veesix24 Posted March 27, 2010 Share Posted March 27, 2010 I have a 1987 dt 125 which I am restoring, The engine fires easily and will run sweet for 30 seconds or so but then it very often bogs down, splutters, backfires lots and dies. The bike will not start or run using choke even from cold which leads me to beleive it is running rich, I have checked the (mikuni)carb settings and they are fine and I have replaced needle jet but still the problem persists. When it is ridden it lacks power and behaves as though the choke is on. I have noticed that the spark plug is fouling from the fuel and the bottom of the engine is collecting a lot of fuel. Although I have experience of car mechanics I am lacking in knowledge when it comes to 2 stroke engines, so if anybody has any ideas as to the cause of this problem I would greatly appreciate any input. If I have been to vague and anybody needs more info to help let me know and I will try to clarify the issue. Thanks Link to comment Share on other sites More sharing options...
Moderator Cynic Posted March 27, 2010 Moderator Share Posted March 27, 2010 I have a 1987 dt 125 which I am restoring, The engine fires easily and will run sweet for 30 seconds or so but then it very often bogs down, splutters, backfires lots and dies. The bike will not start or run using choke even from cold which leads me to beleive it is running rich, I have checked the (mikuni)carb settings and they are fine and I have replaced needle jet but still the problem persists. When it is ridden it lacks power and behaves as though the choke is on. I have noticed that the spark plug is fouling from the fuel and the bottom of the engine is collecting a lot of fuel. Although I have experience of car mechanics I am lacking in knowledge when it comes to 2 stroke engines, so if anybody has any ideas as to the cause of this problem I would greatly appreciate any input. If I have been to vague and anybody needs more info to help let me know and I will try to clarify the issue. Thanks Float height, it is very critical couple of mm too high she'll flood. There are other things, engine needing a decoke, blocked exhaust, blocked filter. But if you have fuel in the crank area then the float height would be my guess. Certanly one of the easier items to check. Link to comment Share on other sites More sharing options...
veesix24 Posted March 27, 2010 Author Share Posted March 27, 2010 Float height, it is very critical couple of mm too high she'll flood. There are other things, engine needing a decoke, blocked exhaust, blocked filter. But if you have fuel in the crank area then the float height would be my guess. Certanly one of the easier items to check. I have checked the float height, admittedly not with the best measuring equipment but it was correct to the specs in my manual, I have just looked at the float needle(?) and there is a slight line worn in to it at the point where it seats could this cause over fuelling? Link to comment Share on other sites More sharing options...
Moderator Cynic Posted March 27, 2010 Moderator Share Posted March 27, 2010 I have checked the float height, admittedly not with the best measuring equipment but it was correct to the specs in my manual, I have just looked at the float needle(?) and there is a slight line worn in to it at the point where it seats could this cause over fuelling? You can typically see a small line where it seats, if all the jets are ok and the associated filters etc are in good condition there is not a lot else it can be. It is a tricky thing to get right, at the coarsest level, ajust the tang on the floats very slightly and see if it improves things, if it is the problem you should not have to adjust it much, maybe a mm or 2. Link to comment Share on other sites More sharing options...
Moderator Airhead Posted March 27, 2010 Moderator Share Posted March 27, 2010 I have checked the float height, admittedly not with the best measuring equipment but it was correct to the specs in my manual, I have just looked at the float needle(?) and there is a slight line worn in to it at the point where it seats could this cause over fuelling? just to confirm its a carburation issue, start the bike then switch off the fuel tap, let it run a while to lower the level in the float bowl, then briefly switch it on and back off top top up the fuel in the carb, do this several times... see what effect this has. As for fuel passing a worn float valve...normally you would see fuel pouring from the carb overflow pipe if it was a bad case. What about the choke plunger, is the seating good and are you sure it is closing off properly? Link to comment Share on other sites More sharing options...
