2005 115Hp Mercury.

[James R]

Some thing strange happening here. Very low hours. Comps 135 all.New plugs. Carbs cleaned and new kits. Ran well in the tub all cylinders working. First time on the lake not more than 3k rpms. Pulled it out. Checked and lower two cylinders not firing. Good sparks. Suspected poss blockage in the lower carbs. Pulled the lower carbs and you know what a pain it is to put it all back. Cleaned the two carbs and yes there was fuel in both bowls. Refitted all and ran on a jug of clean fuel to eliminate possible dirty fuel from the tank.(Needs a big filter, the manuf did not fit one in the boat). Still two lower are not running. Pull the lower two plug leads off while running and no change. Got me guessing. There is one piece in this fuel system that I am not familiar with. Looks like some kind of accelerator pump and runs off the throttle cam. Need help badly guys.

 

[pigeon laker]

Re: 2005 115Hp Mercury.

I'm not sure with a 2005 merc 115,but,the older ones 1990 and up are a 2+2 system where the bottom 2 cylinders only kick in at about 1800 RPM's.Check the carbs to see if there are low speed idle mixture screws,if the top 2 have them and the bottom 2 don't you have a 2+2.I have one and it used to run excellent then one spring I had lost some power and 300 RPM's.Still can't find the problem.If you have any ideas please post.

 

[CharlieB]

Re: 2005 115Hp Mercury.

It is an accelerator pump, the lower two carbs do not have the rich idle mixture necessary for acceleration, the pump provides a short of fuel to the lower carbs on throttle opening.

Check the carb synch very carefully, if the lower carbs are opening slighty late then those cyl's are lagging behind the rest of the motor and act like they are not firing, plugs clean and cold.

Has anyone had any wiring disconnected lately?

Is it possible that wires TO the the coils have gotten switched? If no then double check your link and synch.

 

[James R]

Re: 2005 115Hp Mercury.

Pigeon and Charlie. You are a wealth of information. Thank you so much for your help. All is set correctly and apparently I was unduly concerned about the motor. Located a loose tank coupling so I expect that the fuel pump was sucking air.Will know more after lake test.Yes it is a 2+2 but I am still not clear as to how they achieve this. The sparks are on all four at turn over so they must be shorting the lower two of fuel. I would have thought, if this is the case, that that would create a lubrication problem.
Your Question re 300RPMs down. Could be a whole bunch of things but I would bet that it is fuel related, that is of course if you have the same set up re prop,trim,weight etc..Remember that the crappy fuel we are getting plays a big part in performance. Might be water in there.