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Suzuki Across - Losing power and jittery at high revs (>10k rpm)?

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by nickooolas, Jul 29, 2011.

  1. Hey there everyone,

    So I re-awoke the Across from hibernation yesterday (after being out of action for about a year), starting with a good once-over of everything and grease and lubed, but also did an overhaul of the carbies (just took them completely apart and cleaned out with carby cleaner, put back together)



    Now, it starts first time with no problem and low speeds and RPM (<10k RPM in any gear it is as normal), however at higher RPM and especially in higher gears and speeds, over say 10k rpm it struggles and has random jitters up to full rev limit (whereas before would really easily reach it).

    This can be described as if someone is startving it then letting it have some fuel, then starving again, so it really has the jitters!!

    Any suggestions as to what this could possibly be??

    Thanks in advance!
     
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  2. Hey Nick, I don't know anything about the Across, and I'm not a mechanic - so hopefully you get a more qualified response than mine!

    But with that disclaimer out of the way, three things come to mind:

    • 10K RPM sounds like you're revving that thing bloody hard - is it supposed to rev that high? The symptoms you described sound like what I've experienced with small 4-stroke 4 cylinder motors in cars - the motor just sort of tops out and when it's revving at its limit it sounds a bit "jittery".
    • Fuel supply: fuel filter replaced as part of your service? possible blocked fuel lines? split in the fuel line letting in air? At the top end when the carb is sucking fuel as hard as it can, perhaps something is preventing the fuel delivery system from keeping up?
    • Carb tuning: now what I'm about to type next could be complete crap ... but I know carbs are tuned in different ways for different segments of the overall rev range. Is it possible that your disassembly / reassembly of the carb has affected whatever adjustment or component controls the top part of the rev range?

    KN
     
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  3. Yup as to your not knowing the Across.
    Redline is 15500 , so 10000 is well within the torque curve for the little screamers :butt:

    As for your carbs comment, maybe ??
    There is so much that can be stuffed up in a multi carby setup if you really dont know what your doing, needles on different settings / balance screwed up etc etc , lucky for the OP there is a great Suzuki Across website that has a wealth of info to help those that want to try to work put what is wrong or what they should have done :angel:

    http://suzukiacross.org/
     
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  4. Well since you said you've given the bike a good once over, maybe it's now getting more air than usual when the throttle is open from 3/4-full? If so, then try going up one size on your main jet, see if that helps. If you find that doing this makes your bike a bit less jittery/less loss of power, then go up another size on the main jet, and so on. If you find that you get bog, then go back to the standard size get, you have a different issue.
     
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  5. hey,

    the across is one of those "special species" of bikes - aka 4 stroke 16 valve 250cc that revs out at 16500 rpm :) so 10000 rpm is only it just getting started!

    as for the fuel system - good point will need to check that but replaced the fuel filter only recently, although the fuel line may have got clogged when putting the airbox back on in the dark...

    as far as carb tuning goes - well...i didnt really change anything that could be tuned or modified, but maybe i think i moved the Needle jet - well it actually slid out of its mount....

    does anyone know which jet/setup is necessary for changing full throttle response/operation. here is a schematic of the suzuki across carby.


    http://www.bike-parts-suz.com/suzuki-recherche-bike-pieces_nn.php?compteur=1351&PartsListID=857024


    Cheers guys!
     
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  6. 13383-24D00 for anything above 1/4 throttle and below 3/4 throttle and 09491-90007 for anything above 3/4 throttle mate. try replacing 09491-90007 with 09491-22016. although I think that that jet will probably be a bit too big and will cause you bog, see if you can find a jet somewhere online that is in between the sizes of those two main jets. use a GOOD quality screw driver set and find the flat head screw driver which BEST matches up with the head on the jet. same go with the philips head screws on the carburetor (use philips head screw drivers obviously). when you take the appropriate screws out of the carburetor, first of all spray some WD-40 or some other stuff that helps get stubborn screws out (which they almost always are). spray it onto the screws, with the head of the screw facing up. let it soak in for a few minutes. then, tighten the screw A TINY BIT, and SLOWLY screw the screw out. if it won't budge when applying a little bit of twisting force on the screw driver, try applying a good amount of pushing force on the screw driver at the same time as applying gentle twisting force. you have to be careful with this shit or you'll strip the heads and have to use a screw extractor to get the bastards out.

    or you could just take it to your local bike mechanic to have a look.
    good luck
     
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  7. yeah, well i have pulled the carbs apart before and done a complete overhaul, didn't really play with any of the needle settings or balance adjustments screws, just literally took the bowl apart cleaned out the water in them, and cleaned out the jets with carby cleaner and replaced them... so hopefully that couldnt be the problem, nothing else has really changed apart from that! unless i sstuffed one of the jets when i screwed it back in as it already looked to be slighly damaged from a screwdreiver previously (flathead)

    thanks for your info! the only thing that puzzles me is, how come only now, nothing physically has really changed so not sure whats happening there. as i said above, I had 09494-00707 (above 3/4 throttle) fall out on me (slid out of its placement - and i slotted it back in, although still didn't seem very secure in there, could that possibly be the problem?

    Cheers,

    Nick
     
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  8. you've mentioned one of the jets looks slightly mashed. maybe it was jetted lean by the PO because it was running too rich, maybe now that you have taken it apart and cleaned it, the previously rich condition has been fixed and it is now running too lean. so it might be worth getting the stock main jet (only like 3 bucks), putting it in, and seeing what happens.
    of course I am probably talking shit out of my arse and you should talk to someone who actually knows what they're on about.
     
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  9. Check your main jets, float height & carby balance.

    If it was running fine before, don't change any jet sizes.
     
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  10. Ok so an Update - Still doing the same thing BUT, I noticed if I accelerate hard up to redline (16.5K) with the CHOKE on, she goes up all the way without being limited (albeit, not the smoothest of accelerations, but it actually gets there instead of sitting at 12K RPM)...does this mean it is running LEAN?

    Cheers!
     
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  11. Maybe, did you check the carby settings? Could be a float height issue...

    Strip & clean the carbs, as above, take note of jet sizes & compare to factory settings.
     
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  12. Sounds like its lean, although unless you really changed something in your carbs it shouldnt be that noticable. Check that you put the carbs back into those rubber boot things properly, ive made this mistake before and had it running lean. It takes a silly amount of force to get them back in properly (im not strong and had to use a car jack :eek: )
    Otherwise, check that you havent squashed your fuel line, the pump is pretty weak and it doesnt take much to cut off the fuel supply. If none of that helps, chuck some fuel system/injector cleaner into a tank of fresh petrol and see if that helps.
     
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  13. If it was working before I can't see it being a jet size issue. Normally if the carby hadn't been cleaned then after a year of sitting I would think it needed cleaning but if you have already done this then the next obvious thing is that something is not put back together right.

    However it is also easy to assume the obvious and blame carbs as that is what you played with. Although not as likely it could be a problem not related to carbs.

    How is your spark? Could HT leads or other components be breaking down under high revs?

    Doesn't really sound like air but just in case, how is the air filter?
     
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  14. have you checked for dropped sliders? i've read that can be a problem on the across.
     
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