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Old 06-04-2014, 07:57 PM   #1
Lt. JG
Join Date: May 2012
Location: CT River
Posts: 30
Default Has anyone dealt w/a Carbed Merc 5L that bogs down upon accelerating then RPMs jump??

6/2014 Update: Brewer Dauntless Shipyard mechanic finally "adjusted" the carb for a 2nd time in a year's time, engine now idles but the idle was set to 1,000 rpm in error based on what I've read, which should be @ 650 like its twin is running. How they thought it was ok to have it so out of synch with its twin & out of merc spec is beyond me, but par for their course thus far.. So I lowered the idle, but other problems still exist that Brewer claims was fine when tested:
Problems are as follows:
1) hard & rough start req'ring rpms above 2K until fully warmed or stalls repeatedly, unlike its twin.
2) bogs down & wants to stall when throttled up slowly or quickly in either neutral or in gear. Hear air/sucking sound as it bogs.
3) when throttle is pulled back as it is bogging to prevent stall, the rpms then jump way up to where the throttle was just prior even tho its back to idle position.
4) upper rpm range is totally fine & runs strong thru 3K's
Anyone have this issue or know of an easy fix, ie fuel/air mix etc??

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Old 06-06-2014, 03:51 PM   #2
mmwjr's Avatar
Join Date: Feb 2012
Location: Perry Hall, Maryland
Posts: 6,130

5L so it is a 2bbl carb, correct? Any black smoke? Sounds like it may be running to rich. Float set to high?

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Old 06-06-2014, 09:21 PM   #3
Lt. JG
Join Date: May 2012
Location: CT River
Posts: 30

Hey Mike, thanks for responding. Yes, it's a 2bbl carb/220hp. I haven't noticed unusually heavy or black smoke, just the usual bit of blueish smoke at start up, but I have smelled gasoline while underway at times like its running rich. When I go to throttle up from idle, it bogs & wants to die, so I try to feather it up gently to avoid a stall until the rpms just all of a sudden "kick in" to several hundred rpms higher & all at once; and/or, if I don't bring the throttle quite all the way to where the rpms jump up, but instead I just bring it back down to the idle position, but still in gear, all of a sudden the rpms jump back up to where the throttle was, like its a delayed response. It's weird. I'm hoping to be able to correct it myself if its a simple enough problem & fix. Originally it was an idle problem, where it wouldn't hold an idle beneath 2K rpms, & now it idles but has a short window of bogging until rpms are upwards of 1500 or so & then the throttle is responsive & it runs strong & smooth all the way up from there.
How would I check the float level &/or adjust it? So far, without taking anything off the carb, I've only noticed 2 spring screws for adjusting, the idle screw which is behind the carb & attached to the throttle linkage which I used to reduce the idle that the tech had incorrectly set to 1,000 rpm, which I'm guessing was his answer to fixing the original non-idle problem, and the other screw is at the lower front base of the carb which I'm guessing is a fuel/air adjustment...
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