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Loss of power at high rpms

Discussion in 'Suzuki 250cc In-line 4's' started by Shimmy, Mar 27, 2013.

  1. Shimmy

    Shimmy Active Member Premium Member

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    Hey fellas,


    Seems my Across wants to play another game.


    It kinda happened over the course of one day about a month and a half ago, just been putting up with it since.
    Went for a ride and the further I got the worse it got, I ended up replacing the slide holders which seemed to fix most of it (one was about to drop and the others were very loose).
    By the time I got home, it was struggling to pull 80kph and would not go above 13000rpm.


    So, today I decided to try and fix it, balanced the carbs, checked fuel filter, replaced air filter, checked fuel hoses for blockages, checked plugs then put the old ones back in,
    It's not as bad as it was but still not that great.


    What it's doing now is it gets to around 12000 and the power just gradually dies off, it takes longer to die off now than what it used to take but it's still annoying.
    It pulls harder in 6th from about 8000rpm than it does in 3rd from 12000rpm, although not as noticeably now but still there.
    In neutral though it will rev all the way cleanly with no issues at all.
    It used to pull all the way to 16000-17000rpm easily.


    I'm going to put in some 98 fuel and some carby cleaner additive tomorrow, wont know until I refill with 91 (bike runs like crap on premium but it does have more cleaning additives in it) to see if it helped but worth trying.


    Anyone got any ideas?
     
  2. risky

    risky risky

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    try a cap of auto trans fluid in the petrol. sounds crazy but a mercedes mechanic recommeded it. lubes the valve stems and supposed to decoke motor.
     
  3. Shimmy

    Shimmy Active Member Premium Member

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    Hmm, thats an interesting one.


    Also, not as big of an issue but when the engine is running and the choke put on (either not warm enough or whatever reason), if I put it all on right away it'll stall or if I gradually put it on it will nearly stall then start running like it should.
    Any ideas for this?
     
  4. kiffsta

    kiffsta Senior Member

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    How is the Fuel mixture ?  If it wont rev out, it could be a tad lean, did you adjust the needles ?
    Chris
     
  5. Shimmy

    Shimmy Active Member Premium Member

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    The needles are on #1, leanest it can get.
    It's been on that for a few thousand k's now though and ran great like that.
    Plugs looked fine too.


    It will rev out, just a reduction in power.
    Running some of this stuff in it now http://www.supercheapauto.com.au/online-store/products/Liqui-Moly-Fuel-System-Cleaner-Conditioner.aspx?pid=325542&menuFrom=60302#Cross.
    and got about 4 litres of BP 98 in it to try and clean it out.
    I did run some United fuel through it a while ago, which down here is just crap (had no choice to put it in).


    I'll run this tank through and if I dont see any changes, I'll put the needles back to #2 and see how it is.
     
  6. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    Next time fuel is low have a look inside the tank for rust or crud which will obviously accumulate at the petcock outlet.
    Dont know if the Across has internal tank filters but they were encrusted with crap on the Fizzer.
     
  7. Shimmy

    Shimmy Active Member Premium Member

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    The across has internal filters.
    They weren't spotless but theres no build up of rust that I could see.
    Not that you can see much in the tank of the across due to the shape/position of it.
     
  8. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    Maybe if the other remedies fail it might be worth draining the tank and removing the petcock to clean the tank and filters.....especially if its never been done in 20+ years.
    When your pulling high revs fuel flow would be at its highest and any restriction (rust,dirt,crud) may be hampering that.
     
  9. Shimmy

    Shimmy Active Member Premium Member

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    Removed the petcock, filters had a bit of grit on them but nothing that bad.
    I also checked the fuel pump, it pumps out a lot more than the min spec in the manual.


    Tank seems fine.


    My thought was fuel flow first as well but it seems to be fine at least until the carbs.
     
  10. kiffsta

    kiffsta Senior Member

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    hmm, is it running on all 4 ?  might pay to check coil leads and the plug caps are on properly
     
  11. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    :icon_scratch:

    When u check the leads/caps unscrew the cap off the lead to check theres some nice shiny wire there.....if not, snip a small bit off the lead.
    Also look for corrosion inside the plug end of the cap and the screw in the lead end.
     
  12. kiffsta

    kiffsta Senior Member

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    On one of my acrosses, I had arcing on the coil leads, I didn't notice it in the light, I ran it in a dark garage with the boot off and it was very noticable.
     
