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Project My project MC22

Discussion in 'Your 250cc Projects' started by Krompot, May 21, 2020.

  1. Krompot

    Krompot Active Member Premium Member

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    How
    At the end of the plug. I also checked the gaps, they're all in spec
     
  2. Andych

    Andych Senior Member Premium Member

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    That cylinder is likely flooding and quenching the spark... as I said... too much fuel and it wont fire. try leaning out the mixture screw.
     
  3. Krompot

    Krompot Active Member Premium Member

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    Took plug out and blew compressed air in to help dry it. Plug back in, tried mixture at 1, 1.25, 1.5, 1.75 and 2 turns but same result. No firing. The exhaust pipe gets warm (perhaps from the compressed air?) but not nearly as hot as the others, and the plug is a little fouled, so maybe I'm getting somewhere? the fouling is probably just from the starting fluid. I ran it for 30 seconds, opened throttle a little, waited a couple seconds, sprayed a tiny bit in and the revs picked up a little.

    The slides on the carburetor open in sync with all the others though so i don't think it would be a broken diaphragm.

    Thing is, when i got the bike it was running on all 4, but bike needed a rebuild because the bearings were all chewed up. The only changed variable was the engine.

    Thanks for the replies. I really appreciate the patience.
     
  4. jmw76

    jmw76 Well-Known Member Premium Member

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    Did you say that you have rebuilt the carbs?
    I would be pulling the carbs off and going over them very carefully to make sure they are all ok.
    Check o rings. Check jets and needles. Check intake rubbers. Check needle valves and seats. Check balance between all carbs (this can be done pretty well on the bench by measuring the butterfly gap).
    A mixture distribution issue can foul up plugs pretty quickly and stop them from firing.
     
  5. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    and diaphragm
     
  6. Krompot

    Krompot Active Member Premium Member

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    Hi everyone. Thanks for the suggestions.

    So it's not a carburetor issue. I checked over everything.

    If i swap the leads (put lead 1 into cylinder 4 and lead 4 into cylinder 1) cylinder 4 runs but 1 doesn't. This is with a new (used) coil. Someone mentioned earlier that both coils fire at the same time which is why i figured i could swap them. I measured the pulse generator resistance: 425ohms. Out of spec by 40 ohms, something to worry about? Coils resistance is 3.1 ohms on both (spec is 2.6-3.2)

    Swapped the coils back to what they're meant to be: Cylinder 2 & 4 not running.
    Swapped coils 2&3, Cylinder 2&4 not running.
    Swapped coils 1&4 (so now 2&3 and 1&4 are swapped) Cylinder 2 & 4 not running.

    I unplug and re-plug the spark unit:
    Cylinder 1,3 and 4 running, cylinder 2 having trouble.

    I unplug and re-plug the spark unit:
    Cylinder 1,3 and 4 running beautifully, cylinder 2 having trouble.

    I unplug and re-plug the spark unit:
    Cylinder 1,3 and 4 running, cylinder 2 having trouble.

    I remove the signal generator cover and spin the engine a couple times:
    Cylinder 1,3 and 4 running, cylinder 2 having trouble.

    Swapped all the coils again:
    Cylinder 1,3 and 4 running, cylinder 2 having trouble.

    I waited for the headers to cool down before each test.

    The way I'm checking which ones are 'running' is by checking if water boils off the exhausts. I start it, rev it to 4k for about 10 seconds and check which ones are hot. The others headers get warm but not nearly as hot as the others. Potentially partial combustion?

    Could it be CDI? All 4 connections on the primary side of coils is showing 12.65V. The bike was sat outside without a seat for 2-3 months. Water leaked into CDI maybe? I can't find a diagram of the internal CDI wiring online. Does anyone know where i can find one or how i can test it?
    Thanks for all your help.
     
  7. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    Have you measured the resistance through each spark plug cap (unwound from the coil lead) ?
     
  8. jmw76

    jmw76 Well-Known Member Premium Member

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    With the plugs still in the engine, remove the spark plug cap on all cylinders. Using a multimeter on highest meg ohm range, measure the resistance between the contact on each plug and the engine or frame. They should all appear as an open circuit. Anything different from this, you need to ditch the plug.
     
