TQ piston screw setup

[bvberserk]

Well, I screwed up and screwed this screw back an forth before I've read that it should not be touched ((
Although I have this pic how critical is it to set up properly? Any advice? Should I tune it a bit on a running car?

 

[CBODY67]

Looks like that is a fine-tuning device for the metering rod height. One of those "set at the carb factory" sort of things, but also something that if it was altered a bit, you could not feel it in the engine's performance. A main thing would be emissions compliance and little else, I suspect.

Hopefully, you can get it pretty much back to where it was?

Just some thoughts,
CBODY67

 

[66 Monaco 500 365]

There is an eccentric on the primary throttle shaft that acts on the bottom of that adjustment.
It makes sure that if the primary throttle blades are open a lot, but the vacuum is high, the metering rods are pushed up to make sure the engine doesn't go lean, even though it has a lot of vacuum. if the screw is adjusted "in" it will force the mixture to go richer, if it is adjusted "out" it allows the vacuum in the intake manifold determine the position of the metering rod, high vacuum makes it run leaner and low vacuum the spring pushes the metering rods up making the mixture richer.
If you are getting pinging at large primary only throttle opening (before the secondaries start to open) you may want to turn that screw "in"
If it is too far in,. it would effect fuel economy.
My $.02

 

[70bigblockdodge]

It is the override to make sure the metering rods are all the way up at WOT/no chance of them being pulled down by vacuum.
The power piston that controls the metering rods bridge will be all the way against the retainer at rest with no vacuum/engine off. Hold open throttle at WOT and make sure the bridge/power piston is not being pushed up and into/through the retainer. If not then adjust it downward till the adjuster contacts the lever in the bottom holding the power piston up to the retainer, but not pushing up on it.

 

[Boydsdodge]

Step up piston adjustment is an initial setting of 1.5 turns from fully seated. It is a very fine thread so be gental on finding bottom, I place my finger on the cross arm that connects the needles so I can feel when it bottoms. I lightly turn screw back and forth to confirm it is seated, then turn screw 1.5 turns as a base setting. once the engine is up to temp, the idle mixture and engine timing is set I will test drive, if you adjust too much you can have too much fuel at idle or if not adjusted high enough you can be to lean and have a bit of a stumble. This rod is just one of the many on a properly tuned Thermoquad along with the secondary air door adjustment.

 

[bvberserk]

It is the override to make sure the metering rods are all the way up at WOT/no chance of them being pulled down by vacuum.
The power piston that controls the metering rods bridge will be all the way against the retainer at rest with no vacuum/engine off. Hold open throttle at WOT and make sure the bridge/power piston is not being pushed up and into/through the retainer. If not then adjust it downward till the adjuster contacts the lever in the bottom holding the power piston up to the retainer, but not pushing up on it.

Thank you, makes sense to me. I wonder if it can prevent jet closure with full vacuum - i.e. piston rod will touch the cam(and plate) earlier than rods close out the jets.
Anyway, I assume I will still need several tests - set up the screw according to the pic I made before teardown, then turn it 1\2 here and there and perform drive tests.

 

[bvberserk]

Step up piston adjustment is an initial setting of 1.5 turns from fully seated. It is a very fine thread so be gental on finding bottom, I place my finger on the cross arm that connects the needles so I can feel when it bottoms. I lightly turn screw back and forth to confirm it is seated, then turn screw 1.5 turns as a base setting. once the engine is up to temp, the idle mixture and engine timing is set I will test drive, if you adjust too much you can have too much fuel at idle or if not adjusted high enough you can be to lean and have a bit of a stumble. This rod is just one of the many on a properly tuned Thermoquad along with the secondary air door adjustment.

Thank you, will try this method.