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Low revs issue

wynjim55

wynjim55

Regular Contributor
The answers to my questions on this forum have helped me to rectify a number of problems with my 1978 Mariner 55hp 2 cylinder outboard (Yamaha built), I am thankful to you all for your advice and knowledge.

I've now had this outboard for over 12 months so I'm getting to know it fairly well. It runs well, even starts easily now thanks to some good advice from here on running the engine dry of fuel after each use. I've recently replaced the battery leads to the starter motor and it winds over better than before. I have previously cleaned and rebuilt the carbs and fuel pump, and replaced all the fuel lines (tank connector through to carbs). The charging system is operating well. There is however one persistent problem.

After having been running well and coming back to say a boat ramp, it struggles to maintain low revs for a controlled approach. If I'm quick enough I can go from forward to reverse but I have to keep the revs up a little immediately after the change, same too when I go from reverse to forward again. It makes for some rough changes given that I can't operate slowly. What am I looking at here? At times it struggles to maintain idle before heading out, yet in the driveway it will idle nicely until starved of fuel (causes me to think the idle speed is good).
 
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When you set the idle mixture on the carbs did you richen the mixture a little by turning the screw CCW another 1/4 to 1/2 turn?
 
I actually left that to the marine mechs who synchronised the carbs after I rebuilt them. Could it be that simple? To be honest I haven't got a tacho so have no idea what is set at. I do have an older 4 stroke tach/dwell meter, I guess I could use that and just halve the reading.
 
Could it be that simple?
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Sometimes...just launch the boat and secure it to a dock or leave it on the trailer and back it in the water. Let the engine warm up and turn the idle mixture screws CCW 1/4 turn and then test the boat. You may have to adjust the idle speed but I would do it w/a tach.
 
Thanks for the advice, to be honest I feel really silly having not thought of this and done it when I finished rebuilding the carbs after they were synchronized. Long story short, a half turn on each idle mixture screw and a small adjustment on the idle screw and now I can learn how to control a boat confidently with full rev range in forward and reverse. Life is so much simpler on the water now, and much less embarrassing. Cheers.
 
Embarrassing is when you arrive at the slip and everyone heads for the hills until you're in the water and gone:D:D.A lot of non starts ,but not lately,touch wood.:D
 
A friend of mine joined a local yacht club after purchasing a 25' concrete hull sailing vessel. His first approach to the marina saw another vessel somewhat smaller and lighter launched out of the water and onto the floating pontoons when the concrete hull lightly touched it while manoeuvring into a berth. Every time he takes it out or comes back in everyone present at the club comes down to "assist". That is embarrassing.
 
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