Should the fuel primer bulb remain hard...

[Interloper]

I'll apologize in advance if this is a stupid question. Should the fuel primer bulb remain hard while my outboard motor is running?

I'm breaking in a rebuilt 250 hp 2-stroke Mercury. I'm in the habit of pressurizing the fuel primer bulb before starting the engine. I hadn't paid much attention previously, but I happened to notice today that the bulb goes soft after the engine has run for a few minutes.

 

[Pain Management]

Mine does the same. I asked the dealer about it and he said it was normal.
George

 

[BradV]

Well you have to figure once the line is primed and the engine is recieving fuel that it works like a siphon. So the pressure shouldnt be built up in the line especially the bulb because it has more volume than the regular line. So i would imagine it is normal

 

[DaleH]

Yup, well sorta no siphon at all, as fuel is under vacuum to the OB, measured in inches of mercury, and that is what keeps the check valve in the primer bulb open.

If/when I find a primer bulb that no longer stays hard (no Viagra jokes please ...) I personally replace it, as the rubber/elastomers used does harden in UV exposure. One needs a pliable bulb to help pressurize the fuel priming circuit properly, plus to fill the carb bowls or feed injector rail on newer OBs.

 

[SIM]

Dale,

The primer bulb is located in the fuel system before the engine. If the engine is not running and you pump the primer bulb it will pressurize the fuel system after it.....all the way up to the engine. The bulb remains "firm" or "tight". This is assuming that all is right with the engines fuel system(float bowls shut on carbed models, or VST float needle shuts on EFI engines)

Once the engine starts, that pressurize fuel hose now becomes under vacuum since the fuel pump on the engine is sucking fuel threw it. Since the primer bulb is now not pressurized, if you pumped it, you would be able to do that. It would get firm for a short period and then loose pressure and return to a vacuum state. This is perfectly normal.

What is not normal is for the primer bulb to collapse either with the engine running, or not running.

Its good to be back......its been a while!

Andy

 

[Megabyte]

Its good to be back......its been a while!

Good to see you here Andy! 8)

 

[SIM]

Its good to be back......its been a while!

Good to see you here Andy! 8)

Its always good to be "seen" :lol: :lol:

Andy

 

[HM5]

Andy, good to see you over here. How is the parts website coming?

 

[SIM]

Andy, good to see you over here. How is the parts website coming?

Hey Matt!

We did open the Yamaha site a couple of weeks ago. I'm not sure how Dale feels about links though.

Andy