Major fuel/carb issues

egscharf

Seaman Apprentice
Joined
Dec 2, 2012
Messages
30
1997 Johnson 115 SPL (J115TSXEUA)

Symptoms: engine will not start at idle, only when throttle is significantly advanced. Boat bogs down at full rpms, engine stalls when brought to idle. Heavy smoke in exhaust. Heavy black oily sludge noticed in exhaust. Spark plugs are new and are producing good spark. I took of the air cleaner cover and noticed that the top carb is leaking fuel at idle, not just a drop here and there but a heavy flow, see attached picture for location. Could not find the name for this hole in any diagram. When engine is primed, fuel bulb does firm a bit, but doesn't fully harden and fuel also spews out of the carbs. This is abnormal, correct? Sychronization and Linkage appears to be correct.
I should mention that I recently swapped the plastic float bowl chamber in the top carb for the new metal one, as the drain plug hole in the plastic bowl was stripped. However, the hole for orifice #25C in the metal bowl was of a smaller diameter than the one in the plastic bowl. I was told I could simply tap the hole out to fit orifice #25C, which I did, as the inner orifice diameter was supposedly the same. Could this be the cause of the issue? Does anyone know the part number for the orifice that fits the new metal bowl?

I ran for about 10 hours straight shortly after doing this, and the boat ran fine. She then sat for three weeks, and when I took her out was when she began exhibiting these problematic issues. Carbs were then rebuilt and cleaned. No obstructions noted in any passageways, but no change in symptoms. Tested: spark measured at 7/16" gap, full spark noted. Fuel pump tested by priming bulb with engine running, no change in RPMs. Engine decarbed, no change in symptoms. Ran on external fuel source, no change in symptoms. Carburetors cleaned and rebuilt, no change in symptoms. Timing is good. Idle screws are in place and clean. Could it be a float adjustment?

What do you think?

Thanks for any and all help!
 

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Bosunsmate

Admiral
Joined
Apr 7, 2012
Messages
6,135
Re: Major fuel/carb issues

Is it leaking out the top of the top carb where that arrow is?
Its sounds like its flooding.
Theres an idle orifice up the top there.
What happens when you prime the bulb with the engine off does it keep leaking out of there?
 

egscharf

Seaman Apprentice
Joined
Dec 2, 2012
Messages
30
Re: Major fuel/carb issues

Yes, it is leaking out of that hole with the arrow pointing to it. The idle screws are up top there, they both are present and look clean. When I prime the bulb engine off it floods out of there big time. Could it need a float adjustment?
 

Bosunsmate

Admiral
Joined
Apr 7, 2012
Messages
6,135
Re: Major fuel/carb issues

Yes, check the needle end and the seat for wear too
 

egscharf

Seaman Apprentice
Joined
Dec 2, 2012
Messages
30
Re: Major fuel/carb issues

The needle and seat are brand new, but it sure seems like a stuck float. Will be taking it apart today to see whats doin.
 

pn

Petty Officer 1st Class
Joined
Apr 20, 2013
Messages
374
Re: Major fuel/carb issues

when you have the carb off you could hook up a piece of hose to the inlet and blow... moving the float up/down to see if your needle a acting funny. should stop all flow in the float up position if not then figure out why.
 
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