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Idle problems on a GSF 250 bandit slingshot

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by xa-mont, Jun 1, 2008.

  1. hey everyone.

    Firstly to introduce myself... My name is Travis, im 21, i live in Canberra and have just recently (as of yesterday) become the owner of a GSF 250 bandit slingshot (1989 model with 19k kms).

    and now for the problem...

    the bike was having a problem with stalling sometimes at lights and whatnot, so we figured we would up the idle to a more reasonable rpm (was at like 900 rpm where it should be at about 1450 or something) so we upped the idle RPM which was all well and good but now it seams to have a mind of its own somewhat.

    It will randomly rev up to around 4k at idle (sometimes slowly sometimes quickly), and will sometimes come down by its self, sometimes with a rev or 2, or most of the time if you give the bike a shake it will come down.

    we pulled the carb's off and had a look at the floats and needles and whatnot and everything looked in tip top shape. but we still sprayed everything out with compressed air and made sure they were spotless.

    I also checked the air filter, which was also perfectly clean.

    I currently have some injector/carby cleaner in the fuel and am going for a bit of a ride tomorrow to see if it fixes the problem at all, but i was wondering if anyone has had the same problem (or similar) and could offer a suggestion as to how it might be rectified.

    Cheers everyone,
  2. Air leak somewhere maybe in the lines somewhere?

    Just guessing.
  3. blocked fuel line or pump not working properly.?

    did you balance the carbs????
  4. the fuel line seems to be fine (we blew compressed air down it both ways whilst it was off) im going to buy a new filter for it today though, just in case.

    and it doesnt have a fuel pump, it has a diaphram pressure operated fuel tap, which after some experimenting this morning we are thinking may have some issues.

    when we remove the vac. line from the carbs to the tap it idles fine, when you put it back it goes silly again, so im probably going to pull the tap off/apart and see if its all looking dandy.

    we didnt balance the carbs, but as far as my knowledge goes we shouldnt have to, we only removed the fuel bowls and checked the floats and needles, didnt adjust anything at all so it shouldnt need it.

  5. Firstly, if the fuel lined was partly blocked, that won't affect your idle at all, if the bike still runs fine off idle.

    Whoa there! Back up a bit - what did you do with the vacuum feed from the manifold when you pulled the line off, did you block it carefully?

    Did you remove the float bowls with the carbs in situ, still mounted on the manifold?

    The likely causes are:

    1) Vacuum leak through a fauly/old/damaged carb diaphragm

    2) Leak around an inlet manifold/carb mounting joint

    3) If the vacuum tap is damaged in any way fuel will not flow into the carbs except in the PRI position, unless the valve seat is blocked with rubbish.

    You can easily check this by removing the fuel line from the carb to see if fuel runs out on Run or Reserve with the engine off.

    Next do the "I wanna suck on the vacuum line" trick and see if the vacuum remains after you stop sucking and block the end of the line against your tongue. The vacuum should remain indefinitely unless you have a faulty diaphragm or a hole in your tongue.

    If the vacuum dies away after a second or two you have a faulty fuel tap diaphragm.

    4) Quite likely - poor carb sync. You can really only do that properly with vacuum gauges.

    All the best

    Trevor G
  6. See red above.

    This morning we decided to just give the fuel tap a bit of a blow out with compressed air whilst still on the bike and this somewhat fixed the problem, now it only pops up to around 2k, so im thinking crap in the fuel tap is likely, so next time i have the tank off ill pull the lil falla apart and give it a good old clean out (as well as the tank)

    Thanks for everyones advice.

    The bike went great on a little ride me and my old man went on today (from bairnsdale to ensay and back for anyone who knows the area) It was my first trip around the windeys and it was great fun. Took it pretty easy for the whole thing due to my inexperience on a motorbike, but i still had a ball, and look forward to doing a lot more riding in the future.

    Its amazing how much this thing likes to be revved. Comming from driving an XB falcon with a 351 that revs to all of 5500 its a little bit of a shock but i think im getting the hang of choosing the right gear now.

    anyway enought of my rambling.

    Thanks again everyone.