possible causes if PRI helps
# possible causes if PRI helps
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<u>This problem has been reported by multiple GS riders:</u>
After a few minutes going full throttle on the motorway/highway/autobahn, the GS behaves like the petrol tank is nearly empty and ultimately dies.
After waiting for a few minutes, it normally starts fine and one can ride normally again.
Most people say that putting the [fuel petcock to "PRI"](/petcock-and-petrol-hose-routing/) solves the problem permanently.
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==possible causes if PRI helps==
'''lower petcock restricts petrol flow too much'''
The engine slowly but surely drains the reservoir of the carbs.
I suspect the older lower petcocks (until about 2000) to be a bit undersized.
If the vacuum membrane becomes hard, there is a problem with the flow.
I think SUZUKI didn't change the lower petcock in the newer models without reason.
'''Vacuum hose to lower petcock (yellow) leaks, is flexed/blocked or gone'''
If a bit of vacuum comes through, the petcock opens not fully, leading to the aforementioned symptoms.
=> check hose
'''Petrol hose "ON" (blue) flexed/blocked'''
Can be solved with PRI or RES.
=> Check hose
==possible causes if PRI does <u>not</u> help==
'''Upper petcock not completely open'''
The petcock is open if the slit is vertical, i.e. parallel to the flow. It can be moved from OFF over ON to OFF; no end position is open!
=> take the tank off, open the upper petcock
'''Hose "RES/PRI" (red) flexed/blocked'''
Only happens in RES and PRI, not solved by PRI.
=> Check hose
'''Hose "lower petcock – carbs" (green) flexed/blocked'''
=> Check hose
'''Filter blocked'''
=> Remove and clean upper petcock
'''Petrol tank ventilation blocked'''
If the petrol cap is open, the GS does not die. If you open the petrol cap straight after the machine died on you, you can hear a sibilance.
=> Clear tank ventilation in the petrol cap.
'''Float needle valve dirty'''
This normally shows the opposite symptoms: The float needle valve does not close properly, if the lower petcock is on PRI and the engine not running, the petrol runs through and via the airbox drainage on the floor – or worse, in the engine and in the oil.
But a partly blocked flow needle valve can restrict the flow as well.
=> Clean the carbs.
'''Carbs ice up'''
Can also happen in plus centigrade temperatures!
Sounds exotic, but has been reported by loads of Bandit riders. The evaporation of the petrol uses up heat – thus the carbs are cooler than the surrounding air. If the surrounding air is humid, the carbs can freeze up even some positive centigrees.
Takes quite some time to defrost.
=> wait
'''Tank empty'''
Can't even be solved by PRI.<nowiki>;o)</nowiki>
=> Next round is on you!
'''Airfilter blocked'''
A blocked/old airfilter can produce similar symptoms; the GS mainly struggles to get into high revs.
=> Swap airfilter
==riding on PRI==
This should be considered a temporary solution. Bear in mind:
If you park the bike, you should swith the petcock back to ON, otherwise the carbs get flooded if the float needle valve is broken (not a rare fault).
The petrol now flows through the RES hose, i.e. you don't get any warning and run out of petrol straight away.
As quick and easy solution is to [convert the pettcock from vacuum to manual](/convert-petcock-from-vacuum-to-manual/)!
<u>By the way:</u>
I suggest practising to reach the lower petcock whilst driving without looking. If it should be necessary, it's could to know that you can do it.