Ford 850 TSX593 Carb

ErnieChilton

New User
I am restoring a 1955 Ford 850 and have completely rebuilt engine. The TSX593 carb was very rusty on the inside and I soaked it in rust remover and cleaned as best I could and installed a complete rebuild kit, but could not get the float seat and idle jet out. Cleaned the idle jet with a small wire and put a new float needle in. Reassembled the carb and checked to make sure the new needle/old float seat was shutting off fuel supply. Timed the engine at 5 BTDC statically and started the engine, ran fine but could not get to idle below 1100 rpm. Turning idle screw in/out had no effect. Replaced the carb with a new Zenith 13877. After starting, engine ran very rich (very black smoke out the exhaust) and runs roughly for about 10 sec, then quits. Check float level and OK. Idle adjust had no effect. This carb uses a fixed main jet so nothing to adjust there. So I put original TSX593 back now it runs rich, JUST LIKE THE Zenith!!!!! Now I cannot get it to run at 1100 rpm as before I removed it. Not flooding since no fuel puddles in bottom of carb.

I am completely baffled. Timing checks OK, good spark on all plugs, compression at 125psi on all cylinders. I am now grasping at straws. Can anyone offer a few more "straws" for me to grasp?
 
Linkage problem can cause some of that and also the throttle stop screw on the linkage can cause it not to idle down lower. Also a manifold leak form changing carbs out can cause odd problems
 
First, let's go for the very basics. Make sure the choke linkage is right and working properly. If you are running with the air filter connected, be sure it is free of restriction, like a clogged mesh, or a rag left inside. Don't be offended, stranger things have happened! LOL

Since the carb won't idle down, look carefully at the throttle plate. Possibly it is bent, or loose, installed backward, or misaligned with the bore. The edge of the plate is machined at an angle. That angle will match the bore perfectly, and with the idle stop screw backed off, it should male an air tight seal. If it doesn't seal, loosen the screws and center the plate so it closes completely.

Looking at the upper edge of the throttle plate, where it closes against side of the bore, there will be 2 tiny holes. The upper one is the idle port, the lower one is the mid-range port. With the throttle plate closed, the edge of the plate must rest between the 2 holes. If not, it is bent, mis adjusted, or the wrong plate.

With the bowl off the carb, looking at the idle circuit, there are 2 jets. One is the tiny jet down in the bowl, that is the liquid fuel drawn up by vacuum to the small hole beside the throttle plate. On it's way up, the liquid fuel passes by an air bleed jet, up underneath the top cover. Be sure that jet is clean and free. Also incorporated in that circuit is the idle mixture screw. Unlike most modern carbs, the idle mix works backward. Turning it IN richens the mix by restricting the air bleed jet. Backing it OUT feeds more air, and leans it.

With the upper cover upside down, the float should rest parallel to the gasket surface. If set too high the mixture will run rich, even if it's not overflowing the bowl. Also give the float the "shake" test, listen for fuel inside.

Another thing to check on the idle speed adjustment is the length of the governor link. If it's adjusted too short, the governor will run out of travel before the throttle is pushed closed. Might try carefully starting it up with the governor linkage disconnected, operating the throttle by hand. Just be very careful not to have a runaway!

I found this, it's not for your exact model, but close.

http://www.zucksrototillers.com/ZenithCarbAdjustments.pdf

Let us know what you find!
 
My first thought when you said you could not get the idle down was a vacuum leak.
The poor running with 2 different carbs has me thinking you my have a valve set too tight.
Might want to see if the plugs are dry and clean before digging too deep.
 

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