Fuel reserve? What reserve?

[Dave_A]

You have been running in 'PRIME' though, which means you also may have gas-in-the-oil problems...

CHECK YOUR OIL

It's probably due for an oil change anyway, but how would gas get into the oil?

Dave

On (what seems to be most) old bikes, the carb internals have become 'worn' to the point where they will flow fuel as long as there is fuel pressure... On the GS and most bikes, there is ALLWAYS fuel pressure unless the petcock is closed (either manually or automatically), as a gravity-feed fuel system is used.

The extra fuel flow isn't enough to affect operation, since it's usually less than the burn rate, HOWEVER it poses problems when the bike is let to sit and the extra fuel is not burned off (eg when you park for the night).

This is why bikes with 'manual' petcocks have an 'OFF' position. In the case of the GS, there is no 'OFF' because the designers (quite wisely, given how many people treat their bikes like cars and expect to be able to turn off the key and park it) designed it to automatically shut off when there's no engine vacuum.

Now, if your bike is left to sit, and (like most) the carbs flow fuel while there is pressure, there are only 3 places for that fuel to go: Out the vent tubes, into the airbox, or into the cylinders. Now, the vent tubes are mounted high (as their primary function is to allow air into the float bowls so the carbs operate properly), so it takes ALOT of gas to cause flow out the vents, and generally when this happens, gas is going to one or both of the other 2 spots.

Now, the part that referrs to oil. If your bike is parked with the carbs level or nose-down (eg when it's parked anywhere except nose-up on a steep hill), the gas will flow into the cylinders. Since the rings don't seal tight with the engine not running, this gas runs down past the rings and into the oil.

GAS IN THE OIL IS BAD NEWS -> it (a) thins the oil, and (b) displaces it away from moving parts, removing lube... If this is the case, you will basically be running your engine with Kerosene instead of motor oil...

[Dave_A]

My '80 550L has no reserve, it does haave a gauge though. Two positions and no lever you need a screwdriver to switch between run and prime.

That design is on my '80 850... It's a terrible petcock design...

The '82 design that he has (which is also on my 82 450TX) is MUCH better.

[Anonymous]

Now, the part that referrs to oil. If your bike is parked with the carbs level or nose-down (eg when it's parked anywhere except nose-up on a steep hill), the gas will flow into the cylinders. Since the rings don't seal tight with the engine not running, this gas runs down past the rings and into the oil.

GAS IN THE OIL IS BAD NEWS -> it (a) thins the oil, and (b) displaces it away from moving parts, removing lube... If this is the case, you will basically be running your engine with Kerosene instead of motor oil...

You've convinced me. I've already replaced one engine this year (Pontiac minivan - intake manifold gasket failed, allowing coolant into the oil.). I'm not up for doing it again.

Thanks!

Dave

[snowbeard]

well, I see you've realized the problem, but I wanted to mention that MY bike doesn't work on this basis

PRIME draws from the same spot as 'RUN', IIRC

my prime comes from res, and when I had it all apart, the holes match up to back that up...

disclaimer, many bikes are different so I ain't sayin anyone's wrong, just if you have a GS650G from 1981

[Anonymous]

My '80 GS750L also has no reserve and no lever. I don't know which direction to turn the screw for prime or on. I changed my oil yesterday and I already have fuel in the oil which is noticable by smell (very strong) and my level is above the max in the little window.