Unleaded or Leaded Gas

justbehindit · Nov 6, 2009

I am the 4th owner of a 1982 70 hp Johnson Sea Horse 2 stroke. No one has been able to tell me whether this engine should be run on leaded or unleaded gas. My guess is unleaded based on my knowledge of the automobile industry and the change over to unleaded but I'm not certain that boat motors changed at the same time, and completely.

Any thoughts? I am concerned about piston erosion over time. The engine runs well now that the carbs have been cleaned and the plugs changed. Top speed on an 18ft StarCraft is 32 mph with just me in it.

kenmyfam · Nov 6, 2009

Re: Unleaded or Leaded Gas

Unleaded is fine as far as I know. 87 octane is fine as well.

Welcome to iboats.

bktheking · Nov 6, 2009

Re: Unleaded or Leaded Gas

Ya , they work with both but can you even buy leaded gas anymore? I know they sell a lead additive but you don't need it, I run my 55 7.5 on unleaded.

kenmyfam · Nov 6, 2009

Re: Unleaded or Leaded Gas

bktheking said:
Ya , they work with both but can you even buy leaded gas anymore? I know they sell a lead additive but you don't need it, I run my 55 7.5 on unleaded.

You can get a lead substitute here in Canada but I don't believe there is a need for it in this situation.

bktheking · Nov 6, 2009

Re: Unleaded or Leaded Gas

Yup, Canadian Lire sells it in a Silver Bottle.

Boss Hawg · Nov 6, 2009

Re: Unleaded or Leaded Gas

justbehindit said:
I am the 4th owner of a 1982 70 hp Johnson Sea Horse 2 stroke. No one has been able to tell me whether this engine should be run on leaded or unleaded gas. My guess is unleaded based on my knowledge of the automobile industry and the change over to unleaded but I'm not certain that boat motors changed at the same time, and completely.

Any thoughts? I am concerned about piston erosion over time. The engine runs well now that the carbs have been cleaned and the plugs changed. Top speed on an 18ft StarCraft is 32 mph with just me in it.

I'm old enuff to remember leaded or unleaded gas but too old to remember when that option became ---Well. not a option

justbehindit · Nov 6, 2009

Re: Unleaded or Leaded Gas

I can buy lead additive but I don't want to add it if I don't need it. My concern is piston erosion due to detonation.

PFS · Nov 6, 2009

Re: Unleaded or Leaded Gas

I've not heard of a need for the lead additive, but I've been reading about an additive that deals with the ethanol found in today's gasoline. I believe the ethanol has an effect on the oil mix in the cylinders, but I'm not exactly sure. You can buy a bottle of something called "Star Tron" at the auto parts store which is supposed to work. My 9.5 hp Johnson runs fine with it, and supposedly I don't have to worry about ethanol now. They also sell Star Tron at the local boat store, but it's more money there.

samo_ott · Nov 6, 2009

Re: Unleaded or Leaded Gas

I run many 50's outboards all summer with regular unleaded. I don't think it's a problem. I wouldn't want to add lead in my fuel anyway as they pollute enough as is!

moonfish · Nov 6, 2009

Re: Unleaded or Leaded Gas

justbehindit said:
I am the 4th owner of a 1982 70 hp Johnson Sea Horse 2 stroke. No one has been able to tell me whether this engine should be run on leaded or unleaded gas. My guess is unleaded based on my knowledge of the automobile industry and the change over to unleaded but I'm not certain that boat motors changed at the same time, and completely.

Any thoughts? I am concerned about piston erosion over time. The engine runs well now that the carbs have been cleaned and the plugs changed. Top speed on an 18ft StarCraft is 32 mph with just me in it.

As far as I know, really old two strokes used white gas(unleaded) instead of leaded gas. I think white gas was before my time. As far as I know, your worries are all unfounded but you should learn how to preserve the gas you're putting in your motor now or it'll be something you wish you had done.

cougar1985 · Nov 6, 2009

Re: Unleaded or Leaded Gas

moonfish said:
As far as I know, really old two strokes used white gas(unleaded) instead of leaded gas. I think white gas was before my time. As far as I know, your worries are all unfounded but you should learn how to preserve the gas you're putting in your motor now or it'll be something you wish you had done.

your right.i have a really good artical that also deals with antique boat motors of the inboard kind and they were designed for unleaded back in the 30,s or earlier way before autos.

Vic.S · Nov 7, 2009

Re: Unleaded or Leaded Gas

The lead additive in gasoline served two purposes. It raised the octane rating and it acted as a valve lubricant.

Clearly there is no requirement for a valve lubricant in a two-stroke.

The compression ratios of two stroke engines is lower than that of modern four stroke engines so a high octane rating is not required either.

A two stroke outboard should therefore be run on a minimum octane rating (Road octane number, RdON , Antiknock index, AKI, or Pump octane number, PON) of 87 but 89 preferred. There is no requirement to use leaded fuel or any lead substitute additive.

See question 4 here; http://www.evinrude.com/en-US/About.Us/FAQ/Oil.Fuel.htm?

For completeness it should be recorded that outside the US and Canada most counties use the "Research octane number", RON, for the classification of gasoline and petrol. In those countries 91 or 92RON is the minimum that should be used, being the same as 87 RdON. In the UK ordinary unleaded petrol is 95 RON.

F_R · Nov 7, 2009

Re: Unleaded or Leaded Gas

justbehindit said:
I can buy lead additive but I don't want to add it if I don't need it. My concern is piston erosion due to detonation.

You are correct, lead was added to gas in the old days to raise the octane and prevent detonation. Now they get the octane up there by other means. So, it is still high enough octane to not detonate---without the lead.

Unleaded or Leaded Gas

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