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Primer Bulbs on 4 Stroke EFI's
blacksmithdog	#1  Posted on 08/30/13 - 5:23 AM
Member Personal Page Posts: 417 Comments: 0 Joined: 06/26/06	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?
lrak	#2  Posted on 08/30/13 - 5:31 AM
Member Posts: 62 Comments: 0 Joined: 09/08/07	Only if you lose prime! (Get an air bubble in the system for some reason.)
scrfasteddie	#3  Posted on 08/30/13 - 9:18 AM
Member Personal Page Posts: 21 Comments: 2 Joined: 08/07/12	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. 2007 Montauk 190 - 2013 150 Merc 4stroke
DennisVollrath	#4  Posted on 08/30/13 - 9:32 AM
Member Personal Page Posts: 298 Comments: 0 Joined: 08/29/10	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 1985 Outrage 18 with Suzuki DF140A
blacksmithdog	#5  Posted on 08/30/13 - 10:54 AM
Member Personal Page Posts: 417 Comments: 0 Joined: 06/26/06	scrfasteddie wrote: 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'm thinking about taking the one off of my 90 Merc 4 stroke.
Phil T	#6  Posted on 08/30/13 - 11:26 AM
Administrator Personal Page Personal Album Project Albums Posts: 7043 Comments: 6 Joined: 03/26/05	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.
Derwd24	#7  Posted on 08/30/13 - 1:10 PM
Member Posts: 1607 Comments: 9 Joined: 05/09/07	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? Dave - 1983 Outrage 22
scrfasteddie	#8  Posted on 08/30/13 - 7:20 PM
Member Personal Page Posts: 21 Comments: 2 Joined: 08/07/12	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. 2007 Montauk 190 - 2013 150 Merc 4stroke
tmann45	#9  Posted on 08/30/13 - 8:04 PM
Member Posts: 196 Comments: 0 Joined: 02/18/07	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.
blacksmithdog	#10  Posted on 08/31/13 - 3:29 AM
Member Personal Page Posts: 417 Comments: 0 Joined: 06/26/06	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?