[Shiny]

Thanks rohrt! Isn't it great I can pick up where I left off? Good thing for PY as I sure wouldn't have remembered all that... especially since I tried to forget!

I am going to revisit the throttle blades, as I don't think they are closing as much as they should.... it doesn't feel precise so maybe that's a contributor to the saga. Notice the bypass air hole that should not be there...:


How much of the transfer slot should be showing when the blades are closed?

And looking back at the nozzle "drip" video, I agree it was ugly but that may have been flooding from rust in the inlet. Now that I know the baseplate is wrong, I can look for air moving wrong between baseplate and body.

I asked Quadrajet Power if they had a used baseplate and they do not. I have a couple more Qjet cores but really don't want to start from zero so I hope the baseplate I have isn't too far off. One of my rough cores is a 7040244... another Buick so maybe it has the "right" baseplate... it could happen.

When the engine last ran, I remember the vacuum being good.. like 17 or 18". That was at sea level and the car is now at 5800'. I also checked compression and it was low, but fairly consistent and not unexpected for the <8 CR the engine probably has with #11 heads.

Mike

[shaker455]

I looked over your mainbody pics posted best possible and I do not see any bypass air holes passages in your main body ?
All I see is the holes in the base.
Can you post pics of your full mainbody and inside of airhorn to show your bypass air circuit ?

[400 Lemans]

There should be a raised letter on the driverside back corner of your baseplate. B-buick,P-pontiac, C-chevy,O-olds or L-caddy.

[Shiny]

Originally Posted by shaker455

I looked over your mainbody pics posted best possible and I do not see any bypass air holes passages in your main body ?
All I see is the holes in the base.
Can you post pics of your full mainbody and inside of airhorn to show your bypass air circuit ?

Thanks for knowing what to look for. I questioned where the hole connected but don't know what I'm looking for. I did shove a wire into the hole and it dead-ended, but plan to look when I separate the baseplate from the body. It may well be the holes are there but go nowhere and all is OK. I'll try to get it done tomorrow. I am also concerned if other passages between the baseplate and body are not correct.

Originally Posted by 400 Lemans

There should be a raised letter on the driverside back corner of your baseplate. B-buick, P-pontiac, C-chevy, O-olds or L-caddy.

Thanks. I'll look but the linkage when I got the carb was definitely not Pontiac. I replaced all that.

I'm still curious about the numbers on the baseplates. Are they "assembly" numbers or casting numbers? I looked at my other Buick carb (7040244) baseplate and it is numbered 38753. Delco literature I found says the assembly should be 7036831. Does this mean the numbers are casting numbers? If so, where do I find the correct casting numbers for these carbs?

Mike

[Baron Von Zeppelin]

On Pontiac Qjet carbs the baseplates have the 7 digit casting number cast into a circular pattern.
They are raised numerals and the circular is maybe about the size of a pencil eraser.

The center main bodies use the same format for its 7 digit casting number.

I sort of expect Rochester did all GM carbs that way.
Maybe you have a Carter Qjet ?

[Kenth]

4M Q-jets w/o bypass air do not have provisions for this in the air horn or float bowl besides no holes in baseplate.
Pics on air horn and float bowl for bypass air, marked yellow.

Also, Buick 350 throttle plates has narrower off-idle slots and smaller idle needle holes than Buick 430/455 throttle plates.

[Shiny]

Originally Posted by Baron Von Zeppelin

On Pontiac Qjet carbs the baseplates have the 7 digit casting number cast into a circular pattern.
They are raised numerals and the circular is maybe about the size of a pencil eraser.

The center main bodies use the same format for its 7 digit casting number.

I sort of expect Rochester did all GM carbs that way.
Maybe you have a Carter Qjet ?

Thanks!

Carb is Rochester, and that casting number is clear: 7038888. I interpret this as the raw casting number for the baseplate before machining and assembly. Just guessing, but the same baseplate casting could have been used for multiple carbs by differences in machining and/or linkage.

So maybe the stamped number is indeed an assembly number! I'd still be interested in knowing where those stamped codes are documented.

Whatever the stamped number means, the baseplate on my carb is wrong for a 7029240.

Cliff provided some insight on his forum and I'm now trying to decide if the mismatched baseplate is an issue or just a diversion!

Mike

[Shiny]

Originally Posted by Kenth

4M Q-jets w/o bypass air do not have provisions for this in the air horn or float bowl besides no holes in baseplate.
Pics on air horn and float bowl for bypass air, marked yellow.

Also, Buick 350 throttle plates has narrower off-idle slots and smaller idle needle holes than Buick 430/455 throttle plates.

Thank you Kenth!

Originally Posted by shaker455

I looked over your mainbody pics posted best possible and I do not see any bypass air holes passages in your main body ?
All I see is the holes in the base.
Can you post pics of your full mainbody and inside of airhorn to show your bypass air circuit ?

Thank you shaker455!

Cliff also shared some similar insight on his forum so thanks to him too!

