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Thread: Pit bike wont start

  1. #16
    Should Get Out More Trogladyte's Avatar
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    Default Re: Pit bike wont start

    Quote Originally Posted by maccecht View Post
    If the float height is out it can either get no fuel or way too much flooding it straight away. Do you have a manual to get the float level? Get a bit of clear plastic tube put it in the drain from the float bowl and make a U shape so it is up the back of the carb. Open the drain screw and see where the fuel level gets too it should be roughly 5mm below the top of the float bowl [average on most bikes] . However the manual will give you the correct level. You should get it near enough so the bike will start. Just need to tweak the float tang a little to change the level.

    Thanks for helping to think this through.

    No - there is no manual. It's a Chinese supermoto stylee pitbike. The carb is allegedly Mikuni, but there is no nice drsin screw. It has a large plug in the bottom of the float bowl that take a 17mm spanner. There is also an overflow with a clear pipe on it, but nowhere to attach a u-tube as you describe.But its difficult to see why the float height would have changed. |But...you never know.

    I might just try dropping the float a tad and seeing what happens. At the moment the plug is not getting wet, so something is not happening. And a new carb may be the answer - although irritatingly I cfant actually see a like for like replacement. But I guess any 26mm slide carb is going to work.


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  3. #17
    Should Get Out More maccecht's Avatar
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    Default Re: Pit bike wont start

    Quote Originally Posted by Trogladyte View Post
    Thanks for helping to think this through.

    No - there is no manual. It's a Chinese supermoto stylee pitbike. The carb is allegedly Mikuni, but there is no nice drsin screw. It has a large plug in the bottom of the float bowl that take a 17mm spanner. There is also an overflow with a clear pipe on it, but nowhere to attach a u-tube as you describe.But its difficult to see why the float height would have changed. |But...you never know.

    I might just try dropping the float a tad and seeing what happens. At the moment the plug is not getting wet, so something is not happening. And a new carb may be the answer - although irritatingly I cfant actually see a like for like replacement. But I guess any 26mm slide carb is going to work.
    Plan B then. Take the float bowl off turn on the fuel [assuming it is gravity not pump] If it is pump just rig up a temp gravity fuel feed. Lift the float slowly until the fuel is cut off and see if the float is level. If not adjust tang accordingly and double check the pilot is not blocked as well as any drillings in the float bowl. Did you drop it in some Coke or not bother?.

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    Default Re: Pit bike wont start

    You say valves...its a four stroke then. So as well as ignition timing you need to look at valve timing. Its possible it has no marks, but the valves should rock ( inlet/exhaust both moving) at very close to tdc. Not too hard to check.
    Carbs in coke is a good thing, btw.

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    Should Get Out More Trogladyte's Avatar
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    Default Re: Pit bike wont start

    I didnt try the coke. But I took it to bits and soaked it for an hour in carb cleaner, then used aerosol carnb cleaner followed by compressed air through jets and drillings.

    Yes it's a four stroke. But I can't see how the valve timing can have slipped. And it runs with a good squirt of easy start - so it cant be that far out. Must be a fuelling issue, shirley?

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    Default Re: Pit bike wont start

    Quote Originally Posted by Trogladyte View Post
    I didnt try the coke. But I took it to bits and soaked it for an hour in carb cleaner, then used aerosol carnb cleaner followed by compressed air through jets and drillings.

    Yes it's a four stroke. But I can't see how the valve timing can have slipped. And it runs with a good squirt of easy start - so it cant be that far out. Must be a fuelling issue, shirley?
    Possibly, but don't call me Shirley....

  7. #21
    Should Get Out More Trogladyte's Avatar
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    Default Re: Pit bike wont start

    OK, so I have stripped and rebuilt and cleaned the carb. Fuel comes out when you blast air from a compressor through it. And after lots of kicking and sore foot and shins there is fuel on the plug.

    It will not start.

    There's tons of compression, but every now and then there isn't and it spins over really easily for a few revolutions and then compresses again. WTF?

    So I am beginning to suspect a valve issue. So here's the plan.

    1. Set up the valve timing and clearances. Timing should be right, but worth checking. And get clearances right.
    2. Try to start it.
    3. Assuming no start, time to take the head off and have a good look at the valves.

    Please shout if I am talking bollocks.
    Last edited by Trogladyte; 14-12-16 at 22:44.

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  9. #22
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    Default Re: Pit bike wont start

    You should be able to do a leak down test of sorts with the head on . Remove exhaust and carb so you can see the valves set the engine at TDC so valves are closed and pour some petrol in onto the valves. If petrol disappears you know you have a valve issue and they are not closing/stuck/burnt etc. Syringe will be handy to put the petrol in.

  10. #23
    Should Get Out More Trogladyte's Avatar
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    Default Re: Pit bike wont start

    Think I can do the valves on this thing? Can I fuck.

    I am marginally disabled, with failing vision (bit had my specs on) , and neither thumb works very well. And I have no bench to get the bike up on. I can do the inlet, but the exhaust faces down, and holding a light, a feeler gauge a spanner and a pair of long nosed pliers while lying on my back on a cold concrete floor has defeated me.

    I need to take it to my mate's garage and get it up on the bench. Or I need to make a bench to get it up on - which may actually be possible.

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    Default Re: Pit bike wont start

    Get a head torch, this solves one of your problems!

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    Default Re: Pit bike wont start

    Take the engine out

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    Default Re: Pit bike wont start

    Quote Originally Posted by Doc View Post
    Get a head torch, this solves one of your problems!
    And this turns two into one. Now you've barely got more problems than hands
    http://m.ebay.co.uk/itm/Pitbike-monk...257Ciid%253A12

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    Default Re: Pit bike wont start

    Quote Originally Posted by Trogladyte View Post
    Think I can do the valves on this thing? Can I fuck.

    I can do the inlet, but the exhaust faces down, and holding a light, a feeler gauge a spanner and a pair of long nosed pliers while lying on my back on a cold concrete floor has defeated me.
    Quote Originally Posted by Doc View Post
    Get a head torch, this solves one of your problems!
    Quote Originally Posted by Julian_Boolean View Post
    Take the engine out

    I'm wondering why Trog has never told us how his Son manages to ride the bike despite having no hands? if not WTF isn't he holding the torch and spanner, lazy fuck

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    Default Re: Pit bike wont start

    Quote Originally Posted by melons View Post
    I'm wondering why Trog has never told us how his Son manages to ride the bike despite having no hands? if not WTF isn't he holding the torch and spanner, lazy fuck
    One of them is stuck in Berlin and the other is stuck in his GF IIRC.

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  17. #29
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    Default Re: Pit bike wont start

    Quote Originally Posted by cheb View Post
    One of them is stuck in Berlin and the other is stuck in his GF IIRC.
    What, like 'Stuck' forever?

  18. #30
    Should Get Out More Julian_Boolean's Avatar
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    Default Re: Pit bike wont start

    Quote Originally Posted by melons View Post
    What, like 'Stuck' forever?
    If he's lucky

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