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ns90a rpm

bobbykey

New member
Im running wot at 4000 then all of sudden it may jump to 3000 for a while then it might jump to 5000 for a while . Its always 3000 , 4000 , 5000 rpm at different times When wot and I can tell a differance in boat speed when it changes rpm's.

It still seems to run smooth at all three speeds.

What could be causing this.
 
Almost anything at this point. Grab your trusty Factory service manual, use it as a guide, and start diagnosing the fuel, electrical, and mechanical systems.
 
In the manual it says to check the pulser peak voltage output with a peak voltage meter is this the same as a DMM if not will a DMM work just as good ,and it doesnt show a Resistance check in the specs.Can I check for a resistance on the pulser to see if its ok.
 
You need a good ANALOG (not digital) meter, with DVA (direct voltage adapter) capability to catch the very brief pulse. Or you could use an oscilloscope...
 
I was trouble shooting my rpm problem and the rpms just shot up to about 7000 rpms and the engine would not shut off .I turned the ignition switch off sill didnt stop ,pulled battery cable still didnt stop ,pulled all three plug wires still didnt stop, finally full throttled cards without timing advance and it bogged and stopped engine.What could cause the engine to run smooth at 7000 rpms with no spark plug wires?:confused:
 
the only thing I can think of is maybe the engine has alot of carbon built up in it and the carbon was hot enough to ignite the gas that was spilling into the cylinders from the carbs.Im going to rebuild the carbs and see if that turns it back into a gasoline engine.;)
 
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Without spark, you must be dieseling. Period. Could be a huge accumulation of carbon, but it is still dieseling. You could do a de-carbon, to see if that helps. It never hurts.
 
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