After verifying the inlet valve was holding pressure, I removed the baseplate and am now able to understand: the bypass holes were never drilled in the body, so even though they are (wrongly) present in the baseplate, they were NOT functional. The "never-drilled" passages for bypass air are circled in this photo of the body:



So this may seem like a rat-hole but I'm glad to know what I have and learn from you all.

I plan to trace the idle, main, and secondary circuits tomorrow to make sure the mismatched parts and gaskets aren't somehow causing issues.

Hopefully all is well and I can ask about the tuning once more before putting it back together.

Mike

[Baron Von Zeppelin]

The only reference I found in the Delco listing that says 7036596 is the correct assembly number for my carb.

That will be the casting (7 numbers in a circle) that you would want to hunt down.
If you choose that route.

7038888 is probably a later model unit.
Carb has probably been through a mass remanufacturing facility , and pieces get mixed around routinely so long as they are loosely considered interchangeable.
Airhorns and baseplates rarely find their way back onto the same main body they came from.
These are what people get from parts stores when they trade in their old carb, and the cycle continues.

The stamped numbers you are finding are long gone history now.
Some of the Pontiac stamps are known , but only from comparisons of similar number carbs.
The right casting number will put you closer to right than anything else will.

But in your position, anything you can make work for now is probably fine and well.
Just for comparison sake, there are 4 or 5 of them on eBay that all look to be original as far as the castings.
You could reference some things on them if it helped in some way.
This is what your correct baseplate would look like.
All of them on eBay are just like this one.

[formula kid]

Just an observation in photo 27 where you show that you widened the float so not to rub. I see the needle and seat there is no hanger to hold the needle up when your gas has evaporated after sitting so long. The needle may have been stuck. My thinking is that when the fuel is gone from the float bowl the needle is lifted out of the seat. This way when you start the car and fuel enters past the needle and seat the needle closes when the bowl is full. Just a thought could it be that simple?
Good luck

[Shiny]

Originally Posted by Baron Von Zeppelin

That will be the casting (7 numbers in a circle) that you would want to hunt down.
If you choose that route.

7038888 is probably a later model unit.

Thank you for taking the time to respond with such detail. I really do appreciate the help.

Thanks for clarifying these numbers. This sounds like a good clue to whether a used carb has the "correct" parts.

Carb has probably been through a mass remanufacturing facility , and pieces get mixed around routinely so long as they are loosely considered interchangeable.
Airhorns and baseplates rarely find their way back onto the same main body they came from.
These are what people get from parts stores when they trade in their old carb, and the cycle continues.

Yes, this is clearly a carb with that "rebuilder/part store" history. It was given to me 20 yrs ago by a friend and it was in a rebuilder box. I need to verify the airhorn too!

The stamped numbers you are finding are long gone history now.
Some of the Pontiac stamps are known, but only from comparisons of similar number carbs.

OK, so they may not be knowable. And in a way, doesn't matter in my situation as function is my goal, not a correct restoration.

The right casting number will put you closer to right than anything else will.

But in your position, anything you can make work for now is probably fine and well.

Yes, I just want the carb to work and the baseplate I have may be just fine. So far, I've learned the bypass holes in the baseplate are not getting fed by the body so I'm making progress.

Just for comparison sake, there are 4 or 5 of them on eBay that all look to be original as far as the castings.
You could reference some things on them if it helped in some way.
This is what your correct baseplate would look like.
All of them on eBay are just like this one.

Thank you. I have done a similar search and collected some references images. I think I found an NOS baseplate listing from a similar carb that can show both sides. The gasket is another clue for me.

Originally Posted by formula kid

Just an observation in photo 27 where you show that you widened the float so not to rub. I see the needle and seat there is no hanger to hold the needle up when your gas has evaporated after sitting so long. The needle may have been stuck. My thinking is that when the fuel is gone from the float bowl the needle is lifted out of the seat. This way when you start the car and fuel enters past the needle and seat the needle closes when the bowl is full. Just a thought could it be that simple?
Good luck

Thank you for this. I left the clip off intentionally. I think I read in Cliff's book the spring wasn't needed but I'm open to guidance here. To me, my needle has not been sticking so the missing clip wasn't an issue.

Mike

[Kenth]

DO NOT drill the holes you marked with red rings for bypass air. If you drill from the top, the .180" bit will stick out into the cavities I marked with yellow lines.

[Shiny]

Thanks Kenth

I wasn't planning on trying to add bypass air... just noting there were undrilled holes on the body that appeared to be in the location matching the holes in the "mismatched" baseplate.

I went to measure the lower idle bleed holes in the body. Before I got to it, I fished a large chunk of debris (machining chip) from the idle channel circled here. If you look close, you can see it. I estimate it was blocking more than half the channel.



After that, I looked into the lower bleed holes and they also appeared partially constricted by corrosion products. Harder to see.. The holes are 0.078" dia, but the drill stops short of entering the down-channel.

