115 merc slow speed problems

[tommyb]

I have a 1994 mercury 115 outboard. Lately while crusing at slow speeds, (like through canals and no wake zones) the engine wants to lose power and constantly stall. If i Pump the primer ball or push the choke it seems to come back to life. The engine runs fine at 3/4 throttle and faster speeds. Any ideas? Thanks Tom

 

[JB]

Re: 115 merc slow speed problems

Ahoy, Tommy. It is almost certainly fuel related. My guess is a weakening fuel pump or a crankcase leak. If it were a carb problem it seems to me that the other carbs would keep it running and choking it would kill it rather than revive it.<br /><br />The most likely locations for a crankcase leak are bypass cover gaskets, reed assembly gaskets and fuel pump mounts. The most likely fuel pump problem is a check valve.<br /><br />Check it out and get back to us.<br /><br />Good luck.<br />JB

 

[tommyb]

Re: 115 merc slow speed problems

If the problem was an air leak or fuel pump problem wouldn't the engine also perform badly while running at higher speeds? Is it possible that there's a leak some where in the hoses that supply the fuel causing it to lose its prime? I also haven't replaced the fuel filter.

 

[mbb]

Re: 115 merc slow speed problems

The merc 4 cyls are the 2+2 that runs on only two cyls anyway below 1800 rpm or so. I think basically two cyls have idle restrictor tubes that allow enough fuel to pass for lubrication, but its too lean to fire. I doubt a 4 cyl would idle well on only 1 cyl, so It could be a bad idle jet in one of the low speed carbs that are operational.

 

[ODDD1]

Re: 115 merc slow speed problems

Tommy, what you describe is a classic fuel pump check valve failure.....[like J.B. says...atta boy JB ]....we have had chronic probs with check valves in these fuel pumps, the new check valve and diaphram kits mercury came out with 2 years ago really help....update the fuel pump an your prob will very likely go away........