Kohler Courage Choke Issue

[Cobrargc]

I've got a Kohler Courage XT173-0084 on a walk behind mower. I've had trouble lately with cold and hot starts. The engine choke appears to be controlled by a bi-metal spring on the muffler and assisted by a vacuum diaphragm that pulls vacuum out of the carb. I'm not sure how to diagnose which is bad. The diaphragm rod moves in and out as I apply vacuum to it. Is the carb plugged and not providing enough vacuum to operate the diaphragm? Is the bi-metal choke defective? What is most likely the cause of the choke issue.

One thing for sure is that the choke isn’t coming off as soon as it should once started and it is causing the engine to run rough and rich, which is fouling the plug. If I manually open the choke with a screw driver the engine picks up RPM and runs well.

Thanks in advance

[KE4AVB]

A few tests needs to done.

Disconnect the vacuum hose and attach vacuum gauge to the carburetor hose connector. Now start the engine. You should have minimum of 15" of vacuum. If less than that then you an issue not related to the choke system itself.

If you 15" or more at the carburetor then do a vacuum test on the diaphragm valve assembly. Choke plate should open 1/2 to 3/4 under vacuum and with a minimum of 15" of vacuum. If diaphragm assembly is unable to open choke plate, check hose for cracks, leaks, or restrictions. If necessary replace vacuum hose. If hose is in working condition and choke plate fails to open with specified vacuum, or diaphragm fails to hold choke plate open for a minimum of 3 seconds, replace diaphragm assembly.

Attach vacuum hose to carburetor vacuum fitting. Start engine. Upon start up choke plate should be 1/2 to 3/4 open. Choke plate should gradually change to full open position after 2 to 2-1/2 minutes of running. This action is performed by bimetallic spring assembly being heated. If choke plate fails to open, recheck linkage for binding. If necessary replace bimetallic spring assembly.

[Cobrargc]

Is this 15" Hg? The manual measures in inches of water. I'm only getting about 2" Hg of vacuum. If this is too low, does this indicate a plugged carb? The mower runs fine once off choke. The linkage looks fine. I'm going to have to let the engine cool down before I can check the diaphragm.

Should it take that long to come off choke? The plug was fouled and taking 2 1/2 minutes to come off choke would foul the plug, correct? This thing just spits and sputters until it finally does come off choke.

[KE4AVB]

Is this 15" Hg? The manual measures in inches of water. I'm only getting about 2" Hg of vacuum. If this is too low, does this indicate a plugged carb? The mower runs fine once off choke. The linkage looks fine. I'm going to have to let the engine cool down before I can check the diaphragm.

Should it take that long to come off choke? The plug was fouled and taking 2 1/2 minutes to come off choke would foul the plug, correct? This thing just spits and sputters until it finally does come off choke.

Hg is inches of mercury. When 2" Hg is converted to inches of water it is approx. 27.19" so you have plenty of vacuum. Just check the the diaphragm as noted. When testing the diaphragm is must hold the choke position at 1/2 to 3/4 way open before heat is applied to bimetal spring. When vacuum is applied it must hold this position for at least three seconds or it is leaky. If it works correctly then replace bi metal spring in the system which sounds like you problem.

[Cobrargc]

Thanks KE4AVB

[Cobrargc]

A new carb, bimetal spring and diaphragm and it runs flawlessly. My son took it home and brought it back a few days later and said it wouldn't start when hot. It was cooled off whan I got it so I cut most of my lawn and it ran well. When I intentionally stopped the mower, it would not restart. I checked to see if the coil was firing and it was not. Then I noticed the bracket for the engine bale micro switch was bent and not allowing the cable to come back far enough. The bracket was bent straight again and it runs great. It does appear to be rebending itself once again and will no doubt fail.

[KE4AVB]

Cobrargc, That might take a little engineering on your part to stiffen that area. Here I would weld an add piece of metal but I am experience in the art metal fabrication as I use to repair typewriters, mechancial calculators and check writers where parts were NLA.

[Cobrargc]

Thanks