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Help Bike won't run after carb clean - VT250F

Discussion in 'Honda 250cc Twins' started by iopsd, Jul 10, 2021.

  1. iopsd

    iopsd carbs are scary

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    I've got an 84 VT250F presumably from Japan given the stickers that was quite clogged up when I got it, so I took apart the float bowls and sprayed out the jets... and now it won't start at all? It's got spark, it's got fuel and it should be running great but it won't even start, barely giving me a sputter at best? I'm not terribly familiar with carbs or mechanics in general so would love even just a place to start looking.
     
  2. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    Did it run before u worked on it?

    Hows the air filter?
    Does it have an inline fuel filter ?
    Is the fuel tank clean inside? .... and has fresh fuel?
     
  3. iopsd

    iopsd carbs are scary

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    It ran alright but clearly had a pretty badly clogged carb as it had to be revved to like 5k to not stall out on starting, but the main jets were alright, it was running right up to when I pulled the carbs. It's got no fuel filter and the air filter looks okay, I did try to run it without it but didn't make much difference. Should mention that the fuel has some additives in it I tried before pulling the carb, but the gas is only like a week old at this point so I can't imagine that would spoil it to the point of non running.
    Seriously cannot figure out what is wrong with it.
     
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  4. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    I would strip the carbs again as possibly something (as in grunge, dirt , dry fuel) has moved and created a blockage somewhere/elsewhere .... carbs have to 110% clean

    Have u set the pilot screw?



    vtr carb.png
     
  5. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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  6. iopsd

    iopsd carbs are scary

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    I've cleaned the jets twice at this point and they didn't appear to be terribly dirty the second time around, I feel like I should atleast get a run on choke even if they were.
    I did set the pilots back to the baseline where you would then tune them as recommended by the manual, but it didn't appear to make a difference.
    I should mention that the plugs were wet after the first clean, I assumed it was flooding due to a misadjusted float or an air leak, I am unable to check the plugs again as my ratchet thought today would be a good time to break but I guess it could still be flooding?
     
  7. Linkin

    Linkin The Mechanic Premium Member Contributing Member Dirty Wheel Club

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    You have to make sure the carb body itself is clean as well. There are drillings and passages for air and fuel that must be clear. The standard way to clean these is carb cleaner in a can and compressed air. Lockwire, picks or brushes can be used to clear stubborn blockages, along with soaking. Threebond engine conditioner and heat / hot water is also a good combination, just don't dump the contaminated water down the drain - should go in waste oil/coolant recycling.
     
  8. iopsd

    iopsd carbs are scary

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    Alright, I'll dismantle the whole units and soak them. Will report back if it works.
     
  9. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    Take out the pilot screws and make sure they are setup correctly and the o ring is intact


    vtr carb pilot screw.png

    PilotScrewAssy.jpg
     
  10. Frankster

    Frankster Grey Pride...Adventure before Dementia Staff Member Premium Member Ride and Events Crew

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    Post a pic of the bike and carbs for us to confirm it's a VT250F Japanese import and not a generic USA model (different engines).

    Also, the carbs on your bike are fed fuel via a vacuum valve in the petcock under the tank. If the vacuum hose isn't connected, it won't be giving you any fuel. By-pass the fuel system and just put fuel straight in via an external tank. Make sure you block the vacuum hose coming from the RHS carb before attempting to start it. Do this before you pull the carbs off again, just in case your problem it's carb related. The fuel enters from the LHS carb and flows through a metal connecting tube to the RHS carb. If you've already pulled the carbs apart, you'll know this, so sorry for stating the obvious.

    IMG_1896.JPG
     
    Last edited: Jul 11, 2021
  11. iopsd

    iopsd carbs are scary

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    I have reset them once but haven't yet removed them, I'll give that a go.
    I don't know if this is exactly what you wanted but I can say for a fact all of the stickers are in Japanese, including the gauge cluster. I knew about the vacuum petcock and fuel appears to be reaching the cylinders but won't ignite, so I've been assuming it's some sort of more advanced vacuum problem or airing? But there's not really much in the way of vacuum tubing on this carb. You'll notice the diaphragm cover is kind of off as I tried to remove it to inspect the element but the rusty old screws decided to strip, debating just buying new carbs at this point.

    IMG_20210712_0412036.jpg IMG_20210712_0415105.jpg
     
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  12. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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  13. iopsd

    iopsd carbs are scary

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  14. thebeefsalad

    thebeefsalad Well-Known Member

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    sharp punch, light thumps (hard thumps is a waste of energy). might need to make a divot with the punch before you turn it so that it will drive the head of the screw out.
     
