What is a vacuum switch/Purpose/Gt 150

[mrtool2u]

We are trying to figure out why my buddys GT 150 is losing power. First off,what is the vacuum switch that is inline on the fuel line,and what does it do. If it is not functioning properly,could it make the motor run bad. This motor is weird,,has approx 105 psi in each cylinder,,we decarbed tonight. The boat will take off some times then just slow down. We tore down the carbs and the fuel pump the other day and they were as clean as a popcorn fart. (we ran after and it was no better)Is there anything that is easy to overlook in the fuel pump. We tried a seperate fuel tank and hose to the motor. I cannot believe it is a spark problem,,we never seem to be losing spark. It did seem to run extremley hot,,so we pulled the t-stats for now,will this hurt the motor. What would happen if the exhaust was really carboned/plugged up,would the decarbon of helped this. Sorry for all the questions,but this really has us stumped.

 

[Joe Reeves]

Re: What is a vacuum switch/Purpose/Gt 150

That engine must have thermostats to compenstae for distortion within the combustion chambers. To run without them is inviting piston damage.

You've said nothing about the warning system. Does the warning system horn beep when you turn the key to the ON position?

With the engine not running, but with the key in the ON position ground one of the TAN heat sensor wires at the cylinder heads. The warning horn should sound steady. Does it?

The vaccum switch enables the warning horn to sound constant and steady if a fuel restriction is encountered.

 

[mrtool2u]

Re: What is a vacuum switch/Purpose/Gt 150

Joe,thanks for a response. Yes the horn beeps when we turn on the key, and I grounded both wires from the heads and the buzzer beeps for each side. He ran it today and said it was back up to 47-4800 rpm's which I know is low,but he said it was running better after the decarb and taking the t-stats out for now. He said the boat has never ran over 4800 r's (for his 10 years at more than 25 hrs per year) so I was hoping the decarb would help,,he has never done this. He is currently running a 19 pitch 3 blade Michigan stainless wheel,,the boat is a 18 foot Glasstron. I thought that he should be surely able to spin a 19 pitch more than 4800r's.. Also,how would we know if we still have a obstruction in the exhaust,,can we tell if we remove the lower unit,,could it be so bad that we need another decarb.
I know when I start my 1993 Johnny 120 it takes about 8-10 seconds to pump water out the pee hole,,but this thing is almost instant,,could that be a sign of blockage..