philhill Posted April 12, 2009 Share Posted April 12, 2009 Hi, have been trying to get the fueling right on my new, old DT125MX. I have used the Haynes manual data sheet main jet, a 130 and adjusted the float height to the recommended 21mm. On the 2nd from top needle notch the engine was bogging down still around 5,000 revs, have gone down to top notch this morning and much better but still slight bogging down so will try a 125 main jet and lowest notch on the needle ( am I doing this right? ). Now that I am able get into the high rev range, couldn't before with the 140 jet fitted it came with, a new problem is occuring. I am only able to sustain short periods of high revs, the engine will die and i will have to wait for what feels like the float bowl to fill, or fuel to get through. The flow from the tap appears ok, but I have just filled the tank and will have to drain it to remove the tap and clean, I don't think this is the problem though as it feels like the carb is the problem. Is it likely to be the needle valve and how do you test it? Phil Link to comment Share on other sites More sharing options...
Moderator Airhead Posted April 12, 2009 Moderator Share Posted April 12, 2009 Hi, have been trying to get the fueling right on my new, old DT125MX. I have used the Haynes manual data sheet main jet, a 130 and adjusted the float height to the recommended 21mm. On the 2nd from top needle notch the engine was bogging down still around 5,000 revs, have gone down to top notch this morning and much better but still slight bogging down so will try a 125 main jet and lowest notch on the needle ( am I doing this right? ). Now that I am able get into the high rev range, couldn't before with the 140 jet fitted it came with, a new problem is occuring. I am only able to sustain short periods of high revs, the engine will die and i will have to wait for what feels like the float bowl to fill, or fuel to get through. The flow from the tap appears ok, but I have just filled the tank and will have to drain it to remove the tap and clean, I don't think this is the problem though as it feels like the carb is the problem. Is it likely to be the needle valve and how do you test it? Phil Hi Phil, there is a filter screen in the bowl of your fuel tap, switch the tap off and unscrew the bowl then carefully pick out the screen, while its off place a container under it and switch it on to check for a good flow from tank. sounds like your main jet is a bit big yes...can you see the ID number os the carb? ...Paul Link to comment Share on other sites More sharing options...
philhill Posted April 12, 2009 Author Share Posted April 12, 2009 Hi Phil, there is a filter screen in the bowl of your fuel tap, switch the tap off and unscrew the bowl then carefully pick out the screen, while its off place a container under it and switch it on to check for a good flow from tank. sounds like your main jet is a bit big yes...can you see the ID number os the carb? ...Paul Hi Paul, the no is 4J300. Going to clean the screen and see what happens. Thanks Phil Link to comment Share on other sites More sharing options...
philhill Posted April 12, 2009 Author Share Posted April 12, 2009 Hi Paul, the no is 4J300. Going to clean the screen and see what happens. Thanks Phil Hi Paul, have cleaned the screen and bowl, loads of muck in there but have taken it out for a spin again and still same problem, flow rate appears good from the tap.... more than it can be using! Will try to lower the foat hight a little to see if any difference. Phil Link to comment Share on other sites More sharing options...
Moderator Airhead Posted April 12, 2009 Moderator Share Posted April 12, 2009 Youre 130 jet should be there or there abouts, I would go for a 125 next but maybe a good carb strip and clean would be in order too, blow out the jets and passageways with compressed air, in the side of the needle jet you will see a series of tiny holes, make sure theses are clear also check for wear on the needle and in the needle jet (shown by ovalling in the top), make sure the air jet isnt blocked too, the easiest way to prove that is turn the mixture screw to just closed, the motor should stumble as there isnt enough air in the mixture if so then air jet is good. Finally try to get main jet sorted with wide open throttle and plug chopping before messing with the needle position, do this after main jet is sorted, is it running as starndard with air filter and exhaust too? Link to comment Share on other sites More sharing options...
