Rpm jump

[billnpat]

While underway our port engine RPM gauge jumped from 3300 to 4800 while the starboard gauge stayed at 3300 with no speed increase on the port throttle and our
trim needle was right in the middle,
I tapped the port gauge and she came back down to 3300, hope my gauge is not going..:huh:

Would that be a sign of a Malfunctioning gauge? or just a normal occurrence once in a while???

Thanks.....:smt001

 

[Lazy Daze]

Hi Bill,

Most likely just a normal occurrence. Since you don't have Smartcraft, it keeps things a little simpler. The typical reason for that is the "number of cylinders" switch on the back of the gauge. These gauges can be used with 4, 6, or 8 cylinder engines. The switch is either a small (3/8"?) rotary switch that is flush with the back of the gauge or a small, black "sliding" switch. I think it's the rotary switch in your case, but not sure. Usually all you need to do is "exercise" the switch a few times back and forth to clean the contacts, making sure to leave it on the "8" for 8-cylinder.

 

[dwna1a]

Dennis, one of mine does this same thing, RPMs jump, it almost feels as if it's come out of gear. Then it settles back down and runs great. It mostly does this when the engine and tranny or warming up. Could I have the same switch on my old Merc 350's?

 

[billnpat]

Hi Bill,

Most likely just a normal occurrence. Since you don't have Smartcraft, it keeps things a little simpler. The typical reason for that is the "number of cylinders" switch on the back of the gauge. These gauges can be used with 4, 6, or 8 cylinder engines. The switch is either a small (3/8"?) rotary switch that is flush with the back of the gauge or a small, black "sliding" switch. I think it's the rotary switch in your case, but not sure. Usually all you need to do is "exercise" the switch a few times back and forth to clean the contacts, making sure to leave it on the "8" for 8-cylinder.

Thanks Dennis.....