2005 Mercury 90 HP Fuel issue

georgia088

Cadet
Joined
Aug 14, 2017
Messages
29
I appreciate any help in advance.

I have a 2008 pontoon that did have a 2009 Mercury 50, and I swapped engines out about two years ago. Both engines have had the same issue, so I am assuming it is in the fuel system some how. The boat will typically fire up and run great almost always. However, every so often you can hear the engine start to choke down like it is starving of fuel. Usually this happens at lower rpms, but it will happen while traveling with some speed also. If you go back to the back and pump the "bubble" it will catch up and run fine, but if you don't pump the bubble it will eventually choke down. If you pump the bubble it will usually fire up pretty easily and run fine. I have tried depressing the key to "choke" the engine when it has happened, and it doesn't seem to help either.

It happens very sporadically. Sometimes it may happen 5 times in a day and others it may not happen all day. It seems to happen worse after you have run pretty hard and then shut the engine off. It will then fire up with no problem, but if you travel at low rpms after this the bubble will go flat. We rebuilt the fuel pump in the old engine, but it didn't seem to help. I thought that maybe the fuel line had a small hole in it inside the pump, but it doesn't matter whether the tank is full or not it still will do it. Any help would be appreciated!!

Thanks so much!!
 

wn6ngp

Petty Officer 1st Class
Joined
Aug 12, 2012
Messages
209
Since this happened on 2 different motors and given your comments about the bulb this has got to be a restriction in the fuel line or bulb leading to the tank. It might be as simple as a restriction in the bulb itself.
How long is the fuel line run to the tank, does it make any sharp bends, would it be easy to replace it?

Can you temporarily run a short piece of fuel line to a portable gas tank?
 

georgia088

Cadet
Joined
Aug 14, 2017
Messages
29
Thanks for the reply. Actually, I have replaced the bulb as well. I thought I put that in my original post, but I didn't. There is no kink in the line outside of the tank. There is a nut that holds the fuel line to the side of the body of the boat. I have removed it, but I can't figure out how the fuel line can be removed out of the gas tank. I would like to remove it and see if there is some type of restriction of some sort inside. Any ideas how this fuel line is removed?
I thought it would be simple, but it wasn't for me.

Thanks.
 

Silvertip

Supreme Mariner
Joined
Sep 22, 2003
Messages
28,758
Anytime the primer bulb goes flat that is an indication of a restriction between the primer bulb and the tank. If the tank has an anti siphon valve that can stick and cause the issue.
 

Texasmark

Supreme Mariner
Joined
Dec 20, 2005
Messages
14,544
While you are at it, check for tan scale inside the tank to engine fuel line. My OEM gray silicone possibly fuel line started emitting scale at 10 years and had to be replaced along with the bulb. A lot of tanks have a screen in the tank on the end of the pickup tube that can get clogged with varnish or crud if you buy dirty fuel. Never had an anti-siphon valve so I can't comment on that.
 

georgia088

Cadet
Joined
Aug 14, 2017
Messages
29
Ok, I tried to remove the anti siphon valve from the tank. However, it feels like it is going to break before the threads turn loose. Is there a secret to getting this off? Thanks.
 

Texasmark

Supreme Mariner
Joined
Dec 20, 2005
Messages
14,544
Sorry, I can't help you with that question.....never had that problem.
 
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