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bikes revs up on its own

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skikman
Renault 5 Driver



Joined: 07 Nov 2009
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PostPosted: 21:44 - 06 Jun 2012    Post subject: bikes revs up on its own Reply with quote
here's whats happened.2 days ago i put a complete head on it.[yamaha sr250]it started first time and ran well until this morning,it would'nt start.thought it might have been water had got to it as it rained heavy here last night.checked all conections and went round it all with wd40.still no go so took off carb cleaned it and drained tank.put fresh fuel in and it started but revs up on its own.if i blip the throttle a few times it will come down.ive had the carb off again, cleaned and checked the boots for leaks.ive sprayed carb cleaner around the boots but it makes no difference.im not convinced that changing the fuel made it start as it works ok in my 125 bike.i also checked things on the head.bolts,timming,valve clearence .everything looks good.any ideas would be helpful.
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Pete.
Super Spammer



Joined: 22 Aug 2006
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PostPosted: 21:58 - 06 Jun 2012    Post subject: Reply with quote
Sounds like the carb slide is sticking. Pull the carb off and check the action as you work the throttle.
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good Very Happy
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Ariel Badger
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Joined: 02 Dec 2006
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PostPosted: 22:05 - 06 Jun 2012    Post subject: Reply with quote
Make sure that there is no air leak between carb and head.
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Casper
World Chat Champion



Joined: 12 Jul 2010
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PostPosted: 22:12 - 06 Jun 2012    Post subject: Reply with quote
My GPz750 was doing this after a carb clean. Turned out to be poor adjustment. I had to turn tick over down until bike conked out and bring it back as much as possable with the cable adjusters then set tickover.
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skikman
Renault 5 Driver



Joined: 07 Nov 2009
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PostPosted: 22:22 - 06 Jun 2012    Post subject: Reply with quote
Pete. wrote:
Sounds like the carb slide is sticking. Pull the carb off and check the action as you work the throttle.
i'll give that a go in the morning and let you know how i get on thanks
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Pete.
Super Spammer



Joined: 22 Aug 2006
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PostPosted: 22:52 - 06 Jun 2012    Post subject: Reply with quote
Check that you haven't altered the cable run, and that it hasn't been pinched in the headstock lock-stops too.
____________________
a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good Very Happy
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skikman
Renault 5 Driver



Joined: 07 Nov 2009
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PostPosted: 23:00 - 06 Jun 2012    Post subject: Reply with quote
Pete. wrote:
Check that you haven't altered the cable run, and that it hasn't been pinched in the headstock lock-stops too.
it rev's up without touching the bike
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Usher4566
Spanner Monkey



Joined: 29 Apr 2011
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PostPosted: 06:28 - 07 Jun 2012    Post subject: Reply with quote
Top tip tap carbs with screw driver when they go up c if come down if so sticking float valve
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skikman
Renault 5 Driver



Joined: 07 Nov 2009
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PostPosted: 18:02 - 09 Jun 2012    Post subject: Reply with quote
Usher4566 wrote:
Top tip tap carbs with screw driver when they go up c if come down if so sticking float valve
tried that no difference.right.lowered the float level[bent towards pin],cleaned everything i think off.choke,jets,barrel,pin,diaphram ok and sealing well,every hole i could see.put it back in and took it for a spin.seemed ok but not ticking over.thought it just needed adjusting.brought it back home and went to adjust it and noticed that it started to rev up to 3[without touching it] and stay there.bliped the throttle and back to cut out.started it,it idled then up to 3 and stays there.ive went round it all with carb cleaner and there's no leaks.could the timming be off slightly?the line does'nt line up exactly but i think its wear in the chain
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skikman
Renault 5 Driver



Joined: 07 Nov 2009
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PostPosted: 23:43 - 10 Jun 2012    Post subject: still not sorted Reply with quote
till hav'nt this sorted.have had the carb off 10 times.lowered float hight,choke out and cleaned,diaphfram has no holes even sealed lid down with instant gasket,checked float needle is sealing by tipping carb and blowing in fuel pipe as i cant see any overflow.air/fuel mixture screw 1-1/4,1-/12,1-3/4, 2 turns out.everything/hole i can see out cleaned and blown out,rubber boot to engine out checked for cracks and sealed back to engine.sprayed carb cleaner everywhere while bike running no difference.there is no leaks.i even had head off again today just to make sure everything was on right and its still the same.doing my f ing head in.what am i missing????
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Pete.
Super Spammer



Joined: 22 Aug 2006
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PostPosted: 00:16 - 11 Jun 2012    Post subject: Reply with quote
You're looking in all the wrong places messing with timing etc. If this is true:

Quote:
if i blip the throttle a few times it will come down


It points to a sticking carb slide. Maybe the slide is sticking or the cable is not returning properly.

