We bought this '99 Johnson 70 last year. It's got low fresh water hours and appears to be in excellent shape. P/O said that the carbs had just been synched, but the fuel was likely stale.
After draining the fuel from each carb, I added a fuel stabilizer along with a full tank and some Johnson premix that I had from an old outboard.
The engine will start, warm and settle into an idle w/no problem. It's under gentle acceleration and low speed operation that it stumbles. I'd think electrical, but it will accelerate nicely without missing/stumbling, and doesn't seem to have any fuel starvation issues.
The low speed stumbling is almost as though a cylinder or two is running too lean - or too rich and loading up.
A few bits of info:
I haven't done a compression test, but have checked the plugs. They're in decent shape, the correct plugs for this engine, and have consistent coloration.
Admittedly I've been using 87 street gas with the prescribed amount of Sta Bil ethanol treatment.
The oil injection system has been disconnected. I was told that running the proper gas/oil mixture in the tank was fine (50:1 - 13oz. for 5 gals)
Also of note is that the Johnson premix that I've used is quite old. I didn't think that oil could go stale, so I figured this would be fine.
Before I get into timing, plugs, wires, carb/jet cleaning and professional carb synching, I had a few questions relating specifically to fuel and fuel oil mix:
Thanks in advance -
JP
After draining the fuel from each carb, I added a fuel stabilizer along with a full tank and some Johnson premix that I had from an old outboard.
The engine will start, warm and settle into an idle w/no problem. It's under gentle acceleration and low speed operation that it stumbles. I'd think electrical, but it will accelerate nicely without missing/stumbling, and doesn't seem to have any fuel starvation issues.
The low speed stumbling is almost as though a cylinder or two is running too lean - or too rich and loading up.
A few bits of info:
I haven't done a compression test, but have checked the plugs. They're in decent shape, the correct plugs for this engine, and have consistent coloration.
Admittedly I've been using 87 street gas with the prescribed amount of Sta Bil ethanol treatment.
The oil injection system has been disconnected. I was told that running the proper gas/oil mixture in the tank was fine (50:1 - 13oz. for 5 gals)
Also of note is that the Johnson premix that I've used is quite old. I didn't think that oil could go stale, so I figured this would be fine.
Before I get into timing, plugs, wires, carb/jet cleaning and professional carb synching, I had a few questions relating specifically to fuel and fuel oil mix:
- Can premix go bad? I can't imagine the lubricating qualities deteriorating over time, but what about the chemicals that keep the oil evenly mixed in the gas?
- Are the premixes from today better formulation than those from 10 or 20 years ago?
- Is the gas to oil ratio of 50:1 that I'm using correct for this engine?
- Aside from not containing ethanol, are there other advantages in the formulation of dock gas over 87 octane street gas that I'm missing by adding an ethanol treatment?
- Are 2 strokes more sensitive to today's 87 octane street gas than the big I/O V8's?
Thanks in advance -
JP
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