View Full Version : 50 hp merc dies at idle still/ repost after trying to fix, need help!
93 merc three cyl. tiller, LS, TT, oil injected. So far I have relaced every gas line and fitting from the tank(new) to the fuel pump. I saw air bubbles in the plasitc T right before the fuel pump that appeared to be coming from the fuel line not the oil sender. So I took the fuel line off at the cowling ( so that there was only fuel line to the fuel pump T, which was about 12" of line) and dropped it in a cup of gas, trying to eliminate any thing from there to the tank, same results air bubbles... idles down and dies...
I have a rebuilt kit for the fuel pump, but I replaced it 2 years ago. to no avail.
It has had this problem for some time, I troll with the motor and therefore it is at idle a bunch. If I take my had of the tiller handle, it drops RPMS and dies. If I pump the bulb it will continue to run or if I pump the tiller trottle handle by rotating to more gas a couple of times.
At HIgh RPM (WOT) right after I get on plane, the motor will occasionally die until the bulb is pumped then it will run fine forever at WOT.
Thanks in Advance! It has me stumped!
Eye-catcher
07-21-2003, 11:05 AM
Have you changed the primmer bulb?
Also there is a filter in the tank pickup.
But it really sounds like a fuel pump diaphram is cracked.
Yes, new bulb and no filter on the tank pick up.
I will check for a crack in the pump.
Husky
07-21-2003, 12:24 PM
I would think the air bubble are an indication that air in being introduced in the fuel system somewhere. The fact that the primer bulb needs to be pumped to regain WOT operation confirms this.
Since you have rebuilt the fuel pump I will assume thats OK and not the culprit.(Although it sounds exactly like a fuel pump problem--bad diaphram or just a bad seal between the housings/diaphram.
Also the new fuel hoses remove the possibility of dry, brittle cracking hoses. The connections of all the hoses can still be suspect to leaking air. Double check them to be sure. (Change fuel filter on powerhead while you are at it)
Anything that would impede with the fuel flowing from the tank through the lines, like a partiall plugged pickupp screen in tank, filters that are partially obstructed, will increase the chances of your motor pulling air into the system instead of gasoline through it. Check the vent of the tank to be sure it opens and vents well.
I had a 40 hp MErc tha woud suddenly die at WOT after running a few minutes. After it stalled, it would start up and run fine again ( I could troll and low speed operate for hours on end) Then after 3-10 minutes of high speed operation , it would die.
Turned out to be debris in the tanl. At low speeds there was not enough suction through the pickup to cause the debris to attach and clog the opening. At high speed, enough suction was present and the motor would starve out and die. Once ead, the suction was gone, debris fell to bottom of tank, and it would agian run.
Although this is not your scenario, its just to point out the little things that can cause bog problems. I am sure you are going about this in a methodical manner, and should find the problem soon.
Let us know.
Had a similar problem with my 50 hp Merc. Did all the things you mentioned but still had the problem. Toward the end of the season I took it in to the repair shop. Turned out it was the "little black box". Replaced the electrical box for $200 and it runs like a top ever since.....and that's 4 years ago. Just my .02.
Gary U
07-22-2003, 01:18 PM
make a fuel line attachment using both end connectors and clear hose. you will find out if the air is entering at the mototr or the boat tank. if you do not have a hard primer bulb you will see air at the T. i also agree with the last post regarding the black box could be defective. merc is good about helping out after warrenty give them a call and ask their tech people other causes and diagnostics. good luck hope i helped.