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1998 225 johnson infrequent lean sneeze only when warm?

H

humm9er

Member
1998 johnson 225. I cleaned all 6carbs with new gaskets installed over winter. Boat runs up to 5700RPMS at WOTand idles in great at around 750rpms per my OMC tach. It will idle at the dockfor 20 minutes no problem, and will idle forward when leaving the dock for along time too.


When running theboat at 4000+ RPMS, when I back off to idle forward, it began sneezing lastweek. I used an unlit propane torch to isolate the sneeze to cylinder #5. Iremoved the carb and cleaned the brass idle passage again. Put back on, ran theboat again at idle forever at dock no problem. Ran at speed for a day and whencoming home the boat sneezed at idle fwd twice in about 10 minutes. Stalled oneof those times. If I bump the RPMS to 850/900 or so I never stall.

Any ideas? Thesneeze is so intermittent I haven’t yet been able to use the propane trick tofind the lean cylinder.

I am wondering ifthis is tied to the temp of the engine? Seems to only happen when warm…airleak? Also wondering if I should check #5 and #6 throttle plates for fullclosure but if this were a lync and sync issue wouldn’t it happen at all times/ temps? Only other thought was maybe adjust that carb bleed screw, or remove carband clean the throttle plate passages (I did not do that when cleaning thecarbs)?

Last question – I knowthe idle, mid and high speed jets are separate. With this intermittent an issueonly at low idle, I’m in no danger of leaning out a cylinder at non-idle speedsif I occasionally run the boat while I address this, correct? Have a crewcoming fishing tomorrow and don’t want to cancel.
 
faztbullet said:
Leave the carb alone and check passages and gaskets on throttle bodies....
Click to expand...

I assume I should start on #5 first as that was the source of the sneeze before I went through the idle jet again?

Also, should I spray carb cleaner and run a small wire through the small holes behind the plate on the side of the throttle body? Is that my primary focus on the throttle body? I mean behind item 3 below:
 

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Yep.....also remember that you have a X flow intake as carbs on left actually feeds cylinders on the right(looking at carbs) and vise versa.
 
You've had that #5 carburetor off twice recently so it's highly unlikely that you've missed and bad rear seal rings or gaskets BUT a air leak would result in sneezing... something to think about. And I assume that you're sure that the villain is the #5 carburetor.

Keep in mind that the idle jet is a "Idle Air Bleed Jet", meaning that it measures "Air", and not fuel. To steer away from the lean sneezing and to enrich the fuel mixture, the ID of the jet must be decreased. If it were me, and all else fails, whatever that jet is marked.... I would drop it down a thousand... or more, as needed.
 
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