  13. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    How did u get on with this mate? 

    :D
     
  14. Shimmy

    Shimmy Active Member Premium Member

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    Yup all cyl firing normally.
    Leads are new-ish (done 7k klm and about 4 months old), plug caps are originals.





    Plug caps are clean, havn't checked the leads themselves but being only 4 or so months old I'd doubt it (weirder things have happened though).





    Everything seems to be fine in that area.




    quote author=GreyImport link=topic=1138.msg6330#msg6330 date=1364795336]
    How did u get on with this mate? 

    :D



    Issue is still there unfortunately, still yet to drain the tank with the carby/valve cleaner though.
    Might go for a ride tomorrow to drain it through.


    It doesn't seem as bad as it was but it still dies off.


    I'm thinking it has to be in the carbs.
    Possibly weak spark but the only thing thats not really eliminated are the coil packs.
    There is no miss or anything though.
    Fuel delivery is fine to the carbs.

    New air filter (bout 700klm old)
    New slide holders (bout 3k klm old now)
    On the slide holders though, are they supposed to sit in the little notch in the slides themselves?
    Since the old ones were about stuffed, I wasn't sure if they were supposed to or not, they currently are in the notch.




    I might still lift the needles to #2 yet, being in Tas the air would be cooler and more dense around this time of the year making it run even leaner i guess (although the issue first happened beginning of February.


    Really hoping to get this sorted by Saturday, taking it to the track on Sunday and would be disappointing if it wont pull through the revs.
     
  15. Shimmy

    Shimmy Active Member Premium Member

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    Well, I found the issue...


    It was those damn slide holders, I had them in the notch where they have a litle up and down movement, I moved them out of the notches so they were in solid and the power was all back, it will happily rev out now.


    In other, news, I stacked it today, lol. had a track day and going around a corner the peg dug in and lifted the rear wheel, with another corner quickly approaching and the bike very upset, all over the place so I just tried to slow down and gently go off into the gravel, as soon as I hit the gravel I went down.
    Left hand side all scratched up, broken indicators and a slightly bent headlight frame, all good other than that.
    Went back out for 3 more rounds then rode it home.


    Went quite well I think, learnt a fair bit about my limits and the bike's limits, was lapping the pretty much the whole field by the end.
    I could push harder when I get to know the track better but I can't push the bike through a couple of those corners any harder, unless I lean off a heap more.
     
  16. Shimmy

    Shimmy Active Member Premium Member

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  17. Desmo

    Desmo Member Premium Member

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    That was awesome man  ;D Bummer about the stack though.

    And yea those throttle slides are such a P.I.T.A! I just stuck some m3 stainless grub screws in the "petals" of the plastic clips and forced the lot into the slider. They arent ever coming out now lol.
     
  18. Shimmy

    Shimmy Active Member Premium Member

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    Thats a mighty fine idea, haha.
    I've heard of people epoxying them in but not keen on something that permanent.


    Yeah, it was an awesome day on the track, really enjoyed it.
    Stack was a bit of a downer but I didn't let it get me down, go to a track and play around, pushing limits and stack it, can't go home crying about it, lol.


    The sessions later in the day went pretty good, taking more speed through the corners (aside from the one I came off on, grounded the peg again a couple of times but nothing like the stack), over taking pretty much the whole field (was only a couple I couldnt hang with, mainly on the straights.


    A few more days and I reckon I could shave a few seconds off, but I'm not sure if I'll take the Across again, found it's limits quite easily.
    If the pegs were higher and had harder suspension it would be alright.


    Keen in an FZR250 or ZXR250 for a track bike, I like the GSXR250 but can't say I'm a big Suzuki fan and not really into Honda either.
    Either that or a bigger bike but Baskerville doesn't really need a big bike to have fun/put down decent laps.
     
  19. Shimmy

    Shimmy Active Member Premium Member

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    Oh and brakes, the Across brakes are crap, were alright on the first session, nice and firm-ish with a decent amount of stopping power but by the last session, the lever was coming back to the bar and felt all spongy and just having enough stopping power to slow from 150kph+
     
  20. kiffsta

    kiffsta Senior Member

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    good stuff Shimmy, sorry to hear you dropped it, but at least you and the bike could go on. I have a spare fairing bracket if you need it  :Thumbs_up: 
    Great Vid !!!, I really need to pop my track day cherry
     

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