veesix24 Posted March 27, 2010 Author Share Posted March 27, 2010 Thanks 4 the advice cynic & oldgitonabike, I have just tried controlling the flow of fuel using the tap and it does run better though not perfectly (maybe I need to adjust mixture etc once float level is adjusted), I am not sure how to check whether the choke plunger is seating well and whether it is closing off properly, all I do know with the choke is that it wont stay open, it springs back in immediately, I'm hoping I can sort it rather than buy a new one as they aint cheap. I bought this bike for 30 quid as basically a frame/suspension, engine, some electrics and wheels, I have spent 250 quid on all the rest of the parts (panels, tank, loom, lights, brakes etc). Unfortunately i've hit on hard times and can't afford to spend much more. I know i've probably spent out too much on it but I bought it for the fun of the project, not for a profit and to have something a bit different than a dtr. Thanks again for the help and my apologies for going off topic. Link to comment Share on other sites More sharing options...
veesix24 Posted March 27, 2010 Author Share Posted March 27, 2010 UPDATE I have just double checked float height, book spec is 22mm +/- 1mm, and my reading is 24/25mm so fluel level is too low(?) I have also just noticed 1 float sits about 1mm lower at its base.Is that normal or something that needs correcting? Link to comment Share on other sites More sharing options...
Moderator Airhead Posted March 27, 2010 Moderator Share Posted March 27, 2010 UPDATE I have just double checked float height, book spec is 22mm +/- 1mm, and my reading is 24/25mm so fluel level is too low(?) I have also just noticed 1 float sits about 1mm lower at its base.Is that normal or something that needs correcting? I sounds like something is a little twisted, just twist it back straight. From what you say yes the level would be low but this is a big contradiction to what you have already told us. Unless like has been said the valve needs replacing. Link to comment Share on other sites More sharing options...
veesix24 Posted March 27, 2010 Author Share Posted March 27, 2010 I sounds like something is a little twisted, just twist it back straight. From what you say yes the level would be low but this is a big contradiction to what you have already told us. Unless like has been said the valve needs replacing. Is there a way to test the valve without replacing it with a new one (they aint cheap!!) also I'm not sure how to check whether the choke plunger is seating well and whether it is closing off properly as was suggested in an post earlier, all I do know with the choke is that it wont stay open, it springs back in immediately. Link to comment Share on other sites More sharing options...
Moderator Cynic Posted March 27, 2010 Moderator Share Posted March 27, 2010 Hmm, if you add the LOW float height to a sticky choke we get all the symptoms. Starts easy, cos the choke's on and runs rich as its drowning in fuel or would be if the float level was correct. But being low the carb is leaned out causing the backfires. What do you think OG Link to comment Share on other sites More sharing options...
veesix24 Posted March 27, 2010 Author Share Posted March 27, 2010 Hmm, if you add the LOW float height to a sticky choke we get all the symptoms. Starts easy, cos the choke's on and runs rich as its drowning in fuel or would be if the float level was correct. But being low the carb is leaned out causing the backfires. What do you think OG The problem is that the choke wont stay open the spring clip and rubber are not holding it open it springs shut immediately, if you hold it open it is impossible to start even from cold on a winters day! Link to comment Share on other sites More sharing options...
Moderator Cynic Posted March 27, 2010 Moderator Share Posted March 27, 2010 The problem is that the choke wont stay open the spring clip and rubber are not holding it open it springs shut immediately, if you hold it open it is impossible to start even from cold on a winters day! That would suggest the choke is working ok. If the floats are low then you should be running lean, which is possible as the performance from lean or rich is similar (ish) save for the backfire which could be an indicator of the bike leaning out once its opend up. One possible senario, my DT had some side stand issues that meant she leant over just a little too far. This meant the floats couldn't float and they would stick without closing the fuel off. Thing is the fuel didn't come out the overflow immediately, sometimes not at all but drained into the motor. Litterally filling it up on one occation. I had to shut the fuel tap off whenever i left the bike. Do you shut the fuel off religeously or leave it open? Link to comment Share on other sites More sharing options...