  15. Murdo

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

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    Those carbs need to be completely stripped and properly cleaned (this means ALL jets and screws out and ALL passages cleaned out), otherwise doing a half assed job will only mean you will be doing it over and over again. If you cannot do that then buying new ones from China will be your best bet.
     
  16. Frankster

    Frankster Grey Pride...Adventure before Dementia Staff Member Premium Member Ride and Events Crew

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    I don't know if this is exactly what you wanted.

    Yes, that's what I was after. Congratulations, you've bought one of the harder to work on motorbikes Honda manufactured in the 80's. Good news is, there are plenty of 'experts' on this forum who can't wait to help you get her sorted and running like a new one.

    The very first thing I would do is download the manual from the RESOURCES section of this website. You'll need to join, but it's bugger all to do so.

    @Murdo is correct. You will need to strip those carbs down to their basic bits and check everything is set correctly. some of those screws will need to be sacrificed in order to get to the carbs properly. If you have a Dremel or similar tool, just cut them so that you can get a flat blade screwdriver into them and get them out that way.

    These engines are finicky in several ways. If anything interferes with the starting process, they just won't start. The Regulator/Rectifier is in a nasty spot, so it gets very hot and can often fail. The rear cylinder is prone to overheating and Honda ran a different main jet and needle jet in the carb that feeds this cylinder in an effort to address these issues.

    Carbs.JPG

    Before you pull the carbs apart, you might try running a compression test on the cylinders so we know where we're at. I know you said it was running before, but it won't start now, so lets see what the variables tell us.

    Compression.JPG

    The VT250F has a TCI for each coil/cylinder. There's also a dual-choke system that can play up if not installed or working properly. I know you said there is spark and fuel getting to both cylinders, so I will assume fuel and spark are both there. Have you tried spraying some starting fluid into the carbs while cranking to see if that starts the engine?

    Carb Diagram.JPG

    Let us know how you go.

    Note: Be careful when working on your carbs. Parts for these things are like rocking horse poo...very rare.
     
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    Last edited: Jul 13, 2021
  17. jmw76

    jmw76 Well-Known Member

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    "Note: Be careful when working on your carbs. Parts for these things are like rocking horse poo...very rare."

    Yep. That chock cable connection is a dodgy, fragile piece. Mine is held together with superglue.
     
  18. iopsd

    iopsd carbs are scary

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    I was considering that if the diaphragms were properly rotted; Do you know if later model carbs are compatible with my motor?
    I don't have a compression gauge and was planning on just using the "hold your thumb against the sparkplug hole" trick, I feel as though it's unlikely to be the reason (or more so I just don't want to pull the heads); Do you think the thumb pressure check would be enough? Funds are tight.
    Not yet, however taking the airbox off appeared to give it more will to start, even giving me a little burble before dying.
    gonna dig into this thing tomorrow.
     
  19. jmw76

    jmw76 Well-Known Member

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    if you can get your thumb down the plug hole you have got pretty amazing thumbs. The plug seat is likely to be fairly deep into the head. However, in principal, it should give you an idea whether there is anything major wrong, but not much else.
     
  20. Frankster

    Frankster Grey Pride...Adventure before Dementia Staff Member Premium Member Ride and Events Crew

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    I was considering that if the diaphragms were properly rotted; Do you know if later model carbs are compatible with my motor?

    To the best of my knowledge, there are no other diaphragms that fit the VT250F carbs. The diaphragms in these carbs are very thin. I did find a diaphragm that would fit, but it was thicker rubber and it didn't have the air bleed area cover.

    I don't have a compression gauge and was planning on just using the "hold your thumb against the sparkplug hole" trick, I feel as though it's unlikely to be the reason (or more so I just don't want to pull the heads).

    You don't need to pull the heads. Compression test with a thumb or finger won't really work properly. It will only tell you if you have poor compression, but it's better than nothing, so give it a try with a cold motor (you have no other choice) and see what you think.

    Not yet, however taking the airbox off appeared to give it more will to start, even giving me a little burble before dying. Gonna dig into this thing tomorrow.

    A burble is good. Try 'start ya bastard' or whatever you can get your hands on. if you can get it running with starter spray it might then start without it. I've often found with these bikes that the rear cylinder doesn't want to play ball and the bike is trying to start on the front cylinder only. Check your chokes are working too. You might need them even if its not a cold day. Keep punching. You'll get there.
     

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