mechanic Posted June 17, 2009 Share Posted June 17, 2009 I bought a 1979 DT 250 and the carb was all messed up. As I was taking the carb apart I found that the previous owner had screwed down both air screws. The bike needs trouble shooting, but first I need to know what the factory settting on the screws is first. Any help on the settings will be gratefully appreciated. Link to comment Share on other sites More sharing options...
TylerP Posted June 18, 2009 Share Posted June 18, 2009 It will only have one mixture screw. The other is for the idle. Usually 1 1/2 turns out from a seated position is a good starting point. It makes a difference where the screw is to. Got any pics? Link to comment Share on other sites More sharing options...
JimR Posted June 18, 2009 Share Posted June 18, 2009 I bought a 1979 DT 250 and the carb was all messed up. As I was taking the carb apart I found that the previous owner had screwed down both air screws. The bike needs trouble shooting, but first I need to know what the factory settting on the screws is first. Any help on the settings will be gratefully appreciated. Hi & to the forum it would be good to trouble shoot the bike first off .... as pointed out the air screw should be about 1½ turns out from fully home & the other screw could very well be the idle screw, adjustments of theses screws may have been done in order to mask a problem, but you must have had a problem beforehand in order to strip the carb out ... which was ..... ? Regards Jim Link to comment Share on other sites More sharing options...
mechanic Posted June 18, 2009 Author Share Posted June 18, 2009 Hello and thanks for responding back. I will shortly find how to take pictures and post them but on the carb there is the idle screw on that adjusts where the slide sits but also there air adjustment screw with another screw that is on the carb to reed valve side. And for taking the carb apart I knew I needed to since I got it home and it did what my others did before which was that they would only run with choke and I could ride without choke but I had to keep the engine reved up. Link to comment Share on other sites More sharing options...
JimR Posted June 18, 2009 Share Posted June 18, 2009 Hello and thanks for responding back. I will shortly find how to take pictures and post them but on the carb there is the idle screw on that adjusts where the slide sits but also there air adjustment screw with another screw that is on the carb to reed valve side. And for taking the carb apart I knew I needed to since I got it home and it did what my others did before which was that they would only run with choke and I could ride without choke but I had to keep the engine reved up. Hi, a blocked pilot jet/progression hole then run (idle) idle with choke and run without it .... as regard to the extra mixture screw I guess there is a chance that the US version had some form of emmission control that the UK bike didn't .. to post pictures open a photobucket account & paste the img links to your posts. Regards Jim Link to comment Share on other sites More sharing options...
mechanic Posted June 18, 2009 Author Share Posted June 18, 2009 Hi, a blocked pilot jet/progression hole then run (idle) idle with choke and run without it .... as regard to the extra mixture screw I guess there is a chance that the US version had some form of emmission control that the UK bike didn't .. to post pictures open a photobucket account & paste the img links to your posts. Regards Jim Hi, I have checked all that. I have parts cleaner that I put the carb in, shot water though all of the carb jets, and blowed out all the remaining dirt. What is photobucket and is there another way to post pics. Link to comment Share on other sites More sharing options...
Moderator DirtyDT Posted June 18, 2009 Moderator Share Posted June 18, 2009 Pilot screw 250E 2 turns out, 250D 1 3/4 turns out 250f carb VM28SS model mark 2N600 250e carb VM28SS model mark 1M100 250d carb VM28SC model mark 1M100 The 250f carb seems to have 3 screws Pilot screw, Throttle screw and a Air adjust screw. Look Here According to my book Link to comment Share on other sites More sharing options...
mechanic Posted June 18, 2009 Author Share Posted June 18, 2009 Pilot screw 250E 2 turns out, 250D 1 3/4 turns out 250f carb VM28SS model mark 2N600 250e carb VM28SS model mark 1M100 250d carb VM28SC model mark 1M100 The 250f carb seems to have 3 screws Pilot screw, Throttle screw and a Air adjust screw. Look Here According to my book Hello DirtyDT, so correct me if I am wrong but you are saying that the screw toward the front of the carb is for the pilot. Do you have any knowledge of what the pilot screw should be set to. Link to comment Share on other sites More sharing options...
