Zenith 32s Leaking from Throttle Spindle

356 Porsche-related discussions and questions.
Message
Author
User avatar
Greg Dumond
356 Fan
Posts: 244
Joined: Fri Nov 22, 2013 5:39 pm

Zenith 32s Leaking from Throttle Spindle

#1 Post by Greg Dumond »

Hey Guys I'm hoping someone can give me direction on the problem of why I'm having fuel seeping out of the side of the carbs at the end of throttle spindle. I recently had both Carbs professionally restored but I started noticing fuel building up around the throttle body and working its way down to the manifolds. I asked my mechanic who rebuilt the carbs and he said that these carbs are supposed to sweat a little.

However these carbs are doing a lot more that sweating! I finally figured out where the source of leaking is coming from. I was able to stuff a piece of cotton just underneath and behind the throttle lever spindle nut. The cotton absorbs the fuel successfully and no fuel is spreading while the cotton is in place.

The basic scenario that I have been using to test the timeline when the leaking starts is this. I'll run the car then park it for several days. Obviously there is no fuel leaking while the car is running. Then it's parked for the week without running the motor. The first day after, there is very little evidence of fuel. Then as the days go on 2nd 3rd 4th etc. the fuel keeps expelling out the side of where the cotton is stuffed behind the throttle spindle. When I take the cotton out the fuel once again starts seeping out around the throttle base and down onto the manifolds. What is going on? By the way the float levels are set at 18 to 18.5mm

User avatar
Ron LaDow
356 Fan
Posts: 8092
Joined: Wed Mar 26, 2008 11:45 am
Location: San Francisco

Re: Zenith 32s Leaking from Throttle Spindle

#2 Post by Ron LaDow »

Your fuel level is too high.
1) The floats are now "sinks"; check for leakage into them.
2) The float level was incorrectly adjusted.
3) The float valve is faulty.
4) The float valve has dirt in it, preventing it from closing.
5) Shim washer/valve seating surface has a scratch.
There is no other passage from the float bowls to the throttle bores other than overflowing probably at the base of the auxiliary venturies.
Edit: Add #4, correct spelling.
Edit: Add #5.
Last edited by Ron LaDow on Fri Sep 09, 2016 8:10 pm, edited 2 times in total.
Ron LaDow
www.precisionmatters.biz

User avatar
John Brooks
356 Fan
Posts: 2146
Joined: Tue Jul 08, 2008 11:50 am
Location: Whidbey Island WA.
Contact:

Re: Zenith 32s Leaking from Throttle Spindle

#3 Post by John Brooks »

I agree. Check the float level
John Brooks

62 Roadster
66 912
84 Cab
getting pushed around in porsches since 1965

User avatar
Greg Dumond
356 Fan
Posts: 244
Joined: Fri Nov 22, 2013 5:39 pm

Re: Zenith 32s Leaking from Throttle Spindle

#4 Post by Greg Dumond »

Ron, thank you for the check list. I'll pass this on to my 356 mechanic to go through these items. Could a faulty needle and seat be another item to have checked?

User avatar
Ron LaDow
356 Fan
Posts: 8092
Joined: Wed Mar 26, 2008 11:45 am
Location: San Francisco

Re: Zenith 32s Leaking from Throttle Spindle

#5 Post by Ron LaDow »

GregDumond wrote:Ron, thank you for the check list. I'll pass this on to my 356 mechanic to go through these items. Could a faulty needle and seat be another item to have checked?
Greg, good point; see added #5.
Believe me, gasoline is remarkable in its ability to find some tiny passage and then leak through it. If your wrench is good, s/he won't be using the static test since taking the top off tells you where the fuel level it right then; it does not tell you that it has stabilized at that level.
But regardless, that bowl is overfilling as a result of some problem or other, since there are no passage ways from below the fuel level to the throttle barrels.
Ron LaDow
www.precisionmatters.biz

User avatar
Greg Dumond
356 Fan
Posts: 244
Joined: Fri Nov 22, 2013 5:39 pm

Re: Zenith 32s Leaking from Throttle Spindle

#6 Post by Greg Dumond »

Ron, yes pinpointing the origination point where the fuel was seeping was a tough undertaking. Asking enough pros like yourself gave me enough direction to start the process of elimination.

Another Carb re builder also suggested that I might need to replace the Throttle Bases. The thinking is if the shafts are loose and allow excess fuel squirting from the accelerator pump to hit the Butterflies and then seeps its way through the shaft bores could also be the problem. They mentioned that during the rebuilding process the bores may have increased a bit?

However as you say there are no passage ways from below the fuel level to the throttle barrels. Since I have been absorbing the fuel with cotton for a few days at a time and then pulling out the cotton the fuel continues to leak. Based on this wouldn't the theory of replacing the throttle bases be a waste of time or could there be enough residual fuel on the shaft and in the bores to keep leaking for days? Doesn't seem likely to me.

