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Old 03-06-2011, 02:58 PM   #6
Rapid Dog OP
bikes, booze, broads...
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Joined: Oct 2003
Location: Strangel Living West of Hell, SoCal
Oddometer: 9,661

Noy sure the PO replaved it but it looks new-ish, no wear. The flip up lever feels more plasticky than the metal one on my 1978 /7.
I gave this a try, we shall see what haps GAS CAPS:
From the /7 onwards, BMW changed to a screwable, removable, fuel cap.

See article 1, on fuel filters, petcocks, and caps, etc. for additional information: CLICK

The late 1977 (or perhaps from 1978) gas caps are changed in design, so that they allow air to pass to the inside of the tank, but fumes are not supposed to pass to the outside of the tank. To accomplish this, their are valves built into the cap. The very first of these caps could have problems. The symptom of a venting problem is when the bike starts running very lean, may buck and seem to run out of fuel, and this typically happens after some time on the highway, the time can be shorter if the tank was rather full to start with. OPENING the cap (unscrewing it a bit) will 'fix' the problem within 15 seconds, and this 'test' is nearly 100% for a bad cap vent. The cap can be modified to fix the problem permanently. Put it upside down on your workbench. Drill AWAY from the center, any direction, about 1/2" from the center. Thus the hole you will drill is off-center. Drill, 3/32", from the bottom of the cap, through the metal shell, and continue drilling carefully....go through the air space, and drill into the softer material that you then feel you are drilling is maybe 1/8" thick. Drill through it, and then stop drilling. Clean out the cap as best you can of drilling swarf. Replace the cap on the tank. That's all there is to this.
'91 R100GSPD Derelict Deux , '81 R100RS Rattlecandy Red/'06 950 ADV Orangeboom/91 R100GSPD Derelict etc.

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