretty strong and maybe that is stopping the secondary's from opening all the way?!

It seems to me to be a fuel delivery issue and I thought about the fuel filter but I changed that less than 500 miles ago. I checked the plugs for cracked ceramic and wearing on the firing end. I also double checked the gap (.045 on AC Delco R45TS).

Stock 1976 Trans Am 400 with Quadrajet.

  #2  
Old 05-30-2021, 08:19 AM
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Bogging going from 2nd to 3rd?

Auto trans or stick shift?.....

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Old 05-30-2021, 08:37 AM
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Don’t forget that there is a fuel filter sock on the pick up in the tank also.

If you have a real long stretch of road where you can wind the car out then try this.
Loosen the secondary air flap so there’s minimum tension then take the car on a drive and wind it out slow. If it still flattens out at the top 3rd and in 4th then you have a fuel delivery issue, not a issue of the flap opening too fast or too late!

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Old 05-30-2021, 08:37 AM
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Don’t forget that there is a fuel filter sock on the pick up in the tank also.

If you have a real long stretch of road where you can wind the car out then try this.
Loosen the secondary air flap so there’s minimum tension then take the car on a drive and wind it out slow. If it still flattens out at the top 3rd and in 4th then you have a fuel delivery issue, not a issue of the flap opening too fast or too late!

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And he was not talking about 1/8 or 1/4 mile ETs!

1) 1940s 100% silver 4 cup tea server set.

Two dry rotted 14 x 10 Micky Thompson slicks.

1) un-mailed in gift coupon from a 1972 box of corn flakes.
Two pairs of brown leather flip flops, never seen more then 2 mph.

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Old 05-30-2021, 11:00 AM
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It is an automatic car and it does it from 2nd to 3rd as well.

steve25 may be right. This may or may not have anything to do with it but the gas gauge stopped working last year and it is not the ground, which from what I read, it typically turns out to be.

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Old 05-30-2021, 01:53 PM
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Most likely the carb fuel bowl is going low or empty.

"Bog" would be a transition issue going quickly to full throttle.

If it takes off fine going to WOT pulls hard then has issues at high RPM's or top of 1st or 2nd gear it's another problem.

The easily cure is to install a high-flow N/S assembly in the factory Q-jet. All of my kits for the Pontiac carb come with them. If that doesn't fix the issue start looking at a restricted fuel filter, fuel pump, collapsed fuel line, loose clamps, etc.....

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Old 05-30-2021, 05:25 PM
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Quote:
Originally Posted by Cliff R View Post
Most likely the carb fuel bowl is going low or empty.

"Bog" would be a transition issue going quickly to full throttle.

If it takes off fine going to WOT pulls hard then has issues at high RPM's or top of 1st or 2nd gear it's another problem.

The easily cure is to install a high-flow N/S assembly in the factory Q-jet. All of my kits for the Pontiac carb come with them. If that doesn't fix the issue start looking at a restricted fuel filter, fuel pump, collapsed fuel line, loose clamps, etc.....
This sounds about right "If it takes off fine going to WOT pulls hard then has issues at high RPM's or top of 1st or 2nd gear it's another problem.". Raining here the next few days but as soon as I can get out, I will test again and post my results.

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Old 06-01-2021, 10:34 AM
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Quote:
Originally Posted by steve25 View Post
Don’t forget that there is a fuel filter sock on the pick up in the tank also.

If you have a real long stretch of road where you can wind the car out then try this.
Loosen the secondary air flap so there’s minimum tension then take the car on a drive and wind it out slow. If it still flattens out at the top 3rd and in 4th then you have a fuel delivery issue, not a issue of the flap opening too fast or too late!
Ok, so I was able to get out and try this. Winding it out slow, it starts to bog at high RPM going from 1st to second and from 2nd to third.

