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Carburetors, Mixers, Fuel Pumps and fuel delivery Discussion about misc. carbs, mixers, fuel pumps, injectors.

Carburetors, Mixers, Fuel Pumps and fuel delivery

B&S 9hp 1971 with generator leaded or unleaded?

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Old 12-14-2014, 02:29:36 PM
Rickfa Rickfa is offline
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Default B&S 9hp 1971 with generator leaded or unleaded?

This unit probably does not have 5 hours of running time since new. Engine currently runs great, maybe 2 hours since cleaning the carb and changing the oil . Still have to get generator operating, (another thread though). Since this will be a high load use engine approx 3600 rpm, Do I use leaded or unleaded fuel? I have seen postings that say low load ok, high load need additive, or B&S has always been able to use unleaded, I plan to use the generator a lot. Any thoughts or ideas. Thanks
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Old 12-14-2014, 07:45:05 PM
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John Newman, Jr. John Newman, Jr. is offline
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Default Re: B&S 9hp 1971 with generator leaded or unleaded?

Hello & Welcome to the 'Stak.
Your generator / engine needs to run at exactly 3600 rpm in order to provide the 60Hz frequency that AC appliances need - In theory, at least.
Usual practice is to set it for about 62 Hz (3720 rpm) with no load and accept that it may drop to 58 Hz (3480 rpm) at full load. Or you can set it dead on 3600 rpm with about a 60% load. A handy tool to have when using a generator is an item called a "Kill-A-Watt" meter. Available from many sources on-line and in big-box stores for around $20. Plug it in and it will tell you frequency, volts, watts, amps, etc.
With a 9 hp engine, I would guess that you have a generator labeled as a 5000 watt unit. If you look at the spec tag, it will probably say that it is rated at about 4500 watts continuous output.
I would not be as concerned about the gasoline you put in it as I would be about the oil. A typical Briggs engine that size will probably hold slightly less than a quart of oil. If you run the unit with a fair amount of electrical load, it is going to be working hard & getting hot. Use a good oil made for severe service. Rotella Diesel oil is a favorite with many people here on the 'Stak. Check that it is full every time you start it up and change it every 25 hours.
Good luck, have fun, stay safe and show pictures
John Newman, Jr.
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Old 12-14-2014, 07:56:13 PM
Pat Barrett Pat Barrett is online now
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Default Re: B&S 9hp 1971 with generator leaded or unleaded?

Those Flathead Briggs were low compression, anyhow, like 7:1, or in that range, gas octane will not be a problem, but, the quality of gas is. All will burn good, but some will go to muck after sitting, even with Sta-Bil. A good choice is premium as it stays stable much longer, not for the octane. As above stated, most important is the oil, use a good grade, high quality oil. AND change it before you store it, after use. My boys usta get on me for changing oil on the generator after only 5 hours. I'd tell them that the next time I had to get it out and use it, it might be for 25 hours and I didn't want to have to worry about how many hours the oil had on it before I used it, this time. I use Castrol partial synthetic "Syntec" and have had good results. Other oils are just as good, that's just what I've chosen.
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