Need Advice On Properly Tuning Both Hitachi Su Carbs

[Jarvo2]

I've had great success with my needle height by following the Z-Therapy approach.  Dial the knobs all the way in, then loosely screw the needle into the piston & then push the piston into the carb body.  Pull the piston out & tighten up the needle set screw.  Then adjust down 2.5 turns out on the dials & begin to tune the carbs.  This allows for variation in the 40+ year old equipment, and possibly newer / rebuilt nozzles.  

[psdenno]

Well, that explains the dry cleaning charge my mechanic adds to all his bills.

Dennis

[240260280z]

NOTE:  Early SU carb's AIR balance can be adjusted for both idle and off-idle however there is only one FUEL adjustment  that can be optimized for idle OR off-idle. (both fuel balance between carbs and fuel).   If the carbs are not worn, the mechanical design will keep the idle and off-idle fuel differences minimal.
 
To set up off-idle:
 
Warm up the car
 
Attach the rod linking the throttle shaft (11) to the Aux. Throttle Shaft (8)
 
Turn the fast idle screw (see picture below) to get the idle ~ 3000 rpm
 

 

 

Measure the air flow into the front carb then turn the Balance Screw (14) to adjust the air flow into the rear carb.  Match the rear carb's air  to that of the the front carb. (here is how to use a unisyn)

 

 

Once the air is balanced, lift the piston in the rear carb and note the RPM where the engine settles (the car is now running on the front carb only).

 

Next lift the front carb's piston and note the RPM where the engine settles (the car is now running on the rear carb only).  Adjust the fuel height of the rear carb's jet so that the RPM's match that of running on the front carb.

 

Repeat the three steps above to confirm air is balanced and RPM drop is the same

 

Back off  the fast idle screw completely so that it does not touch the plate. Leave a 1mm gap from the screw end. 

 

Final adjustments:

 

Drive it, read plugs, and note power.  Adjust jets up and down (in equal turns) to match your target plug colour.

 

Enjoy the car!

 

Thanks to SteveJ (Georgia's SU expert) for helping refine the above tuning procedure.

[jalexquijano]

NOTE:  Early SU carb's AIR balance can be adjusted for both idle and off-idle however there is only one FUEL adjustment  that can be optimized for idle OR off-idle. (both fuel balance between carbs and fuel).   If the carbs are not worn, the mechanical design will keep the idle and off-idle fuel differences minimal.

 

To set up off-idle:

 

Warm up the car

 

Attach the rod linking the throttle shaft (11) to the Aux. Throttle Shaft (8)

 

Turn the fast idle screw (see picture below) to get the idle ~ 3000 rpm

 

 

 

Measure the air flow into the front carb then turn the Balance Screw (14) to adjust the air flow into the rear carb.  Match the rear carb's air  to that of the the front carb. (here is how to use a unisyn)

 

 

Once the air is balanced, lift the piston in the rear carb and note the RPM where the engine settles (the car is now running on the front carb only).

 

Next lift the front carb's piston and note the RPM where the engine settles (the car is now running on the rear carb only).  Adjust the fuel height of the rear carb's jet so that the RPM's match that of running on the front carb.

 

Repeat the three steps above to confirm air is balanced and RPM drop is the same

 

Back off  the fast idle screw completely so that it does not touch the plate. Leave a 1mm gap from the screw end. 

 

Final adjustments:

 

Drive it, read plugs, and note power.  Adjust jets up and down (in equal turns) to match your target plug colour.

 

Enjoy the car!

 

Thanks to SteveJ (Georgia's SU expert) for helping refine the above tuning procedure.

Thanks to all of you in this great fórum, i finally tuned my car properly and have no backfire. I reviewed both, your notes and the JUST SU Video. I did noticed that if i parked the car and returned after say 20 minutes, it takes a couple of seconds for the car to reach to 1,100 RPM which is my goal. Maybe this could be normal! I adjusted the mixture knobs to 2.5 turns.

 

Have a Happy New Year!!!!

[240260280z]

Happy New Year!

 

 

I missed meeting you last December but will look you up the next time I'm in Panama.

[siteunseen]

Are your valves adjusted properly? It helps a lot.

[bartsscooterservice]

That's some nice shop clothes there, jacket and cuff links. 

 

 

Good old days

[jalexquijano]

Happy New Year!

 

 

I missed meeting you last December but will look you up the next time I'm in Panama.

Please let me know when you come back to Panama, so i can show you my Project car and have your opinion on it! My e-mail is info@quijanorichard.com

[SSS280Z]

This topic is very helpful to me. I have owned 210's with twin mikuni carbs and a single weber dcoe however I have never dealt with su carbs. I recently bought a 04/1978 280Z with su carbs and got norvey oil (zoom spout)from a local Ace hardware. It is 10W and the owner recommend Oatley oil part #40404. He said that's 20W.