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Hi, I have a 1992 Montauk 17 which we got recently with the original Evinrude 90hp V4 on it. My daughter is 2yrs old and does not like it at all when boat goes on plane. So when she comes along I am relegated to puttering around the harbor looking at boats and wildlife for now. I have heard that 2 stroke motors can foul plugs at low speeds, wondering what speed would be considered too slow. We are usually around 1500 to 2000 rpm, I think somewhere around 6-10mph for about 45minutes or so.
Would that be cause for concern for plug issue (or other issue such as overheat) ?
VRO is disconnected and I mix 50:1. Unfortunately no manual came with the motor. Just wondering what threshold is between fouling and not fouling when running a consistent speed.
Lucas, My Evinrude 90hp, “non VRO” never had any issues running at the RPM’s you mentioned. To ease your mind replace your water pump and carry a new set of plugs along with a socket.
The OMC/Johnson/Evinrude 88/90/110/112/115 V4 Crossflow two stroke outboards should have the combustion chambers treated to remove carbon deposits approximately every 50 hours of operation.
The manufacturer recommended product is call the BRP/Johnson/evinrude Engine Tuner fluid.
Johnson Evinrude OMC Engine Tuner is for removing gum and varnish build-up, excessive carbon deposits from rings, pistons, valves and ports. Spray through air intake of 2 and 4 cycle engines for improved performance. Not to be mixed with oil.13 oz. Spray Can.
When operating underway, You can maintain a headway speed, slightly above idle, and then transition to planing speed, activating the high flow carb jets.
You should avoid operating your boat for a long period of time at a speed where you are "plowing water" with your bow, and not quite on plane. That type of operation will "coke" up your combustion chambers quickly.
You should always run your outboard at full throttle for a short period (2-3 minutes) after prolonged low rpm operation.
You should be fine. Just go for a quick blast around after you drop your daughter off at the dock to clear things out.
I would avoid the high end of your range (2000 RPM, 10 MPH). At that speed you'll be almost trying to plane, and pushing a lot of water - if you look, you'll see you're making a lot of wake. That low speed, high load operation will cause almost any outboard to overheat. You're burning a lot of fuel but not running enough air and water through to cool the motor. Stick to speeds where you're only making a small wake and you'll be good.
