bike fails after warm

[magelord]

So ive got my gs250T. Just cleaned the carbs after winter, put the baby back together and my idle problem at cold and startup went away. Had a gummed pilot jet. So i set my idle screw while it was cold (75 degree's in the sun cold) knowing id have to reset it once the bike was fully warm. I drive about a mile with it running great. Then i come to a stop at a light. The rpm calms down to 2000, just above where i set it at idle(cold) and it floats there for about 30 seconds. Then it starts dying. the rpm drops quickly but not instantly to 1500 and lower the bike shuts off. If i give it a little throttle it revs up just fine (making me think its not a gas problem) but its as if the idle is set too low for the bike to keep running.
I drive it to the next light just fine while its working, come to the next stop and i get the same problem. It floats at the set speed of 2000 for about 30 seconds then starts to die on me.
Just fyi the carbs are spotless. The gaskets and orings inside the carbs are not brand new but all there. the air jets have not been balanced.
Any takers in this gathering of knowledge?

[Nessism]

Did you change the intake boot O-rings? They are a very common vacume leak source.

[duaneage]

Spray wd-40 around the rubber boots on the intake side and airbox side, looking for an increase in idle speed. If it runs up fix the leak by tightening a clamp or replacing the o rings under the boot clamps.

Are you using an OEM air filter or anything unusual there?

[Nessism]

Not trying to put down duaneage's suggestion, but the WD-40 test is unreliable and only shows gross leaks.

If the intake boot O-rings have never been changed before it's almost certain they are flat and if they are not leaking now, they will be soon. Just change them.

[magelord]

Nessism - i have not changed the intake boot Orings. are we talking the fuel intake before it splits to the carbs? I might need a picture.

duaneage - Ill try the spray test once i find out where to spray. And im using OEM air filter.

So im getting the impression its a vacume/sealant problem?

Thanks guys

[duaneage]

More than likely it's the intake boots that go between the head and the carbs. That's a problem area. Do you have a fuel filter in the hose? Large fuel filters can cause vapor lock and weird problems too.

Start with the intake boots. Spray wd-40, water, red wine, or any other safe liquid around the boots when it is hot and see if the idle quality changes.

[magelord]

Update*
So i haven't changed anything but the idle screw. Going to do the wd40 intake test after i buy a new can tonight.
But now ive got her set to idle at 1500 RPM warm, but the idle screw has to be so far up that theres a long (2-3 seconds) delay on down reving.
So when i throttle up to 5k or 6k rpm and let go, the throttle springs back to start instantly but the engine takes a second to rev back down to 1500.
If i back the idle screw out any i wont have idle and any further just makes the down throttle delay longer.
Is my throttle cable to loose?

[850 Combat]

On a Norton a sticky / worn mechanical advancer will do that, but I woulf look for vacuum leaks first.

[mighty13d]

no your cable doesn't appear to be. that nut that is screwed down against the bracket holds it in place.

[duaneage]

Update*
So i haven't changed anything but the idle screw. Going to do the wd40 intake test after i buy a new can tonight.
But now ive got her set to idle at 1500 RPM warm, but the idle screw has to be so far up that theres a long (2-3 seconds) delay on down reving.
So when i throttle up to 5k or 6k rpm and let go, the throttle springs back to start instantly but the engine takes a second to rev back down to 1500.
If i back the idle screw out any i wont have idle and any further just makes the down throttle delay longer.
Is my throttle cable to loose?

Make sure the throttle cable is routed properly and not binding under the tank. Too tight a turn and it can hang up the throttle. This is also a safety issue. That throttle should shoot right back when released, and the carbs should close the valves right against the stop.

The end appears to be a little rusty where it attaches. Might be needing a little grease on the cable too.

[mighty13d]

Those screws need to be tightened though. I replaced mine with stainless allen head ones, but that's just a personal preference. They won't be a pain like the stock one to get back off at a later date if replaced with normal hex head bolts or something.

[Nessism]

What's up with those screws? Thought you went though those carbs and fixed them up?

Hanging idle indicates a lean fuel mixture. I still say it's most likely the intake O-rings, but I've also seen lean pilot screws cause the same problem. Try setting the mixture to 2.5 turns from lightly seated and see what happens. If the idle is still hanging, go after those O-rings...and fix those carbs regardless.