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Help 1992 mc22 overheating idle

Discussion in 'Honda 250cc In-line 4's' started by Milan Andrews, Jun 27, 2020.

  1. Milan Andrews

    Milan Andrews Member Premium Member

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    Hey guys,
    I bought an MC22 a months ago and it had flat spots in the revs and wouldn't idle reliably. I opened the carbs and found superglue everywhere inside of it so i replaced it with another set of carbs. Right now the bike is stock except for a full exhaust and 110/112 main jets with 40 pilots jets (2.25 turns out on the pilot screw).
    It idles happily anywhere above 1000 rpm after running for 10-20 seconds with choke but when I start riding and then stop at a red light the bike starts overheating reaching around 3/4 of the temp gauge and then does not want to idle anymore unless its at 2.5k rpm and engine becomes slightly rougher. When I ride off the temp gauge goes back down to about a quarter of the temp gauge.
    Any tips on what might be wrong?
     
  2. Murdo

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

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    Your fan is not working.
     
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  3. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    If your fan is working then look at blocked radiator/cooling system or blown head gasket. Start by removing the thermostat and inspecting that. It will give you a fair indication of how much crud is in the cooling system.
     
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  4. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    Welcome to the forum,
    I think the radiator core's may be blocked too if the thermofan work's
     
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  5. Milan Andrews

    Milan Andrews Member Premium Member

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    Thanks for the help guys. Gonna order a new thermostat and check out if the fan is working or not. Hope everything goes smoothly but I'm pretty sure I'll be chasing some other problem afterwards lol.
     
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  6. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    Replace the coolant and clean out the coolant overflow bottle as they usually have sludge in them ... or in your case possibly residue super glue :D
     
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  7. kiffsta

    kiffsta Administrator Staff Member Dirty Wheel Club Contributing Member

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    when you say full exhaust system, do you have aftermarket headers as well ? Like TSR ?

    Before we go too much further, what year is your bike , 90-93 were L and N models with 45hp, 94 onwards were the R models and had 40 hp , we need to know this for your air / fuel mix screws.

    Lets look at your overheating issues, first off, id open the thermostat housing and check if there is one, Honda do replacement ones but they are around $100 , a cheap option is a Tridon tt239-180 which you can get from repco \ supercheap. Do you have coolant in there or water ? Radiators can get blocked up, but remember these bikes do run hot. An easy check if your fan works is to unplug the wire from the side of your radiator which goes to the thermo switch, then earth it to the frame, if the fan spins then you know it is good.

    mc22_thermofan.jpg

    The thermo switches can fail, they are the trigger for the fan to kick in, they can be bought here if it is faulty. https://www.xcitebikes.com.au/37760-mr1-003/

    Does your radiator have a plastic shroud around it ? see pic above, they are really important for airflow into your radiator.

    You could try flushing your radiator with water and see if any junk comes out, you can use products like CLR to flush it out too. Make sure you use a good quality coolant when you refill it.

    With reference to your idle issues, your pilot jets should be be 35's, while 40's might be okay, id be going back to stock, your main jets are also much bigger, bigger jets don't mean more power.

    MC22 Jet Sizes (Stock)

    CBR250RR(L+N); 1990 - 1993
    Main Jet : Cylinders 1+4 : #105
    Cylinders 2+3 : #102
    Pilot Jet : #35

    CBR250RR®; (1994 onwards)
    Main Jet : Cylinder 1+4 : #112
    Cylinder 2+3 : #110
    Pilot Jet : #35

    Carburettor Pilot Screw Mixture Settings

    CBR250RR(L+N) : 1 3/4 screws
    CBR250RR® : 2 1/8 screws


    You say that you have set your AF mix screws to 2.5 turns out, I would be pulling them all out and making sure that you have the AF screw, then a spring, then a metal washer, then a rubber o ring. if any of these are missing then you will have loads of trouble. Depending on your model, set them to stock first , then tune from there... I remove the pilot jets and AF screws and make sure the passages are clear, I use threebond engine conditioner (pertol version) to clear out these passages, as well as compressed air.

    If you are missing the O rings or the metal washers, you can get them from Honda or a whole rebuild kit from Litetk
    https://litetek.co/Carb_Kit_Honda_CBR250RR_MC22.html

    Bigger jets don't mean more power... oh hang on, I have already said that.

    Also check your carb insulators (rubber between the head and the carbs) for cracks, these are a common failure, chinese ones are rubbish, only use OEM.

    Good luck ,

    Kiff
     
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    Last edited: Jun 27, 2020
  8. Milan Andrews

    Milan Andrews Member Premium Member

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    The headers look like this and has a CBR racing muffler, now that I think about it might just be stock because the other stock exhaust I used for roadworthy was from an mc19 and didnt have the flange from the one in the link.

    Its a 1992 model imported from japan. The superglue ridden carbies has 112/115 main jets with 35 pilots (2.5 turns out) but struggled to start without the choke and the mechanic who gave me roadworthy said it was running lean due to the high-flow exhaust and to let him put bigger jets in it later.

    I found an old owner of the bike who had it a year ago and he said he ran 110/112/40 jets with the same exhaust and it looked like someone else took the carbies off and just chucked on a random pair to sell it off (the orignal owner installed a litetek rebuild kit).

    I got new carb boots after finding out that one of them were cracked which helped with problem of the bike running on 3 cylinders at idle at times.

    I went for a ride today with a mate for about 2 hours and saw a few drops of coolant coming out of the thermostat housing after i'd parked it so pretty sure its the main culprit. The bike never went above a quarter of the way of the temp gauge probably because I was going through backroads and twisties without needing to stop anywhere unless I was parking. When I got back home and checked out the bike after it'd cool down fully there was still coolant when i opened up the radiator cap. I used a flushing agent and flushed out the old coolant twice with demineralised water then put in new coolant a month or so ago but barely saw any gunk come out.

    For the AF screws I had it at 2 turns at first but was sputtering a lot at the low revs, wouldnt idle below 2.5k rpm and wouldnt take off from the lights unless I rev the **** out of the engine. 2.5 turns would die at idle with the slightest bit of choke so right now I'm at 2.25 turns and the bike feels good and accepts the the choke at idle but doesnt feel like its quite perfect yet.
    I think tuning's gonna be pointless for now unless I fix the overheating and underheating problem since its happy at 2.25 turns as a cold engine but no idea what it wants at operating temp (probably something closer to factory like you mentioned).

    I'll install the thermostat once it arrives, clean out the carbs,maybe flush out the coolant if there's see any junk in it and then try tuning the bike again.
     
  9. kiffsta

    kiffsta Administrator Staff Member Dirty Wheel Club Contributing Member

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    Good news you got out for a ride

    Definitely stock mc22 headers , as you have a n model , carbs should be set at 1 and 3/4 turns , + or - half a turn , the next time you have the carbs apart , I’d take the air fuel screws out and check there is a spring, metal washer and rubber washer on each of them.

    FC4CDD4B-9DDF-44D3-9240-1544B913F4D5.jpeg

    When you doing the thermostat , Pop Your plugs out and see how they are. Post a pic as it is a good tell how it is running.
     
  10. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Sounds like your making progress.
    and what the mechanic said is complete nonsense. Put standard jets in it.
     
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