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ZS Question for 76 1500 midget

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My magic 8-ball still thinks you're running rich because of the carb, and flooding the engine when its warm. Definitely pull the plugs and check. When you rebuilt the carb, did you replace the jet as well as the needle? Zenith needles are spring-loaded and run against the side of the jet, which can run the jet oval over the years.

Is your float valve leaky, or the float porous, or set incorrectly? The fuel level will then be too high in the bowl, and the jet will always push too much fuel through.

Is the butterfly rod loose in the bushings? If so, it may be the source of a vacuum leak that drives the Zenith richer.

And the big question: are you running the original air cleaner? Zeniths are calibrated to take the restriction of the air cleaner into account. If you use low-restriction, high-flow air filters, it'll "fool" the carb into running too rich.

It's true that most problems that look like fuel are really electrical, but if your electrics are in good nick, there're a lot of Z/S issues that can be caused by vacuum leaks. All the small leaks are additive, and they all have the same result: drive the system richer.
 
I will pull the plugs and check. In the meantime, I did replace the jet as well as the needle. porous float and float valve leak, don't know until I tear the carb apart again. Set incorrectly, not unless it's changed itself for some reason. Butterfly rod was good at the time of rebuild. Yes, original air cleaner still intact and filter is good although I think I'll replace it this week anyway. I tried new fuel filters but no luck. I just a few minutes ago tried to lean out the mixture just a slight bit and now it's running worse, so I think that was ok. I'll pull plugs and replace since I was gonna do that anyway, and advise.
Thanks!
Jeff
 
OK, I pulled the plugs and they are all equally dry, sooty, and black. Looks like carbon buildup. Haynes manual says rich mixture or ignition problem. Maybe it's just time for new plugs. Guess I'll do a compression check too while I've got the plugs out. I'm using AC/Delco R44XLS plugs. Thats what all the books at the auto parts store specified. Should I be going a little hotter? Any recommendations from other 1976 1500 owners?
Thanks!
Jeff
 
Compression test revealed #1@155, #2@120, #3@125 and #4@125. Is one high cylinder an indication of a bad exhaust valve or are 2, 3 and 4 low? I can't find any specs that say what compression should be? Does anyone else know on a 1500?
thanks!
Jeff
 
I'd say #155 is about right. Low compression could be a whole slew of things. I would run some Sea Foam through the intake and see if that doesn't bring your numbers up. After that, you can squirt oil into each plug hole and see if that does not bring your numbers up. If your compression comes up after squirting oil, the problem is likely your rings. If not It's likely your valves... or a blown head gasket, which in my experience is super common on 1500s.
 
I moved the compression test questions to a new post but am still wondering if these AC/Delco R44XLS are the correct plugs or if I should go hotter.
 
"90% of all carburetor problems are electrical"

Bill asked earlier about your electrical system. When the problem occurs have you checked to see that you have good spark? If you are still running an original OPUS electronic ignition, or aftermarket replacement for that matter, you may be having issues there or with the coil. Might save you a lot of fiddling to run it a couple miles, bring it home and see if you can reproduce the problem in the driveway. Then you can check for spark and either confirm or eliminate that as a problem.

It's not LBC but I offer up my kids '88 tbird as an example. The car would just die at random intervals. Short drives, long drive, it didn't matter. It would just die and would take 10 to 30 minutes of sitting, and then it would start back up and run fine for a while. I traced it to a module internal to the distributor. Over the years they get out of spec and fail intermittently, progressing to total failure. I had to press the distributer apart to replace it.

Anyway, check for spark next time it fails, it can’t hurt and it may answer some questions.
 
Good point Rich. I had the same issue with an 80's era cavalier Z24. I am running pertronix ignition in an MG distributor. Only 2 years old but could definitely be a coil issue too. Plug wires are 2 years new as well. I have been doing exactly what you said. Going for a short drive around town which duplicates my trips to the store or the gas station, then arriving back home. Waiting a few minutes, as if I was gassing up, and then trying to start it again. Next time it happens I will check spark.
 
I always had trouble getting my spec'd plugs to not foul with my ZS. I switched over to Bosch Platinum+, and those guys will fire through anything. After I got the carb sorted, I kept running them, and they've worked great for me.
 
bthompson said:
I always had trouble getting my spec'd plugs to not foul with my ZS. I switched over to Bosch Platinum+, and those guys will fire through anything. After I got the carb sorted, I kept running them, and they've worked great for me.
Click to expand...

Likewise here, could never get the ZS right so swapped an SU HS4. In fairness, I wasn't using the original air cleaner and all the smog stuff was off.
 
I am using the original air cleaner. All my smog stuff was removed years ago by prev. owner. ZS Has always worked well for me, even after rebulid. This only began after I changed out ancient loud fuel pump for nice quiet new one.
I just went for a short drive and came home. Waited a few minutes and then tried to start it. Would not start so I checked spark and have a good one. So not a spark or ignition issue. I'm back to either carb or fuel pump. Next I will do the seafoam cleanout and then we'll see. Gonna check my brand new plugs also and see if they immediately got fouled.
 
That definitely sounds like the common "pump is too powerful for your float" issue, then. Here's how it typically plays out:

1) You replace your old tired pump with a newer much more powerful one.
2) While your car is sitting, fuel evaporates out of the bowl, so on first start everything works fine.
3) You drive around, run inside a store for a quick errand, and when you come back out your car won't start. What is happening is that now your bowl is full. Even so, your new powerful pump pushes the float open and floods your carb.

The typical solution is to install an inline pressure regulator.
 
I think I will give it a try. Should it be mounted near the carb or near the pump? What should I dial it in to, 1 pound? Pump is supposed to pump between 2 and 3.5, guess I'll just experiment with it until it works.
Thanks!
 
Yep, I'll concede. As much as I love to blame Zenith-Strombergs for everything from rough running to flat tires, and hate them with a great bloody passion...it sounds like yours is in good shape. The old trick -- go back to the last thing you did before things started going wrong. And that was the pump. One pressure regulator later, voila.

Unless it IS the ZS... Viton-tipped float valve needle in the rebuild? Some say the viton needles are no good.
 
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