1996 Mercury 115 2+2 idling issues

[Napoleon]

I’m new on this site and this issue might have been addressed in the past, however here we go. I’ve recently picked up a Mercury 115 2+2 whith the oil injection system removed. I run a 50:1 mix of synthetic outboard oil. The engine runs great above 2000 RPM but rough below that because as you know, the lack of idling jets on the lower 2 carbs. I’ve read many discussions regarding carburation on this type of engine, but has anyone tried to replace those lower carbs with carbs that do have idling jets like those similar to the top 2.

 

[racerone]

Not a good idea and has been tried I believe.-----Done a compression test ?

 

[Napoleon]

No I haven’t done a compression check, however the engine and carbs were completely rebuilt 2 years ago...about 20 hours of use. The boat is in storage until next April, so I can’t access it. Why don’t you think it wouldn’t be a good idea to replace those two lower carbs with some with idle jets like the top ones?

 

[racerone]

Find some on E-bay and give it a try.

 

[Napoleon]

Yes, there are some on E-Bay and have seriously considered bying some, however I just wanted to check to see if anyone had experienced this type of instalation.

 

[Johnson110]

It will not work from what I hear engine is designed that way, you can not change a engineering design or everyone who has this motor (myself included) would be changing the carbs.

 

[Napoleon]

Ok thanks, ...It’s not really that bad at lower speeds....the boat is a 19.5 Wellcraft CC, weighing about 2400 lbs and at 2000 RPM ( pretty smooth) I get 6 to 7 mph...at WOT ( close to 5000 RPM) it cruises smoothly at almost 40 mph.
So I guess I’ll pass on the carburator replacement.

 

[flyingscott]

Get a factory manual for your motor and do a proper link and sync. Was the boat stored correctly because 2 yr old gas in carbs is enough to cause problems. That should be a smooth running motor some investigating needs to be done. The people I know that have them would not change anything.

 

[Napoleon]

I agree that stale gas can play havoc on carburators. My main concern is the fact that since the oil injection system has been removed, I want to get more oil to the bottom cylinders at lower RPMs since there are no idle jets to feed these 2 cylinders. I’ve read that there is an orifice in these lower carbs that do permit a small amount of fuel, thus an oil mixture...but can anyone confirm if there is an orifice.?.....this could be critical if not.

 

[racerone]

Sure there is !!----It is fixed at the factory.----Lets in a small amount of fuel / oil for cooling and lubrication.

 

[Napoleon]

Great, thank you