  9. Krompot

    Krompot Active Member Premium Member

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    Done, all is well. I used the continuity checker.

    I haven't. I took each lead off of their plugs and checked the maximum spark distance from the plug to the frame and it was about 2.5cm for all 4 leads. Figured it was good enough haha.

    I'm away from home for the next while so i won't be able to test anything.

    Thanks a lot for the replies,
    Kyle
     
  10. Murdo

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

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    Looks like one of your plug caps is dead and to keep swapping them around just confuses the problem.
     
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  11. Krompot

    Krompot Active Member Premium Member

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    How would the plug cap be dead if spark was coming through on all 4? I rethreaded the high tension leads and no difference. Still waiting for CDI to come in the mail.
     
  12. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    How many Ohm's do your spark plug cap's measure ?
     
  13. kiffsta

    kiffsta Administrator Staff Member Contributing Member Dirty Wheel Club

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    i doubt it is the CDI as one coil drives cylinders 1 and 4 and one coil drives 2 and 3, but I have been proved wrong before.

    The spark system on an MC22 is super easy, there is a single pickup coil which is excited as it passes the trigger wheel when the engine is cranked, the pickup coil sends signal to the CDI to tell the ignition coils when to fire. As the Mc22 uses a wasted spark system, cylinders 1 and 4 fire at the same time, hence why they share a coil. That is the same for 2 and 3

    A simple test is to remove all 4 coil caps from your plugs ,plug in a spark plug to your coil cap and ground the side of the plug to your frame and turn the bike over using your starter, you should see the end of the plug sparking. Rinse and repeat for all 4 plugs , hopefully you find that you have spark on all 4. Poorly setup carbs will kill plugs quicker than look at them ( mc22 even more than most) , and you cant clean the the ends of plugs , products like Start Ya Bastard kills plugs too, Id grab some spare plugs and ditch the starting fluid.

    If cylinder 2 isn't running but the other 3 are then you could have either a compression or fuel issue as that is what is needed for the bike to run. A good set of compression gauges will tell you if each cylinder is creating the required internal cylinder pressure to achieve combustion. On a cold MC22, id hope to see 120-160 psi per pot with all 4 plugs removed and your carbs off the head, with a nicely warmed up engine you should see compression readings of 160-220 psi which is the sign of a good healthy engine.

    Conversely if it is a fuel issue, ie your pilot jets are blocked then the cylinder will stay much cooler than the other 3 as it wont allow fuel into the cylinder, pulling the carb off and remove the pilot jet, yould be bale to see a pin ***** of light, if not, then you need to clean that jet . The pilot circuit uses the Air / Fuel mix screw to get the required mix into the cylinder, hence why in previous posts I harped on about the importance of checking your AF screw to check that you have the metal washer and rubber seal in there, I have seen so many bikes where back yarders loose things like those washers or crush them in the housing and the bike wont run anymore, these are super important getting a good mix into the engine. Another possibility is that your balance screw on your butterfly are so far out causing 2 not to sire, google bench syncing to understand that process.



    Watch this vid to the end, it explains how a CV carb works



    Finally, could be a cylinder head valve issue, but that's rare and Id do the following first.

    Once you have confirmed spark on all 4 coil leads by grounding a plug to your frame or engine, a carb clean and check of your pilot jet and AF mix screw should be done on number 2, if that doesn't solve your issue then compression test should be the next step to help you diagnose your issue.

    There are some very knowledgeable guys on here who have given you some pearls of wisdom, please use them.
     
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  14. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    I'm still waiting for the compression test numbers.
     
  15. Krompot

    Krompot Active Member Premium Member

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    Thanks a lot for replying. I really appreciate the help guys.

    Spark is coming through on all 4 high tension leads.The reason why i think it's spark timing is because initially cylinder 4 wasn't firing, then cylinder 1, then cylinder 2. It seemed to change overnight. There is spark on all 4. I've already synced the carbs with a carb sync tool. They were bench synced when i i first got the bike (when it was running on all 4 but needed new bearings). I went through and checked everything - i changed the mixture from 1 turn out all the way to 2.5 turns, adding 1/4 of a turn each time. They are set to stock now. Needles are clean. Diaphragms are fine. I was using old plugs and when i i ran into issues i bought new ones. Nothing changed. I have new carb boots installed. The vacuum ports are all plugged up.

