A friend of mine had a problem with his Yami 2004 SX150. His motor would bog down and stutter at about 1700 rpm but run perfectly OK above and below that speed. In addition, on the water not only did it bog down at that speed but it stuttered when hitting swells.
The second symptom made me thing that something electrical was loose.
The first symptom made me think there was a TPS issue.
His parts dealer said to replace the VST filter.
Now i always though that as VST filters get clogged, speed falls off at higher RPMs first and the motor has trouble going above that speed, so I didn't suspect the VST.
The motor at the dock could be made to bog and stutter just be reving it in neutral to about 1700- 2000 rpm. Pumping the primer didn't make any difference at all so lp pumps were probably not the issue.
I tested the tps for continuity across it rotation and it looked fine.
We drained the VST into a container to examine the gas and it was clear with no apparent contaminants or sediment.
I was baffled but my friend went ahead and bout a VST filter and gasket.
Yesterday we replaced the filter. The old filter was fairly clogged with a very fine dust like substance, somewhat whitish or tan, You could not see clearly through the filter but you could easily blow through it.
Filter replaced, all bolted back up, primed and started.
Guess what? The motor runs fine, no bogging at the dock or at sea.
I honestly do not understand how the dirty filter explained the symptoms but nothing else was changed. Why would the motor bog at mid speed only and when hitting swells???
I hate it when I am wrong but I learned something new.
The second symptom made me thing that something electrical was loose.
The first symptom made me think there was a TPS issue.
His parts dealer said to replace the VST filter.
Now i always though that as VST filters get clogged, speed falls off at higher RPMs first and the motor has trouble going above that speed, so I didn't suspect the VST.
The motor at the dock could be made to bog and stutter just be reving it in neutral to about 1700- 2000 rpm. Pumping the primer didn't make any difference at all so lp pumps were probably not the issue.
I tested the tps for continuity across it rotation and it looked fine.
We drained the VST into a container to examine the gas and it was clear with no apparent contaminants or sediment.
I was baffled but my friend went ahead and bout a VST filter and gasket.
Yesterday we replaced the filter. The old filter was fairly clogged with a very fine dust like substance, somewhat whitish or tan, You could not see clearly through the filter but you could easily blow through it.
Filter replaced, all bolted back up, primed and started.
Guess what? The motor runs fine, no bogging at the dock or at sea.
I honestly do not understand how the dirty filter explained the symptoms but nothing else was changed. Why would the motor bog at mid speed only and when hitting swells???
I hate it when I am wrong but I learned something new.