smac
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| posted on 13/6/11 at 10:47 AM |
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Bike carbs holding revs when off throttlle
Just fitted blackbird carbs to my Zetec. It runs fine and goes like the clappers but when you come off the throttle the revs hang on a bit to long
before going down. Ive got an extra return spring on the throttle pedal and the throttle butterflies themselves seem to be snapping shut quickly on
no throttle but the sensation persists. Anyone any thoughts?
Simon
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vyperstrype
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| posted on 13/6/11 at 11:03 AM |
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Take your Divers Boots off before you go out in the car! 
Where there's a will, there's a death!!
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HowardB
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| posted on 13/6/11 at 11:22 AM |
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air leak?
Howard
Fisher Fury was 2000 Zetec - now a 1600 (it Lives again  and goes zoom)
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scudderfish
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| posted on 13/6/11 at 11:27 AM |
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You're actually running an F1 exhaust blown diffuser?
Disconnect your throttle cable and try it by hand. Connect your cable and try again, both at the carbs, and poking the pedal. You may find that
there is sufficient drag in the cable/pedal to slow the closing down.
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flak monkey
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| posted on 13/6/11 at 11:34 AM |
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Air leak is the usual suspect....
Sera
http://www.motosera.com
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robocog
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| posted on 13/6/11 at 12:14 PM |
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The order I would tackle if the butterflys are definately snapping closed cleanly
Airleak check
use of a colourtune on each pot to check they aren't running lean
and a damned good balance
I had this on my (single cyl) motorbike recently
I stripped and cleaned the carbs and re-seated everything and it still did it
stripped down again - used rubber grease to aid the seal between carb and head...but it still did it
Stripped the carb AGAIN, no rips or nicks in the rubber diagphram and nothing seemingly gummed up/dirty or worn out
Re assemebled and re checked the float height - still did it
Couldn't identify any air leaks and nothing to balance (being a single!) and had me a bit stumped
making it run a tad richer by tweaking the idle mix screw out less than 1/8 turn seems to have cured it for me
I didn't have any over run popping or surges or coughing/spitting through the carb so I wouldn't say it was running lean when it was doing
it - plug colour was OK (light tan) as well - my engine must just be a bit fussy like that
If nothing else found I'd just fatten the mix a tad and see if its any better
(BTW the method I used to find "the initial sweet spot" for the carb's idle mix screw was start at 2 screws out from just seated and
turn it in or out till you find an "area" that gives the highest and "cleanest" sounding RPM and set the screw to halfway
between the "dips" )
This method is much more of a pain on 4 cyls of course, so a colourtune would definately assist getting this close
Good Luck
Regards
Rob
[Edited on 13/6/11 by robocog]
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austin man
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| posted on 13/6/11 at 03:52 PM |
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My zetec does the same just makes for faster cornering on change down
Life is like a bowl of fruit, funny how all the weird looking ones are left alone
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FASTdan
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| posted on 13/6/11 at 05:15 PM |
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quote:
Originally posted by austin man
My zetec does the same just makes for faster cornering on change down
I really dislike that sensation. Could be to weak on idle or as said air leak.
We found we needed quite a strong spring on the carbs
NEW danST WEBSITE NOW LIVE! Bike carbs, throttle bodies and more......
http://www.danstengineering.co.uk/
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NOTE:This user is registered as a LocostBuilders trader and may offer commercial services to other users
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Rena
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| posted on 30/5/16 at 08:24 AM |
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An old thread - but I also have the same problem.
The R1 carbs have a strong spring but maybe not enough strong.
Where and how should I attach the spring? Pictures?
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chris
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| posted on 30/5/16 at 08:47 AM |
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I have put a strong spring on the pedal so the spring on the carbs is only having to return the cable
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Rena
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| posted on 30/5/16 at 09:07 AM |
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quote:
Originally posted by chris
I have put a strong spring on the pedal so the spring on the carbs is only having to return the cable
Good idea!
Will try! thanks
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