    Just went and bought one of those rubber things you press over the spark plug hole to check compression, possible leaking - it's not very high quality but i i checked the accuracy of the actual meter by using my air compressor and it seems accurate.

    Cyl 1 - 120 psi
    Cyl 2 - 105 psi
    Cyl 3 - 105 psi
    Cyl 4 - 105 psi

    This is on cold engine. I have brand new rings installed - i assume they haven't worn in yet. New head gasket, bolts torqued to spec.

    Measured high tension leads:

    HT lead 1 - 4.6 kilo ohm
    HT lead 2 - 5.76 kilo ohm
    HT lead 3 - 5.01 kilo ohm
    HT lead 4 - 4.3 kilo ohm

    1&4 secondary coil with leads - 25.1kohm
    2&3 secondary coil with leads - 23.2kohm

    High tension leads don't seem to have a measurement in the service manual but the secondary coil with HT leads installed is in spec.

    Thanks guys.
     
  16. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    It has spark and it has compression, that leaves fuel. Assuming the dead cylinder has fuel in the bowl the next suspect is a blocked pilot circuit.
     
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  17. Krompot

    Krompot Active Member Premium Member

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    What i did is i ran the bike on 3 cylinders until it stalled and checked the bowls of the carbs to see if fuel wasn't being delivered - they were all at the same level (nearly empty). I've checked all the jets 3 times over, just did a third check and everything seems fine. I removed the pilot screws and they have the small o-ring and washer installed. Set them back to 1 3/4 turns. I have L&N model carbs.

    I'm pretty dumbfounded.
     
  18. Andych

    Andych Senior Member Premium Member

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    Read what is above... especially from @maelstrom .... he doesnt say a blocked Pilot Jet.. it is most likely a blocked pilot circuit... these guys know their beans... take the time to understand what they are saying... not what you think they mean.
     
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  19. DannoXYZ

    DannoXYZ Well-Known Member

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    Yes there's A LOT more to fuel-flow path than just jets. I compare it to garden-hose sprayer nozzle. When there's problem, most people focus on the nozzle (jets). But what about 30m of hose with golf-balls stuck inside? That contributes to way more problems than just jets.

    Once you've removed jets and cleaned them, 1st 5% of job is done, there's more. Here's photo of CVK30/32 carbs that frequently have issues. Yours may have differently shaped passages, but idea is exactly same. Beyond jets, you need to scrub fuel-circuits after the jets with brushes using PEA-based fuel-system cleaner. Follow passages all way through carb-body to venturi. Then scrub from other side starting at carb-throat all way back to float bowls.

    Then soak entire carb in ultrasonic cleaner for 4-6 hours using polar solvent. Rinse, dry and micro soda-blast to clean out fuel-circuits. There will be chunks and flakes of dried petrol clogging passages. There's plenty of people who can rebuild entire engine using only their teeth with hands tied behind their backs who've had to remove carbs 4-5x for ever deeper cleaning until they were finally clean enough to run engine smoothly.

    Also remove slides and diaphragms and inspect rubbers to make sure they're no holes or rips.

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]
     
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  20. DannoXYZ

    DannoXYZ Well-Known Member

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    Also inspect emulsion-tube and pilot jets very carefully. They may have lateral bleed-holes for vapourising petrol. Be sure to poke through and floss those holes with soft copper wire of matching diameter. Be careful not to scrape of metal from tube and jets.

    [​IMG]

    Also given age, it's best to replace all rubbers, O-rings and seals. O-rings at end of mixture-screws. O-rings in fuel-distribution line. Float-valves. Float-bowl seals.

    Idea is to restore carbs to factory-fresh condition. Bike ran great when leaving showroom floor with factory-fresch clean carbs. It will again when carbs are restored back to factory-fresh condition. Fact that it doesn't, means carbs aren't factory-fresh clean.
     
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