rohls Posted May 4, 2014 Report Share Posted May 4, 2014 Hi All, So I finally got my new-to-me JTR250 up and running. I'm new to trials bikes, but not to motorcycles. It starts great on the choke (the little black lever pointed up vertically), and will idle all day like that. The thing is as soon as I put the choke lever down, the engine bogs and eventually dies out. ;( I'm imagining the carb is running too rich because i think the choke on this carb restricts the air flow during start-up, and as soon as I remove the choke, the amount of air in the mixture is too great and the fuel is not compensating.... I started with the air-mixture screw at 3.5 turns out and the idle is a few turns out too. I just cleaned the jets and carb. I didn't pay attention to the needle postion...:/ Thoughts? Who sells a rebuild kit for this carb...? I am in the states. Thanks!! Quote Link to comment Share on other sites More sharing options...
dadof2 Posted May 4, 2014 Report Share Posted May 4, 2014 The "choke" lever does not restrict the air flow, it lets extra fuel and air in (at a richer mixture than normal) Assuming you float height is correct - float tangs about level with carb upside down and you probably want the needle clip on middle or upper notches. Low speed mixture screw wants to be abut 1.5 turns out, 3.5 is far too much. See http://www.dellorto.co.uk/images/parts/PHBH_l.pdf I have a feeling the floats can be put in wrong way round or upside down, if this is done the bike may start and run but not much more. Check the weight of your floats, will be stamped on them in grams. Quote Link to comment Share on other sites More sharing options...
bilks Posted May 4, 2014 Report Share Posted May 4, 2014 (edited) Well this is a screenshot from Gas Gas Usa maybe u have a air leak somewhere.causing it to run weak.if your jets all clear. i have run my previous Gas Gas models around 3 1/2 turns out give or take a bit either way. float weight should be 2.8 grams. so you could check them in some premix, they should float approx half way.you say u set your idle screw out a few turns,I used to start with the mixture screw as recommeded 3 1/2 turns then adjust the idle screw ( slide ) to get a decent tickover, then when engine had warmed up,screw the mixture screw in or out to see if the speed picked up or dropped,then back of on the idle screw until i got a even tick over .also blipping the throttle make sure no hesitation on pick up. Edited May 4, 2014 by bilks Quote Link to comment Share on other sites More sharing options...
rohls Posted May 5, 2014 Author Report Share Posted May 5, 2014 Well this is a screenshot from Gas Gas Usa gas carb settings.JPG maybe u have a air leak somewhere.causing it to run weak.if your jets all clear. i have run my previous Gas Gas models around 3 1/2 turns out give or take a bit either way. float weight should be 2.8 grams. so you could check them in some premix, they should float approx half way.you say u set your idle screw out a few turns,I used to start with the mixture screw as recommeded 3 1/2 turns then adjust the idle screw ( slide ) to get a decent tickover, then when engine had warmed up,screw the mixture screw in or out to see if the speed picked up or dropped,then back of on the idle screw until i got a even tick over .also blipping the throttle make sure no hesitation on pick up. Thank you, that is what I saw as well. I'm thinking I do have an air leak somewhere...What is the best way to test? I started the bike and sprayed choke cleaner around as best I could to no avail... With the choke up/ON: the idle screw is kind of responsive. The mixture screw is responsive, but it takes a rotation to see the difference. I might order a couple parts for it, but since they mostly ship from the UK, it'll be a while. THanks, and anything else would help. Regards.... Quote Link to comment Share on other sites More sharing options...
rohls Posted May 5, 2014 Author Report Share Posted May 5, 2014 So I torn part my carb, scrubbed everything out again. She fired up nicely! She now runs with the choke off (yay!), but still not a crisp as I imagine. Any ideas on how to make er run more responsively? Where can I find replacement reeds for this bike? I'm sure they are worn. Any other ideas? I am running the following jets; I think this is what they are called.... (#66 from the diagram above) = 115 (#3 from the diagram above) = 270k (#8 from the diagram above) = 60 (#9 from the diagram above) = 200 (#7 from the diagram above) = 38 (How does one insert a picture?) Thank you. Thanks! Quote Link to comment Share on other sites More sharing options...
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