Troubleshooting a flooding Zenith Carburator
 

Hi all,

The Zeniths on my 2.4 T (1973)has been recently rebuilt (very few miles since the date) but i still have a quite constant random poppping through exhausts and from intakes (mainly on idle or on decel).

Timing is OK and in spec, not the same for carburators fuel float levels.

Right carburator seems ok because float level is exactly beetween the two lower lines (with engine off and with engine idling)

http://forums.pelicanparts.com/uploa...1517270621.jpg


Left bank seems to be the beast... When I plug the gauge tool and turn the ignition on the level start to rise up to the lower mark and then, VERY SLOWLY!!, it continues to rise up until 1 mm over the higher float gauge mark (the higher mark is for Webers).


http://forums.pelicanparts.com/uploa...1517270621.jpg


I thought it was a worn needle valve pair on the left carburator so I've replaced them without fixing the problem.
I've also tryed adding/removing shims under the needle valve without success.

Can anyone help ?

I've just ordered a fuel pressure meter even if I'm running with an original Pierburg fuel pump so I think fuel pressure has to be in specs ... wrong assumption ?
(If fuel pressure was too high don't I have to see left and right carbs flooding ... why only one ?)


Exept of fuel pressure what else to check ?


NOTE: After removing the top carburator cover i've found fuel in carburator top recesses: is this normal ?

http://forums.pelicanparts.com/uploa...1517270621.jpg

I’m not an expert by any means but I fixed that same condition with a
Holley fuel pressure regulator.
Don’t remember which model.

Have you noticed if fuel comes out of the float bowl vent tubes? I had a similar problem when I rebuilt my Zeniths last spring except that the flow never stopped. Turns out a float was getting stuck on one of the ridges on the bottom of the bowl (see black particles on the bottom of the bowl). I rounded off the corner that was getting stuck with a soldering iron and the float was free to rise and turn off the flow.http://forums.pelicanparts.com/uploa...1517274071.jpg
http://forums.pelicanparts.com/uploa...1517274071.jpg
http://forums.pelicanparts.com/uploa...1517274071.jpg

No fuel do not spill out.
What is strange is that just one carb has a float level higher and the other carb seems ok.

Also what leaves me stranded is seeing fuel in carb recesses (as in previously posted photo).

Anyway I'll check pressure and if higher than 3.5 PSI (as per spec) I'll add a pressure regulator.
As suggested from lrodri64 Holley's regulator do not seems invasive and it should be available trough out host.

float level
 

The float level is adjusted for each carburetor bank independently as described below. Thee are shims/rings that are installed under the float needle valve assembly that raise/lower the float/fuel level depending on the number of shims used.



http://forums.pelicanparts.com/uploa...1517379890.JPG


regards,
al

Dear Pelicans,
Here is the thread follow-up.

Jesterday I received my fuel pressure meter and after hooking it up at the carb inlet I read 3,86 PSI.
If I remember well fuel pressure measured at carb inlet should be 3.55 PSI.

So I have about 10% more pressure over specs... It seems time to buy a FPR.

you have the same pressure to both carbs...one float level is ok, one is not.....change the float level on the one that is too high.

regards,
al

al lkosmal,
thank you for your reply.

I've already tried to change float level (on Zeniths its done by adding/removing shims) but this hasn't fixed the problem. (Also tryed with no shims at all).

Float needle valves are new.

When I activate the fuel pump (ignition on) I see fuel level raising up in the gauge very quickly (from level 0 to the lower lines in approx 1-2 seconds), if I leave full pump on the fuel level slowly rises up... (1 min).
This behavior let me think to a "valve leaking" problem, after replacing valves with new ones the problem persist so probably valve leaks because of too pressure.

Do not seems reasonable ?

P.S. I also should consider that with engine idling I probably I'll read higher pressure due to alternator supplying power instead of just on batteries.

I do not think that your pressure is too high, but i do think that perhaps the one valve is not closing completely due to the float level not being adjusted. try adjusting the float level on the high one to see if it fixes your problem. Easy fix, if it works.