1996 75 hp mercury elpto bogs down mid range

meerkat

Seaman Apprentice
Joined
Sep 21, 2009
Messages
45
The last couple of times I have been out, my motor bogs down between 3000 & 4000 rpm. When it starts to bog down if I put it to WOT it opens up to 5400 without a hitch & will run at 5000 rpm no problem. If I leave it between 3000 & 4000 sometimes it will even quit altogether but if I pump the primer bulb it will keep going. It seems to start and idle fine but every now and then will quit at idle.

Normally I would go to "fuel pump" but the carbs and fuel pump were rebuilt this last winter - may still be that but looking for more ideas before I do the rebuild again.

So here is what I am seeing and what I have done so far:
I attached a pipe to the fuel tank pickup point and can suck and blow on that no problem (so no blockage at the tank). The primer bulb does not get pinched at any speed but does empty itself at the 3000 - 4000 rpm (if I pump the bulb it will keep going). I connected the motor to a portable tank with clean gas & there is no difference to the motor's behavior. I ran iso-heet through the portable tank in case there was water in the carbs - no difference. I replaced the in-line fuel filter on the motor.

Replaced fuel hose and primer bulb - no difference.

I am thinking a small air leak between the fuel hose connector and the fuel pump or maybe a hose that pinches at higher vaccum?

Like I said could be the fuel pump but I am looking for other possibilities. Any help would be most appreciated. I am pretty good with a wrench but this one has me stumped.
 

meerkat

Seaman Apprentice
Joined
Sep 21, 2009
Messages
45
Re: 1996 75 hp mercury elpto bogs down mid range

Okay - so here is what I did and here is what I found so far.

I followed the Mercury manual troubleshooting and put a piece of clear pvc hose between the pump and the carbs to check for air bubbles. Well I have lots of air bubbles which go away when I pump the primer bulb.

I bypassed the fuel line connector (fuel line to motor) with a piece of 3/8 copper pipe. Still have air bubbles so it is not sucking air through a bad fuel line connector.

I hooked up my kicker motor fuel line to the 3/8 copper pipe to check the integrity of the fuel line back to the built in fuel tank. Still have bubbles so it is not sucking air somewhere between the bulkhead and the pickup point in the tank.

Also with the engine running I disconnected the kicker fuel line from the portable tank I use for the kicker. The motor sucked the primer bulb flat and the primer bulb stayed flat after I switched the engine off & until I plugged the fuel line back into the portable tank. So it looks like I am not getting the bubbles between the fuel pump and the built in tank.

So it has to be a fuel pump problem that is generating the bubbles.

I have a fuel pump kit on order.

Must have screwed something up when I rebuilt it over the winter. :mad:

I will report back when I have rebuilt the pump.
 

meerkat

Seaman Apprentice
Joined
Sep 21, 2009
Messages
45
Re: 1996 75 hp mercury elpto bogs down mid range

It is the fuel pump. I took it apart and the boost gasket is broken.

My Bad! :( When I assembled the pump last winter I must have had the gasket slightly off center and the thin piece of gasket that separates the pump inlet and outlet compartments has blown out.

Parts are on order. I also paid attention to some of the other possibilities mentioned in the comments & am replacing the hoses, fuel line connector, etc. They may be fine but they only cost a few bucks & I don't want a repeat performance if I am out 20 miles with a storm coming in....

The key was hooking up the clear pvc between the pump and the carbs and seeing the bubbles.

Joe S.
 

meerkat

Seaman Apprentice
Joined
Sep 21, 2009
Messages
45
Re: 1996 75 hp mercury elpto bogs down mid range

I rebuilt the fuel pump and installed it. I swear I did not touch anything electrical but now it will not start. :confused: I checked for spark and there is none.

Anyone got any ideas on why I have no spark? (I did check the dead-man switch).
 
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