Punching it from a standing start results exactly the same with it bogging from 1st to 2nd and never shifting. Same thing with doing 60 and punching it....goes for a bit and then bogs at higher RPM in 2nd before it reaches 3rd.

As a side note, when I parked it this time and gave it a little rev, it backfired through the carb and then the rpm increased a bit.

I'm going to change the fuel filter as it may have picked something up and then after that, I think my issue may be the sock.

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Old 06-01-2021, 11:36 AM
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Back firing like that out of gear is a sure sign that if nothing else there is not enough fuel at low fuel pump actuating rates to even keep enough fuel in the Carb to work the accelerator pump.

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And he was not talking about 1/8 or 1/4 mile ETs!

1) 1940s 100% silver 4 cup tea server set.

Two dry rotted 14 x 10 Micky Thompson slicks.

1) un-mailed in gift coupon from a 1972 box of corn flakes.
Two pairs of brown leather flip flops, never seen more then 2 mph.

Education is what your left with once you forget things!
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Old 06-01-2021, 11:39 AM
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See if the cam is broken off that lifts the secondary rods when the air doors open.

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Old 06-01-2021, 04:54 PM
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I chased a bogging problem when launching. The air valve was working. I finally had qjet carb on bench just playing with air valve,finally it stuck, here I noticed mark's on the carb body where valve was scrapping. It was a brand new SD NOS carb. The valve needed to be slightly adjusted. Screws just loosened enough to adjust. Now fine.

  #12  
Old 06-02-2021, 03:11 PM
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Default It sounds more like you have is a fuel starvation issue, not a bogging issue.

Textbook definition of a bog is that when you stomp on it - standing or rolling - it stumbles, flutters, doesn't get-up-and-go.

With fuel starvation, you stomp on it, it gets up and goes hard, then lays down like you let off the gas. Because the carb is running out of gas.

Lots of good suggestions from Cliff R above. Work your way from back to front methodically and you'll figure it out.

We had a 1973 Formula that did this many moons ago and it was driving me nuts. Rebuilt the carb, new mechanical AC fuel pump, replaced the sock and cleaned the tank, replaced the rubber lines front and rear and double-checked the fuel pressure. Everything was good.

Turned out that there is a 4" rubber hose in the center of the car, between the rear metal line and the front metal line and THAT little chunk had a tiny split and it was sucking air on hard acceleration. Never dripped or smelled of fuel, just let air into the system.

Also verify that your mechanical secondary butterflies (in the carb's base) are opening all the way when the gas pedal is floored and that there is not a lockout on the carb that is sticking. Many qjets have that lockout to keep you from flooring it when the engine is cold. There are two lockout possibilities - one on the butterflies and another on the air flap. We usually disable both of those.

And it's normal to only see the secondary air flaps (on the top) open slightly when you wing the throttle wide open. They react to the need to airflow and sitting still, the engine doesn't need very much.

You mention that you don't hear the 'roar' of the secondaries when you floor it? No roar at all, or is it muffled but still there, just not as loud as you think is should be? The later TAs had that plate blocking the scoop specifically because of the roar we all love. There were noise restrictions and it couldn't be too loud, so Pontiac closed off the scoops starting in 1973. Thankfully, most of those block-off plates have magically been removed.....

Good luck!

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Old 06-02-2021, 03:54 PM
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That’s one that I have have also in regards to the reply above of sucking air in which is much easier for the pump to do then yank on fuel!

You started this post if I recall right that the car was put away running fine , so another Winter of dry rot aging on rubber line could by why now it’s doing what it is!

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Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs!
And he was not talking about 1/8 or 1/4 mile ETs!

1) 1940s 100% silver 4 cup tea server set.

Two dry rotted 14 x 10 Micky Thompson slicks.

1) un-mailed in gift coupon from a 1972 box of corn flakes.
Two pairs of brown leather flip flops, never seen more then 2 mph.

