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SRX 250 revving high when hot!!

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by rodgonzbea, Feb 11, 2010.

  1. Hello.. heellp!! I have an srx250 (yamaha), '85.. i use for commuting to from work (+- 70 kms return) in Adelaide.. by the time im gettng home or to work, at traffic lights, the bike instead of idleing..starts revving higher and higher..i have to either engage it in gear and half let go, to slow th engine down.. or even kill it... Ive notice it usually happens when the weather is hot... bloody embarrasing when you stop next to a car, people look at you saying " oh yeah.. nice little old bike.." and then th stupid thing starts screaming at about 7-8 thsnd revs!!! let alone thinkng what if the clutch snaps....oh look at th nice little bike..plasterered on that truck!!
    When cold..it idles at 1-2000, when hot up to 3, but now, after 30 k's of city riding.. every time I stop...it jumps up..
    I used to use high octane (93-95)petrol...until I was told to just use 91...done.
    I am currently using synthetic automotive oil (10-30), as I was told it would be good for it.. maybe that has smthng to do with it... Ill start by chnging oil & filter this weekend..maybe ill folllow on that thread and try diesel oil??
    I dont know what to try.. it definitely stresses an old engine.. have put enough money on it that it still has payed itself off.. dont want to blow it..
    I checked the carb..(visually) and throttle and return seems to work ok..
    I do know the CDI is old and looks like crap.. a new one is about $400, ive only found one at a wrecker for 100,l but he's had it sitting outside for like a year, still on the wreck... so i dont want to change it unless I really have to..
    So...I DON'T KNOW WHAT TO CHECK.... Hopefully the mixture of clever brains present in this forum can guide me...(sucking up time!!!) Thanks anyway!!!

  2. Hey rodgonzbea, the first thingt to do which is reletivly inexpensive is to clean the carbs. If you pull them apart or just spray carbon clean though it that'll surly help. Then! ballence the dam things.

    This worked fixing the same problem on my mates olg gpx250 hopefully it'll help with yours too.

    As far as the oil does im running delo 400 diesel oil in my fzr600 and its running beautifuly! i highly recomend it
  3. check/replace all your fuel and vacuum (in particular) hoses. Engines rev when they lean out and the heat can cause hoses to leak. A leaking vacuum hose can shut off the petrol tap.

    for a few dollars it's worth replacing them all. If you can put clips on them, but it's not always easy with bikes.
  4. +1 to both the above.

    Also, there is a possibility that the rubber stub connecting the carb to the head has cracked with age. This is quite a common old bike problem and will also cause a lean mixture and ridiculous idle revs. Traditional check is to spray WD40 all over it with the engine idling and see if the idle revs change.
  5. Cool..bt.. what do you mean balance the carbs.. mine is a single..?
  6. what will the WD40 do?
  7. The WD40 seals the leak for a few seconds. A change in idle will confirm Pat's theory and it is a good one.
  8. I always thought it was 'cos the engine would see the WD being pulled in through the leak as fuel, changing the mixture strength.

    Still, regardless of the mechanism, a change in idle would indicate a buggered inlet stub. Not sure what the supply situation would be like for new ones, but I've seen successful temporary repairs made by wrapping the whole thing in pvc duct tape.
  9. +1 Hence the alternative version of using a dropper or something to put a drop of fuel on the suspected leak point.