User avatar
Ron LaDow
356 Fan
Posts: 8092
Joined: Wed Mar 26, 2008 11:45 am
Location: San Francisco

Re: Zenith 32s Leaking from Throttle Spindle

#7 Post by Ron LaDow »

GregDumond wrote:Another Carb re builder also suggested that I might need to replace the Throttle Bases. The thinking is if the shafts are loose and allow excess fuel squirting from the accelerator pump to hit the Butterflies and then seeps its way through the shaft bores could also be the problem.
Accel pumps tend to function on opening the throttles and the discharge doesn't last long; I can't say for sure, but I'm guessing most of that ends up in the chamber.
Regarding the throttle bores, here's an early iteration of some test tooling:
This is a close up of the tooling:
002.JPG
This is a 'leak-down' timed test before I scribed the lines:
tb_tool (2).jpg
It was presumed that *IF* the throttle stop screws could be backed out and that caused engine stalling, leakage past the shaft bores was irrelevant. Dyno-testing a series of throttle bodies said that a 20-second leak-down on that tool (after it was scribed) meant the TB was good.
Zeniths have a chrome-plated brass shaft running in a LOOONG cast iron bore; some engineer spec'd that in the late '40s and went home happy that night. Those are gonna wear out right after the Pyramids. Typically, one of 15 or so tested bad. And those tended to be obvious; you could rattle the shaft in the bore and wake the dog.
Ron LaDow
www.precisionmatters.biz

User avatar
Greg Dumond
356 Fan
Posts: 244
Joined: Fri Nov 22, 2013 5:39 pm

Re: Zenith 32s Leaking from Throttle Spindle

#8 Post by Greg Dumond »

Ron thanks for sharing your test research. Looks like I can take the Throttle bases out of the equation. I feel better knowing that they will last longer than the Pyramids!!!

User avatar
Larry Coreth
356 Fan
Posts: 1930
Joined: Sun Apr 20, 2008 12:48 pm
Location: NE N.CAROLINA

Re: Zenith 32s Leaking from Throttle Spindle

#9 Post by Larry Coreth »

Greg,

As Ron said the only way to get fuel to the throttle plate area is through the float bowels. So any wear of the throttle bodies/shaft is irrelevant, i.e. the proverbial "red herring" ! I suggest any mechanic who tells you that the throttle shaft body interface is the source, obviously does not understand carburetors well.
So as a temporary fix turn the fuel cock to off ("Zu") when parked. This will at least limit the volume of leakage. This is a good idea regardless as the fuel tank is above the level of the carbs when full to 1/3 full which means that fuel will flow by gravity to the float valve even when parked with motor off.
Attachments
Fuel Tank Level.jpg
Larry Coreth
Roanoake Rapids, NC

User avatar
Greg Dumond
356 Fan
Posts: 244
Joined: Fri Nov 22, 2013 5:39 pm

Re: Zenith 32s Leaking from Throttle Spindle

#10 Post by Greg Dumond »

Larry thank you for your input and seconding the notion that the throttle bodies/shafts are not the problem. Also your suggestion is well noted, I will get in the habit of turning the fuel cock to the off position as a precaution. In the meantime hopefully my frustration will end soon once the problem has been correctly diagnosed and finally fixed!

User avatar
Wil Mittelbach
356 Fan
Posts: 1019
Joined: Sun Apr 13, 2008 8:58 pm
Location: Huntington Beach, CA

Re: Zenith 32s Leaking from Throttle Spindle

#11 Post by Wil Mittelbach »

Re. Larry's response -
++100%

User avatar
Mervyn Hyde
356 Fan
Posts: 797
Joined: Wed Nov 25, 2015 9:12 pm
Location: Sunshine Coast Australia

Re: Zenith 32s Leaking from Throttle Spindle

#12 Post by Mervyn Hyde »

I have a slight weep as shown in the image below. The float levels are correct, even a little lower than normal (using the Pre Mat gauge), jets correct, the carbs are clean, throttle shaft is good with correct end-play, all mating surfaces flat and clean and the carb runs fine. I just get this annoying little weep in the area shown. I turn off the fuel cock after running and that minimises the effect anyway. It just annoys me ...

The fuel 'appears' to migrate from the throttle plate area below. I could try my old trick of cleaning and drying the area and then puffing a little Johnsons Baby Powder on the area to see where the weep starts.

Could there be a small crack in the lower body of the carb there?
Attachments
Carb Weep.png
Merv
TYP356
1963 356B T6
1968 911 SWB

User avatar
Larry Coreth
356 Fan
Posts: 1930
Joined: Sun Apr 20, 2008 12:48 pm
Location: NE N.CAROLINA

Re: Zenith 32s Leaking from Throttle Spindle

#13 Post by Larry Coreth »

Mervyn,

The leak appears to be coming from a factory plug which has after 50 years has begun to leak. Shocking !
The throttle body could not be an influence as this would require the fuel to run up hill !! Not likely
You could get a new plug pressed in, or seal with RTV or such, even temporarily to see if it leaks elsewhere.
Larry Coreth
Roanoake Rapids, NC

User avatar
Mervyn Hyde
356 Fan
Posts: 797
Joined: Wed Nov 25, 2015 9:12 pm
Location: Sunshine Coast Australia

Re: Zenith 32s Leaking from Throttle Spindle

#14 Post by Mervyn Hyde »

Thanks Larry. I am stumped on this one. I may pull the carb again. I had it on the test bench for some time filled with mineral spirits and with some puffs of talcum powder on the outside area affected and seemed to manage no wet spots eventually. It may be that inserted plug. I have not heard of that one.

Fuel can migrate in lots of interesting ways.
Merv
TYP356
1963 356B T6
1968 911 SWB

Dick Weiss
356 Fan
Posts: 4181
Joined: Sun Apr 20, 2008 12:54 am

Re: Zenith 32s Leaking from Throttle Spindle

#15 Post by Dick Weiss »

Either carb series rely on fuel pressure being w/in 2.5 to 2.8PSI or NOT exceeding 3! If you have an electric pump w/o a regulator, you may get 6PSI! Also, after a drive & turning off the engine, the fuel will slightly expand due to rising heat thru the carb(s) if the float levels are on the high side even if you shut off the petcock--better to do that about a 1/4 mile before parking (or garage) to lower the float level & lessen 'spill-over'.

Post Reply