Slight miss when coming off closed throttle when warm?

Discussion in 'Bonneville' started by Triumph Beaver, May 20, 2016.

  1. Triumph Beaver

    Triumph Beaver New Member

    May 15, 2016
    4
    3
    West Yorkshire
    #1 Triumph Beaver, May 20, 2016
    Got the bike running better now, thanks to everyone’s help.. so been out on it tonight and have another small issue.

    When it’s hot (after about 2 miles), it can miss on opening the throttle (just of closed position). Does not do it when under load.. you let off and wind back on again, it’s okay... It does it when you’re going downhill on over-run, then you slightly open up... just one miss then off... Or if you’re at tick over.., just one miss and off.... or over-run on the flat... just a miss then off....?

    Any thoughts?... got a Boyer fitter... could it be the bits getting warm... pulls like a train otherwise and Amal MK2’s... could it be air screw (1.5 turns out).. or some other jetting issue? :) cheers
     
  2. stevethegoolie

    stevethegoolie Elite Member

    Oct 16, 2014
    2,455
    800
    East Riding of Yorkshire
    #2 stevethegoolie, May 20, 2016
    Is there an air leak twixt carbs and cylinder head? Start engine and spray Easy Start over inlet manifolds. If revs increase then there is a leak. I have heard that WD40 has the same effect. If you have a manual choke then just give it a smidgen of richnessosity to see if that makes a difference.
    Certainly sounds like carbs to me.
    My Daytona 955i stuttered a bit when getting back on the throttle which was, apparently, due to an aftermarket end can weakening the mixture slightly.
    Could even be a little bit of muck in the carbs.
     
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  3. Triumph Beaver

    Triumph Beaver New Member

    May 15, 2016
    4
    3
    West Yorkshire
    #3 Triumph Beaver, May 20, 2016
    Last edited: May 20, 2016
    Hi Steve.. that does sound like a good call as the rubbers are cracked and perished a tad... will have a squirt tomorrow ;) but its the 'when warm bit?' would this not happen all the time when off choke? thanks again... John
     
  4. stevethegoolie

    stevethegoolie Elite Member

    Oct 16, 2014
    2,455
    800
    East Riding of Yorkshire
    #4 stevethegoolie, May 21, 2016
    When warm there is no additional richness with the choke fully off, just what the carbs and the rest of the inlet side feeds in, so any leaks or poor settings will be affecting the mixture. So a little bit of choke will compensate for any 'leaks', if you see what I mean.:)
    If all is well, try setting the air screw by getting one cylinder to tick over (plug out on the other cylinder and engine hottish - don't burn yourself!) and turn the air screw to set the idle speed at its fastest. Then back it off with the tickover adjuster to a reliable slow speed. Repeat with the other side. Replace plugs and leads and fire it up again, but reduce tickover speed by the same amount, again using the adjuster, on each carb until running beautifully.:cool:
    I'm sure that is how we did it when I were a lad - but it is/was a long time ago!:eek:
    Make a note of what the original settings were that you had, just in case you need to revert back to them.
    NB This information has been stuck inside the void that is laughingly called my brain for some 48 years, and may have deteriorated gently over that period. Please be kind to an old fart!:p
     
  5. Triumph Beaver

    Triumph Beaver New Member

    May 15, 2016
    4
    3
    West Yorkshire
    #5 Triumph Beaver, May 21, 2016
    Yes.. Will have a play.. I'll make sure they are synchronised on the cables having taken them apart and cleaned everything and inspected the rubbers. The plugs run a tad black so they are running rich... But the air screw only covers the transition so may need to be enriched there... See where the needle is for future reference as it may need dropping?....I start the bike and take the choke straight off.. But its only after its fully hot after 2 to 3 miles it starts to miss. Been on 10 mile hike with my sons Cubs today so cant move at the moment cheers
     
  6. mixifix

    mixifix Active Member

    May 7, 2013
    108
    43
    mansfield
    #6 mixifix, May 23, 2016
    Sounds like a bonnie to me
     
  7. Triumph Beaver

    Triumph Beaver New Member

    May 15, 2016
    4
    3
    West Yorkshire
    #7 Triumph Beaver, May 23, 2016
    Having pulled the carb's out last night, they are two differant age age of carb.. US spec so 200 main... but the needle is set on position 2 going up?.. Amal say 3 and I think I've seen 4 somewhere... so no wonder screwing the air screw out to 2 full turns helped things... Any idea what the std setting is?
    also the tube going into the main area where the slide is is differant.. One (the older one) is about 2mm proud where as the newer one is about 4-5mm.. will this make any odds?...

    SAM_1526.JPG
     
  8. mixifix

    mixifix Active Member

    May 7, 2013
    108
    43
    mansfield
    #8 mixifix, May 23, 2016
    Should be 2 and half standard setting
     
  9. Triumph Beaver

    Triumph Beaver New Member

    May 15, 2016
    4
    3
    West Yorkshire
    #9 Triumph Beaver, May 23, 2016
    Ok... And tubes the same length also now 2 hours with a Swiss file and all is well
     
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