Carb Bench Syncing issues

Discussion in '1st & 2nd Generation 1983-1989' started by RockvegasVFR, Nov 14, 2017.

  1. RockvegasVFR

    RockvegasVFR New Member

    Country:
    Australia
    Joined:
    Jan 17, 2015
    Messages:
    5
    Likes Received:
    0
    Trophy Points:
    1
    Location:
    Rockhampton Qld
    Hello All,
    My RC24 is an '88FJ, Australian delivery, and I'm looking for advice on bench syncing the carbs prior to refitting them for a final check with my Carbtune kit. . She was running fine, when I decided to get my valve clearances checked as they had not been done in the 2 years I've owned the bike. Given how difficult it is to access the valve adjusters I got the local Honda dealer to do this, and asked them to check the carb sync whilst they were at it. All checked out ok, except the dealer advised that I had a crack in one of the plastic fuel tubes between the carbs. I had not noticed a leak prior to this, however in the interest of safety they disconnected the fuel and advised that a replacement part would take some time to arrive if available. I advised that, given the age of the whole tube set, I preferred order a set of aluminium tubes from the US that I'd heard good reports on. So the bike was transported home.

    Have pulled the carbs, and separated them just enough to install the new rails (which look like great quality) - i.e the adjustment gear on each carb was left intact - with the choke mechanism being the only bits that needed to be re-joined. All back together now with cleaned jets and clean float bowls installed with new o rings. The air screws have been left untouched behind their covers. Have run some fuel to ensure there are no leaks (fuel lines replaced prior to the current issues).

    My references for the carb work have been the Honda RC24 shop manual, plus a fairly comprehensive carb overhaul resource I found on this VFR World site. I have 2 questions re bench syncing prior to installation and searches of this forum haven't indicated any earlier answers re this. Both references advise aligning the butterfly valve relative to the "by-pass hole". Honda advise to adjustment to the edge of the hole (which edge is not specified), whilst the other source says leave half of the hole visible. On my carbs, though, there are 3 pin holes (pictured) so I'm unsure which one the butterfly should be aligned to (see picture attached).

    The second issue is that carbs 2 (adjusted by idle screw) & 4 have a fair bit of adjustment and can both be adjusted to the bottom of the outside hole, whilst 1 & 3 seem to have less and wont adjust beyond the middle hole. Is this normal or have I missed something? All the springs are in place as I found them - the manual and the Honda parts diagram are not very illuminating if you were starting assembly of the linkage from scratch though.
    Thanks in advance for your advice - the annual Xmas Toy Run is coming up in a fortnight, and I'm missing riding my old girl. Justin
     

    Attached Files:

  2. Captain 80s

    Captain 80s Member

    Country:
    United States
    Joined:
    Apr 25, 2009
    Messages:
    2,873
    Likes Received:
    662
    Trophy Points:
    158
    Location:
    Edmonds, WA
    Map
    I doesn't really matter what reference you use, it's just that they all have to be the same. You can use the holes (edge, half) to get you in the ball park so it runs and you can final adjust with gauges. The idle screw is what will set the final position of the throttle plates all together. I cut about a 5mm wide strip out of good paper stock and use it as a feeler gauge. Get the same "pull" off of each plate and they are very close. Actually when I put the vacuum gauges on later I didn't even bother making an adjustment.

    A while back when I replaced my fuel tubes (with the aluminum ones), I also ran into one screw that was pretty much out of adjustment, and another that wasn't far behind. I couldn't really find a reason, but attributed it to higher mileage carbs (50K+). I swapped positions of a couple of the screws and gained just enough adjustment to get them in.

    Hope this helps.
     
  3. RockvegasVFR

    RockvegasVFR New Member

    Country:
    Australia
    Joined:
    Jan 17, 2015
    Messages:
    5
    Likes Received:
    0
    Trophy Points:
    1
    Location:
    Rockhampton Qld
    Thanks captain.
    I now have all carb butterflies aligned to the bottom of the first hole (the one closest to the engine side), as this is the position on carb 2 that allows the throttle plate to be closest to the idle screw. As you can see on the attached photo I have no adjustment left on the idle screw and it doesn't touch the throttle even when screwed all the way in.
    Any suggestions on what might be hooked up wrong?
     

    Attached Files:

Share This Page