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unleaded fuel on a 77' 750?

  • Thread starter Thread starter Anonymous
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Anonymous

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Hello,
I have had some time to browse around in old posts, and once again I have found out what a fantastic place the GSResources is.

One thing I am stil confused about is the issue about leaded/unleaded fuel. Here in Denmark we no longer have leaded fuel. Instead we have something called 95 octane which is fuel with led replacements.
And then we have the unleaded ones: 92, 95 and 98.

NOW. Some people say that running on unleaded (95 unleaded is by far the most common one here) will damage the valves on my GS 750 from 1977.

AND a lot of people say that I will have no problem running on unleaded fuel. Some of you guys in here have even said that the GS engines were made for unleaded fuel in the 70's.

SO, my question really is: should I put some of that 95 unleaded fuel in the tank (it is cheaper than the one with lead replacements) and take the bike for a spin?

OR, should I first check the jetting and replace the valves before I think about changing fueltype?

The big problem is that it is becoming more and more difficult to find the led replacement fuel in service stations. And it is probably going to disappear due to some future enviromental law put out by the European Union.

That was a bit long, sorry.
Cheers...
 
Correct me if I'm wrong but back in the day when high performance engines were first being developed and required higher octane gasoline, the technology hadn't been developed to produce high octane gasolines from crude oil. The gasoline available had extremely low octane numbers which we all know is bad news in a high compression engine. To remedy this problem tetra-ethyl lead was added to the gasoline to increase the octane number and make it useable in the high compression engines. The problem was the polution that the leaded gasoline created.

The only reason the lead was put into the gasoline was to increase the octane number. I don't know if there would be any difference between an engine made during the leaded gas days, and one made more recently or not. I would say that unleaded gas, if you have high enough octane number shouldn't hurt valves on an engine designed for use with leaded gas because they are basically the same thing.
 
The lead also lubricated the exhaust valves. That's why some guys switch to stainless vavles in older motors so they won't have a problem running unleaded fuel.
 
unleaded fuel on a 77' 750?

Greetings:

On this side of the pond, unleaded fuel as been the standard since the 70's and most manufacturers made changes to the vehicles to avoid issues. If available locally, I'd recommend a lead substitute designed for older vehicles if your model isn't a US spec machine.

I run unleaded 89 octane (RM method) in my '77 GS750 without any problems.

GM
 
I have used 95 unleaded fuel for years, without any problems. Like stated above, unleaded fuel is standard in the US since the 70's, and our bikes were designed to run on unleaded, even the European ones.
 
I happen to have the factory manual for the GS750. It specifies minimum 90 RON unleaded or low lead fuel. RON is the Europen way of quoting octane

Many Japanese engines were designed for unleaded in the 70s. It seems to be the cars that may have been modified for export markets to run on leaded. This is probbaly what people are thinking of. Bikes are the same all over and were not modified (for leaded fuel) for particulat markets. Unleaded runs cleaner, less junk etc, so that is why Suzuki recommends no lead or low lead.

The lead replacement fuel in Australia is rubbish, so I hope it is better in Denmark! I have to run higher octane fuel (95 or above) due to engine midifications. Lead replacement fuel ran dirtier and was noticeably not running properly on the bike. The same octane unlead runs heaps better! better additive package, slightly more expensive, but I get better performnce and fuel mileage, so overall it is better.
 
I've run my 79 750E on 87 octane unleaded about 30,000 miles with no problems at all. I've also used unleaded in every bike I have owned the past 30 years or so and have never had an engine problem due to the unleaded gas. I wouldnt run leaded gas anyway because it burns dirtier.

Earl
 
Like billy said, the lead also served to lubricate the valve seats, the change to unleaded fuels was a issue for older engines with iron heads, the valve seats were not very hard and excessive seat wear resulted when run on unleaded fuels, it wasn't overnight but did take some time to happen, (well over 50,000 miles) our bikes use aluminum heads and they have hardened seats already due to aluminum being unable to withstand the hammering from the valves.
unleaded gas started to be fazed in in the early seventies, so the GS's already have hardened seats.
 
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