Moderator Airhead Posted March 27, 2010 Moderator Share Posted March 27, 2010 Is there a way to test the valve without replacing it with a new one (they aint cheap!!) also I'm not sure how to check whether the choke plunger is seating well and whether it is closing off properly as was suggested in an post earlier, all I do know with the choke is that it wont stay open, it springs back in immediately. You should buy a new Float valve, its also worth mentioning here that the float valve seat should sit on a gasket to stop the fual from bypassing the valve. When you have got one fitted do the float height properly. These parts may be less expensive than you think! Give Steve at motocarb a ring Motocarb Link to comment Share on other sites More sharing options...
veesix24 Posted March 27, 2010 Author Share Posted March 27, 2010 I always make sure I shut the fuel off, I have to as a fuel leak where i keep my bike would be catastrophic! I have heard of other dts with the side stand issue so I only ever turn the fuel on once the bike is level. I will give motocarb a try thanks, i've struggled to find aftermarket parts so i've been going on yam main dealer prices. I have just noticed that the worn needle (main jet) i replaced was slightly bent could that damage the main jet and cause this problem? If so I might try and get a kit with all needles, jets, washers etc (is that possible?), at least i'll know i'll have a trouble-free carb for a bit then. Thanks again, it's good to know there are people willing to help someone less knowledgeable. Link to comment Share on other sites More sharing options...
Moderator Airhead Posted March 27, 2010 Moderator Share Posted March 27, 2010 a bent needle will not damage the main jet but could possibly damage the needle jet, there are numbers and letters stamped on them, you may need a magnifying glass to read them. Compare these numbers to the numbers in the workshop manual if you can, and you will need to quote these numbers when trying to source new parts. Link to comment Share on other sites More sharing options...
veesix24 Posted March 27, 2010 Author Share Posted March 27, 2010 a bent needle will not damage the main jet but could possibly damage the needle jet, there are numbers and letters stamped on them, you may need a magnifying glass to read them. Compare these numbers to the numbers in the workshop manual if you can, and you will need to quote these numbers when trying to source new parts. Sorry I did mean the needle jet, i know what it all does when i'm looking at it but i dont have a clue what half the parts names are. thats the problem when teaching yourself i guess. Thanks for all the advice oldgitonabike and cynic you've been a great help. Hopefully you wont hear from me again on this subject. THANKS BOTH OF YOU! Link to comment Share on other sites More sharing options...
Moderator Cynic Posted March 27, 2010 Moderator Share Posted March 27, 2010 Sorry I did mean the needle jet, i know what it all does when i'm looking at it but i dont have a clue what half the parts names are. thats the problem when teaching yourself i guess. Thanks for all the advice oldgitonabike and cynic you've been a great help. Hopefully you wont hear from me again on this subject. THANKS BOTH OF YOU! Don't be a stranger let us know what sorts it. It may help us/somebody in the future. Everybody is learning all the time. Its when you think you know it all that you have problems. Good luck....... Link to comment Share on other sites More sharing options...
Moderator Airhead Posted March 27, 2010 Moderator Share Posted March 27, 2010 Sorry I did mean the needle jet, i know what it all does when i'm looking at it but i dont have a clue what half the parts names are. thats the problem when teaching yourself i guess. Thanks for all the advice oldgitonabike and cynic you've been a great help. Hopefully you wont hear from me again on this subject. THANKS BOTH OF YOU! I have a workshop manual for a DT125LC, I dont know whether you have but I can tell you the numbers and sizes of the jets if you want...If you do want this info then the first thing i need to know is the carb id number...something like 34X00 Link to comment Share on other sites More sharing options...
veesix24 Posted March 27, 2010 Author Share Posted March 27, 2010 Don't be a stranger let us know what sorts it. It may help us/somebody in the future. Everybody is learning all the time. Its when you think you know it all that you have problems. Good luck....... So true. I will post when the problem is solved. Now to try and find some rocking horse dung (sidepanel which covers exhaust) in the for sale section. Link to comment Share on other sites More sharing options...
veesix24 Posted March 27, 2010 Author Share Posted March 27, 2010 I have a workshop manual for a DT125LC, I dont know whether you have but I can tell you the numbers and sizes of the jets if you want...If you do want this info then the first thing i need to know is the carb id number...something like 34X00 Thank you but I have one, I only use it for part codes and torque wrench settings as I prefer looking and learning for myself, it sticks better than just following instructions that way for me. Surprisingly all the codes and sizes are very clear on my carb parts. Link to comment Share on other sites More sharing options...
Recommended Posts