TR4/4A SU HS6 jet initial adjustment jet not flush with bridge

[Federalees]

I am tuning the SU HS6 carbs on my TR4A. For the initial setting, the manual states "screw the jet adjusting nut until the jet is flush with the bridge of the carburetter or fully up if this position cannot be obtained". My situation is that the jet on the back carb is flush, but the jet on the front carb cannot reach the bridge to be flush. I lowered the back jet the the appropriate amount by turning the nut 12 flats. With that done, the front jet as far up as it will go, is the same depth as the back jet once the back jet was adjusted. Do I use this as my starting point for adjustments? Or, do I turn the nut on the front carb the 12 flats which will result in the jet being lower than the rear for the initial start?

 

[charleyf]

I am tuning the SU HS6 carbs on my TR4A. For the initial setting, the manual states "screw the jet adjusting nut until the jet is flush with the bridge of the carburetter or fully up if this position cannot be obtained". My situation is that the jet on the back carb is flush, but the jet on the front carb cannot reach the bridge to be flush. I lowered the back jet the the appropriate amount by turning the nut 12 flats. With that done, the front jet as far up as it will go, is the same depth as the back jet once the back jet was adjusted. Do I use this as my starting point for adjustments? Or, do I turn the nut on the front carb the 12 flats which will result in the jet being lower than the rear for the initial start?

Very interesting.
I have 3 cars with HS6s. I have always just used the 12 flats as a starting point. Never paid attention to the height of the jet. But I would be looking for the reason why the front jet does not reach the bridge or at least is at the same height as the rear in the starting position.
Is the choke connection pulling the jet down? Or some other adjustment causing the problem?
Charley

 

[Fern]

Very interesting.
I have 3 cars with HS6s. I have always just used the 12 flats as a starting point. Never paid attention to the height of the jet. But I would be looking for the reason why the front jet does not reach the bridge or at least is at the same height as the rear in the starting position.
Is the choke connection pulling the jet down? Or some other adjustment causing the problem?

Very interesting.
I have 3 cars with HS6s. I have always just used the 12 flats as a starting point. Never paid attention to the height of the jet. But I would be looking for the reason why the front jet does not reach the bridge or at least is at the same height as the rear in the starting position.
Is the choke connection pulling the jet down? Or some other adjustment causing the problem?
Charley

I believe Charley is right on the money…if it’s not the choke assembly pulling down on the jet….examine the jet assembly. Could be something foreign in there or out of place or cork seal not seated properly. Both carb jets should be flush in the throttle body before setting. Good luck! Fern

 

[Federalees]

Very interesting.
I have 3 cars with HS6s. I have always just used the 12 flats as a starting point. Never paid attention to the height of the jet. But I would be looking for the reason why the front jet does not reach the bridge or at least is at the same height as the rear in the starting position.
Is the choke connection pulling the jet down? Or some other adjustment causing the problem?
Charley

Thanks Charley,
The choke seems to be working properly. I can’t see that the jet is sticking or being pulled down after the choke cable has been pushed back in. The spring above the adjustment nut is completely compressed, so I can’t see how the jet can go any higher. The jet bearing appears to be the same size as the one on the rear carb. I tried to start it with the jet up as far as it would go, making it even with the back jet that had been adjusted down, and it wouldn’t run. I then adjusted the front jet using the 12 flats starting point and was able to get it running and then able to fine tune the mixture. So, it’s running now but is still a mystery. Unfortunately, even with both carbs adjusted and balanced, I still have the issue of missing/hesitation under acceleration load. On to ignition troubleshooting!

 

[charleyf]

[QUOTE="Federalees, Unfortunately, even with both carbs adjusted and balanced, I still have the issue of missing/hesitation under acceleration load. On to ignition troubleshooting!
[/QUOTE]
Does that missing, etc. stop after you ease up on the accelerator?
Is so it is likely the carbs. First you do have oil in the upper chamber. If so then it is probably still related to the carbs. One carb is rich and the other is lean.
I am posting some pics of the bottom of the HS6 carb, namely the jet. In the first two the jet is up tight to the nut in the third pic the jet is pulled down by the choke lever.
When the jet is up tight it should also be at the bridge.
Charley

 

[bobhustead]

Is it possible your front jet is designed for other carburetors and is actually shorter? Stranger things have happened. I recall the endless fiddling
Charley had with wrong angle float bowls on a TR6 several years ago that put out the fire when he turned left. But they looked fine. I would pull the front carb and disassemble it to look for the problem and, if it doesn't appear, take the back one apart to look for discrepancies.
Bob

 

[Federalees]

[QUOTE="Federalees, Unfortunately, even with both carbs adjusted and balanced, I still have the issue of missing/hesitation under acceleration load. On to ignition troubleshooting!

Does that missing, etc. stop after you ease up on the accelerator?
Is so it is likely the carbs. First you do have oil in the upper chamber. If so then it is probably still related to the carbs. One carb is rich and the other is lean.
I am posting some pics of the bottom of the HS6 carb, namely the jet. In the first two the jet is up tight to the nut in the third pic the jet is pulled down by the choke lever.
When the jet is up tight it should also be at the bridge.
Charley
[/QUOTE] yes, the missing mostly stops when easing up on acceleration. You might feel a slight hesitation just cruising. My jets looks slightly different than what you posted, but you can clearly see them moving when pulling on the choke cable.

 

[Federalees]

Is it possible your front jet is designed for other carburetors and is actually shorter? Stranger things have happened. I recall the endless fiddling
Charley had with wrong angle float bowls on a TR6 several years ago that put out the fire when he turned left. But they looked fine. I would pull the front carb and disassemble it to look for the problem and, if it doesn't appear, take the back one apart to look for discrepancies.
Bob

I guess it’s possible. I will pull them out and compare when I get a chance.