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NSF18B2 Problem

Z

Zorro

New member
Hi,

We have an 18hp 4 stroke that gets used at most 2 hours a month. Whenever the plugs get a thin coating of medium brown residue the motor will not run- it only seems to want to run with brand new plugs. Should you have to change the plugs 3 times a year on this engine?
 
That's not normal. Tan color of the plugs would indicate proper combustion. These motors should run even with sooted-up plugs. I would do a full diagnostic check on the motor, starting with the ignition system, assisted by the trusty Factory service manual. Don't forget to test the auto-by-starter enrichment solenoid (choke-like device), and verify fresh fuel as well.
 
Thanks Paul for your answer. To check the choke, can I just wire it to a 12 volt car battery?

Also, can you or someone else give me a brief rundown on the main circuits in the carburetor on this motor and how they work, just for general knowledge?

Thanks again.
 
Yes, the heater and moving mechanism can be checked that way. If you apply 12v to it, the heater should warm up and the pin should move, albeit slowly. Takes several seconds, maybe a minute, for the ABS unit to completely extend or retract. The technique is in the Factory service manual, available from any dealer, including me.

The carb on these is a fairly simple, straightforward, 2-circuit design, with midrange ports to allow a fairly smooth transition from idle to power, and the internals/flow theory is not documented very well in the manuals. The usual rules of cleanliness, maintenance, and fuel quality apply. If needed due to idle problems, the only failsafe method is to do a complete disassembly and put the bits in a real carb dip such as Tyme, for about 4 hours at room temperature, then blow out and reassemble.
 
pvanv said:
Yes, the heater and moving mechanism can be checked that way. If you apply 12v to it, the heater should warm up and the pin should move, albeit slowly. Takes several seconds, maybe a minute, for the ABS unit to completely extend or retract. The technique is in the Factory service manual, available from any dealer, including me.

The carb on these is a fairly simple, straightforward, 2-circuit design, with midrange ports to allow a fairly smooth transition from idle to power, and the internals/flow theory is not documented very well in the manuals. The usual rules of cleanliness, maintenance, and fuel quality apply. If needed due to idle problems, the only failsafe method is to do a complete disassembly and put the bits in a real carb dip such as Tyme,
pvanv said:
Yes, the heater and moving mechanism can be checked that way. If you apply 12v to it, the heater should warm up and the pin should move, albeit slowly. Takes several seconds, maybe a minute, for the ABS unit to completely extend or retract. The technique is in the Factory service manual, available from any dealer, including me.

The carb on these is a fairly simple, straightforward, 2-circuit design, with midrange ports to allow a fairly smooth transition from idle to power, and the internals/flow theory is not documented very well in the manuals. The usual rules of cleanliness, maintenance, and fuel quality apply. If needed due to idle problems, the only failsafe method is to do a complete disassembly and put the bits in a real carb dip such as Tyme, for about 4 hours at room temperature, then blow out and reassemble.
Click to expand...
Click to expand...
 
pvanv said:
Yes, the heater and moving mechanism can be checked that way. If you apply 12v to it, the heater should warm up and the pin should move, albeit slowly. Takes several seconds, maybe a minute, for the ABS unit to completely extend or retract. The technique is in the Factory service manual, available from any dealer, including me.

The carb on these is a fairly simple, straightforward, 2-circuit design, with midrange ports to allow a fairly smooth transition from idle to power, and the internals/flow theory is not documented very well in the manuals. The usual rules of cleanliness, maintenance, and fuel quality apply. If needed due to idle problems, the only failsafe method is to do a complete disassembly and put the bits in a real carb dip such as Tyme, for about 4 hours at room temperature, then blow out and reassemble.
Click to expand...
What is the method for checking the power source for the ABS
 
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