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250 jetting question

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My Dr250 is a bitch to start cold. I have run it up using a colourtune kit and to get a blue spark on tickover I have to have the mix screw just over 2 and a half turns out. Am I right in thinking I need a bigger pilot jet? If so what size is standard? ( airbox and exhaust has been opened up)

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Posted (edited)
4 hours ago, Jon Stewart said:

My Dr250 is a bitch to start cold. I have run it up using a colourtune kit and to get a blue spark on tickover I have to have the mix screw just over 2 and a half turns out. Am I right in thinking I need a bigger pilot jet? If so what size is standard? ( airbox and exhaust has been opened up)

if it gets fuel, air and a spark at the right time it should run.  you are probably too lean on the fuel.  you need to increase all the jets.  you have huge increase in air but did not increase the fuel.  you changed everything.  depending on how much you opened up the air flow increase the main by 20,  increase the pilot 10 and put the air screw back to 2 turns and see where it goes.  if you want you can raise and lower the main jet needle.  jetting is very time consuming especially after doing mods like opening up the air flow and exhaust.  it changes everything on the fuel air ratio and tuning. 

Edited by chuck12345
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Cheers. I got the bike like this so I have no idea what jets have been changed (if any). The needle does have notches and I believe I am currently in the second notch up. Do you happen to know what size jets it has as standard? It's a mikuni push/pull throttle carb

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Posted (edited)
8 hours ago, Jon Stewart said:

Cheers. I got the bike like this so I have no idea what jets have been changed (if any). The needle does have notches and I believe I am currently in the second notch up. Do you happen to know what size jets it has as standard? It's a mikuni push/pull throttle carb

no i dont know what the original factory jets were.  i would use that as a starting point because factory jetting is usually not good and very lean.  try and keep the needle in the middle so  it will give an option of lean or go more rich in either direction.   you might need to change the needle to a smaller tapper and use washers to raise/lower because they usually dont have notches.  the factory needles have a wide tapper.  not good for mods and better jetting.   do a search on the year of that bike and see what comes up.  heres a link.    

https://www.google.com/search?rlz=1C1OKWM_enUS777US777&ei=hFHKWsGsPNGusAXyiZg4&q=dr+250+factory+jetting&oq=dr+250+factory+jetting&gs_l=psy-ab.3...22294.22294.0.23346.1.1.0.0.0.0.81.81.1.1.0....0...1.1.64.psy-ab..0.0.0....0.E7-YCQsqt-U

Edited by chuck12345

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Posted (edited)

Not yet. The colourtune kit gave a decent result so maybe it not a jetting issue (as it usually starts ok warm and I'd done all the hard work getting it running to use the colourtune kit). It occurred to me that I might need to check that the choke is working correctly. I'll have a look this weekend 

Edited by Jon Stewart
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16 hours ago, Jon Stewart said:

Not yet. The colourtune kit gave a decent result so maybe it not a jetting issue (as it usually starts ok warm and I'd done all the hard work getting it running to use the colourtune kit). It occurred to me that I might need to check that the choke is working correctly. I'll have a look this weekend 

your having a lot of probs with that carb.  look it over good and make sure it clean.  maybe get a new float needle valve.

if its a CV carb look  at the rubber diaphram in the slide.,  it might have a hole in it.  

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I have a 91 350 and had the worst time starting it. Incleaned it out once but that didnt help. I finally did a full rebuild back to stock on my carb and its runnin better than ever. I changed out everything, needles, jets,and orings.  Starts within 3kicks everytime now. No other mods are on the bike only whatever crap the previous owner did to the carb which screwed it all up. 

My mechanic highly recomended getting mikuni oe jets. Saying that any after market stuff is really a crap shoot. 

I bought a few additional main jets since they were only a few dollars extra in the event i needed to further tune.

 

 

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