Take the top off the carb and remove the cable. Take hold of the end of the throttle cable and push/pull on it - you should be able to snap the throttle tube open and shut with no effort just by moving the cable.
If you can't, find out why. Remove the throttle tube and clean the handlebars and the inside of the tube with WD40 or something then dry with a paper towel. Don't oil the tube or the bar, they are supposed to be fitted up clean and dry. Re-assemble it and see if the movement is free and easy.
If not, you might want to clean the last couple of inches of the throttle cable if it's a bit gummy. Again, clean with WD40 and then dry it off. The action should be very light.
If this has improved things, put it back together and see if it will now return to idle. Make sure you have some slack in the cable - it's supposed to be a little loose.
If you are still having problems returning the engine to idle, then remove the slide and inspect it for burrs. Check down the emulsion tube to make sure there is no crap down the hole and make sure there are no burrs on the needle check the action of the slid in the carb bore and see that it closes right down to nothing with the idle adjuster screwed right off.
____________________
a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good Very Happy
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skikman
Renault 5 Driver



Joined: 07 Nov 2009
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PostPosted: 08:50 - 11 Jun 2012    Post subject: Reply with quote
Pete. wrote:
You're looking in all the wrong places messing with timing etc. If this is true:

Quote:
if i blip the throttle a few times it will come down


It points to a sticking carb slide. Maybe the slide is sticking or the cable is not returning properly.

Take the top off the carb and remove the cable. Take hold of the end of the throttle cable and push/pull on it - you should be able to snap the throttle tube open and shut with no effort just by moving the cable.
If you can't, find out why. Remove the throttle tube and clean the handlebars and the inside of the tube with WD40 or something then dry with a paper towel. Don't oil the tube or the bar, they are supposed to be fitted up clean and dry. Re-assemble it and see if the movement is free and easy.
If not, you might want to clean the last couple of inches of the throttle cable if it's a bit gummy. Again, clean with WD40 and then dry it off. The action should be very light.
If this has improved things, put it back together and see if it will now return to idle. Make sure you have some slack in the cable - it's supposed to be a little loose.
If you are still having problems returning the engine to idle, then remove the slide and inspect it for burrs. Check down the emulsion tube to make sure there is no crap down the hole and make sure there are no burrs on the needle check the action of the slid in the carb bore and see that it closes right down to nothing with the idle adjuster screwed right off.
its a cv carb.the neddle and slide are returning ok,i had it out and put wd40 around it.diaphram it ok even sealed lid down with instant gasket,float and neddle ok,no leaks in boots,cable is ok,jets are cleaned,every hole i can find is blown out,heads away with it[my head]
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Casper
World Chat Champion



Joined: 12 Jul 2010
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PostPosted: 08:59 - 11 Jun 2012    Post subject: Reply with quote
What about the screw clip round the carb to engine rubbers. If mine are at an angle they touch the throttle return spring on the carbs. Yours could be rubbing something.
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skikman
Renault 5 Driver



Joined: 07 Nov 2009
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PostPosted: 14:29 - 11 Jun 2012    Post subject: Reply with quote
1888 wrote:
What about the screw clip round the carb to engine rubbers. If mine are at an angle they touch the throttle return spring on the carbs. Yours could be rubbing something.
all clear and spring working well.ive ordered new jets,lets see what that does.
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bodger
Nova Slayer



Joined: 18 Apr 2012
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PostPosted: 08:03 - 12 Jun 2012    Post subject: Reply with quote
Just a thought . You say you put a head on it 2 days ago.
Could,nt be that you have a air leak at the cylinder head gasket could it?
As I say just a theory
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skikman
Renault 5 Driver



Joined: 07 Nov 2009
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PostPosted: 22:03 - 13 Jun 2012    Post subject: Reply with quote
bodger wrote:
Just a thought . You say you put a head on it 2 days ago.
Could,nt be that you have a air leak at the cylinder head gasket could it?
As I say just a theory
i took the head off again to check that everything was on right and its ok.and why are people going on about the cable.ive said its a cv carb.slide works with vacuum not cable and its returning ok.ive had the bike out for a run and it still wont idle also its backfiring when i let the throttle off.sounds like maybe the pilot jet so ive ordered a new one.should be here about sat.i'll let you know what happens
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skikman
Renault 5 Driver



Joined: 07 Nov 2009
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PostPosted: 18:03 - 16 Jun 2012    Post subject: sorrted Reply with quote
[quote="skikman"][quote="just to let you know i got it sorted.it was a cog off the timming.i was thinking that a while back but never altered it as everyone said it was a carb issue.i thought the bike would'nt have run as well as it did with timming off.it just would'nt idle and the odd rumble and backfire when letting throttle off,other than that it seemed to run fine.a well you live and learn.thank fock its fixed.again thanks everyone for the help
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