2000 Mercury 115 low speed coughing

Tim Matter

Recruit
Joined
Apr 20, 2003
Messages
2
Can any of you Mercury outboard guys help me out? The motor has basically ran this way since new. It's gotten to be quite annoying. Here are the symptoms:<br /><br />1. It starts good but at warm up and idle RPM it coughs, sneezes, and sometimes dies. This is most prevalent at high idle (1500-2000 RPM). If it continues to run after a cough, it will slowly regain RPM till it does it again. Approximately 5 seconds between coughs.<br /><br />2. Engine and air temp do not affect the way it runs at all. <br /><br />3. When under way it runs extremely rough till about half throttle, then bang, immediate smooth power and RPM without warning. Passengers are really impressed with this. It does this every time without fail.<br /><br />4. I also noticed the bottom two carbs do not have idle mixture adjustment screws??? and there is some sort of enrichment(???) valve activated by the throttle arm on the left side of the block. What gives here? How does the fuel system operate?<br /><br />5. Also changed spark plugs; no change. <br /><br />Any explanations or ideas ?<br /><br />Thanks<br />Tim
 

Boatin Bob

Lieutenant Commander
Joined
Sep 24, 2001
Messages
1,858
Re: 2000 Mercury 115 low speed coughing

I was just looking at a 2003 115 with carbs on the weekend, salesman told me that up to approx 1800 rpm these things only run on 2 cyl and then the other 2 kick in, supposed to run real smooth and lean in the low rpm's, just wondering if maybe your only running on one?
 

Tim Matter

Recruit
Joined
Apr 20, 2003
Messages
2
Re: 2000 Mercury 115 low speed coughing

I did notice the bottom two cylinders don't fire at idle when I was fogging it last fall. That throttle activated valve (enrichment ?) I mentioned is teed into the fuel supply on one side and goes to the right side transfer ports of at least the bottom two cylinders. I can't see if the top two cylinders are fed by this device as well. I'd like to know how this contraption and the rest of the fuel system is supposed to operate. Maybe it would shed some light on the way it runs and which part may be responsible.
 
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