Re: Zenith 28g carburetor diagram FE35

Re-designing a carb, eh?
I believe that hole was there to prevent, theoretically, the engine from flooding with the fuel left on while not running.
If the engine is fluctuating in RPM with a solid throttle, then it is possible you have an internal problem.
I am quite sure that by now you have inspected the distributor to ensure the springs on the flyweights are not broken and
allowing the distributor to advance timing uncontrolled.
I am also quite sure that you have already also taken a can of carb cleaner and lightly sprayed around the intake gasket. Glad to
not read of your getting carb spray too close to the ignition wires while running. The resulting fire can be a problem.
With those checks done, and a varying RPM, then fuel delivery can be checked and you already did that also, right?
With all the checks you have already done, I am not sure what else to tell you.
You could do what it is that I have done and purchase a new machine, 30 hours on it now, and keep this old iron around just to toy with at
your leisure. No? There is also a possibility of picking up another carb, other than Zenith and seeing what it is you get for results.
After all, every time an engine has a problem, the first thing you do is adjust the carb. That mystery box has to be the answer.
No? Then consider yourself among a rare few.
This has been entertaining, as I sit here at the beginning of a 100 degree day at my end of the world.
Have you had it running and turned off the fuel flow to it while running? That is one old trick to dislodge debris from the float
circuit.
As a last resort, with the engine running, place your hand over the intake. Now the trick is to operate the throttle and try not to kill
the engine by flooding it but to bog it down at full throttle.
You will find the space between your fingers or the web of your hand to be the best way to do this.
If the engine stalled, pull the plugs, dry them off and do it again.
Again, isn't this fun?
Try it again.
Your getting the hang of it.
Try it again.
Once more.
Your getting there.
Again.
By now it's either fixed or you never will achieve the ability.
You should try it on an automotive engine.
A bit more suction.
Don't you wish there was a zipper kit on spark plugs?
How many times have you pulled them to dry them?

Sounds like a clogged idle/midrange circuit, maybe the throttle plate is misaligned or in backward,
worn throttle shaft, or vacuum leaks around the intake gasket or the carb flange gasket.

Also where the carb bowl meets the top housing, the surfaces bust be flat so the gasket seals around
the small passage where the idle/midrange fuel is drawn up. If the venturi is in upside down it will
warp the housings when the screws are tightened. It can be filed flat.

Does disconnecting the air cleaner tube make a difference? If it does, the filter mesh is clogged
and will need to come out and be cleaned or replaced.

Gentlemen, thank you for your helpful posts. After realising how far away I was from diagnosing let along fixing the problem I'm afraid I bought a new carb. The 28G is not available new in England but the 24T fits. Here is a pic of the undersides of the two, showing the sintered bronze plug in place in the new one. I installed the new carb and then had to make a new copper fuel line as the inlet is on the front edge of the 24T. That took a lot of careful bending before I could eliminate leaks at the gravity filter end. But in the end I was able to start it up and guess what - it worked pretty well. The hunting has stopped and it ran nicely at idle for maybe ten minutes before stopping and refusing to start again, but I think I will continue the story in the electrics section as whatever the problem is now it is not related to the 28G !