vapor lock?

[Tom Basile]

I have an older boat that was repowered with a 1999 merc 350. The boat is used mostly for fishing.Any time i let it idle for aprox. 1/2 hour<br />and then power it up it dies.Checking the carb. showes no fuel.The fuel path is from the tank to a water seperator to a carter electric low presure fuel pump to a holley carb.The fuel pump uses a oil presure switch to feed it 12 volts when the key is in the on pos and oil presure is above 8 lb.{ must have oil preasure to run pump ].This switch is ok.If I let it sit for aprox. 1/2 hour than turn key to on and jump switch I will get gas after 2 or 3 min.At this point I can start the boat and is fine until I idle again for say 1/2 hour.??

 

[denniz]

Re: vapor lock?

Why do you let it idle for 1/2 hr? trolling?What temp does your engine reach. If its over 180 you maybe vaporlocking. How does it run at top end?

 

[Tom Basile]

Re: vapor lock?

The motor is raw water cooled and runs at 140 degrees.We drift live bait on reefs at night.

 

[Tom Basile]

Re: vapor lock?

The boat runs great at top end.

 

[denniz]

Re: vapor lock?

Your not vapor locking, Heat causes vapor lock. Id check the pickup or anti siphon valve, then carb rebuild

 

[loadnet]

Re: vapor lock?

Check the gas line between the pump and the water separator for cracks or a bad clamp.. you may be sucking air 'there' or at the seperators gasket itself..<br /><br />If the line looks good, by pass the water seperator and see if the problem duplicates itself..<br /><br />If it does you may want to run a direct gas feed line from the pump right into a gallon of gasoline to see if the problem dupicates..<br /><br />If it doesn't at least you've narrowed down the problem to your tank - lines and VENT on your gas tank.<br /><br />CaptainHooknFinger

 

[kenimpzoom]

Re: vapor lock?

Are you sure it's not a bad pump. Sometimes pumps only fail when they get really hot. ideling will put a lot of backpressure on the fuel pump and may get it hot enough so that it wont pump properly. One easy way to check things is to run a temporary fuel pressure gauge. Also, rig up wires to that you can easily monitor the fuel pump volts and amps with a multimeter.<br /><br />Vapor lock usually doesnt happen with an electric pump, but anything is possible.<br /><br />Ken

 

[Tom Basile]

Re: vapor lock?

I'll try the fuel pressure gauge and go from there<br /><br />thanks, Tom

 

[DaveM]

Re: vapor lock?

If I were me in your shoes, I would look at replacing the anti-siphon valve first (because they are cheap) and then the fuel pump. I may be all wet, but it does not make sense to me to rebuild the carburator if the engine runs great, especially at WOT.<br /><br />Just my opinion, it's worth exactly what you paid for it!

 

[Tom Basile]

Re: vapor lock?

I agree

 

[MrBill]

Re: vapor lock?

RodKnocking has advised correctly, your carb is not holding the fuel pressure when shut down. Depending upon carb mechanics your problem should be able to be isolated to anti-siphon valve (which ever type is used, ie; float activated, etc.). This seems to be why 2 or 3 minutes of fuel pump operation provides sufficient flow to keep engine running properly.