Kawasaki misfire under load

[theoldwizard1]

Helping my buddy with remote diagnosis. He has an older (20 yo?) Bobcat (painted green if that means anything) ZTR with a Kawasaki engine. Sorry, no specific model numbers. About a year ago it started to occasionally misfire. Now it is a lot more frequent, but only under load (blades or drive wheels engaged). My guess is that it is a lean misfire and the soot is from the unburned mixture, but I could be wrong (why would only one cylinder be running rich and only under load?)

Compression is good in both cylinder (145, 165).

The misfiring cylinder has a very sooty (but new) plug. It also has a new coil/magneto (what is the correct gap or is the business card trick adequate?) The Nikki carb has been disassembled and cleaned more than once (no ultrasonic cleaner available). Last, he checked all of the gaskets from the carb to the cylinder head for leaks using propane.

 

[sgkent]

swap the plugs and see if the problem changes sides.

 

[txmowman]

The compression is likely high. Has the valves been adjusted? If the spark plugs are sooty, this indicated a rich run condition.

 

[theoldwizard1]

The compression is likely high. Has the valves been adjusted? If the spark plugs are sooty, this indicated a rich run condition.

I would say 145-165 is high compression ! Some how we missed valve adjustment ! Hopefully today !!

Do you know the correct setting ?

 

[txmowman]

There is no "correct" setting with compression. On this engine, closer to 100 psi would be more typical. If the valve lash is properly set to around .005", and "your" gauge shows 145+, then thats what it is. If you have or know someone with another gauge, see what that one shows.

 

[slomo]

My thought was a dirty carb. Also dump the fuel tank and super clean it out.

 

[txmowman]

Agree 100%, slomo. There are few good reasons to 'replace' a carburetor.

 

[theoldwizard1]

Agree 100%, slomo. There are few good reasons to 'replace' a carburetor.

Not my money, but my friend order a new non-OEM carb from Amazon. Sigh.

 

[slomo]

To do list.

1.Boil clean the carb and clean out fuel tank.
2.Valve adjustment - yearly for a good running engine. Only takes a few minutes.
3.Clean block and cooling fins - yearly or more often if you bag. Engine damage alert if neglected.
4.New fuel lines, shutoff valve and paper filter probably wouldn't hurt.
5.Verify carb linkages and choke are proper per service manual.
6.Spray wd-40 around intake pipes and carb looking for vacuum leaks.
7.Test for strong spark. Used plug gapped to 1/4". Should have nice blue spark.
8.Verify the cooling fins on the flywheel are all present. Some of these fins are plastic and seen them broke off. Leads to overheats and sticking valves.

 

[slomo]

Not my money, but my friend order a new non-OEM carb from Amazon. Sigh.

Okay not too much money. Not a fan of Chinese carbs. Some actually work but not recommended on most. If parts are gone, gotta do what you can.

Clean the OEM in a yard sale crock pot at 200F. Simple dishwasher pod soap deal and scrub her down.

One low running sooty cylinder is my concern. Wondering if the cooling fins have never been cleaned leading to sticking valves on one side? Most people have no clue about these fins.