I assume I should drill these out to get a clear 78-mil diameter, correct?



I guess I will be looking harder at all these ports and channels!

Mike

[Shiny]

Originally Posted by Kenth

DO NOT drill the holes you marked with red rings for bypass air. If you drill from the top, the .180" bit will stick out into the cavities I marked with yellow lines.

Kenth, I want to correct an error and clarify your comment before I re-assemble the carb.

First, I mislabeled the ports in the body and I think you were warning me!

The bypass air holes in the baseplate are connected to cavities in the body as shown in green. The gasket has holes that make these connections. These cavities are "blind" so no air can flow into the baseplate holes.

The orange hole in this image I mis-labeled. This opening has nothing to do with bypass air but rather, provides the "ported" vacuum signal to the distributor advance (orange line).



So.... is there any reason to seal the bypass holes in the baseplate? I guess not since there is no path for airflow but wanted to make sure.

At this point, I have no reason to add bypass air. If I need them, I'll ask how, but I assume the answer is to drill into these two cavities, correct?

Thanks again,

Mike

[shaker455]

Well that maybe the reason your getting nozzle drip so having some bypass air will allow the throttle blades to be closed more than you have now.

You did not post up a pic of the inside of your airhorn so we could see if it has a bypass passage

[Dick Boneske]

The most comon cause of poor idle with Quadrajets is the idle tubes being plugged. Seeing what may be in your idle circuit, it is mandatory that the idle tubes be removed and cleaned. They arethe brass tubes located adjacent to the tapped holes next to the primary venturis. There is a procedure to remove them on YouTube. They cannot be cleaned properly without removal.

[tom s]

You might think about sending the carb to someone that does them for a living like Shaker or Sean at SMI.Not sure if Cliff is taking any carbs in these days.JMHO,Tom

[Shiny]

Originally Posted by shaker455

Well that maybe the reason your getting nozzle drip so having some bypass air will allow the throttle blades to be closed more than you have now.

You did not post up a pic of the inside of your airhorn so we could see if it has a bypass passage

Thanks for the help. As a "frankencarb", it has a mismatched baseplate and a mismatched airhorn from it's time in rebuilder hell.

The original carb was apparently used on 69 Buick 430 and as I understand, did not have bypass air.

My current thought is to try to get it idling without bypass air. To your point about blades being too far open, Kenth thought if more than 0.40" of transfer slot was exposed at idle, it would be OK to add some bypass air.

I had asked for help with bypass air on Cliff's forum here which led me to discover the airhorn and throttle plate mismatch. I then tried to walk through all the systems, following Cliff's book, to see if the mismatch created any obvious issues. I found none, but definitely found some changes from the original configuration that were caused by the wrong baseplate and airhorn.

Please tell me if I missed something but here's my thoughts on the bypass air.

The airhorn does have passages that could feed bypass air (in orange). Remember this is the WRONG airhorn for a 29240 MD carb.


But the gasket Cliff provided based on the body (carb PN) blocks these passages:


And even if the gasket had openings, there are no mating passages in the body. This is consistent with the 29240 MD configuration Kenth shared. There was no bypass air on the original Buick application.


I have zero experience "tuning" a carb, but understand the newer fuels require "more" fuel, so the recommendations from Kenth and Cliff have been to increase the idle tube orifice diameters, which I've done. I have not increased the idle downchannel restriction nor increased the idle airbleeds. Kenth also recommended I increase the primary jets to 73 from the current 70.

I plan to follow Kenth's recommendations as a starting point as I totally trust and respect him. But to your other comment, he hasn't seen all the images either so please let me know if anything else jumps out.

Mike

[Shiny]

Originally Posted by Dick Boneske

The most comon cause of poor idle with Quadrajets is the idle tubes being plugged. Seeing what may be in your idle circuit, it is mandatory that the idle tubes be removed and cleaned. They arethe brass tubes located adjacent to the tapped holes next to the primary venturis. There is a procedure to remove them on YouTube. They cannot be cleaned properly without removal.

Thank you. I understand the warning and have addressed... at least twice now! Still working on cause, but unstable idle timing may have been a factor. Rust in the gas tank another... and... and....and...

Originally Posted by tom s

You might think about sending the carb to someone that does them for a living like Shaker or Sean at SMI.Not sure if Cliff is taking any carbs in these days.JMHO,Tom

Yup!

If I just wanted to get it running and cost was no object, I could do that. They would immediately toss this monstrosity carb refugee from the set of the Adams Family and tell me to buy a better core! It's more about the challenge and learning for me. Being retired I now have more time, less money, and I'm finally starting to understand some of the mistakes I made in the past. And I do have another core that is more likely to be "intact" if I abandon all hope. And I know how to buy a carb as a last resort.

Mike

[Kenth]

The location for bypass air entering thru the carb starts at the openings in airhorn marked yellow, continues thru floatbowl, marked yellow and exits at the throttle plate.