Vaughan Posted August 16, 2012 Share Posted August 16, 2012 Hey guys, having a cold crank problem. 1981 DT175 , just had bored to 3rd over and installed a Yamaha Art piston and rings. New intake and gasket ,new NGK plug cap and B9ES at .028. The carb is from a 1978 DT125 (original one was butchered) , jetted mains to 175 spec (150) , pilot (22.5) and new slide and needle for this 1978 carb . The carb is spotless ( did clean emulsion tube) , first had needle clip in middle and now dropped to 4th which helped a little . Even when warmed up the air screw has no effect when turning in (even closed) . After kicking and playing with the choke about 10 kicks it cranks , after warms up it runs pretty good but could idle better. I set the float at 21mm (was higher and cranked a little better then) , one thing i had not checked is the timing and don't know how to with CDI . Thinking on resetting float to maybe 18mm which would raise it and wonder if pilot may be the problem ? Both carbs are 22.5 stock . Any ideas ? It really needs a correct carb body that i can't find ,Mikuni 3J1 00. Only PDF manual i found is the Clymer . Also i was told this has a MK2 ignition and the Clymer book is showing a MK1 . So my timing is good as in my pic ? Here's where it is now, Uploaded with ImageShack.us This is what Clymer shows for F,G and H model Uploaded with ImageShack.us Pick up coil's position now , Uploaded with ImageShack.us Pic shown in Clymer book , Uploaded with ImageShack.us Link to comment Share on other sites More sharing options...
Vaughan Posted August 17, 2012 Author Share Posted August 17, 2012 Got a 25 and a 27.5 pilot coming. Never found a better PDF manual ,but you were definently right on the MK2 iggy and timing was OK . Have hunted up and down for a 3J1 00 carb body ,but looks like a dead end and he'll have to use the 78 125 one . Got my fingers crossed that bigger pilot and raising the float will fix it. Also may be buying a 75 DT175 for myself , $200 ,complete ,but pretty rough and does run. Link to comment Share on other sites More sharing options...
Vaughan Posted August 19, 2012 Author Share Posted August 19, 2012 Well no replys , we found a correct 1981 carb and going to build it when it shows up and hopefully be done with it to do another bike. Link to comment Share on other sites More sharing options...
Sacha Posted August 19, 2012 Share Posted August 19, 2012 Let us know how the new carb works out. Link to comment Share on other sites More sharing options...
gemini Posted August 23, 2012 Share Posted August 23, 2012 Even when warmed up the air screw has no effect when turning in (even closed) . this is due to the pilot jet size, float height wont affect it, but main jet size does slightly, better to start of with the standard jets and go from there Link to comment Share on other sites More sharing options...
Vaughan Posted August 25, 2012 Author Share Posted August 25, 2012 At first second correct 1981 175 carb did not fix it , I never went through this with either of the RD's i had . This bike has me baffled !! Same deal with this fresh carb that i very carefully went through,same have to kick and kick and kick like with other carb, when it finally cranks and warm it up it runs and revs out better now . When idling it doesn't want to idle smooth, if i set it at 1500 it skips between it and 2000 . Also same deal with air screw ,i can be at 1 1/2 and slowly close it completely and no effect at all , if i back out it eventually starts to idle down . This is the correct 81 carb , stock 150 main,upped to 27.5 pilot (stock 22.5) , stock needle and slide with clip at stock middle , air screw 1 1/2 to 2 turns. New NGK B8ES at .028 , fresh top end job , new prem. gas with marine Stabil , oil pump correct , tank is clean and petcock bowl and sock clean. Today i found it bogs if clip is second , cuts up at 4th or bottom and perfect in middle . Next the air screw , i tried 2 turns out at cold start and had to crank the idle screw way in to get to idle . Next after about 3 hour cool down i tried 1 turn out and this is the best this thing has ever run . It started 1st kick with full choke , i immediately took the choke off and it wanted to bog if i didn't feather the throttle. After it warmed up i rode around the neighborhood about 5 miles and ran the best it ever has . I'm going to try spray around the running flywheel , is propane better ? Also how can i test the coil ? Thanks !! I'm almost tempted to swap the 150 main with a 155 or 160 to see if if may help even more , it a tad sluggish and slight surge at times ? Link to comment Share on other sites More sharing options...
dt502001 Posted August 25, 2012 Share Posted August 25, 2012 That was my thought leaking crank seals. I use propane to check O next time can you change your font it's realy hard to read tiny little words Link to comment Share on other sites More sharing options...
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