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Maxim 550 Carbs - #4 flooding & routing drama

Discussion in 'XJ Technical Chat' started by taildragger, Nov 21, 2008.

  1. taildragger

    taildragger Member

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    Got the new / used wire harness on ok.

    xj550 Max has always run with mind of its own re: #4 Carb overflows intermittently.

    Here's 2 pics of the carb set and the union seals between each pair of carbs on the rack.
    PO had sealed up leaking union O-rings? between #1 - #2 and #3 - #4 with blue plastic caps and glue ( I know) groans & applause pls.

    Questions:
    Should the bike be operated with fuel entering the Lower - Center union (see red hose clamp in pic) ? Will this inlet style change any running / operating characteristics? Suffer from Fuel Starvation etc.?

    Do xj550 Max v.s. Seca models differ by using carb sets with different intermediate fuel union seals? Some came with & some came without?
    See list owner's pic below showing his carbs without dual inter-connecting fuel tubes between #1 - #2 etc.

    WHAT IS the PROPER FUEL TUBE SET-UP - LAYOUT, WITH HOSE ROUTING for the MAXIM 550? Caps for emphasis.

    [​IMG]

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    [​IMG]

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    Not my carb set: these are from another list members xj550

    [​IMG]
     
  2. HalfCentury

    HalfCentury Member

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    In the picture #4 level looks a little high
    I would lower the float 1-2 mm
     
  3. taildragger

    taildragger Member

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    thanks Half -C

    Will lower the float like you say & replace the Inlet Valve since I have new ones.
    Rest of the carb(s) look very clean - no crud or gum anywhere.

    Will also polish the bores and throttle slides per RickoMatic's post.

    Would those capped carb connectors and the center Fuel Inlet change basic engine operation?
    Thrashing it - WOT is not my style.
     
  4. bigfitz52

    bigfitz52 Well-Known Member Premium Member

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    They shouldn't. The capped connectors are for the overflow tubes I do believe; center fuel inlet is like that on both my 550 Secas and my spare rack o'carbs which came off a Max, pretty sure thats standard on 550s.
     
  5. taildragger

    taildragger Member

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    Was a pic of xj550 Max's present float height set at 22/32nds = 18 mm from the blue tape to the float's part line.

    edited: This setting is incorrect for the xj550 BS28 carb.

    According to Chacal the BS28 uses a 21.5 mm (55/64ths) dry float height setting.

    Confirmed: The xj550 carb Floats are "dry set" at 21.5 - 22 mm height using the Q-Tip method. Q-Tip slightly off vertical in pic.
    Confirmed: Their rise is 13/16ths when they close the needle valve.

    [​IMG]

    Next: Do a Fluid Level Check for all four carb bowls.
     
  6. RickCoMatic

    RickCoMatic Well-Known Member

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    Those Floats are within the +/- area for acceptability.
    You look at the low point of the fluid in the hose.
    I wouldn't make you adjust that out unless it acted-up.

    It's frightening to see what some people will do to Carbs rather than spend the time on them and fixing them right.
    That Epoxy and Cap fitting needs to be open to atmosphere.
     
  7. taildragger

    taildragger Member

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    #4 Float submerged & tested - it floats!

    Fluid test with Clear Lines:
    All four carb bowls carry same fluid level @ correct specs per RickoMatic & others' posts.

    Float supports, pin and inlet valve (new) are clean & shiny.
    Passes the 'clunk' test.

    Cutting tops off those blue plastic caps.

    Saturday: bike gets hot test to check carb tune.

    [​IMG]
     
  8. taildragger

    taildragger Member

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    RicKoMatic -

    Punched 2 small holes in the sides of the Blue Caps on intercarb vents in the pics you saw.

    Started & ran bike 8-10 mins. today. After warm-up the IDLE speed suddenly went crazy, climbed up to 4,000 rpm.
    Other than the 2 new holes nothing else was changed. Backing off the large center Idle Speed Knob under the rack did nothing.
    I checked fuel flow is OK, no pinches or kinks in throttle cable, works smooth.
    I'm at a complete loss to explain the sudden and sky-high idle speed. No other caps are off or damaged.
    Could the carb holders have developed an air leak around their circumference when I re-installed the carbs?
    Could it be a bench sync is needed to re-establish a bench-line rpm?

    thanx, Rob
     
  9. RickCoMatic

    RickCoMatic Well-Known Member

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    Test for leaks by spraying some Carb Cleaner on the Manifolds when the Bike is running.
    Also:
    >>Where Manifolds meet the Head
    >>Where Carbs are mounted in Manifolds
    >>Both sides of Carbs at the Throttle Shaft Pivot Seal

    If the RPM's rise ... you have AIR Leaks to contend with.
     
  10. taildragger

    taildragger Member

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    Rick -

    Recalled I turned out the pilot / idle screws just a bit (very precisely).
    That small change may be contributing to the high idle speed as well.
    So back clockwise they go in before anything else is done.
    Other than the fuel leak from #4 the engine had been running ok.

    Re-installed the Carbs & tested for leaks; re-sealed them with high temp silicone.
    There are no cracks thru the carb holder walls.

    Engine still has an uneven "hunting" and high idle.
    So I resealed the blue caps. No real idle speed change.

    Looks like these carbs have developed internal leaks, like the caps / shaft seals / tube seals are passing air.

    Time for new O-rings and RTV around those black intercarb tubes

    thanx, RJ
     

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