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Rough running CBF250

Discussion in 'Tech Help' started by Paris Hilton, Dec 26, 2012.

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  1. Paris Hilton
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    Paris Hilton Member

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    Took the plug out, zapped the hell out of my thumb, swore a bit, threw it back in and now it idles, runs and sounds good. Picks up revs as normal but seems a bit... Slow? No hesitation just... Slow... May just be the bike though, I've only ever dealt with triumph 900's... Choke works...
     
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  2. Paris Hilton
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    Paris Hilton Member

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    The idle mixture screw I just screwed in, with no regard to what it does... Makes sense now. Of course now I need to take the carb out again to get to it to adjust it!
     
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  3. supamodel
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    supamodel Secret Aaaaaagent Man Staff Member Moderator Supporter

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    Could have two screws for idle adjustment: one for mixture, one for throttle opening. Aim usually is to go for minimum throttle opening for the correct idle revs.
     
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  4. Paris Hilton
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    Paris Hilton Member

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    Ah yep. I got it to idle by turning the throttle "stop" (if that makes sense) screw right in. I guess that's not ideal as it means at WOT it won't have full power... With the mixture screw, im assuming the further out it is, the richer?
     
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  5. supamodel
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    supamodel Secret Aaaaaagent Man Staff Member Moderator Supporter

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    Depends, some are richer the further out they are, some are leaner. Depends how they work (air bleed or fuel aperture). 1.5-2 turns out on the mixture screw, get it idling at the correct speed, turn the mixture to get maximum idle speed, then readjust throttle stop to correct idle speed is a simple way to get it roughly ok.
     
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  6. Paris Hilton
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    Paris Hilton Member

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    Hmm, there must be an easier way to get to it as at the moment there is only a few mm between the screw and the frame...
     
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  7. DonT
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    There's probably a $25 honda tool that looks a bit like a bent bit of wire, maybe you need one?
    At least it sounds like its getting there, really needs a hoon around the block now by the sounds of things:)
     
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  8. Paris Hilton
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    Paris Hilton Member

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    I've ridden it up and down the street, wearing a 70's spec helmet... I really want to take it further but being unlicensed and inexperienced makes it a bit risky...
     
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  9. Paris Hilton
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    Paris Hilton Member

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    Too rich, no power. I think the timing may be off...
     
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  10. supamodel
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    supamodel Secret Aaaaaagent Man Staff Member Moderator Supporter

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    On something like the CBF the timing is set by where the CDI pickup is in relation to the crank, that's really it. CDI units usually just fail rather than spark consistently early or late.
     
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  11. Paris Hilton
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    Paris Hilton Member

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    It seems someone has had the head apart before and done a shonky job, silastic everywhere. I was more thinking maybe one of the cams is out of sync (teeth on the chain etc)

    It is able to be riden up and down the street and that's about it. It has no power, you can get into second and that's about it. Top speed? about 10km/h.
     
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  12. DonT
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    Your early symptoms did remind me of a rehab I did on a girl friends bike after her dad had put in a new camchain. Have you got a manual yet? I think no matter what your problem is you should go right over the bike as there can easily be other things.
    I hate silicon sealer, some people love it but a friend of mine (& I've heard of many others) devastated a Norton with a blob of silastic bunging up an oil passage. I also reckon they ruin gaskets that may very well last 25 years of consistent removal/replacement and still work fine.
     
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  13. Paris Hilton
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    Paris Hilton Member

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    Yeah i've tallied up what I need so far after the motors working properly, new chain, new cogs and new tyre...

    I have a manual yes, thank god for the internet.

    I hate silastic too, almost as much as I hate removing it!

    I think i'll pull the motor down. I'll learn a thing or three. I can do it on a bench, i'm loving this, don't need an engine crane or anything... :cool:

    That said, I also can't just go to a mates house and grab what I need for testing, I can't find a cheap CDI anywhere... I don't want a brand new one until I confirm that's the problem.
     
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  14. supamodel
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    supamodel Secret Aaaaaagent Man Staff Member Moderator Supporter

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    Should be able to check cam timing without pulling the whole thing down: just pull the valve cover off and there would be somewhere with crank marks somewhere.

    (also unlikely the head has been silasticed, that stuff sucks as a head gasket. More likely it had the valve clearances done - which does require the valve cover off and that is a likely candidate for silasticing depending on how it is gasketted).
     
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  15. gazman
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    bent valves maybe or not seating properly ?
     
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  16. supamodel
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    supamodel Secret Aaaaaagent Man Staff Member Moderator Supporter

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    Only things I have had with bent valves made an absolutely hideous noise and wouldn't run at all. Compression test also might not go astray, either.
     
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  17. Paris Hilton
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    Paris Hilton Member

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    Unfortunately my compression tester doesn't have the adapter for a 10mm spark plug, d'oh.

    Another thing a mates suggestion is to check that the exhaust isn't partially blocked.
     
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  18. gazman
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    wasps like to make nests in mufflers. I had a XR500 with bent valves it would start and idle, I could give it a tiny bit of throttle but after that it would have nothing wouldn't pick up revs even if held flat.
     
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  19. supamodel
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    supamodel Secret Aaaaaagent Man Staff Member Moderator Supporter

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    Compression tester adapters are cheap on fleabay and handy if you plan to stick with motorbikes. (Or you buy a Ferrari that uses 10mm plugs).
     
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  20. gazman
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    did you get any info from the previous owner as to why it doesn't run .
     
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