Zenith 40 tin flooding- please help

tornik550 · 06-05-2016, 04:44 PM

I recently installed a pair of zenith carbs on a 2.7l. They are freshly rebuilt and I just removed the enrichment circuit. I have never used these carbs before. I installed them, and started the engine. It started up right away however the 4,5,6 bank didn't seem to be firing. I checked and one of the float bowls was flooding (left bowl in the picture). I would completely overflow. I switched the float valves from the two different bowls and I continued to have the same problem with the same bowl.

Considering that I am quite a novice with these carbs- can anyone shed some light on what might be causing this issue. Could I have messed something up with the enrichment circuit?

Any help or ideas would be greatly appreciated.

tornik550 · 06-05-2016, 04:45 PM

lrodri64 · 06-05-2016, 06:35 PM

Fuel pressure?

1QuickS · 06-05-2016, 08:01 PM

I see you have a float level gauge. You should first set float levels before starting and then once running verify they are still good. The Zeniths use the lower set of fuel level lines (three of them) and Webers use the top two. You will need to create shims to adjust height of needle valves to adjust fuel levels in the bowls.

Also, fuel pressure should be 3 to 4 pounds.

James Brown · James Brown's Garage

might want to disable the enrichment circuit to see if thats the culprit by turning in the big screw. along with checking the float level as noted above

Neffets · 06-05-2016, 11:01 PM

I have Zenith's as well. Mine overflowed because the copper crush ring was to hard. So it would pass the float valves and overflow the carbs. These were copper rings that came in a kit with different thickness. Solution was just to heat them up and cool them in oil to make them soft again.

tornik550 · 06-06-2016, 05:33 PM

So now I am extra frustrated. Here's the various things I have tried.

-checked fuel pressure. All ok. I have a pressure regulator attached and turned it down to 1.5 psi so see what would happen and I still had the issue.
-check float level- tried with several different sized shims- no changed. Even tried with no shims- no change.
-enrichment circuit is removed. Made sure mixture screw turned in all the way and none of the plugs are leaking.
-removed carb, removed needle valve- turned upside down, looked through the needle valve hole and both floats seem to be moving properly.
-removed all jets and completely cleaned the carb and all jets.
-I cannot say for sure however I do not believe that I am having leakage from between the carb body and the needle valve. I put a little bit of gas around it and the gas did not drain into the bowl.
-I have tried a few different needle valves and nothing changes. The other needle valves work fine in different float bowls.

Nothing has made any difference.

I am out of ideas. Anyone have an extra zenith 40 tin laying around?

James Brown · James Brown's Garage

with the top of the carb off and the floats hanging down, see if you can use a hose and blow in the fuel inlet and pushup the floats up and see if there seating/closing (air should stop)

1QuickS · 06:51 PM

Check all four floats, simultaneously in gas to see if there is an issue with buoyancy. Also, compare floats to see if there is an obvious difference in geometry. Changing shims should result in demonstrable results on the float gauge.

Compare your 123 top cover side with 456 & look for physical differences in geometry. Hold top covers upside down which replicates fuel pressure on floats.

You can also swap 123 side top cover with 456 side to see if problem follows the top cover.

lrodri64 · 06-13-2016, 03:08 AM

I had a similar situation and yesterday a fuel pressure regulator was installed.
In my case the condition was corrected.
Also, my idle was very high (1500rpm) and after the regulator now is at 1200 rpm. (Don't ask me why, have no idea)
I'm using a carter fuel pump but I don't know which model. But sure it is for carburators.

al lkosmal · 06-13-2016, 06:42 AM

It sounds like your float is not making contact with the float valve. Are the floats, in the float bowl that is flooding, actually actuating/contacting the float level valve? You've swapped out the valves and changed shimming, etc.... but how about the floats in that bowl? Verify that the float makes contact with the valve.

regards,
al