Mercury starting problems

chkm8

Cadet
Joined
Jun 21, 2008
Messages
28
Advised to come here and ask the experts so here goes. I will try to give as much info as possible,

Mercury 115hp approx 1984 model.
2stroke straight 6 cylinder with surface gap plugs.
Starting has been a problem since getting this boat last year. Though once running it seems to run perfectly at all speeds.
Starting sequence prime until bulb firm. Push in key to apply choke turn key and throttle forward as it starts to catch. (No choke and it def won,t start though when it eventually starts loads of blue smoke).
Sometimes this results in a first or 2nd time start other times you could almost risk running the battery down trying.
Starter motor just serviced at start of this season.
I replaced both batteries since buying the boat and they are fully charged as of start of season and minimal use.
I also changed the priming bulb as it was pretty old and not remaining firm no matter how much you primed it. This did help in that successful starts are more frequent but it has not totally solved the problem.
I also noticed the fuel line from tank to bulb is a narrower diameter than from bulb to engine not sure if this is normal or contributing to the problem and if so which do I change for best the narrower or wider diameter tube.
It was also suggested to me I reduce the oil mix I currently add 400ml to 20litres = 50-1mix
Am reluctant to do this but would try it if it solved my starting problems.
Runs well at idiling and all other speeds just so tempermental when starting.
Any suggestionsmore than welcome.
 

blazer81.6

Seaman
Joined
Jan 25, 2009
Messages
57
Re: Mercury starting problems

I've actually owned an inline 6, 87 model 115hp. It also seemed to be harder to start than other outboards previously owned. I installed new plugs (slightly hotter than what was taken out). This seemed to enhance the starting process.

* Syphon valve was a good place to start.
 

blazer81.6

Seaman
Joined
Jan 25, 2009
Messages
57
Re: Mercury starting problems

I wouldn't recommend mixing leaner than 50:1. Although your engine may not need that ratio down low it most certainly requires it at WOT. I would rather have slightly rich down low than lean up high.
 

chkm8

Cadet
Joined
Jun 21, 2008
Messages
28
Re: Mercury starting problems

Thanks for the advice. I will keep the mix as it is and go with a new set of plugs. Maybe the combination of new plugs and replacing the faulty syphon bulb will make enough of a difference.
 

thelm

Cadet
Joined
Jun 11, 2009
Messages
13
Re: Mercury starting problems

You might try opening the idle mix screws a bit. 1/4 or 1/2 turn each might help starting without hurting idle.
 
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