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Help CBF250 cranks won’t start, tried everything, advice needed please

Discussion in 'Honda 250cc Singles' started by hogclassics, Jun 30, 2022.

  1. hogclassics

    hogclassics Active Member Premium Member

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    Hi

    My name is Hog and I live in the UK.
    I’ve recently bought a Honda CBF250 2008 for my daughter.
    I’ve had to change the starter motor, battery and ultrasonically cleaned the carb out.
    The bike now cranks with gusto but will not fire up.
    I’ve downloaded the only service manual I can find on the 250 and
    found it to poorly translated, but also confusing.

    The bike coil produces a tiny orange spark, but on cranking the bike
    no fuel is getting through to the spark plug, it’s dry.
    I opened the carb drain screw and the fuel is there, but it’s not getting to
    the engine.

    I normally work on much bigger bikes and coils primary resistance is normally between 3-5 ohmns.

    On the CBF250, I can only get a primary ohmn reading of 0.5 ohmns and the secondary
    is 13,500.

    However in the service manual it doesn’t mention ohmns at all for the coil resistances
    only voltage.

    I’ve also used a multimedia on the clutch and side stand switches. They start up at 1 and end up
    at 0.2, both work. The kill switch is working as switching it off, only the bikes lights work and nothing
    else works.

    The pulse generators are working as I’ve a spark.

    I don’t understand why my engine isn’t getting fuel?
    All the pipes are ok, no splits.

    Does anyone know if the coil at 0.5 ohmns is the correct primary resistance
    or do I buy a better coil, with more ohmns.

    I’m frustrated as I’ve tried all the above and my plug is dry and my fuel
    isn’t getting to my engine and also not firing?

    I just want to get this bike going for my daughter.

    Can anyone help please.

    Many thanks riders and wrenchers.

    Hog
     
  2. hogclassics

    hogclassics Active Member Premium Member

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    ‘Multi meter’ , sorry everyone, busy day and spell checker took over!
     
  3. Murdo

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

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    Welcome.
    What are the valve clearances like? How good is the compression? Can you do a leakdown test?
     
  4. hogclassics

    hogclassics Active Member Premium Member

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    Hi the good Doctor Murdo!

    Happy to be here with all you like minded folk!

    Only just bought the bike and I didn’t have any compression test adapters that small. As you know the bike needs to normal running temperature and I can’t perform a leak down test when the bike cranks fast , but won’t fire up!
    Thanks again Murdo!

    Hog
     
  5. hogclassics

    hogclassics Active Member Premium Member

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    Hi again Murdo.

    I don’t have a leak down tester or the knowledge yet to able to do the procedure. I’ve never had to that before. Usually just check things basically, not tdc etc. Only had to do that twice on the timing belts of my Goldwings.

    I just don’t understand why gas isn’t getting my engine?

    Thanks again

    Hog
     
  6. jmw76

    jmw76 Well-Known Member

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    Have you tried a squirt with aerostart or just a mist spray of petrol into the intakes. This might give a clue as to whether it is spark or fuel related.
     
  7. Dingleberry

    Dingleberry Member

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    If gas isn't getting to engine it sounds like there is a problem there. Maybe valves are stuck open, maybe you have a great big hole in your piston crown.
     
  8. Murdo

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

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    Take the spark plug out and stick a finger over the plug hole while you crank it. This will tell if you have any compression.
    Also think about a blocked exhaust pipe.
     
  9. Andych

    Andych Moderator Staff Member Premium Member Contributing Member Dirty Wheel Club

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    Plus... if you are not getting any fuel to the plug it may well be that your jets etc are clogged up with varnish (old fuel).
    Bunging the carby into an ultrasonic cleaner wont clean out all those small orifices, channels etc... If you have fuel in the bowl then......theoretically it should draw at least some in during cranking if it can get through.
     
  10. hogclassics

    hogclassics Active Member Premium Member

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    Hi Murdo.

    I tried a squirt of starting fluid into the intakes while cranking it
    and it didn’t do any, no change at all.

    I also checked the compression and it flew my finger off, ;).
    Just awaiting the compression 10mm threaded bit for spark plug hole.
     
  11. hogclassics

    hogclassics Active Member Premium Member

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    Hi Dingleberry.

