Leaking Zenith 32 NDIX

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Peter M. Zimmermann
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Leaking Zenith 32 NDIX

#1 Post by Peter M. Zimmermann » Thu Oct 31, 2019 5:52 pm

The '58 356A Super is running perfect. It starts OK, idles perfect, and accelerates well. Just went for a test drive, got back to the house, did my routine check, and found the right side carb going drip, drip, drip...from the throttle body shaft at the control rod end. What am I missing?

Pete Zimmermann

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Don Gale
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Re: Leaking Zenith 32 NDIX

#2 Post by Don Gale » Thu Oct 31, 2019 6:11 pm

Mine did that, only on the left side. In my case, the float valve didn't seal and the float bowl overflowed. Mine has an electric fuel pump as the main with the mechanical pump blanked off. On the level, the tank is higher than the carbs and it siphoned and overflowed the carb.

If that's what happened to yours, be sure to remove the sparkplugs and crank it to make sure you don't hydro-lock it. If yours still has the mechanical pump, that scenario is unlikely but perhaps if the fuel pump push rod is in an intermediate stroke, perhaps it could still happen(?). Your carb may have simply heat soaked after park and overflowed. In any case, err on the side of caution and remove the sparkplugs and crank it before starting until you can find the cause, maybe the float level was set a little too high on that side.

In my case, it was a full-on gusher, copious amounts of gas flowed out of the carb bowl vent, ran down the intake manifold, filled either #3 or #4 cyl, wept thru the valve guides, filled the valve cover and flowed out of the valve cover vent and onto the garage floor, huge puddle.

Regardless, get in the habit of closing the tank petcock when you park it.
1958 356A 1600 Super Sunroof Coupe
former 1966 Euro 912 Sunroof
former 1978 Intermeccanica Speedster w/'68 912

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Ron LaDow
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Re: Leaking Zenith 32 NDIX

#3 Post by Ron LaDow » Thu Oct 31, 2019 6:12 pm

The float valve is not shutting off for one reason or the other. Shut off the fuel at the tank valve and let the fuel evaporate out of the carb throttle bore.
Pull the plugs and turn the engine over with a wrench on the crank pulley bolt to make sure it isn't hydro-locked. Pull the dipstick and sniff for gas in the oil.
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www.precisionmatters.biz

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Don Gale
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Re: Leaking Zenith 32 NDIX

#4 Post by Don Gale » Thu Oct 31, 2019 6:17 pm

Could a cracked or pinhole in a mechanical fuel pump diaphram still function while running but let fuel siphon thru the pump when parked?
1958 356A 1600 Super Sunroof Coupe
former 1966 Euro 912 Sunroof
former 1978 Intermeccanica Speedster w/'68 912

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Peter M. Zimmermann
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Re: Leaking Zenith 32 NDIX

#5 Post by Peter M. Zimmermann » Thu Oct 31, 2019 8:28 pm

Hey, guys, thanks for the replies! I found Ron LaDow's fine article regarding Zenith carb leaks in the 3/4 2017 Registry magazine. I removed the needle/seat valve and found some bits of crud (a couple were 3mm across) in the passage that leads to the valve. All with a new gas tank, new petcock valve, new hoses, rebuilt pump and new filter. Maybe the crud came from the inside of the metal fuel line behind the shroud? I'm having difficulty thinking how some crud would cause a slight overflow, rather than a lower than correct fuel level, but I will figure this out.

Anyway, tomorrow I will blow that line out, remove the plugs and hand crank the engine a few times, put the carb back on, check the float level and start the car.

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Re: Leaking Zenith 32 NDIX

#6 Post by Martin Benade » Thu Oct 31, 2019 9:28 pm

Once the plugs are out it wouldn’t be hydrolocked any more. It’s a little messy but I’d crank it to blow out the maximum amount of fuel from the cylinders. Better than turning it with a wrench.

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Re: Leaking Zenith 32 NDIX

#7 Post by Don Gale » Thu Oct 31, 2019 9:54 pm

Martin Benade wrote:
Thu Oct 31, 2019 9:28 pm
Once the plugs are out it wouldn’t be hydrolocked any more. It’s a little messy but I’d crank it to blow out the maximum amount of fuel from the cylinders. Better than turning it with a wrench.
Yes, and disconnect the coil wire so you don't get an unexpected surprise.
1958 356A 1600 Super Sunroof Coupe
former 1966 Euro 912 Sunroof
former 1978 Intermeccanica Speedster w/'68 912

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Re: Leaking Zenith 32 NDIX

#8 Post by Martin Benade » Thu Oct 31, 2019 10:28 pm

That’s an important detail that I neglected.

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Peter M. Zimmermann
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Re: Leaking Zenith 32 NDIX

#9 Post by Peter M. Zimmermann » Fri Nov 01, 2019 11:33 am

LOL! Thanks, Martin. Those "details" are kinda important!

Ron, if you're reading this; I have a new needle & seat valve from a kit produced years ago. The body of the new valve is about 1mm longer than the one I just removed, and that one had two copper (brass?) washers under it. The new valve came in a sealed bag along with a fiber washer. Is there a reason to not simply try the new valve/washer and see where the float level ends up? The ball in the end of the new valve is a bit tighter than the ball in the old valve, which is probably to be expected. The ball's shaft in the new valve rides in a metal ring, while the old valve's ball shaft rides in what appears to be a non-metal, brown material.

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