Big twin 40 hp thermostat question

[bikecop1]

Took my 40 hp evinrude out the other day and it would run and then quit on me as if it were running out of fuel. I have been running it without the tstat and seemed to have no problem during the summer with warm water. Can running it without the tstat in cold water cause this. I've just installed a new tstat and will test it when it warms a bit. Thanks for the help.

 

[racerone]

Re: Big twin 40 hp thermostat question

Not sure why folks would leave a thermostat out at all.---------Those motors are unique in that after a long wide open run they have water vapour and hot water pouring out the exhaust relief.-----This only lasts a little while.---------I guess most folks jump to the conclusion that it is overheating, when it is not.------Maintain the waterpump and install the thermostat along with the poppit valve found in there and you are good to go.-------Bonus is they idle a lot better with a thermostat.

 

[oldboat1]

Re: Big twin 40 hp thermostat question

agree it's not a good idea to run without a t.stat, whatever the lake temp. If your motor has a hot water activated choke (a really neat device from the early 60s), the t.stat is probably vital. There is probably another reason for the motor quitting, more likely fuel supply (fuel pump, crimped or broken fuel lines (check around connectors for cracks), carb that needs cleaning. Operating temp should be in the range of about 130 degrees, give or take. If you can briefly keep the side of your hand on the top of the head while it's running, it's not overheating.

 

[Bosunsmate]

Re: Big twin 40 hp thermostat question

Keep priming the fuel bulb, see if that helps, if so replace fuel pump.
As above, dont run without a thermostat, the cylinders will take a lot longer to get to temp and you will end up slowly adding up carbon deposits to the rings which will seize a lot earlier than if it was run with a thermostat. Run some seafoam if you can to make up for what you have being doing to it!

 

[bikecop1]

Re: Big twin 40 hp thermostat question

Priming the bulb seemed to help but the fuel pump was replaced last year. Tried it on two different tanks and did it on both.

 

[Bosunsmate]

Re: Big twin 40 hp thermostat question

It shouldnt help any unless the pump is broken somehow. If it doesnt quit then you know its your problem, unless you have two faults. Then you will need to check spark, compression and timing, bad compression will affect your fuel pumping

 

[oldboat1]

Re: Big twin 40 hp thermostat question

believe I would rule out fuel supply issues before proceeding to anything else, since priming with the bulb makes a difference. That's a traditional test for a faulty fuel pump, but it could be other fuel related issues -- air leak in a fuel hose (cracks around a fitting?), or a carb issue. It isn't a big deal to remove the carburetor and clean it, making sure that all openings are clean. The carb needs to be disassembled for cleaning. Use small diameter wire, 400 grit wet/dry sandpaper and carb cleaner. I soak the disassembled carb in lacquer thinner (metal parts only) before hands-on cleaning. It doesn't hurt to have a kit on hand for parts as needed (normal advice is to replace all gaskets, but I find that isn't always necessary -- but you have to get at them in order to know.)

btw, if you can keep it running by choking and releasing, you almost certainly have a carb issue.

 

[bikecop1]

Re: Big twin 40 hp thermostat question

The only other thing that concerned me was once when I was pumping the bulb with the engine off fuel came out of the front of the carb at the air intake.

 

[racerone]

Re: Big twin 40 hp thermostat question

Fuel leaking like that means that the carburetor needs attention.---------Float valve is sticking or there is dirt in there.