240Z, 260Z, 280Z Performance / Technical Discussions related to performance motor enhancements, upgrades.

runs like crap part of the time

Old 10-30-2005, 06:43 PM
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runs like crap part of the time

I got my Z back up and running after a new head and all, and the car was running pretty good earlier today, not fully in tune, but timing is set, new cap, plugs, rotor, wires, and timing is dead on. It still runs a little like crap, and I think it's a carburetor problem. I rebuilt the carburetors, and I am having trouble getting them perfectly into tune. I searched and found a page about how to sync the carbs and set the mixture, and I followed the instructions, but either I messed it up or something is wrong with my carburetors. When setting the mixture, the front carburetor idle would rise and then fall back to normal after I lifted the lifting pin, like it should when the mixture was right. When I went to set the mixture for the rear carburetor and used the lifting pin, it would run like crap, like it was going to die. I went to adjust the mixture, and no matter which way I turned the mixture nut, it wouldn't make any difference at all. It would do the exact same thing no matter where the mxture nut was. I seated it fully, and the car still ran no matter what I did, but ran like crap. I finally just turned it to ~2 1/2 turns out, and left it there. When I went to double check the first carburetor, it did the same thing when I lifted the pin, it tried to stall out and die.

Also, when synching the carburetors, I was unable to figure out how to use the throttle stop screws on the carburetors themselves to sync them. I ended up having to use the two little screws on the linkage itself to sync them to the best of my ability.

I drove the car after that, and it ran great, with the choke out. It surged once while driving (like it would cut out and buck for some reason) but didn't do it again after that until I drove the car home. I drove home a couple hours after that, and the car ran like crap again. I pulled the choke to help it warm up, and that made a difference, but when it warmed up and I took the choke out, the car tried to die, the idle would drop to 550 rpm's. What could cause this sporadic problem, and what would cause the carburetor to do nothing when adjusting the mixture nut?

I noticed that when I pull my choke and close it again, sometimes the throttle shafts (I believe they are called that, they are the things that the needles go down into) will be stuck. Is there a way to make it so that they slide easier?

Last question: my car liked to leak water into the cylinders on the last head, and I have a feeling this would cause it to run like crap, and I think I have narrowed it down to the head being the cause, hence the reason I bought a new head (old head leaked, second hand head given to me didn't leak as far as I saw, so I bought a new head), and I'm slightly afraid that the head may not have been the issue (but I believe it to be), so if water were leaking into one or more of the cylinders, could that cause the problem I am experiencing? I'll find out tomorrow if it's leaking, I'll pull the plugs and see if any water shoots out like it did with the old bad head.

Last edited by Fast240Z; 10-30-2005 at 08:19 PM.
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Old 10-30-2005, 08:00 PM
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correct me if I'm wrong, but in theory, if the engine was leaking water into the cylinders, the water level in the radiator would be down by a bit, right?

If this is true, the water in my radiator is the same as it was when I filled it up before I fired it for the first time this weekend, so therefore no water is leaking.
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