No gas su l28

[evan_s30]

Recently swapped from a 4bbl to round top su carbs. I'm pretty positive I have all the linkage right, but it won't get gas. It's not the pump, and my floats appear to give good. The only way I can get gas to the carbs to to pull the linkage that opens the path from the float to the carb. My throttle linkage didn't do this, only if you do them both at the same time with your hands is when it runs. And help or leads would be greatly appreciated. Thanks!

[Miles]

If you are new to SU carbs then you need to buy the "Just SUs" video at

 

http://www.ztherapy.com/

 

After viewing this video you will be able to maintain, adjust and repair SU carbs. 

 

Ztherapy also carries parts for SU carbs.

 

 

Do you know about the mixture adjustment nuts on the bottom of each carb?

 

 

If you Google SU carb adjustment  or SU repair  you should get some how to work with SUs write ups by Z car owners.

 

Also, search Hybridz  and classiczcars.com  as there are many posts on maintaining SU carbs.

Edited February 24, 2015 by Miles

[mgreen]

Your description doesn't make much sense but I'm going to try my best.  Let's assume that you have your throttle linkage set up right.  A common issue is the butterfly valves getting stuck so I would verify that those move with the linkage.  You can get some aquarium line or clear fuel line to see the gas going into your float bowls.  When I first fired up my 240z with an su carbed l28, there was a lot of dirt and varnish in the port in the bottom of the float bowl.  Putting some premium (detergent) gas in and using carb cleaner helped a lot.  And when you say it runs when you pick up the linkage, do you mean the piston inside the mouth of the carb?  That would signify to me that you are running extremely lean to where you aren't getting combustion.  Su's lift up when the engine pulls more air past them, which lets more gas through the needle and seat.  Like Miles said, use the adjusting nut at the bottom to tune it to get it running.  I would richen it.  Hope this helped you a little.

[Miles]

Recently swapped from a 4bbl to round top su carbs. I'm pretty positive I have all the linkage right, but it won't get gas. It's not the pump, and my floats appear to give good. The only way I can get gas to the carbs to to pull the linkage that opens the path from the float to the carb. My throttle linkage didn't do this, only if you do them both at the same time with your hands is when it runs. And help or leads would be greatly appreciated. Thanks!

 

Once you watch the video you will understand why your carbs are not working when you move the throttle linkage. The linkage that you are pulling on the bottom of the carb  is the choke which causes more fuel to enter the carb as long as you hold the choke open.  On the other hand, the throttle linkage only opens a butterfly valve. That's it.

 

Basically, fuel flow into the carb is controlled by the piston lifting a precision tapered needle  up inside its tapered valve seat which allows more fuel to drip out of the bowel and get sucked in by high velocity air into the carb where it  is mixed with the air forming the correct air-fuel mixture. Some refer to this as a "controlled drip". Mixture adjusters on the bottom of each carb determine the correct mixture. 

 

It is a bit long and complicated to explain how the SU carb,  throttle and linkages work. 

 

The video explains  the theory of operation along with tuning  which is the best way to learn SUs.

 

Or download SU instructions off the net.

Edited February 24, 2015 by Miles