06 F60TLR possible vapor lock ???

[Fred Pittman]

I'm still somewhat confused as to why pumping the primer bulb (boosting the line pressure to the vst) was helping to keep motor running when it started to stumble.
I understand that , at idle speed, under load, the motor isn't using much fuel and that the fuel pump doesn't speed up or slow down related to RPM's so probably 95% of the fuel is being recycled thru the pressure regulator and down thru the non-functioning fuel cooler , then returned into the bottom of the vst. I also read that , under a vacuum, the boiling point of ethanol blended fuel can be as low as 50 degrees F. ( much lower than non-ethanol 87 octane )
I try to run non-ethanol fuel only, but lately I have been topping off my tank at the local c-store with ethanol blend 87 and adding a dose of Biobor EB.each time.
My theory is that , without the fuel cooler able to function, the bypass fuel is constantly being recycled thru the heat producing fuel pump until the boiling point at the fuel pump pickup (vacuum) is being reached, thus creating the vapor lock situation inside the pump itself. When I pump the primer it's allowing a little fuel ( much cooler) into the vst where the cooler fuel wants to settle to the bottom and thus drop the temp of the fuel there to below the boiling point?
A couple of trips ago, I started off my *****ing run with the cowling off and it never stumbled and died even after a couple of hours at 700 RPM's. I then replaced the cowling and ran mid-throttle back up the lake , dropped back to idle, and the stumble started after just a few minutes. The cooler air without the cowling on , (I presume) allowed enough air flow around the VST to keep the fuel slightly above the boiling point.

[99yam40]

looking at it again it shows flow from cylinder body to exhaust outer cover
then to TT and cooler

as I said it shows flow before the stat heading that way

strange ,I thought the stat would allow more flow to the head when opened on most older motors.

the newer ones I do not know maybe they do just allow more flow thru the whole motor and dump it to the exaust just like the PRV when it opens.

I would be nice to know what motor that diagram is for

[99yam40]

I'm still somewhat confused as to why pumping the primer bulb (boosting the line pressure to the vst) was helping to keep motor running when it started to stumble.
I understand that , at idle speed, under load, the motor isn't using much fuel and that the fuel pump doesn't speed up or slow down related to RPM's so probably 95% of the fuel is being recycled thru the pressure regulator and down thru the non-functioning fuel cooler , then returned into the bottom of the vst. I also read that , under a vacuum, the boiling point of ethanol blended fuel can be as low as 50 degrees F. ( much lower than non-ethanol 87 octane )
I try to run non-ethanol fuel only, but lately I have been topping off my tank at the local c-store with ethanol blend 87 and adding a dose of Biobor EB.each time.
My theory is that , without the fuel cooler able to function, the bypass fuel is constantly being recycled thru the heat producing fuel pump until the boiling point at the fuel pump pickup (vacuum) is being reached, thus creating the vapor lock situation inside the pump itself. When I pump the primer it's allowing a little fuel ( much cooler) into the vst where the cooler fuel wants to settle to the bottom and thus drop the temp of the fuel there to below the boiling point?
A couple of trips ago, I started off my *****ing run with the cowling off and it never stumbled and died even after a couple of hours at 700 RPM's. I then replaced the cowling and ran mid-throttle back up the lake , dropped back to idle, and the stumble started after just a few minutes. The cooler air without the cowling on , (I presume) allowed enough air flow around the VST to keep the fuel slightly above the boiling point.

Maybe the VST pressured up from the vaporizing fuel and caused the needle and seat on float to seal off and you had to over come that pressure to get the fresh fuel in.

Just a wild guess, as I do not know if or how the VST is vented

you did say you needed to pressure up to 10 psi to get the fuel into the vst at one time.

[Fred Pittman]

OK,guys..... Out on the water today...3 hours in, 95 degrees outside, steady 700 rpms without a sputter...... Think the problem has been solved.... Thanks to all who have helped..... Fred

[99yam40]

bet the wife is happy now, or maybe not with all of the time and money that was spent to finally find out a piece of wire shoved down that hose fixed it.
maybe you need to keep that to yourself.

Glad you got it solved

[Fred Pittman]

Didn't really waste any money, other than a used VST , a new OEM lift pump, an aftermarket fuel pump ( $43.00), and a few clamps. I already had the other stuff lying around. I can recoup a good but from Ebay by reselling the spare stuff. I'm just glad the problem is solved. I just got home from the lake but motor ran like a champ. Ran for 5 hours nonstop, mostly at idle speed without a stumble. Thanks 99yam40 for your help.
I read lots of threads on this board and it seems , to me, that lots of the posters here fail to post the results of their repairs or show any appreciation for the help that you, Rodbolt, Boscoe, and others give. It's like when they find the problem and fix it, they leave the thread hanging which doesn't help folks like me that need that info at times. Just a pet peeve of mine I guess, but just so y'all know, your advice and opinions matter very much to me. Thanks again, Fred

[99yam40]

thank you for helping others down the road

[rodbolt17]

***
3 weeks over 3 pages and the first reply to the thread asked a direct question concerning the fuel cooler.

[99yam40]

yep, just because there was no blockage in the cooler itself and the tell tail showed flow all of the time does not mean there was flow thru the cooler.

who would have thought there was no water flow thru the fuel cooler without some kind of indicator that there was a problem

I never would have thought Yamaha would design something like that .

[fairdeal]

so do I have this right -

that hose barb on the exhaust guide is not water going TO the cooler -

but rather the water exiting the cooler?


the water TO the cooler comes from the exhaust cover,

but is limited to whatever doesn't first escape via the telltale?

[99yam40]

sounds like it, strange aint it

I guess the TT has a restriction that allows only some much water out, so there should be enough flow thru the fuel cooler

[rodbolt17]

if it cannot EXIT the cooler, it fails to cool.
a simple disconnect the t fitting and blow air would have found it.

same as the raw water cooled manifold/riser on a stern drive.
doesn't matter how much sea water pressure ya got, if it cannot EXIT it does not cool.

[99yam40]

but this guys F60 had flow out the tell tail the whole time from what I gather and not back into the motor (hole plugged at that point)

[cpostis]

but this guys F60 had flow out the tell tail the whole time from what I gather and not back into the motor (hole plugged at that point)

Yes, the blockage was after the fuel cooler exit hose at the nipple to the exhaust guide. But, this will not flow through the motor, it will run down the mid section. Think of the attached diagram as a branch of the water pump supply. One branch flows through the hoses, fittings, and fuel cooler. The other branch ( not shown) feeds the block and heads through the thermostats. See this attached diagram.

[Fred Pittman]

Yes, Rodbolt...You were right on your first post. Kudos to you .... Although in your first post you told me to check if the fuel cooler was clear. I disconnected the hose at the elbow ( there's no "T" in this line ) where water exits the fuel cooler and had good flow thru the cooler. The line from that elbow back into the motor lies underneath a bunch of other hoses and wires. I mistakenly assumed it was tied into the telltale (as a newbie) . I now know better....