Rodbolt; Need input re Yam Vapor Recovery System

[boscoe99]

Rodbolt,

I am trying to map out what I will call the vapor recovery system in an F225 as the motor was modified by O2003-020. Unfortunately, Yamaha never documented this in any place that I know of.

Please take at the illustration and let me know if you agree or disagree.

Also, the connection the air intake silencer has got me confused. When the VST vents into the recovery system what is to prevent the fuel fumes from simply going to the silencer via the orifice air vent instead of flowing to the charcoal cannister via the pressure relief valve? This assumes the vent is really just a vent and not something more complex.

As you know, Yamaha will call a pressure relief valve a check valve. Two totally separate parts with different functions in my mind.

[rodbolt17]

ok
#19 is an atmospheric vent that allows air into the canister,#25 is a one way check valve that allows air into the VST.
#40 is a one way pressure valve that allows vapors under pressure into the canister.
at the next engine restart vapors and air are drawn into the throttle plates via the ISC valve.

the intent is to allow vapors escaping the VST to be stored in the canister until the engine is running again.
has NOTHING to do with vapor lock and everything to do with an excessively rich A/F mix at the next hot restart.

later fourstroke V6 models had a vapor shut off valve that limited HOW MUCH vapor was released from the canister back into the intake air stream.
all of it EPA and hard hot restart driven.
its also why hulls made after jan 2010 have to have vapor recovery systems and portable tanks hold pressure until about 5 PSI.
EPA says NO vapors are allowed to be vented to the atmosphere now.

does that help at all ?

[boscoe99]

You will need to take up the issue of a motor not starting or running due to vapor lock with Yamaha. That is their verbiage, not mine.

Yes, you have helped clear this up. I was not aware that item 25 is a check valve. Yamaha referred to it as an orifice air vent. I was presuming an orifice air vent to be a tiny hole that allowed gases to flow either way. This did not make sense since a tiny hole that allowed gases to flow either way would not let the pressure relief valve (item 40) do its job. With item 25 being a check valve then item 40 can do its job.

But hell, Yamaha calls a pressure relief valve a relief valve in one place and a check valve in another place. Must be the translation.

So, with an F225 that has the modification, if it is hard to start under a hot condition after having sat for a while, after running normally, what might you suspect the problem to be? Is it related to the vapor recovery mechanism or possible a lift pump/VST pump issue? I am thinking that the vapor recovery system is not doing its job and perhaps allowing fuel vapors into the air intake system causing an overly rich mixture but...

[rodbolt17]

easy way to tell, reroute the airbox vent or isolate the ISC line.
all the valves can be tested with a mity vac.
yea sometimes jinglish suxs and sometimes swinglish(Volvo) suxs.
some manuals actually refered to yamahas having a fever.

vapor lock is well noted and can be googled.
its also why EFI systems rarely see this.
fuel under pressure wont boil easily and the WHOLE reason for the VAPOR SEPERATOR TANK(VST) is to provide the pump with a VAPOR free fuel supply.
second way is to simply advance the warm up lever a bit and see if the hot restart goeas away cause you mechanically added extra air.