I should have also said I disconnected the 12V to the choke so it is inoperative.

My original carb did not have the anti diesel cutoff, nor did the replacement. I believe that was for 1972 model only. It does not have any of the other add ons you mentioned. Yes. as mentioned previously all jets and bleeds are correct per the spec sheet.

Yesterday, I disconnected the throttle link arm to the auto choke and rotated the choke housing so the choke was just fully closed. Started the engine and the unloader opened the choke to the recommended opening. The engine now runs great at idle and high speed with choke about 90% closed. So I guess I will leave it that way for now. Not sure how the engine would performed using the power, accelerator, or secondary mode but since I don't need that it won't matter. As I said earlier the engine only needs to idle or mid throttle for working the 8000 lb. winch and the 2 gpm hydraulic pump.

Agreed. Have you checked to see which jets are actually in the carburetor?


> Now that the engine runs smooth at idle should show no vac leaks.

A common thought but not entirely accurate. Vacuum leaks can occur above idle. Besides the two diaphragms you mentioned (advance and choke unloader) there are even more on some A12s including EGR, spark control, heated air cleaner, throttle opener, brake booster, altitude compensator, etc.

Being as your engine is not powering a car, it may not have some of those.

I've already checked the vacuum advance line. I sucked on the hose going to the distributor and the advance works and holds. No leaks. Did the same to the choke unloader dash pot and it moves and holds. No leaks. Now that the engine runs smooth at idle should show no vac leaks. There are five functions to a carburetor. Idle, above idle to max throttle, power, accelerator pump and choke. Something is screwey when an engine idles but needs 90% choke to run above idle.

Too little fuel causes lean. But more common is too much air.

If there is an air leak, it causes the air/fuel mixture to go lean. Check all the hoses, especially the one to the distributor (plug it, it, will run OK with it plugged).

It warmed up today so installed the carb on the engine. After it warmed up I got the engine to idle real good. But when I advanced the throttle to fast idle or higher the engine will start to miss and stall. If I close the choke to about 90-95% it runs OK. So the fuel mixture is too lean. Same problem as before with the original carb. The fuel level in the sight glass stays right on the dot during this time so the carb is not starved for fuel, I'm at a loss. I could install a larger primary main jet and see what happens.

$30 good deal for a clean rebuild able carb. My only advice is check for radial play of the throttle shafts - there should be none. If they are loose it wreaks havoc with low-throttle air/fuel mixture.

Thanks guys. I found a used carb on ebay, same model as mine for $30. I carefully disassembled it and compared the jet sizes, air bleeds etc. against what should be in there for a standard 1972 production A12 engine. All jets and bleeds matched against the chart you provided. Cleaned and blew out all passages. The accelerator pump check ball was missing and the choke unloader unit diaphragm was ruptured so used my old one that was good. While turned upside-down the primary emulsion tube fell out. Good deal. All holes were clean. The secondary tube wouldn't come out so figured it was OK. The secondary part of the carb is never used anyway as I never run the engine RPM high enough for it to open Installed a new carb kit and is now all reassembled. Waiting for zero degree weather to go away before I install on the engine and check it out. I don't use my windmill boom truck during the winter so it's parked in the non heated part of my building. I am using a electric fuel pump that I originally installed 14 years ago. It keeps the fuel level in the sight glass right on the center dot. I checked the fuel pressure at the carb inlet anyway after starting to have problems to see what it was doing and it was 2-3 psi.

my primary main jet is 97 my secondary main jet is 145.
The emulsion tubes should come out easily. My carb sat for 15 years, it does not seem as good as it used to be but it works.
You gave an excellent description of it in your post, sounds too lean. It is more common for jets to clog than the much larger passages, but nothing is impossible. I have had to remove lead plugs and drill out clogged passages on Webbers
Not hard to do. Fishing line shot weights can be used to plug the access holes again.

The jetting is only correct for a 1200 carb.

Most DCH-306 have larger venturis so technically require larger jets when used on a 1200. But in practice they usually work OK with factory jetting.

See Carburetor Specifications and Jets.