View Full Version : z-s carb piston sticking

Rob DeScherer
05-27-2004, 11:13 AM
Anyone ever have this problem? The piston in the front carb on my 74 TR6 will get stuck in a lifted position once the car warms up and has been driving for 20 minutes. I have just had the carbs rebuilt by Joe Curto, and the problem still exists. Any ideas?

05-27-2004, 11:44 AM
If these were SU's I'd say you need to re-centralize the jets.......
The time lapse seems to indicate a heat expansion problem. Did you remember to install the ceramic spacers when you put the carbs back on?

I don't know how far you are from Queens, but given what Joe charges for a rebuild and his reputation as the know-it-all--- I think you have some cumstomer service coming to you.
Good luck,Andy

Rick O.
05-27-2004, 01:02 PM
I'm with Dave . . . take it back to Curto. Perhaps the piston was inadvertantly swapped; they are supposed to be matched at the factory with the carb body. Unlike the SU's where the jet/needle is centerable, the ZS has no such adjustment.

05-27-2004, 01:48 PM
I'll go out on a limb though an suggest something else. There is a chance that something is messed up with the capor the piston. I know it sounds far fetched but stranger things have happened with the ZS's before. Try taking the cap off and rotating it into another position and putting everything back together. I had a very similar problem to what you are having two years ago and this turned out to be the culprit. I'm not sure why but the piston would just get stuck after the engine was warm, but after I turned the cap and tightened everything back down it worked fine. Mind you I had to turn the cap twice before things started working right so the marks on the side were 180 degrees off but it worked. Hopefully it might work for you too.

05-29-2004, 03:33 PM

I'll just add to what Walter is suggesting. While you have the dashpot off check for debris... replace it trying to match the other caruretor.. I believe that there is a raised piece of alumininum that serves as a marker for which screw holes go to their mate on the carb body (or match the "Zenith" lettering to that of the other carb). Then, as you tighten each one check the movement of the piston. This can be done with trial and error and sometimes the tightening order determines the freedom of movement for the piston. It is a very precise assembly and this is just another part of the tuning procedure. By the way, make sure that the rubber diaphragm is installed and seated correctly as this is important to piston operation as well. If all of this fails, give Joe a call right away. I have spoken to him at least once and he is an expert and a very nice guy. I am sure he will correct any problem immediately. Good luck.