Last of the super reliable 2 stroke light weight motor. Motor is oil injected and has power tilt and trim. 1998 Mercury 90hp outboard motor model number 90ELPTO 20 shaft length.
The duty cycle used by the EPA to measure outboard emissions is weighted 40 percent to operation at idle speed but just six percent at wide-open throttle. Lean to be Clean The carbureted Honda BF90 was tuned on the lean side at idle speed to keep it smooth and clean at trolling speeds, and also to help it meet emissions regulations. So since personally experiencing this lean-bog on a Honda BF90 last summer, I've been looking for ways to solve the problem. It certainly is the model that put Honda on the map in the walleye belt.
Living with Lean One of those techs is Aaron Jacoby, the Honda man in the shop at Norton's Dry Dock near Princeton, Wis. Now, this does not happen in all applications, but it must happen frequently, because every Honda tech I've talked to is aware of the problem. By then the motor is starved for fuel and dies. There's a split-second lag as fuel is drawn through the venturi of each carb, and it then has to travel all the way down the intake runner. Punch the throttle on the BF90, and the motor gets a big gulp of air. So a motor that makes very low emissions at idle can be tuned to run richer at higher speeds, which can be good for performance and long-term durability.
But Jacoby points out that the rev limiter on the carbureted BF90 is set at 6600 rpm, "so you got a lot of rpm left to work with." If your BF90 bogs, try dropping down one prop pitch size, and see if it helps. If you prop to 6000 rpm with a heavy load, you'll need to watch the tach with a lighter load and avoid over-revving the motor. Aluminum props will usually slip more on hole shot and let the motor rev quickly through the lean spot. This is especially true if the prop is an aggressive stainless steel model. Too much prop pitch puts extra load on the motor when the throttle is dropped - it's like trying to start a stick-shift car in second gear - and this exacerbates the effect of the lean carb tuning.
"Guess you just have to learn to power it on to begin with," he said. How about pushing the boat on a trailer? Jacoby shrugged. Then nail it and the boat should accelerate smoothly. This gets fuel flowing through the carbs and puts the motor past the lean spot.
Start by turning each screw out (counter-clockwise) two turns. Don't try to pry the cap off - you'll just break off the head of the screw. (My finger is pointing to the cap in the photo) When the epoxy melts, the cap will come right off, and you'll see the slotted head of the jet. Place the hot iron right next to the cap (keeping it away from fuel lines!) while you also grip the cap with a needle-nose pliers. The caps are secured with epoxy, and you'll need a 100-watt soldering iron to melt that glue.
Engine Type: Honda BF90D5XRTA Four Stroke Horsepower: 90 hp Cylinders: 4 cyl. And if anyone asks, I did not tell you how do this.2019 Honda 90 HP BF90D5XRTA Outboard Motor.
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