Education is what your left with once you forget things!
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Old 06-02-2021, 05:04 PM
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Back in the day most common problem was people who woud just back the secondary opening spring off all the way and were surprised when it bogged

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Old 06-02-2021, 07:06 PM
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"Turned out that there is a 4" rubber hose in the center of the car, between the rear metal line and the front metal line and THAT little chunk had a tiny split and it was sucking air on hard acceleration. Never dripped or smelled of fuel, just let air into the system."

Everyone should read this several times and log it into your memory banks.

I could fill many pages with stories from customers who thought they had a fuel pump or carb problem only to find out they were sucking AIR someplace in the system instead of fuel. I've seen old rotten fuel lines that didn't leak one drop of gas put would suck gobs of air and the carb would NOT refill for any reason until the carb was primed enough to get the fuel pump going several hundred RPM"s.

I'll bet I get a half dozen calls a week from folks who tell me the bottom plugs in their carb are leaking (mostly a myth but I'll go into detail about that on another thread on another day) and they have to pour fuel either into the carb or down the throat of the carb after it sits a few days as will absolutely NOT start simply cranking the engine and pumping the accelerator.

I even had a recent customer BITCHING about his carb not working correctly. I asked about fuel lines, hoses, etc and he said the car was a fresh "high end" restoration and the tank, lines and hoses were all new. Turn out after countless emails and calls back and forth someone missed a clamp tucked up by the tank during the install and it was sucking air but didn't leak a drop of gasoline!........

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Old 06-02-2021, 07:47 PM
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If it still has a catalyst on it, they can mimic fuel starvation if plugged. Not sure this fits the symptoms, though, without driving it.

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Old 06-03-2021, 07:39 AM
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Quote:
Originally Posted by Joe's Garage View Post
Also verify that your mechanical secondary butterflies (in the carb's base) are opening all the way when the gas pedal is floored and that there is not a lockout on the carb that is sticking. Many qjets have that lockout to keep you from flooring it when the engine is cold. There are two lockout possibilities - one on the butterflies and another on the air flap. We usually disable both of those.
I verified that the butterflies are fully opening a few days ago as that came across my mind as well.


Quote:
Originally Posted by Joe's Garage View Post
You mention that you don't hear the 'roar' of the secondaries when you floor it? No roar at all, or is it muffled but still there, just not as loud as you think is should be? The later TAs had that plate blocking the scoop specifically because of the roar we all love. There were noise restrictions and it couldn't be too loud, so Pontiac closed off the scoops starting in 1973. Thankfully, most of those block-off plates have magically been removed.....

Good luck!
Probably more my imagination then anything. The shaker is open; the block of plate is on hinges but nothing holding it shut so it stays open all the time.

I'll have to get it up in the air and start from the front and go over the fuel lines to see if maybe there is something in that regard.

Thanks for the information.

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Old 06-07-2021, 08:30 AM
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Update....

Apparently the car was low on gas (gauge does not work) as I ran out of gas on Thursday so that may account for starvation at WOT. Filled the car up and it still hesitates/bogs at WOT but at a higher RPM right before it shifts from 1st to 2nd or 2nd to 3rd. I checked the secondary flaps and they were still a bit loose so I have tightened them a 1/4 turn and will hopefully get out and test today.

If that does not solve it, i will start chasing the other suggestions mentioned.

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Old 06-11-2021, 12:09 PM
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Just an update for those who may find this or are following.......

Changing the fuel filter resolved the issue. Must have got something stuck or had its run and was done. Works good now.

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Old 06-11-2021, 12:36 PM
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I hope your running a paper one and not a sintered Bronze type?

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And he was not talking about 1/8 or 1/4 mile ETs!

1) 1940s 100% silver 4 cup tea server set.

Two dry rotted 14 x 10 Micky Thompson slicks.

1) un-mailed in gift coupon from a 1972 box of corn flakes.
Two pairs of brown leather flip flops, never seen more then 2 mph.

Education is what your left with once you forget things!
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