vacuum switch? 150 hp johnson

[keefallan]

I have an '85 johnson 150(j150tlcos). I just got my factory service manual. It shows a vacuum switch in the electrical schematics. I don't have one on my frankenstein motor. What does it do? Is it necessary to have it?

 

[emdsapmgr]

Re: vacuum switch? 150 hp johnson

The switch is a safety device. It measures fuel line vacuum. When the fuel line vacuum gets up to 7 hg of vacuum, a warning horn will sound indicating high fuel pump suction in the line. At this point, you run the risk of running the engine lean at high rpm's-possibly damaging the powerhead. The V6 engines have this feature, the sister 4 cyl crossflows do not. The engine will run fine without it. It's your call to run with/without it.