F115 Hot Start "Vapor Lock"

[JonnyW.]

Well, I'm wondering if the fact that my 2002 F115 can generate a vapor lock in the VST tank and refuse to start until it has cooled down (20min) means that:
- the med-press fuel pump is running too hot and may be going bad?
- the Ethanol E10 fuel is to blame?
- a fuel line is too close to the head?
- or a combo of the above?

(I am pretty sure it is a vapor lock situation causing the motor not to start: there fuel pressure at the fuel rail is normal, spark is normal, VST screen filter is clean, etc..)

Rodbolt, or any other mechanical guru's out there, have any thoughts for me??

 

[JonnyW.]

Re: F115 Hot Start "Vapor Lock"

PS: Redbolt: I live on a small island (Kauai) and have no access to a dealership with cert mechanics, so I am on my own!

 

[JonnyW.]

Re: F115 Hot Start "Vapor Lock"

A mechanic just told me that 'vapor lock' on the F115's is common. Something about the VST being too close to the head?

 

[rodbolt]

Re: F115 Hot Start "Vapor Lock"

vapor lock isnt really that common, the return fuel is water cooled and fuel under pressure boils at a much higher temp than fuel under a vacum.
what can happen is the fuel vapors can and do vent to the intake, this can and will create an excessivly rich mix that may not burn.
next time it happens onpen the throttle about 3/4, this will shut down the injectors and place it in a flood clear.
be aware when it starts yoiur going to have to slow it down rapidly.
if you think its vapor locked simply check rail pressure, if its 45PSI or so its not vapor locked.
your drawing out of a tank thats supposed to be vapor free, thats why they call it a vapor seperator.

 

[JonnyW.]

Re: F115 Hot Start "Vapor Lock"

Rodbolt, thanks!! for the comments and the tip about opening throttle to 3/4 to shut injectors and place in flood clear.

I will try and measure fuel rail pressure next time it happens.

What do you think about the theory (posted on the forums) that vapor lock on the F115's can be caused by a med-press fuel pump going bad, getting excessively hot and heating up the fuel in the VST?

 

[rodbolt]

Re: F115 Hot Start "Vapor Lock"

I think its a bogus theory myself.
why do you think they call it a vapor seperator.
its a gas tank.
the pump sits in a tank of liquid fuel,the intake is submerged several inches deep. at key on this pump pressureizes the rail. gasoline under pressure,loke most liquids, has a higher boiling point.
maybe if the symptoms were it will start,run a bit and die but your theory is bo go tron.
there is no medium pressure pump on an f115.
there is a mechanical lift pump and an electric high pressure pump and return fuel from the rail goes through a fuel cooler. the electric pump is a flow through design and its cooled by the fuel and at key off has no heat.
ill stick with the excessivly rich theory.

 

[JonnyW.]

Re: F115 Hot Start "Vapor Lock"

Rodbolt, I totally agree with you - after the motor starts, it runs perfect. Thanks again for sharing your knowledge!! If you ever come to Kauai, you've got a free fishing trip on my boat anytime!!

 

[JonnyW.]

Re: F115 Hot Start "Vapor Lock"

Rodbolt: just to clarify:

is there something abnormal causing the vapor lock / excessively rich mix? or is it just a matter of knowing it can happen on the F115 and letting the motors cool down for a few minutes before shutting down>?

 

[99yam40]

Re: F115 Hot Start "Vapor Lock"

I believe the owners manuals say to run for a few minuets after coming off of high RPMs to help cool down motor before turning off, but I never knew why.

Is it possible you have a pin hole in the lift pump diaphragm causing fuel to enter the oil sump and that causing over rich condition when that is vented to intake?

 

[JonnyW.]

Re: F115 Hot Start "Vapor Lock"

99yam40,

Interesting idea: I will check it out. The problem only occurs rarely, and when motors have been run hard and shut down quickly. My guess is that 3 min of cooling off at idle will prevent from occurring in the future.

Thanks for your ideas!

 

[rodbolt]

Re: F115 Hot Start "Vapor Lock"

check the 02 and 03 tech bullitens. there is a vapor shutoff and recovery kit avalible.

 

[JonnyW.]

Re: F115 Hot Start "Vapor Lock"

Thanks Rodbolt,

I will check it out!

 

[egstasea]

Rodbolt,
I know this is an old post, but this might be the best place to ask the question as I have the exact same symptoms on my 2005 Mercury FourStroke AKA Yamaha F115.
I can always get the engine started by advancing the throttle, but I don'd want my wife and kids to have to do that. Is that vapor shutoff and recovery kit still available, does anyone have a part number? Is it safe to just disconnect the line to the intake?

 

[99yam40]

Rod does not post here anymore , another reason not to be posting on old threads