Am I Vapour Locking? MerCruiser 140 Alpha

[baker274]

I've had this issue three times now. Engine runs great for 30-45 minutes. We'll stop, sit around for a while, and then I can't get it to turn over -- cranking, but not starting.

Last time this happened I took the clear drain line (from the back side of the fuel pump running to the carb) off the bottom of the fuel pump, cleaned it out, and it started right up. Did this release vapour from the system?

I'm confused. I've heard MerCruisers typically have this issue.

Any thoughts?

 

[tommays]

Re: Am I Vapour Locking? MerCruiser 140 Alpha

There should not be anything in that tube

Its there to warn you that the fuel pump is leaking and needs to be replaced


Tommays

 

[Reel Poor]

Re: Am I Vapour Locking? MerCruiser 140 Alpha

What is in the tube that you are cleaning out ?

Like tommays said, there should not be anything in the tube.

 

[Don S]

Re: Am I Vapour Locking? MerCruiser 140 Alpha

I really don't understand your " I've heard MerCruisers typically have this issue" statement.
I've been a marine tech for more years than I care to admit too, and I've never heard it was a typical Merc problem.
First of all, since you called it a 140 that means its between a 1969 and an 1986 model, so it's at least 20 years old. That clear tube on there gives a path for gas that has leaked past the diaphram and would have leaked into the bilge except for that tube. It gives a path for the gas to go when the fuel pump leaks. When this happens, the carb gets way too much fuel and runs rich and floods the engine.
Since you drained the tube, you have a chance to get it started before it starts it all over again.
It's called a bad fuel pump, not a Merc problem. Merc doesn't manufacture fuel pumps.

 

[baker274]

Re: Am I Vapour Locking? MerCruiser 140 Alpha

I repect your posts Don, and read them daily, but in this case it's not necessarily "called a bad fuel pump." I understand the function of the tube, and understand that if it were fuel in it, the pump would be the issue. What I cleared out of it was not fuel. It was caked with gooey green stuff -- fuel vapour I'm guessing, that's built up over time.

The engine is indeed an 86. The reason I point to MerCruiser having the vapour lock issue is that when you go to their website, and look under FAQ's, the topic of "vapor locking" pops right up -- as if it's a fairly reknown issue. See:

http://www.mercurymarine.com/technical_information_faqs

I'm gathering from your responses that the drain tube would not allow for vapour to escape from the system... is this correct?

Again, my question -- am I vapour locking?

 

[Don S]

Re: Am I Vapour Locking? MerCruiser 140 Alpha

Do you have a vapor lock? Without checking, who knows.
Do you have fuel pumping from the accelerator pump nozzles when it won't start? Is it a weak flow when it does start?
It may very well be a vapor lock, IF, and that is a big IF. IF, the engine compartment is very hot, it possibly may be. You didn't say anything about temps. Was it a hot day?
It may also be that the time you had the engine compartment open while messing with that clear line, it cooled off enough to work. But that line shouldn't have anything to do with curing the problem. It's open at the carb end.
So to answer your question, if it was a hot day, and your engine compartment was hot, and the fuel vaporized, yes you could have had a vapor lock.
Follow the Merc suggestion in the reply in that link to the FAQ's you posted and see if the problem clears up. That should answer your question if it was a vapor lock or not.

 

[baker274]

Re: Am I Vapour Locking? MerCruiser 140 Alpha

Just to finish up this thread:

I was vapor locking. Reason being that my water pump impellar needed to be replaced. I wasn't pumping much water at all, and running too hot. Not overheating, but causing the fuel to vaporize before it could reach the carb.

Thanks for the help.