Ever changing float height- help!

[chrishiggs]

Hi folks,

Sorry if this has been done before- checked posts but not 100% sure I've isolated the problem.

Bought a '99 GS500 with just over 10k miles recently. Was running fine but the left float height was slightly high causing a slight leak from the float gasket. Removed carbs, set float heights, everything great. Tried to start bike several days later and it wouldn't turn over. Fuel had filled the left cylinder and had hydrolocked. Left float height now way too high. Drained/changed oil and filter, reset float heights (checked once refitted using u-tube first), bike runs fine. Balanced carbs. Recheck float heights again- fine. Bike now running very sweetly after carb balance...Try to start bike after 3 days- hydrolocked again. Left cylinder filled with petrol. Oil diluted with fuel again Left float height way out again....F**K!!!

Anyway here's my questions: What could cause the float height to change like this? (There is no crud getting into the carbs to block the float needles.) Could I have a faulty petcock? When I set the floats both times all of the parts looked brand new: O-rings, float needle/seat etc. The floats moved fine and everthing looked and seated perfectly. I did not leave the bike in Prime at any point other than to check the float heights and there is no blockage in the carb breather. Surely even if the petcock diaphram was knackered or even if the bike had been left in the Prime position the floats (if set correctly) should prevent excess fuel entering the carbs? Also, I must say having stripped carbs on many different bikes I find setting the float heights on the GS a very complex affair. It seems to me that the way that the float needle is linked to the tang on the float by what is essentially a bent bit of wire is a tad dodgy in itsellf. When the tang is bent to tweak the float height the wire is able to move along the tang to a certain extent making setting the float height a hit and miss affair. Anyway I'm just pissed that I've done like 20 miles on the bike in total and I've got to drain the oil and start again with not much idea of what I've done wrong! Sorry for the rant and any advice most welcome!  Chris

[werase643]

sounds like two problems

1 the needle/seat is leaking by the needle and the seat

2 something is allowing your petcock to flow fuel when there is no vac

cheapest fix.....

install an inline fuel shutoff between the vac op switch and the carbs
or replace the vac op switch with a shutoff

[chrishiggs]

Thanks for that. Is this a common fault? Any suggestions as to what to use for fuel shut off valve or am I better off just fixing the petcock itself? Presumably the diaphragm can be replaced?
Thanks again.

Chris

[scottpA_GS]

The petcock is a VERY common problem w/ the GS.. you can get one from a CRF150? or search petcock fix... there are numerous posts on how to make it "non-vac" so its just off and on... 

[Paulcet]

there is an o-ring around the outside of the needle seat.  It could be worn/flat/cracked, allowing fuel to bypass the needle.