Merc 115 No Power and rough at Higher RPM.

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MARCnAZ

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Oct 7, 2006
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Hi I have a 1996 Merc 115 OB. Ran great about 4 weeks ago. I go out firly often so gass should be ok. Took it out last weekend and couldn't get much over 2000rpm or on plane. Idles ok, but cuts out and starts running rough when it gets up in RPMs. Good (new plugs/wires) spark all cyl good compression. When I spray carp cleaner in top 2 cyl it slows down and wants to die (like is should?) When I spray in bottom 2, it revs up a bit. When I pull plug wires on either of bottom 2, little or no change. Is this a carb problem on bottom 2 carbs/cyls? Or something else like a dirty filter or weak pump. Thanks in advance for any help or advice!
 
Boatin Bob

Boatin Bob

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Sep 24, 2001
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Re: Merc 115 No Power and rough at Higher RPM.

These are the 2+2 motors, only runs on the top 2 carbs up to approx 1500-2000 RPM's then the bottom 2 kick in. The bottom 2 don't even have low speed circuits but they do have a special circuit in them to allow just enogh fuel in to keep them lubed but the power generated is negligble until the high speed circuit starts. I think there is a cam and linkage to engage the bottom 2 carbs, possibly check it out.
 
M

MARCnAZ

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Oct 7, 2006
Messages
3
Re: Merc 115 No Power and rough at Higher RPM.

Boatin said:
These are the 2+2 motors, only runs on the top 2 carbs up to approx 1500-2000 RPM's then the bottom 2 kick in.
Click to expand...

Ahh.. Thanks... I saw the cams on the linkage and was wondering about. Disconnected the linkage at each carb and all are running well enough to at least rev engine some when individual carb is throttled. My initial thoughts were also that I may have spun a prob hub, but I didn't have a marker to mark hub and retest. May have just been the plugs and wires which are now new. Also used a can of carb cleaner on the carbs. It's hard to say if running well without getting it out for a test run at a lake. Think I'll try tomorrow and take a spare prop to test that too. Thanks for your reply, that explains the issuse I noted on my original post!
 
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