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Questions about carburetors Yamaha zeal 250(FZX 250)

Discussion in 'Yamaha 250cc In-Line 4's' started by Yakob, Apr 8, 2014.

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  1. Yakob

    Yakob Member

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    Thanks, I will do it
     
    Yakob, Apr 25, 2014
    #21
  2. Yakob

    Yakob Member

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    always different, on the two floats height of about 10 mm on the other two floats height of about 12 mm
     
    Yakob, Apr 25, 2014
    #22
  3. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    Yakob - great work you do no need to wait for me to show you how to measure fuel levels.

    for your situation I would possibly suspect that your fuel pump is a problem, that fuel level is far too high.

    If your fuel pump is putting out too much pressure then the fuel level will be too high.

    The correct fuel pump output pressure is very low - 1.5 PSI

    If any fuel has leaked into the engine then it would be best to change the oil also.

    Try running a fuel line straight from the fuel tap - bypassing the fuel pump and see what you have when you measure the fuel level.
    If it is much lower then I would suspect the fuel pump is your problem

    don't worry about the difference in the fuel levels whilst they are all too high, find the reason for that first, then once they are back closer to what they should be you can get them all correct.

    peace out

    Glenn
     
    ruckusman, Apr 26, 2014
    #23
  4. Yakob

    Yakob Member

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    To adjust the fuel 10.5mm I had to much to bend the float tab, I think it should not be
     
    Yakob, Apr 26, 2014
    #24
  5. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    have you checked the fuel level without the fuel pump?

    Seems as though too much fuel pressure would cause your problem
     
    ruckusman, Apr 26, 2014
    #25
  6. Yakob

    Yakob Member

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    Yes I did it. Fuel level without pump approximately 5 mm lower than with it...Maybe it's broken? Earlier before dismantling motorcycle worked normally....
     
    Yakob, Apr 27, 2014
    #26
  7. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    I would definitely suspect the fuel pump.

    Guys would air somewhere in the fuel system between the pump and carburettors play havoc with the fuel levels?

    Just wondering if air would cause the fuel pressure to fluctuate too much and cause erratic behaviour
     
    ruckusman, Apr 27, 2014
    #27
  8. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Yakob,
    First when you measured the float height, like the image with the playing card, the tip of the float needle must just touch the float tang. You must NOT let it compress the internal spring in the float needle. Please tell us how you did this as it is very important.

    Secondly, as Willrcr15 pointed out, the o-ring that seals the float needle seat is very important. Under pressure it may be allowing fuel into the float chamber.
    cheers
    Blair
     
    • Like Like x 1
    maelstrom, Apr 27, 2014
    #28
  9. Yakob

    Yakob Member

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    Yes, I did not press on the float, I replaced o-ring seals (I checked them, the air did not pass), my fuel pump Mitsubishi probably is not original. If the level is slightly higher than necessary(2-3 mm higher), Can I start a motorcycle?
     
    Yakob, Apr 28, 2014
    #29
  10. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    I would think that it should certainly start.
     
    maelstrom, Apr 28, 2014
    #30
  11. Willrcr15

    Willrcr15 Well-Known Member

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    Are you sure the inlet needles & seats are holding ?
    They could be leaking & allowing in extra fuel & shutting off late.
    The fuel pump will be ok, it will hold up the head / weight of fuel in the tank hence the different readings & I'm starting to think that's why they put a pump on at the factory, there's been reports of running without them without any problems, I didn't have one for a while & no problem & the guy I got the bike from didn't run one for years before me.
    I think you need to do a complete carby overhaul & see what happens then.
     
