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Carby Problems. Not sure if its too lean/rich

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by L0Ki, Dec 4, 2008.

  1. Here the situation.

    Bikes a GPX250 BTW. Cant tell you what revs and all that its doing as i only have a temp gauge connected.

    The bike will start when cold or colled down with full choke and blipping of the throttle. Now im not sure whether thats its saying its lean or rich because the extra fuel the choke gives it i get, but the opening of the throttle is a sympton of rich mixture. Well thats what i think?

    Then once it hot the idle will all of a sudden be sitting relatively high then drop and if i dont catch it and give it some revs its will cut out. Just makes that noise like it either has too much fuel or too little. (i cant tell between rich and lean mixture noises).

    Then i cant get it started again even with mixing around with the choke and throttle position, maybe i just a few splutters. But no starting until cold again.

    Also should note i adjusted the floats to 17mm (manual spec) exactly each making sure it wasnt pushing the spring of the needle down. Re-measured too so i dont think its that.

    One more thing is that it has no mufflers on it as ive just rebuilt the engine. Not totally but it had exploded and ive got it running. So this means my mixtures will have to be richer than usual but the floats shouldnt need adjusting should they to compensate?

    Also the bike revs out very nicely at the top of the rev range. Im guessing ive gotten it to about 7K maybe less and it sounds good with a crisp throttle response when blipping it.

    Its just that annoying problem when i leave to idle then the revs drop right down and its cuts out unless i catch it in time.

    So guys/gurls. What your explanation of the events im experiencing.

    P.S: Carbys have been fully cleaned and no gloged up jets and needles. Fresh fuel, Spark plugs arnt the newest. In fact im not sure of there age. and its cooling fine, not overheating (unlike my other bike).

    Thanks for any helps guys. Help bring my project along and getting closer to racing. :)


     
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  2. How's the air screw positioning and pilot jet? If it's running rich, you'll smell it.
     
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  3. You've got an air leak or a fuel tap problem or similar.

    Does it do this on the "pri" position?
     
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  4. Its on the about 3 turns out on the mixture screw. And i dont have a PRI position on the petc0ck unfortunately.

    Also should note the fuel tank and petc0ck is off my other bike that works fine with none of this bikes symptoms.

    I'll check for any vacuum leaks but I'm pretty sure theres not. Is there anywhere in particular i have to look?

    Thanks so far.
     
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  5. What's the manual say for the number of turns out for the airscrew? Start with the simple things and go from there.

    Check that the carb bodies are correctly seated to the inlet manifold, hoses are all in good condition and there are no kinks etc.

    It sounds like the bike is lean at idle more than anything, hence check the air scew specs etc.
     
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  6. The manual doesnt actual state an exact amount of turns. But the online NinjaFAQ say 2.5 turns out is a good start.

    I have a feeling its the mixture screw setting too atm. Need to play around with it a bit more tommorow.
     
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  7. The workshop manual should have that information, along with the needle specs and jet sizes. Take it back to 2.5 turns out and see how it goes.
     
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  8. Vac hose not connected maybe ..or bad plugs are the plugs fowled with fuel when it stops..
    I think the bike might have a vac hose to the origanal fuel tap ..
     
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  9. Nope, gravity fed. You flood the left cylinder if you leave them parked with the fuel on for any length of time.
     
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  10. The balance might be well out as well ,eg only 1 carby is providing enough fuel and the other is to little or to much ,makes it run with the choke cold wont run when hot...
     
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  11. Got a worse problem now. Its only running on one cylinder and its not the spark or the spark plug. Switched them around.

    Weird thing is it was running fine yesterday. Then i went to start it today and it was very hard to get going and when it did it was very boggy. So i checked the sparks and the right cyclinder was basically white from running lean? and the left wet and not burning.

    So i switched the spark plugs and same thing. Checked the spark and its getting spark. Also check to se if a rocker had snapped or something and nothing wrong there.

    So thats leaves and lectrical fault. Not enough power in the spark or fueling. Carbies are set at 2.5 turns out each on the mixture screw.

    Im stumped. It was even more embarressing than anything because here i was saying how id fixed it then this happens. :(

    Very Sad!

    Any Ideas now what this could be lol.
     
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  12. What actual happened in the first place .It might give us some clue you mentioned a rebuild of sorts what did you do ,what happened etc...
    If one is white its to lean is the carby getting fuel is the float not working ,why did you reset them...
    Lets start at the begining :wink:
     
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  13. i dont know the beginning. I got the bike as a spares bike with my current bike.

    When i pulled it apart it had a snapped conrod and two exhaust rockers were broken. Piston was pretty stuffed too so that all got replaced.
     
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  14. Well one cyclinder is lean so you have to sort that ,have you balanced the carbs there should be a section in the manual on how to set the carby..Have you checked both bowls for petrol ?
    Have you got your valve timing right .?
     
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  15. The manual says to make sure there straight by eye (the throttle bodies). Then adjust later whern the bikes running.

    Havnt checked both bowls for petrol. I'll pull the carbs out again today. Have a look around and see whats going on.

    And the valve timing is right after 3 attempts i finally got it right. This was an issue before when it wouldnt start. Had the camshafts in the wrong positions intake/exhaust wise.
     
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  16. Yeah, try balancing the carbs - the Ninja 250 wiki has a pretty sweet way of doing it with two bottles, I used that and I think it helped a lot.

    Just try to do it as quick as possible - don't start up the bike, fail to balance them properly, put the fuel tank back on, take it off, start up again, fail again, start up again etc like I did or you'll flatten your battery :(.
     
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  17. Hey guys bad news.

    It was in the head that was causing the probelms. I dont know how i didnt see it before but one of the rockers was broken and had jammed the camshaft and it broke thus only opening one intake valve on the 1st cylinder. the rest of the intake valve were just closed or partly open.

    So im stuffed. The whole head would need replacing because when the cam broke it scraped the journal the cam sits in. And it would just scrape the hell outta a new one.

    But that hasnt stopped me. Ive already said my friendly wreckers an email asking for prices.

    Worse case a new engine will go in its place. I really wanna race a GPX for some reason.

    If you want pictures i can take some. Its not very common for a camshaft to break. (or is it?)
     
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  18. Maybe a crack from previous damage or you done something wrong while you assembled it ..If the engine was seized there could be other things wrong with it that wont show there ugle heads until later ...
    Without knowing the cause of the original damage we can only guess maybe over heated ,lack of oil what ever it was has caused some major damage it might be easyer to start again ,this time check everything top to bottom ,bearing tolorance ,warped head, bent cranks, damage to gear box it can all mount up ..
    It could be cheaper to get another Running engine from a good wreakers..
     
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