fuel and oil

mcgyver6857

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May 24, 2008
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22
I have a 1970 Johnson 70hp and was wondering what kind of oil and gas everyone was running. Should I be running 93 or is regular 87 enough? Also oil choices? Currently I am running Ams Oil synthetic race oil I run in my dirt bikes mixed at 50:1. Is this ok, or should I go 40:1 being synthetic like the bikes? What is the best thing going for oil? The reason I am asking all the questions is that recently I picked up a new boat and the first two times taking it out it would push 30mph and seemed to plane much easier. The last two times on the water it seems sluggish and I have lost 5mph. The motor seems to run a little rougher also. It was just serviced two weeks ago and it still runs well but I have lost a bit of power. Would it be possible the throttle cable stretched? Or fouled plugs?
 

Hoss the Hermit

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Aug 7, 2007
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454
Re: fuel and oil

Well, I would stay away from the dirt bike oil, it's for air - cooled engines. You need to run TCW3, it's made for outboards. 50:1 should be correct mix ratio.
 

tashasdaddy

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Re: fuel and oil

You need to run TCW3, it's made for outboards. 50:1 is correct mix ratio.
 

JB

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45,907
Re: fuel and oil

Anything over 87 octane is just a waste of bux. There may be some small advantage in running a TC-W3 rated synthetic oil, but I have found it an expensive way to reduce smoke.

My 70s ran great on unleaded regular and WalMart SuperTech TC-W3 oil.
 

mcgyver6857

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Re: fuel and oil

well all my race bikes have been liquid cooled what I was wondering is if running that would effect preformance? What is the difference between a marine oil and an oil that is designed to protect an engine in excess of 12000rpms? Also what could be other causes? strectched throttle cable? fouled spark plugs? The boat was just serviced so it has to be something simple. 5 mph seems like a huge loss and I would like it back.
 

tashasdaddy

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Re: fuel and oil

how long have you had the motor? the motor was designed, to run with TC-W3, it's your motor run what you want it. not going to get into another oil debate, there are many in the archives.

what have you checked. spark on all 3, compression, are all 3 getting fuel.

did you change the lower unit oil? did you use Type C premiun blend from a dealer? if not you have the wrong oil in the lower unit. you have a hydro-electric shift.

Hydro Electric Shift)
(J. Reeves)

The shifting setup of the lower unit is what's called a "Hydro Electric Shift", which is quite complex consisting of voltage being applied to solenoids in the lower unit which in turn change oil passages via a oil pump that supplies various pressure on a spring loaded shifter dog. The wires leading to the lower unit (at the powerhead) are "Green" and "Blue". The engine must be running or cranking over in order to shift out of forward gear.

You CAN NOT use HI VIS lube in that lower unit. You MUST USE what OMC calls "Premium Blend" lube, commonly called "Type C". (A thinner lube)

In neutral, you need 12v to the "Green" wire.
In reverse, you need 12v to both wires, the "Green" one and the "Blue" one.
In forward, there should be no voltage to either wire. (The spring loaded shifter dog forces the unit into forward gear)

To check the lower unit for proper shifting to make sure you have no trouble there, remove the spark plugs to avoid problems and to allow a higher cranking speed.

This next step eliminates the actual shift switch in case problems may exist there.... Disconnect the blue & green wires at the knife connectors (the rubber insulated boots) leading to the lower unit at the powerhead, then using jumpers, take voltage direct from the starter solenoid to apply voltage to the "Green" wire for neutral, then both wires 'Green" & "Blue" for reverse (Remember the engine must be cranking over in order to shift).
With no voltage applied, the unit should be in forward. No need for a ground jumper... the lower unit's already grounded. You may crank the engine with the key switch or by energizing the starter solenoid with a jumper wire.
 

mcgyver6857

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Joined
May 24, 2008
Messages
22
Re: fuel and oil

No I have not had the motor long, yes the lower oil was changed by the johnson dealer with the correct oil. If it requires marine oil what would you suggest? Would running the synthetic I am running effect preformance? Is there anything else I should check? The motor was just serviced professionally it still runs well it has just lost some power from the first two times I had it on the water.
 
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