Fuel Petcock Issue (same old song)

[crash]

Hi Folks

I have the classic "runs on PRI, but stalls on ON/RES" problem.  Naturally, I searched the forum and read up on faulty fuel petcocks.  I have performed the very scientific test of sucking on the vacuum hose and watching nothing come out of the to-carbs spigot.  Then, I replaced the old diaphragm (and rubber seals) in the petcock with parts from the K&L 18-2763 kit, as suggested in this wiki.

Unfortunately the problem still exists!  Fuel (and bike) run when petcock is turn to PRI, but fuel stops running when petcock is on ON/RES.  The sucky test confirms no flow.  What gives?!  Before I turn to a "petcock-delete" option, does anyone have any other ideas on what may be going on?

Thanks.

[J_Walker]

Hi Folks

I have the classic "runs on PRI, but stalls on ON/RES" problem.  Naturally, I searched the forum and read up on faulty fuel petcocks.  I have performed the very scientific test of sucking on the vacuum hose and watching nothing come out of the to-carbs spigot.  Then, I replaced the old diaphragm (and rubber seals) in the petcock with parts from the K&L 18-2763 kit, as suggested in this wiki.

Unfortunately the problem still exists!  Fuel (and bike) run when petcock is turn to PRI, but fuel stops running when petcock is on ON/RES.  The sucky test confirms no flow.  What gives?!  Before I turn to a "petcock-delete" option, does anyone have any other ideas on what may be going on?

Thanks.

well if you've got an inline fuel filter, rip that off.

frame petcock delete.. well I'm for it, but just getting rid of the non-rebuildable OEM one for something else.. I've personally ran a fuel pump on the GS500 for awhile, but I went back to OEM when I wanted to use the fuel pump for something else.. and have yet to find a good aftermarket replacement petcock that doesn't restrict the fuel flow, I can find crappy little chinchin ones and dirtbikes but never a real proper replacement.

you want something to Y in the two lines, and at least an On/Off valve so when you park the bike, you don't come out with a puddle under it, and outta gas.

[nicksmo]

For sure get the fuel filter out.  Most are a coarser mesh than the one in the tank, so unless something is getting into the line between tank and petcock (should not happen) it is unnecessary.

Additionally, the smaller diameter tube running from left carb to petcock on inside of petcock is likely leaking and not drawing on the petcock diaphragm to open it.  I did the same flammable gas check and it actually came out negative, even though there was a leak (I'm thinking it must not get drawn into the system noticeably).  Anyways, hose clamps on either end fixed it for me, next would be a new hose.  Either way, both easy fixes.  How is the idle and throttle response?  Do the RPM drop quickly or do they lag on their way down?