Replacing an older 70–90 HP two-stroke with a current Mercury 90 FourStroke EFI can improve starting, noise, fuel handling, and serviceability on a compatible 17-foot aluminum runabout. This is an illustrative planning example. HBW confirms motor weight, hull rating, controls, fuel system, propeller, and the current written quote for the actual boat.
Last reviewed: 2026-07-18
Quick answer: This illustrative scenario replaces an older 70–90 HP two-stroke with a Mercury 90 FourStroke EFI on a properly rated 17-foot aluminum runabout. The pricing reference shows the current bare-motor price; removal, controls, propeller, fuel-system work, rigging, and testing require a boat-specific quote.
Replacing an older 70–90 HP two-stroke with a current Mercury 90 FourStroke EFI can improve starting, noise, fuel handling, and serviceability on a compatible 17-foot aluminum runabout. This is an illustrative planning example. HBW confirms motor weight, hull rating, controls, fuel system, propeller, and the current written quote for the actual boat.
Key facts
- Old motor: 70–90 HP 2-stroke (Mercury Sport or discontinued Evinrude legacy)
- New motor: Mercury 90 HP FourStroke EFI
- Boat: 17-foot aluminum runabout
- Pricing: current bare motor in the pricing reference; installed quote depends on the boat and rigging
- Boat with us: 2 to 5 days (motor lead time separate)
- Warranty: Mercury Limited Warranty, confirmed at quote
- Noise and fuel use: compare with measurements from the actual old engine and boat
What was on the boat before?
The starting motor is a 1990s-or-early-2000s carbureted 2-stroke in the 70–90 HP range. Sometimes it's an older Mercury Sport. Often it's a discontinued legacy 2-stroke from Evinrude, a brand that stopped making outboards in 2020 and is no longer supported by its original parts pipeline. Either way, the motor is the same story: it ran for a long time, it's finally tired, and parts for a proper rebuild are harder to find than they used to be.
The boat is usually a 17-foot aluminum runabout owned by someone who has had it for 15 to 25 years. They love the boat. They aren't interested in trading it. They just want a motor that doesn't need a 2-stroke oil top-up at every fill, doesn't blow smoke on cold starts, and doesn't rattle the dock when warming up.
Why upgrade from a 2-stroke to a Mercury 90 FourStroke EFI?
Reliability is the headline. Modern EFI 4-strokes start clean on a cold morning without choke fiddling, idle smooth, and don't foul plugs sitting overnight. They're computer-managed, no carbs to clean, no float bowls to drain, no jets to rebuild.
Noise is the second. A current FourStroke can be quieter and smoother than an older carbureted two-stroke, but the difference depends on the specific engines, installation, and operating point.
Fuel is the third. Modern EFI eliminates two-stroke oil mixing and may reduce fuel use, but HBW would not promise a percentage without baseline fuel data from the actual boat and a comparable water test.
Warranty closes the deal. A brand-new Mercury carries the current Mercury Limited Warranty plus any active promotional coverage, which we confirm at quote. That factory backing is the kind of peace of mind no 25-year-old 2-stroke can offer.
What did the job involve?
The work is a little more involved than a Mercury-to-Mercury swap. We confirm the transom rating, pull the old 2-stroke, and inspect the transom skin carefully, older 2-strokes sometimes leave water intrusion or stress cracks that need to be addressed before a new motor goes on. If the transom checks out, we install the Mercury 90 FourStroke EFI with new bolts, new controls, new throttle and shift cables, a new tach harness, and a new fuel primer bulb.
Because the old motor used a different control layout, we always replace the helm controls rather than try to make old ones work. That's included in the quote. Propeller selection, usually a 13.25-inch diameter aluminum or stainless in the 17–19-inch pitch range, happens on the water during the test.
Water test on Rice Lake confirms WOT RPM lands in Mercury's spec band, gauges read clean, and steering is right. Pickup-only at Gores Landing, we don't ship or deliver. See our repower process page for the full sequence.
What did it cost?
Use the pricing reference for the current bare-motor price. The installed quote adds only the work the boat actually needs, which may include removal, controls, cables, steering, propeller, fuel-system remediation, and water testing. Trade value depends on the exact old motor and its condition.
Discontinued legacy 2-strokes have less trade value but we still take them case by case.
HBW can arrange financing through DealerPlan and Canadian lenders on eligible purchases of $5,000 or more at the current 5.48% APR promotional APR through Dec 31, 2026 (OAC). The financed quote includes the $349 DealerPlan documentation fee where applicable and discloses the contract term, amortization, and any balance due at maturity. A $500 deposit holds the order.
Frequently Asked Questions
- Can you repower an old Evinrude with a Mercury?
- Yes. Evinrude is a discontinued legacy 2-stroke brand and we replace them often. The mounting pattern is similar enough on most transoms that the swap is straightforward, though we always confirm the transom condition and may need new bolts and a new throttle harness.
- Why move from a 2-stroke to a 4-stroke?
- Four reasons to compare them are modern EFI starting and idle control, quieter operation, no two-stroke oil mixing, and the current Mercury Limited Warranty. The actual noise and fuel difference depends on the old engine and boat, so HBW does not promise a generic percentage.
- Will the controls from my old 2-stroke work with a new Mercury?
- Usually no. The throttle and shift cables and harness are different. We include new Mercury controls and cables in the repower quote so everything is matched and warrantied.
- How long does this kind of repower take?
- Two clocks. Your boat is with us for 2 to 5 days, drop-off to pickup (a little longer if we find transom rework on an older boat). Motor lead time is separate: in-stock motors ship immediately, special orders wait at Mercury (the wait depends on the model and current Mercury availability), and your boat stays with you until the motor arrives. Pickup-only at Gores Landing.
Visit Harris Boat Works
Harris Boat Works · 5369 Harris Boat Works Rd, Gores Landing, ON K0K 2E0 · Phone (905) 342-2153 · Family-owned since 1947 · Mercury Premier Dealer, selling Mercury since 1965.
We're the repower side of Harris Boat Works, a family marina in Gores Landing serving boaters since 1947. Two-stroke-to-FourStroke jobs are some of the most satisfying work we do, the boat sounds different the moment you leave the dock.
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