    Willrcr15, Apr 28, 2014
    #31
  12. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    ruckusman, Apr 29, 2014
    #32
  13. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    I would get the pump out of the equation and remove it and see how it runs.

    its only a detuned Zeal .... not a screaming Fizzer
     
    GreyImport, Apr 29, 2014
    #33
  14. Murdo

    Murdo The Good Doctor Staff Member Contributing Member Ride and Events Crew

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    Murdo, Apr 29, 2014
    #34
  15. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    interesting - can you elaborate because I couldn't find details on how fuel pressure regulators work - I'm interested to know
     
    ruckusman, Apr 29, 2014
    #35
  16. Murdo

    Murdo The Good Doctor Staff Member Contributing Member Ride and Events Crew

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    A true pressure regulator has a valve, diaphragm, spring (to return the valve to the closed position) and a vacuum port to manifold. Fuel pressure is 'held' at the preset pressure by the valve until the pressure drops (ie fuel is used) then the vacuum pulls the diaphragm against the spring, opening the valve until pressure returns to the set limit.
    A restrictor type is set to a pressure with the fuel flowing at a constant rate (a garden tap or squeezing a hose), but when flow stops the pressure will build again.
    I have used S.U. carbs in most of my supercharger installations which need only 1/2lb pressure due to the short float arm not giving much leverage to shut the needle into the seat. I set them up with a small canister (about 200cc) mounted above the carb taking full pressure from the engine driven pump, with a return line to the tank fitted with a restrictor to give no more than the 1/2lb required. A line from the canister then runs to the carb. Carbs need flow, not pressure, and to this end I fitted a half litre fuel bowl to the 2Lt Ford Escort that ran 15lb boost (above atmospheric, 29lb absolute) and this was sufficient for it to run flat out for 10+Km (until we ran out of road).
     
    Murdo, Apr 30, 2014
    #36
  17. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    Yakob - just an FYI -
    I tried unsuccessfully to fit what is clearly a non-standard fuel pump and couldn't get the fuel level to stay at the correct level - the bike would flood at idle - so if the pump is putting out too much pressure it probably won't even start - let alone run

    peace out
     
    ruckusman, May 4, 2014
    #37
  18. RosscoM

    RosscoM Active Member Premium Member

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    The float height from the carby body is meant to be 10.5mm, this is a primary adjustment, I dont know where 16mm comes from?? the fuel level, is a fine adjustment, the 400 manual says 4.5 to 6mm below the fuel line, and that is done without running the fuel pump, so it is allowing the fuel level in the carby to drop when you open the screw, but no extra fuel enters the carby float chamber.

    400FLA.png
     
    RosscoM, May 24, 2014
    #38
  19. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Hi Rossco,
    A lot of water has gone under this bridge. Please see Mr Grey's epic thread "My Fizzer".
    The carbs you are referencing are not the BDSTs that are fitted to the Zeal and later 400s. They are from the 1WG, those carbs are completely different animals. The 16mm float height was determined by Mr Ruckus after a lot of careful work. There are a mountain of posts on this subject in thread I referred to and multiple references to different fuel levels for BDST carb across different models. The 1WG manual states that the screw float bowl drain screw should be loosened as step 3 so the float bowl will not be draining into the hose after you shut off. It will maintain the level that the float determined whilst the drain screw was open. I hope this clears up some of the issues.
    cheers
    Blair
     
    maelstrom, May 24, 2014
    #39
  20. RosscoM

    RosscoM Active Member Premium Member

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    the 400 manual references the carby as a BDS32... my 1WG has these, they are just a bigger version of the BDST... not exactly a different beast, look the same on the outside, insides all work the same... maybe the earlier 400 had a different carby? I had problems getting the right windscreen for mine, as the 88 model was completely different to the 89...

    for some dumb reason I cant access the resources here, but there's a pic in this thread from a workshop manual (presumably Zeal) saying Fuel Level FL is 10.5mm... there should be an accompanying image showing if this is fuel level above or below the line on the carby, like the 400 manual. I was confusing FL to mean Float Height. Trying not to muddy all that water...

    I cant find a post in that thread that gives a yamaha spec for different models?? 2KR, 3LN 1, 3, 5, 7, Zeal???

    Do Yamaha actually give a spec for float height for the BDST(the 1WG manual doesn't for the BDS32)? If not then I'm happy to go with the 16mm Ruckusman determined.
     
    RosscoM, May 24, 2014
    #40
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