---

I almost hijacked the thread entitled "1987 Evinrude 150 - losing acceleration: Couple of questions" because there was talk about primer bulbs on there, but I decided to do the right thing instead.

So, my last three outboards have been 4 stroke EFI's. They've all had primer bulbs in the fuel system. The first of those three was a Merc 25 on a 13'. One day we launched the boat and in a hurry to get it off the trailer I didn't squeeze the primer bulb. It started up just like any other time, no problems what so ever. The engine had probably been sitting for a week to two weeks without running.

The next spring when I started the motor up for the first time that year I decided to do a test. I didn't squeeze the primer bulb before starting the motor and it fired right up, didn't crank any more times usual.

My current Whaler has a 90hp Merc EFI 4 stroke on it. I replaced 10' of fuel line from the tank to the water separator. I decided to do another test. I didn't squeeze the primer bulb, and the motor fired right up.

My current primer bulb never gets firm, it may be bad, but there are zero issues with the motor getting fuel.

Are primer bulbs really necessary on 4 stroke EFI's?

---

Only if you lose prime! (Get an air bubble in the system for some reason.)

---

My new 150 merc 4s doesn't have a bulb in the line. I put an inline water separator on and it primed itself up and started just fine without any help.

---

I never need to use the primer on my Yamaha F70, even after extended periods of non-use of the boat.

It might be interesting to see what happens with one of these modern motors on start-up with a new fuel system (no gas in the hose).

Dennis

---

I'm thinking about taking the one off of my 90 Merc 4 stroke.

---

I never used the primer bulb, installed by a previous owner, for my Yamaha F115. It was very useful in draining my below deck tank so I left it installed.

---

So if you ran out of gas and switched the hose to a new full tank, the engine would prime itself? Do you just leave the key in the on position or are you cranking?

---

when I put the water filter on, I had to add about 5 feet of hose to the line. Hooked it all up dry and she primed up and fired right up. The hose and the new filter were both empty and it didn't seem to matter.

---

Most or all of the new fuel injected engines have a small "tank" (VST, vapor separating tank on Yamaha) under the cowling. The fuel in this tank allows the engine to start and run while the fuel pump is priming and getting fuel to fill this tank. There is another pump in this tank that supplies the high pressure for the injectors.

---

There's also one of those water separator filters in the fuel system, the kind that looks like a automotive oil filter. How do you change those things, and how often?