Re: orifice idle jet 40/50hp motors

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fleetwin

US Member - 2 Years
Replies: 4737
Topics: 46
#70644

It is like Bill says, these engines are so "over engineered", really can be a pain to deal with sometimes. These engines are so reliant on exhaust pressures/back pressure to run correctly, so I’m thinking the shorter exhaust hsg might be the reason different metering air bleeds/jets are used. So, there is no ID tag on the transom bracket, and no serial number welch plug on the powerhead? Oftentimes these carbs have a part number stamped in ink on them or there is an ID tag attached to the carb bowl with the part number for the complete assembly, either of these numbers there?
What is it about the carbs that make you think they are for a 50hp? Those jets you a referring to are actually intermediate circuit air bleeds, they meter air, not fuel. So, a smaller air bleed will create a richer mixture. Changing an air bleed by .003" is roughly the equivalent of changing a fuel metering jet by .001"…So, the different sized air bleeds you are seeing don’t make much of a difference at all. The air bleeds in your engine will create a slightly richer mixture off idle. I wouldn’t worry about it, just be careful setting up the carb sync, follow the book exactly. The engine must be run on a boat in the water for the running adjustments also, don’t attempt this on a flushette or in a test tank. Those little needle valves control the idle mixture, can’t remember what their initial setting is though. I’m guessing the short shaft engines use larger air bleeds to create a slightly leaner off idle mixture due to lower engine height and higher exhaust back pressure.
Sounds like we really don’t know what year/hp you have there. If it was mine, I wouldn’t worry about it, just set it up carefully according to the manual, I’m sure it will run fine.