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Mercury 35 hp. What is this unattached hose on the carb?. Total newbie here.

D

dantabletop

New member
Hi. I have a boat I got recently, and it was running great. The other day however it was struggling to stay running without giving it throttle. Putting in idle would kill the engine. When putting in forward I'd have to give it occasional throttle to keep it going. However after a while of playing with the throttle, it'd eventually run fine at idle and run without having to keep giving it throttle


I decided to take the cover off and have a look. I noticed a hose on the carb not attached to anything. I'm not much of an engine person, so this may seem dumb, but be patient with me.

Would this lack of hose be tthe reason for trouble with idle and low rpms? Is it easy enough to fix while the boat is on the water. Will connecting the hose cause any issues that may not be easy to fix as a newbie.

I found a parts diagram for the carb, but this hose isn't labeled on it.

This is the hose here - https://i.imgur.com/NOTOYKbr.jpg

I assume it should reach and connect to this?

https://i.imgur.com/ahJXBmBr.jpg
 
What year is your Merc? How many cylinders? Looks like one carb. I have a '92 40 Merc 4 cylinder 2 stroke and your carb is very similar to my 2 carbs; however, mine do not have that hose. Sorry no help here.
But, at 9 oclock in your first photo, there is the slotted head of the idle mixture screw same as mine; it should be about 1 1/4 turns out to begin; with this screw you can richen the idle mixture by turning CCW. Read somewhere that an engine will not idle well if this mixture screw is not set right or the carb is dirty inside. If you go for this screw, be very gentle while turning inward (lean) so as not to distort its needle tip end. To adjust the mixture, you turn CCW (rich) till engine loses RPM, then turn CW (lean) till engine loses RPM. then set the screw to the middle with favor to setting it rich.
But, I am no mechanic - a little knowledge is a dangerous thing.
 
That hose is a back something or other (dumb) idea they tried to save gas (and burned pistons instead). You don't need or want it.

Plug it up and readjust the idle mixture screw for best idle, warmed up and in gear. Then add a 1/4 to a 1/3 turn OUT and go boating.

Jeff
 
Thanks for info Jeff, I forgot to mention the warm up part and it is critical to set the mixture while in gear. My Merc shop manual specs the idle speed in gear at 600-700 rpm; but, from my dash tach that comes to be 775-800 rpm; and out of gear in neutral my dash tach shows 975-1000rpm.
 
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