Mercury 70

[Plan-b]

Hello,

I am wondering if anyone could help me out, I have a 1980 mercury 70 and can’t find too much info about these motors. What I have found is that the top hole has a tendency to go lean. Is there any way to fix this problem? Does anyone know the rev limit of this motor… how tight can I spin it before it throws a rod? Does changing to a fiber reed increase performance or is it just for a safety factor? Are there any easy ways to make this motor faster? I am new to the two-stroke world… so can you please tolerate me being naïve.

Thanks

[Mark75H]

The 3 cylinder Merc is not a candidate for hot rodding. The limiting factor is the 2 carbs and 2 reed cages. Fiberglass reeds won't make it any faster. Merc made a hi-performace version with 3 carbs and better reed cages but that does not overcome the motor's short comings. Later Merc triples have a different crank with a different firing order to reduce their bad vibration at high rpm (I don't know what year the change was made)

They do not have a mixture problem with the top cylinder, they have a cooling problem. Later motors came with a vent at the top of the block to release air and ensure full water filling ... early motors should have this retrofitted

You can spin the motor as fast as you wish without worrying about throwing a rod, if you can stand the vibration.

The best thing you can do for more speed is to trade the Merc for an OMC triple (I'm a Merc fan ... thats a 6 cylinder Merc in my signature)

[7500Blizzard]

Not saying this motor doesn't have its problems. But how is 2 carbsand cages any worse than 2 carbsand cages for a 4cyl or 3and 3 for a six?

[Mark75H]

I never said it was worse on the triple.

Its the choke point for all of those motors; the triple has a way around it, but has its other issues which I think are mostly related to being a big bore deflector motor. With the blind bore non-removable heads, deflector pistons and internal reed cages none of them are ripe for hot rodding

[Roy Hodges]

I never said it was worse on the triple.

Its the choke point for all of those motors; the triple has a way around it, but has its other issues which I think are mostly related to being a big bore deflector motor. With the blind bore non-removable heads, deflector pistons and internal reed cages none of them are ripe for hot rodding

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Well,............ your S I X cylinder has non removable heads, deflector pistons and internal reed cages ,also .

[Mark75H]

Well,............ your S I X cylinder has non removable heads, deflector pistons and internal reed cages ,also .

Yep makes it a real pain to make much more power than came out of the box. If you had a shop do the work I've done to increase the power from 60 to 88 hp, it would probably cost $4,000. You can usually buy a pretty good used 100 hp motor for $4,000. You could certainly buy a used OMC triple, soup it up some and have cash left over.

Anyone know where I can find 2 more sets of these?