1806 cub cadet carburator

[jdudding]

I was wondering if anyone could help me with my 1806 cub cadet.I installed a brand new carburator on it and it still won't run right.When you start the tractor it is very rough idling and sometimes backefires when you bring the throttle up.The tractor also starts to smoke when it idles for while I have adjusted the carb on it the way the manual says to.What else could I check on it that I might not have thought of?Thanks,Joey.

 

[jchamberlin]

Joey: I think you need to eliminate a mechanical cause of your problem. One test I found very revealing on a twin cylinder engine is an engine balance test as described in the Briggs & Stratton "L" Head Repair Manual. The manual reads, "If the engine is hard starting and runs rough, misses, or lacks power, perform a cylinder balance test to determine if both cylinders are operating to their full potential." I won't cite the entire entry, but they recommend first checking to see if the spark is equally strong at both cylinders, and if it is, proceed to the second step. "Start and run the engine running at top load speed. . . . Ground out one cylinder with a screwdriver . . .. Note RPM loss. Then ground out the other spark plug and note the RPM loss. If the difference between the two cylinders does not exceed 75 RPM, the amount of work the two cylinders are doing can be considered equal."

The manual goes on to note that, "If the RPM loss is less than 75 RPM between cylinders and the engine runs poorly, the problem is common to both cylinders." It then lists the "Things which Affect Both Cylinders"

1. Carburation
2. Crankcase Vacuum
3. Ignition timing, including a parially broken flywheel key

Getting down to brass tacks, "If the RPM loss is greater than 75 RPM, this indicates that the cylinder with the least RPM loss is the weakest of the two cylinders. Look to that cylinder for the problem" They offer the following example:

Engine RPM - Both Cylinders = 3400 RPM
Engine RPM - #1 Cylinder Grounded = 3300 RPM
Engine RPM - #2 Cylinder Grounded = 3100 RPM
Conclusion: #1 Cylinder is weakest of the two cylinders

The items listed under the head "Things Which Affect One Cylinder" include:
1. Spark Plug (A fouled spark plug may indicate that the carburetor is out of adjustment.)
2. Leak in spark plug wire
3. Head Gasket
4. Intake Manifold (A leak at either end of the intake manifold wil only affect one cylinder, not both)
5. Valves
6. Rings
7. Piston
8. Cylinder

Finally the manual goes on to note that "The cylinder balance test will also detect a cylinder that is not functioning. When grounding out one cylinder there will be no RPM loss. When the other cylinder is grounded out, the engine will stop." The manual notes: "NOTE: A twin cylinder engine will run well on one cylinder as long as the power required for the application does not exceed the power produced by the one cylinder."

(I'm not sure the last item applies to Kohlers, but I think the rest of it applies to any two cylinder motor, and the balance test is an easy test not available to the single cylinder owner.)

In my personal experience, I performed the test as described above because I was curious about the condition of my engine, and I had a new tachometer I wanted to try out.

I can't remember the RPMs very well, but I do remember that when I grounded out one of the plugs the OTHER cylinder started smoking like crazy!

NOTE: The motor failed completely less than 10 hours later. It threw a rod. But I can tell you that the valves were functioning perfectly and new springs had been installed. Nothing like fixing the wrong problem!

Hope you find what's ailing your 1806, and I hope you are able to recover full functionality short of replacing the motor (which is what I wound up doing).

 

[raweaver]

Sounds like it is running lean to me