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1972 240z One SU Carb Not Running

Old 02-19-2016, 10:16 AM
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1972 240z One SU Carb Not Running

Hey yall!

So yesterday I took the newly running z for a spin to get the carbs running so I could tune them. After taking the SU carbs apart, I cleaned all the components- they were VERY dirty! Before reinstalling them, I set the jets to the baseline setting (completely flush then 12 flats down). I installed the carbs as usual and started the car and let it run till it was warm. I used the method of using a flathead screwdriver to push up on the pistons to test whether each carb was running rich or lean. One carb was right on the money. The other one I couldn't really get it to affect the engine at all when I lifted the piston. After playing around for awhile with the jet adjusting bolt to no avail, I decided to just check it out with the Unisyn tuning device. When I stuck it on the one carb that was operating perfectly, the engine bogged down as usual and the device gave me a reading as usual. When I put the device on the other carb, it had no affect on the idle of the engine and gave me no reading. This leads me to believe that only one carb is actually sending fuel into the engine- and that the other one isn't doing anything. I can't seem to find anywhere that talks about this occurrence, so I thought I'd see if anyone else has had any experience with this problem. Thanks in advance for the help

Here is the video I learned this method
I did exactly what he did, so this should be helpful. He talks about the flathead screwdriver method at around the 15 minute mark.
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Old 02-20-2016, 06:52 AM
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Check the compression on the engine. If the compression is low, the carburetor will appear dead. Check the float level and filter on the carburetor that is not pulling.
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Old 02-20-2016, 07:03 AM
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Thanks Steve! I appreciate the guidance. I'll check all that out today
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Old 02-20-2016, 09:44 PM
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Old 02-21-2016, 06:32 AM
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You probably have a stuck float on the rear, or it is set so it can't shut off the fuel.
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Old 02-22-2016, 07:10 AM
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More than one issue

From what I can see the main jet (the one under the carb with the thumb nut) something is missing or worn out. The float is not closing the fuel inlet.
The rear carb runs the rear 3 cylinders so the header won't be hot on the rear 3. Also the rear butterfly might be closed off.
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