GSF250 fuel mixture screws

[infrag]

Hello

I've purchased a gsf250 some time ago and I've been having problems getting the fuel mixture right.

When I first got it the bike was running rich and fouling plugs because of it on a regular basis.I've cleaned the carbs out since it was left for some time without draining fuel. After cleaning I I did some test runs and it was still running really rich so I adjusted the clip to to the top setting to make it lean as possible (it was set to 2). This fixed the midrange fuel rich problem and made the bike run heaps better. However it was still way to rich low end. I checked the mixture screws and they were 3-4 turns out. From my understanding to tune these screws you start at 1 1/2 turns out and adjust to get to the highest rev point in the range. However for this to happen for this bike I need to turn these screws all the way in (or very very close)

My question is what can cause this to happen since it seems like all stock parts etc. Can someone point me in the right direction?

Also other than running rich it seems to run fine for a bit from cold but after 10-15 minutes of driving it starts to stumble badly low revs and has less take off power. If I have to stop at an intersection I can barely get going. I'm assuming this is linked and hopefully clears up when I get the richness problem sorted?

After stalling sometimes it will only start with full throttle but wont rev up it will just idle. Its like its misfiring too since its pretty rough. If I can somehow get it to rev up (by rolling down an incline and letting clutch out) then it kicks in again and I can rev it up like normal again. However when it goes to low revs it will stall and happen all over again. I've been stuck on the side of the road with the bike just idling at full throttle and not being able to get it going.

This finally happened today in front of my house while I was testing it out. I turned the bike off and got it in the garage with it still doing its thing. I tried a couple of things.. I pulled the lead off plug 4 which made no difference. I pulled the lead off plug 1 and all of a sudden the bike reved to life... I'm not sure if I disturbed the wires going to the coil but i couldnt get it to fault again in my garage and ran out of more time to test :(

Thanks!

[ventYl]

don't know exact composition of GSF250 carbs, but GSF400 Mikunis have several O-rings around floating bowl assembly which if are cracked or not sealing make bike run rich. another quite tricky O-ring lives between slide assembly frame and carb body which can make bike run right or lean too.

another thing to check is if ignition coils are OK after they get warm.

[infrag]

Thanks for replying :)

How do I check the coils after they get warm? Unplug and check the resistances etc?
Its just hard to get this problem to happen in a convenient location and often when I get it back in the garage its gone or not consistent enough that I'd be able to get a reading in time.

Maybe I should just buy a second hand coil pack of ebay and replace one of them at a time to see if it fixes it?

[ventYl]

yes, absolute resistance values would not be interesting, but some significant change may be.

for the case that coils are faulty after warming up - there are two of them so either both have to be faulty in similar way or you should feel that bike is running just on two cyls.