REVIEW: TOHATSU M5B VS MFS 5C LPG

The M5B is the longest-running two-stroke 5 on the Aussie market. Originally released in 1985 to replace the air-cooled M5A, the water-cooled M5B featured electronic ignition timing advance and a through exhaust gas hub system to extract the maximum amount of power and torque from the single-cylinder loop-charged engine. A full gear shift, six trim positions, a single shallow-water drive setting and automatic reverse and full tilt locks plus twist-grip throttle control were provided.

Initially, two separate models were available, one with a 2.5lt integral fuel tank and the other with a remote 12lt tank, but more recently these were combined to offer anglers the choice of integral and remote tanks. Five different prop pitches were available to suit a wide variety of hulls.

Apart from changes to the cowl shape the current M5B remains the same as in 1985, including using a 50:1 premix after the first 10 hours on 25:1.

Released last year and based on the MFS 6C introduced in 2000, the 5C LPG runs on propane or LPG and is Australia’s cleanest-running 5hp engine. Some top-end power has been lost compared to the 6C but bottom-end torque is the same and because the LPG burns so thoroughly the 5C LPG has way lower vibration levels making it the smoothest-running single-cylinder five I’ve ever tested. A rev limiter cuts in at 6300. The leg, transom bracket and lower unit are the same as the M5B but only a remote tank model is available, normally connected to a 7.5kg (14.7lt) fibreglass SprintGas bottle.

The overhead valve engine has a gear-driven camshaft operating push rods for the rockers and pressure lubrication with low-oil warning light on the engine pan. And the upfront gear shift makes using the 5C LPG so much nicer.

During testing I measured gas usage by weight so fuel usage at a given set of revs wasn’t possible, but overall the loan 5C LPG used slightly more fuel than the 6C under identical test conditions.

Power head access in both engines is excellent and servicing intervals are every 50 hours or annually after the first 20 hours. The recreational usage warranty is three years for both engines.

SEA TRIALS

Single M5B and MFS 5C LPG on flat-bottomed 2003 Sea Jay 3.4 punt, swinging 8-inch and 7-inch props and pushing 285kg and 290kg respectively. Average of two-way runs on Lake Macquarie, NSW, in calm water. Range is in nautical miles for the 2.5/12lt tanks and 7.5kg gas bottle respectively with a 10% reserve. In reality the 7.5kg bottle shouldn’t be filled to more than 80% capacity and this is also listed in the following figures.

"Loop" of cruising with 10% WOT and 40% trolling operation, averaging 4kts

SPECIFICATIONS: TOHATSU M5B

ENGINE

TYPE Loop-charged 2-stroke

RATED BHP/MHP* 5/5 at 5000rpm

WOT RPM RANGE 4500 to 5500rpm

DISPLACEMENT 102cc

BORE X STROKE 55cc x 43cc

GEAR RATIO 2.15:1

DRY WEIGHT 20kg

RRP $1,387

RRP gas bottle ———

OEDA stars 1

*Brake horsepower/metric horsepower. Note that M5B retails for only $78 more than Tohatsu MFS 3.5B

SPECIFICATIONS: TOHATSU MFS 5C LPG

ENGINE

TYPE OHV 4-stroke

RATED BHP/MHP* 5/5 at 5500rpm

WOT rpm range 5000 to 6000rpm

DISPLACEMENT 123cc

BORE X STROKE 59cc x 45cc

GEAR RATIO 2.15:1

DRY WEIGHT 27.2kg

RRP $2,084

RRP gas bottle $198

OEDA stars 3

*Brake horsepower/metric horsepower.

Check out the full review in issue #502 of Trade-a-Boat magazine. Subscribe today for all the latest boat news, reviews and travel inspiration.