Tired of squeezing the old balls...

[ScottyCee]

Made you look!

During my rebuild I discovered that both of my fuel priming bulbs were shot, so instead of buying new ones I opted to replace them with little line pumps. They were half the price of Atwood bulbs and work like a charm - they're both on one switch, so I flip it for a few seconds and presto. Obviously, I didn't invent this - I had a Progression 22 with a Mercury Racing 300 on it that had an automotive fuel pump about the size of a tennis ball can to always keep fuel pressure to the motor regardless of the G-forces. The big Merc was happy with that, but I'm curious about the Yamahas.

Observation - if I turn the little pumps on while I'm cruising, the fuel management gauge spikes for a few seconds and then settles back to where it was.

Question - what exactly am I pumping up? What are the ramifications? Are Yamaha 4-strokes happy with pre-pressure? Should I just leave them on or use them only at startup? Or does it make any difference at all?

Thanks (again) in advance!

 

[wrxhoon]

You don't need to pump them at all, just like you don't need to use the priming bulbs. The only time they are useful on injected four strokes is when you change fuel filters.

 

[Sparkdog118]

With Efi, exactly what wrx said. They are used mainly now to pump up carbureted motors before starting. Do not run them unless you change the fuel filter or drain the vapor separator tank for storage. I have seen in some cases where those type of pumps create a fuel restriction. IMHO for the 10 seconds a year you will need to pump up your fuel system, I would get a quality primer ball that lasts a good 5 to 7 years and not worry about a fuel restriction. If you leave them on, it could cause damage to your low pressure fuel pumps which depending on your pump style, could fill the cylinder behind the fuel pump and create a hydro lock. That would bend a rod for sure.

 

[ScottyCee]

Thanks for the input, guys.

These pumps are rated at 30 gpm each, so no worries about flow restriction. The fact that they show exaggerated consumption at high throttle proves that they can easily deliver more than the motor can consume. So I'm not worried about damage in that regard.

Interesting - I have never owned a boat were I didn't need to pump the fuel up after some down time. This one seemed to be the same, but those pumps were installed at the same time as I finally got them running nicely so I guess I'll never know first hand...

Sounds like they will be best used simply to prime...

 

[Bloodweiser]

if you switch between tanks, do you need to give the primer bulb a pump??

 

[Sparkdog118]

No. Switching between tanks it is not necessary. Only if you run the engine completely out of gas.

 

[Sparkdog118]

The fuel restriction happens when the pumps are off. They should never be run while running the engine.

 

[Bloodweiser]

thanks Spark

 

[Sparkdog118]

Anytime

 

[seasick]

Thanks for the input, guys.

These pumps are rated at 30 gpm each, so no worries about flow restriction. The fact that they show exaggerated consumption at high throttle proves that they can easily deliver more than the motor can consume. So I'm not worried about damage in that regard.

Interesting - I have never owned a boat were I didn't need to pump the fuel up after some down time. This one seemed to be the same, but those pumps were installed at the same time as I finally got them running nicely so I guess I'll never know first hand...

Sounds like they will be best used simply to prime...

If the pumps delivered more fuel than the motor could consume, where did that extra fuel go

It would guess that the system has a fuel flow meter and it reads the initial in-rush flow and that skewed the consumption estimate. The new pumps produce a lot less pressure than the high speed pumps do and therefore would not affect actual fuel consumption.
There is another possibility though that can be an issue though. If the pressure is more than the needle valve in the VST tank can 'hold' that tank will overfill and will vent the excess gas (which will end up running down the lower assemble and into the water.

 

[wspitler]

Not sure what Yamaha motor we are talking about here. The V6s have an electric LP (backing) pump that feeds the VST, whereas the 4 cylinders have two vacuum operated LP pumps, both feed the VST and thereby the HP pump. In the case of the V6, the VST has a bypass that bypasses excess fuel back, downstream of the electric LP pump. I suspect the electric LP pump needs to keep some level of flow at low consumption. I have found that even after putting on a new (empty) water separator filter the LP pumps will suck enough fuel through the primer bulbs that priming with the bulb is unnecessary and, at times, doesn't work anyway.

 

[seasick]

Good points. I assumed motor had vacuum lp pumps. Perhaps not but if it had electric, I wouldn't expect the need to prime unless the pumps were dead. The electric pumps with the pressure bypass would might explain the initial jump in fuel consumption assuming a simple 'one pipe' fuel flow meter

 

[ScottyCee]

"If the pumps delivered more fuel than the motor could consume, where did that extra fuel go"

that is exactly what I was asking. It's only momentary and then as I said it resumes to indicating the correct amount, but there is obviously room to put a little bit of fuel in there somewhere.

Motors are 2005 f225s. All of the pumps were replaced last month during my motor rebuilds.

But I've heard enough. I'm just going to use the little auxiliary pumps to prime.

Thanks again, gentlemen.

 

[seasick]

One last question
Did the motors loose prime before the rebuilds?

 

[ScottyCee]

Yes, but the bulbs were no good. I think air was being sucked...