Moderator DirtyDT Posted June 19, 2009 Moderator Share Posted June 19, 2009 yes. to the left of the throttle set screw. screw it in fully (carefully) and then back it off about 1 1/2 turns as advised by JimR etc. run the bike and adjust the throttle screw to about 1500 revs. then slowly screw in/out the pilot to get the best (higest revs) running speed. Then adjust the throttle to tick over again. Not sure about the other screw but I would ride the bike and check the spark plug adjusting that screw if you need more/less air. Link to comment Share on other sites More sharing options...
Moderator Airhead Posted June 19, 2009 Moderator Share Posted June 19, 2009 Hello DirtyDT, so correct me if I am wrong but you are saying that the screw toward the front of the carb is for the pilot. Do you have any knowledge of what the pilot screw should be set to. A picture would help, see FAQ's for pics. The pilot screw on these 2 strokes is normally an air screw and sutuated towards the back of the carb, not the front. Link to comment Share on other sites More sharing options...
JimR Posted June 19, 2009 Share Posted June 19, 2009 Hi, I have checked all that. I have parts cleaner that I put the carb in, shot water though all of the carb jets, and blowed out all the remaining dirt. What is photobucket and is there another way to post pics. Hi, how did you check the progression hole/tube ? photobucket is a simple host for pictures and you just post the img link in to your posts ... you could use any repository on the net as long as you point the html to the photo's storage but tbh photobucket produces the link for you !! I would have thought the last thing you need to do is run water thro a carb as that would produce build up of crud within the internal drillings/jets when it reacts with the fuel... unless you blew the carb out with high pressure air a few times over a few days in order to allow everything to be 'water free' tbh water in Carbs is a definate no no Regards Jim Link to comment Share on other sites More sharing options...
mechanic Posted June 19, 2009 Author Share Posted June 19, 2009 Hello to all who are trying to help me out. I blow the carb out with my compressor and made air shoot out every passage with getting all the water out as well and as for a picture I did get it to work so here it is. The pilot jet though doesn't it deal with the choke? Link to comment Share on other sites More sharing options...
JimR Posted June 19, 2009 Share Posted June 19, 2009 Hello to all who are trying to help me out. I blow the carb out with my compressor and made air shoot out every passage with getting all the water out as well and as for a picture I did get it to work so here it is. The pilot jet though doesn't it deal with the choke? Oh Ok I now remeber !!!! the bike did have an odd carb (photo's remind you !!!) ... both screws were set at 1½ turns out but there was a point where the inner screw needed to be adjusted to sort out bad starting & kickbacks via the kickstart shaft and again from memory that screw was adjusted to suit the bike running/starting correctly ... sorry I'm getting old and some points have been lost !!! Regards Jim Link to comment Share on other sites More sharing options...
Moderator Airhead Posted June 19, 2009 Moderator Share Posted June 19, 2009 Never seen a carb like that myself, looks like its got two mixture screws. The filter side being an air adjustment, in to richen and out to lean. And the engine side being a fuel adjustment, out to richen and in to lean. Just a guess! Link to comment Share on other sites More sharing options...
mechanic Posted June 19, 2009 Author Share Posted June 19, 2009 Oh Ok I now remeber !!!! the bike did have an odd carb (photo's remind you !!!) ... both screws were set at 1½ turns out but there was a point where the inner screw needed to be adjusted to sort out bad starting & kickbacks via the kickstart shaft and again from memory that screw was adjusted to suit the bike running/starting correctly ... sorry I'm getting old and some points have been lost !!! Regards Jim OK I have the air screw at 1 1/2 but the other day when my dad and I were doing this it really didn't make a difference the bike is a challenge since of the wierd carb. Every bike I own have a mikuni with 1 air screw that is set at 1 1/2. I'll try though again. thanks for the advice and help Link to comment Share on other sites More sharing options...
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