    Thanks for reply. I’ve now tested the compression and it’s perfect.

    Best regards

    Hog
     
  12. hogclassics

    hogclassics Active Member Premium Member

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    Hi again Murdo

    Compression tested good, got a fantastic pop from my finger.
    Also the whole s/s exhaust is all new. Made in a factory for the CBF250.
     
  13. hogclassics

    hogclassics Active Member Premium Member

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    Hi Andych

    Thanks for your reply buddy.

    Just clarify my carb cleaning, which is very thorough.
    The whole carb was taken apart, piece by piece and the butterfly was zip tied open, to fluids
    to flow through every channel etc.
    The fully bare carb body was ultrasonically cleaned thoroughly firstly a bit of washing up liquid.
    Followed by distilled water and ultrasonic cleaning fluid. The jets were cleaned separately and air blown and tested with an led light to prove no jets blocked.
    The final soak was just in distilled water, to remove any residue from cleaning and then warm air dried with a hairdrier.
    Then everything reassembled.
    I’ve had many motorcycles spanning 30 years, mostly classics 1980-84 and always done
    this the logical way.

    Best

    Hog
     
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  14. Dingleberry

    Dingleberry Member

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    Sounds very strange that fuel is not getting to engine. Have you taken covers off to confirm your inlet valve is lifting? If it's not lifting off seat for some reason you would still feel compression.
     
  15. hogclassics

    hogclassics Active Member Premium Member

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    Hi Dingleberry.

    Thanks for your message. I’ve been generally lucky with my
    motorcycle buying, never had had to check the inlet valve, as yet.

    Test 1) I did some multimeter checking today and discovered that is no continuity
    to ground through the 3 yellow wires.

    Test 2) There are no breaks in the wiring.

    Test 3) The ignition pulse pick up coil shows 233.

    I’ve attempted to remove the stator cover and all bolts have
    been removed. There is hidden bolt, behind the round 3 bolt
    starter motor spline cover, no removed.
    This cover has been on since 2008, this is going to be fun, removing it.

    Q) Buddies have mentioned, drain the engine oil, before removing the cover.
    Is this necessary as the manual doesn’t mention to do so?

    * Engine cranking and not firing is because there is not enough electricity being generated
    by the stator to the CDi/ICM and not energising the coil to the plug.
    Fitting a new stator should remedy this.

    Many thanks everyone.

    Hog
     
  16. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    * Engine cranking and not firing is because there is not enough electricity being generated
    by the stator to the CDi/ICM and not energising the coil to the plug.
    Fitting a new stator should remedy this.


    What? No this is completely wrong. Digital ignition units require 12V from the battery not charging fram an AC coil.

    You have described the spark as feeble and if it won't fire even when you throw some fuel into the carb mouth then best to start there.
     
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  17. Dingleberry

    Dingleberry Member

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    Sounds like you have a few problems there. I'm no expert but I usually just work backwards from spark plug ie if weak spark at plug then how does spark look between ht lead and ground? Good primary voltage at coil? Most importantly, good battery? The starter can have a large enough draw to make spark pretty pathetic if battery is low. Go through and make sure all grounds are clean and well connected. Check all relevant ignition wiring. Just the basics first.
    Still weird how no fuel is getting sucked into engine. Have you confirmed all valves are doing what they should be doing yet?
     
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  18. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    This is where you should be looking first - the spark should be big, fat, bluish purple - I got shown a spark plug testing machine once and as compression increases more voltage is required to make a decent spark - as they increased the pressure in the machine, the spark eventually stop firing

    So if you're getting a tiny orange spark in open air, chances are that you are not getting any spark with the cylinder compression taken into account.

    If there is a resistor in the plug cap AND where the plug goes a slot for a screwdriver, then the brass insert can be removed to inspect the ceramic resistor, check for corrosion.

    Then work backwards from the plug cap -> coil -> ignition box checking and inspecting wires/connectors for corrosion or signs of arcing [burning]
     
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  19. jmw76

    jmw76 Well-Known Member

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    Also the TCI boxes tend not to be waterproof. Any water in this area will result in problems.
    You might want to carefully open up the box and have a look.
    This is what water does to a TCI unit when it gets in. Surprisingly, this unit was running for quite some time before it gave up on the race track.

    750-tci-failure.jpg
     
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