How to troubleshoot a carb float

[jmshepard]

I am having some flooding issues with a pair of Zenith 40TIN carbs. The pair just returned from a rebuild by a reliable mechanic. Upon installation the pair are flooding. Each carb has one bowl that overflows. The PMO fuel pressure regulator is reading 3 PSI although a cheap FP gauge indicates 5 PSI. I removed the single washer under the needle valves and swapped the valves between floats. The same bowl floods. I think I have narrowed this down to the floats. How do I insure that they are free and clear in the bowls?
Thanks,
Jim S.

Also, the PMO valve is fully down and the regulator is still allowing fuel to the carbs. Is this the way this device operates?

[Gogar]

pull the float out and make sure it "floats" in a little bowl of gas. It could have a little crack or hole in it that will render it totally useless no matter how clean or perfect everything else is.

[jmshepard]

thanks

[austin552]

Remove #5, #7 and you can stick a long bolt down the hole to see if the float moves freely in the bowl.




Here is the manual:
Zenith 40 TIN Carburetor Manual

[James Brown]

Do you have the littke glass sight gage to check the float level? It screws in the fuel bowl drain plug. This should have been done by the rebuld shop. take them back and have them check them. If you can't, you must do it yourself. also, check the float needle valves to make sure they close when the float moves up. The floats are foam and can get saturated if damaged over time. You can try to add a fiber washer under the needle valve and see if that helps but they should be set by the shop that rebult them. fuel bowl settig is critical in a zenith.

[jmshepard]

Gogar-Just finished checking the floats in a bowl of fuel. The suspect float looked to be as buoyant as a "working" float.

A552-I'll check the float response through the needle valve hole.

JB-I have removed the single washer from the needle valve. I thought this should lower the fuel level. Not ready for the float bowl gauge yet. Fuel is coming though the bowl vent tube.

Thanks

[James Brown]

you have to have the gauge to set the floats.

[jmshepard]

JB-I have the float gauge and the vial for the accel pump.

I can report success on one of the carbs. I removed the needle valve and used a straight pick to push on the float. It did not move. The good float had some give when pushed. Clearly the flooded side float was stuck. I removed the top plate and ran a piece of thread through the needle valve hole and looped it around the float. I reinstalled the top plate. I tugged on the thread and sure enough the float didn't move. A slight jerk on the thread freed the float. Pulled on one end of the thread and removed it from the bowl. A quick test with fuel pressure reveals no more flooding. On to the next carb.

Might be a good idea to reassemble the carbs with the thread in place to avoid this in the future.

Jim S.

[James Brown]

great job on troubleshooting!!! If you have the top off, you can move the floats up and down and see where they stick. They should move with almost no pressure. Did the carbs sit for a long time after they were rebult? It always is sad to fix things after a "reliable mechanic" rebuilds things. The god news is you are now about 60% schooled on how to rebuld your own Zeniths! They really are simple to work on and it only costs a gasket kit to rebuld! Great info (with pics!) on how to do the overhaul on this BB. Could save you some coin in the future. How much was the rebuild if you don't mind me asking?