Weird mixture screws

[thethee]

Been messing with the mixture adjustment for the thermoquad for a while now and today, for some reason I can't think of right now, I decided to pull the mixture screws. It didn't look right to me so I compared it to the mixture screws in my old TQ.

Side by side, top is new, bottom is old:

The top one is notched at the tip and no, this is not because of overtightening. Haven't tried putting the old screws yet, but has anyone seen this before? Am I right in assuming the top one is wrong?

"New" TQ is 9054S
"Old' TQ is 9058S

 

[thethee]

More detailed shot of the tips:

 

[68PK21 440.6bbl]

Is this ""New" TQ is 9054S" brand spanking new as in just manufactured or NOS?

Or is it just a re-manufactured/rebuilt new to you carb?

.

 

[thethee]

Remanufactured by Autoline

 

[68PK21 440.6bbl]

Return it, it's junk!

 

[thethee]

Not that recent a remanufacture

 

[68PK21 440.6bbl]

Welp some hammerhead took a big screwdriver and cranked that mixture screw in to tight to damage (ridge) the needle and the seat in the carb is most likely damaged (junk).
Now this re-manufacture could be from a 'batch' rebuild and that jet screw could not be from this base but who knows?
Most quality rebuild kits come with brand new idle air screws (and caps if acceptable) so who knows what else is eff'ed up in that carb.
Personally in all my years I only rebuild my own & customer carbs, re-manufactured over the counter rebuilds are crap IMHO.

What is the shape of the original (old) carb? Or did you already turn it in as a core?

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[thethee]

The old carb is definitely in worse shape than this one and not rebuildable. I do still have it though since returning the core would mean shipping it across the Atlantic and that is more than the core is worth. I figured the ridge was by design cause for someone to damage it like this you'd have to screw it in really tight, like ridiculously tight.

Engine ran pretty decent with it and if I didn't pull the screws I never would've known about the ridge. But thanks for confirming my suspicion. Will pull the carb this weekend for further inspection and probably put in the old mixture screws to see what that does.

 

[CBODY67]

"To point or not to point"? I'd use the bottom one as it appears to be real metal, rather than a softer cast metal. Don't worry about the point length as it's where that taper hits the idle mixture hole in the throttle body that really matters. In that respect, they look pretty close to each other, just that one has a longer point past that contact point.

The one with the knurls on the edge of the screw head looks more accurate for an OEM item, to me. FWIW In the close-up picture, the top screw looks to be cast from the same softer metal that some later GM engine oil pan drain plugs are cast from. Which is a softer metal, by observation that they used to use in the 1970s, by observation. Which might well explain that deformed area on its tapered area.

Just some thoughts,
CBODY67

 

[68PK21 440.6bbl]

OK before you go and do much of anything you have a 400ci carb.

From the 'A Carter Thermo-Quad Guide'

Forget about the "S" letter but it appears the primary jet and rod are different.
One thing you have to be concerned about is your new primary jet screw has a broken off tip, sometime this tip can be lodged in the throttle bore orifice.
DO NOT INSTALL YOUR OLD SCREW UNTIL YOU ARE SURE THIS BROKEN TIP IS NOT IN YOUR CARB!

Another read/information about rebuilds.

Commercial rebuilders:
Carburetors that are mass rebuilt by commercial rebuilders have their useful service life shortened or ended. This usually stems from mixing parts, bad service procedures, and cleaning by tumbling or blasting. Tumbling and blasting removes the factory finishes. This leads to accelerated wear and corrosion problems. In the case of the TQ, the factory linkage was cadmium or irridite finished. The throttle shafts were Teflon coated. Tumbling or blasting removes these finishes and will lead to corroded sticking linkages and binding or leaky shafts. The TQ phenolic fuel bowl can be damaged by tumbling or blasting. Jets, rods and internal orifices are further damaged by these processes. Mixed parts without proper analysis can result in a poorly performing or useless unit. A carburetor from a rebuilder of this nature requires careful examination to determine its future usefulness.

A Carter Thermo-Quad Guide


.

 

[thethee]

OK before you go and do much of anything you have a 400ci carb.

From the 'A Carter Thermo-Quad Guide'

View attachment 461748

Forget about the "S" letter but it appears the primary jet and rod are different.
One thing you have to be concerned about is your new primary jet screw has a broken off tip, sometime this tip can be lodged in the throttle bore orifice.
DO NOT INSTALL YOUR OLD SCREW UNTIL YOU ARE SURE THIS BROKEN TIP IS NOT IN YOUR CARB!

Another read/information about rebuilds.

Commercial rebuilders:
Carburetors that are mass rebuilt by commercial rebuilders have their useful service life shortened or ended. This usually stems from mixing parts, bad service procedures, and cleaning by tumbling or blasting. Tumbling and blasting removes the factory finishes. This leads to accelerated wear and corrosion problems. In the case of the TQ, the factory linkage was cadmium or irridite finished. The throttle shafts were Teflon coated. Tumbling or blasting removes these finishes and will lead to corroded sticking linkages and binding or leaky shafts. The TQ phenolic fuel bowl can be damaged by tumbling or blasting. Jets, rods and internal orifices are further damaged by these processes. Mixed parts without proper analysis can result in a poorly performing or useless unit. A carburetor from a rebuilder of this nature requires careful examination to determine its future usefulness.

A Carter Thermo-Quad Guide


.

The casing number being for the 400 ci carb was the first thing I noticed too when I got it and that had me concerned, but when I opened it up it had the right jets and rods for the 440 ci, so 4099, 5137 and 2109, so I figured it would be okay.

Don't think the tip is broken off as both of the mixture screws look identical, but I will look into that.

 

[Dana]

I’ve never seen a TQ with those brass Idle mixture screws from the factory. Factory are steel, so they aren’t able to develop that ring from over tightening. Both brass and steel will distort the baseplate. Get rid of the top screw in your photo. Don’t be cheap by putting them in a little drawer for (just in case). Throw them away. I’ll send you some factory steel ones if you need them. The “screws” are actually valves that regulate a predetermined mixture established by the idle air bleed and the idle feed restrictor.

 

[thethee]

Man I wish I knew about this site when I got the car, learning more every time I log on.

I’ve never seen a TQ with those brass Idle mixture screws from the factory. Factory are steel, so they aren’t able to develop that ring from over tightening. Both brass and steel will distort the baseplate. Get rid of the top screw in your photo. Don’t be cheap by putting them in a little drawer for (just in case). Throw them away. I’ll send you some factory steel ones if you need them. The “screws” are actually valves that regulate a predetermined mixture established by the idle air bleed and the idle feed restrictor.

They're gone. Will use the old ones for now, might get back to you about those factory steel ones. Thanks Dana

 

[thethee]

Pulled the carb, base plate is in good shape so luckily no damage there. However, I found that the primary jet wells are leaking like crazy. Need to reseal those, what would work best with ethanol fuel? Here in Netherlands we pretty much only have E5 and E10 nowadays...

I’ve never seen a TQ with those brass Idle mixture screws from the factory. Factory are steel, so they aren’t able to develop that ring from over tightening. Both brass and steel will distort the baseplate. Get rid of the top screw in your photo. Don’t be cheap by putting them in a little drawer for (just in case). Throw them away. I’ll send you some factory steel ones if you need them. The “screws” are actually valves that regulate a predetermined mixture established by the idle air bleed and the idle feed restrictor.

Sent you a PM @Dana

 

[thethee]

Forgot to conclude this one, but big shoutout to @Dana for hooking me up with the proper mixture screws and main jets! Engine runs much better with them. Turns out brass is much more easily deformed than I thought and the old srews were indeed just over tightened.