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2004 115hp 2+2 wont run on 4

B

Big Brown

New member
I've got an 04' Merc 115hp 2+2 that stopped running on 4. I have been out on lake michigan regularly and with the rough waves I have had alot of idle time and rarely have been able to get it up and cleaned out. Last time out it would not pick up the bottom 2 cylinders for some reason? I checked spark-good spark (I felt it all the way to my toes when removing the plug caps) on both the cylinders in question. Swapped cdms around-that didnt do anything. I put new plugs in it and put the muffs on it in the driveway and revved her up to about 3000rpms and she will not pick up the other two cylinders? I sprayed starting fluid in those carbs and it lights right off? Thinking maybe a carb issue but why would both main jets get plugged at the same time? I pulled the lines off both carbs-they have fuel going to them. I took the fuel filter off and it was spotless. I am stumped here? My next move is to remove both the bottom carbs and inspect but I am really skeptical they both got plugged at the same time? Especially when I have been running the boat 3 or 4 days a week. Could it be my fuel pump is not building enough pressure?

I was able to get it up and running on 3 cylinders (thank god I was 7 miles out) but it would not pick up the fourth? It picked up for a second and died again. put new plugs in it and tried running it again-same thing. Came back both plugs were dry and looked new. WTF is going on here? I got off plane and it would only run on 2 again? Any ideas?

I assumed the other 2 cylinders would pick up above 2000rpms while in neutral but I am thinking the motor can free spool 3000rpms on 2 cylinders no problem.

Thanks
 
Does the motor have to be under load for the other 2 to pick up? I can't rev the piss out of it in my driveway and get fuel through the other 2 main jets?
 
Clean and inspect the carburetors--------------------Remember if you do not have enuff fuel going in , then there is little oil there to lubricate the moving parts.------Never let carburetors sit with fuel in them for prolonged periods of time.
 
As I understand it, the 2nd two cylinders kick in based solely on throttle opening which (under load) is usually around 1800 RPM. Running in Neutral it will probably rev way beyond that on the top two carbs alone. If this were done for long periods, lubrication to the bottom cylinders would become a serious problem. Check the linkage for proper adjustment. Some areas to investigate would be low fuel pump pressure and the enrichment and accelerator pump systems which are "Teed"off the fuel lines from between the top carburetors. A Temporary block off of those systems would help diagnosis. The fuel pump diaphragm is a source of possible trouble. Try opening the throttle under load and pumping the fuel line squeeze bulb to see if this helps.
 
The bottom 2 carburetors have no idle adjustment screws but do have very small fixed idle fuel passages...these allow enough fuel mix to reach the cylinders for lubrication purposes at idle, but not enough to provide a combustible mixture. Spark is constant on all cylinders regardless or speed or throttle opening. As the throttles are opened, the main jets take over for lubrication and fuel supply and the motor runs like any other two stroke. Be sure the throttles are opening and the linkage did not become loose or disconnected. Search the archives from last year and the year before for 2+2 and you should find several posts regarding these motors.
 
I will check the linkage. Boat has run great all summer. Never sat for more than a wk without running. I will post back my findings. Working insane hrs. Thanks for the help thus far
 
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