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Fuel Starvation at high speed

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Will Kraham
(@13766)
Posts: 1
New Member
Topic starter
 

1995 R100GS
Fuel starvation above 4Krpm in 5th gear only
Seems to happen with full or almost full tank - venting issue?
Vent holes in cap are clear but new fuel caps are no longer available anyway and opening cap does not solve problem
Suspect issue with SHED system

 
Posted : 11/01/2018 16:52
Richard W
(@wobbly)
Posts: 2597
Member
 

Instructions for removing the SHED system: http://www.bmwmotorcycletech.info/pulseair.htm

Fuel "starvation" could have several different causes...

1. Fuel not getting to the carbs
Have you removed the float bowls and tested the fuel flow from each petcock? Petcock packings can rotate and block the flow. Ethanol fuel and sediment deposits can also block the flow.

2. Fuel not able to move through the carbs
Ethanol fuels left standing in the carbs will form a varnish on all parts. If this varnish is allowed to coat the jets, it will be as if you installed jets 2 or 3 times smaller than standard. A 1995 model is already running fairy lean when perfect, and doesn't require any more "help". This type issue would be far more prominent at higher speeds.

3. Air leaks making the fuel system unable to maintain the correct fuel/air mixture
Most of the "rubber" parts were designed before ethanol fuels came into common use. Ethanol advances the hardening and aging process of these parts, making them tend to harden and crack. Either of these 2 conditions can allow small air leaks to develop further leaning out the already lean-ish mixture. If you haven't done so in the last 5 years, then I highly suggest you replace the rubber intake hoses, the diaphragms, the float needles, and all the o-rings in the carb bodies. Disassemble 1 carb at a time to keep from mixing carb parts.

Hope this helps.

Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.

 
Posted : 11/01/2018 17:40
Jim Wilson
(@1559)
Posts: 206
Estimable Member
 

some ideas about petcock tubes and repair & issues

 
Posted : 12/16/2018 16:54

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