fuel pump not sucking

[illMATTic]

with my 86 all stock 2.4 i am having trouble with the fuel delivery. i can run wot until i am at a 1/2 tank of gas. once at 1/2 tank the engine will run lean at anything over 6k rpm and fall on its face. 3/4 throttle is fine. once i fill the tank it is fine.

i have all new fuel line inside and out, new filter, removed the screen from the pickup in the tank, and new pump. still does the same thing before and after all the new items. i only have a 16 gal tank so this happens often.


what can i do to fix this?

[j_martin]

Mercury fuel pumps normally suck:D

Seriously, you might have a small leak in the pickup up tube in the tank. Some of them are just plastic pressed over a metal barb, and can leak with age. I usually replace them with a piece of tygon fuel line and a heavy end so it hunts for the low spot in the tank, or goes to the side of the tank with the fuel in a cornerering situation. You could verify this by putting a short piece of clear vinyl hose in the fuel suction line where you can see it. There should never be any bubbles in it while running.

An old primer bulb can do the same thing. Aftermarket bulbs are somewhat famous for it.

The one part that had me baffled for a long time is the bayonet connector for the fuel line. The previous owner had replaced the stock mercury one with a plastic aftermarket pos. It aparently decayed somewhat, and would choke off the flow at high rates. I chased the problem down with a pressure gauge, and eventually, in desperation, bypassed the connecter and connected the bulb line directly to the oil injector fitting. Now I have the fuel pressure needed.

hope it helps

John

[1BadAction]

anti-siphon check valve?

[illMATTic]

well the pick up in the tank is built in. it is 1/2 alum stright down. there is a 90 fitting on the top. all my hose is 3/8 or larger. i guess the next step is to re seal any place the fuel flows through.

the more i think about it it sounds like i have a leak somewhere.

what is the smallest fitting size i would want to run? ill have to chack those as well.

[j_martin]

Merc on that engine is normally 5/16" hose, 1/4 NPT fittings.

[rock]

I had a pin hole in my pick up tube once that did exactly what you are describing. It looked like there was a line around the tube that had corroded. Pin hole was in that line. Likely had fuel at that level during storage at some point in it's life. I changed everything till there was nothing else to change. Finally removed tube and there it was. Good luck.
Rock

[David Borg]

the problem seems to be in the pickup , If there was a problem elsewere it would do it all the time and not when you have half tank empty..

good luck