YPVS TONE Posted April 12, 2009 Share Posted April 12, 2009 Hi phil The standard settings for the DT125MX are Carb type / I.D mark VM22SS / 4J300 MAIN JET = 130 NEEDLE CLIP POSITION = 2nd DOWN FROM THE TOP Pilot jet = 22.5 Air screw turns out = 1 and 1/4 Float height 21mm Are you getting a good flow from the tap with the pipe removed because as well as the filter in the bowl of the tap there is also a filter screen over the on / reserve pipes of the tap inside the tank. When you checked the float height did you remove the gasket between the carb and float bowl and measure from the gasket Face of the carb to the bottom of the float with the tang of the float JUST touching the needle valve but NOT compressing the spring in the needle valve.Has it still got the original air filter fitted as this could require cleaning out and reoiling. If you move the clip on the needle from the 2nd to the top you are actually lowering the needle and making it weaker and by moving the clip from the 2nd to the bottom position this will raise the needle and make it richer .Hope this helps. Tony. Link to comment Share on other sites More sharing options...
philhill Posted April 13, 2009 Author Share Posted April 13, 2009 Hi phil The standard settings for the DT125MX are Carb type / I.D mark VM22SS / 4J300 MAIN JET = 130 NEEDLE CLIP POSITION = 2nd DOWN FROM THE TOP Pilot jet = 22.5 Air screw turns out = 1 and 1/4 Float height 21mm Are you getting a good flow from the tap with the pipe removed because as well as the filter in the bowl of the tap there is also a filter screen over the on / reserve pipes of the tap inside the tank. When you checked the float height did you remove the gasket between the carb and float bowl and measure from the gasket Face of the carb to the bottom of the float with the tang of the float JUST touching the needle valve but NOT compressing the spring in the needle valve.Has it still got the original air filter fitted as this could require cleaning out and reoiling. If you move the clip on the needle from the 2nd to the top you are actually lowering the needle and making it weaker and by moving the clip from the 2nd to the bottom position this will raise the needle and make it richer .Hope this helps. Tony. Hi, thanks for the info, aware of most of the above but I haven't measured the float height correctly. I am not sure you are correct measuring from beneath the gasket as this will be hard to do, I will check with the manual, i measured from the top of the lip with the carb upside down. the clynes manual does say that I should measure with the needle uncompressed, just touching as you describe, which i didn't do and which i will correct. I thought i had ordered an air filter to go into the air box but was sent a K&N type which i have twisted and contorted to fit with the airbox, the box is still fitted because otherwise no support for the battery and i want to use the original type later. The filter may be slightly restricted due to the twisting. The exhaust is standard as far as I am aware but the silencer is marked FRESCO. There is also a slight leak from the exhaust gasket and I have a new one on order. Thanks for the input, I will get there eventually. Phil Link to comment Share on other sites More sharing options...
Moderator Airhead Posted April 13, 2009 Moderator Share Posted April 13, 2009 Hi, thanks for the info, aware of most of the above but I haven't measured the float height correctly. I am not sure you are correct measuring from beneath the gasket as this will be hard to do, I will check with the manual, i measured from the top of the lip with the carb upside down. the clynes manual does say that I should measure with the needle uncompressed, just touching as you describe, which i didn't do and which i will correct. I thought i had ordered an air filter to go into the air box but was sent a K&N type which i have twisted and contorted to fit with the airbox, the box is still fitted because otherwise no support for the battery and i want to use the original type later. The filter may be slightly restricted due to the twisting. The exhaust is standard as far as I am aware but the silencer is marked FRESCO. There is also a slight leak from the exhaust gasket and I have a new one on order. Thanks for the input, I will get there eventually. Phil As Tony says, you measure from beneath the gasket, remove the gasket as you do so, you will notice a cut out in the lip (see photo), this is where your ruler will sit and thats why there is a cut out there, spring un compressed as has been said Link to comment Share on other sites More sharing options...
philhill Posted April 13, 2009 Author Share Posted April 13, 2009 As Tony says, you measure from beneath the gasket, remove the gasket as you do so, you will notice a cut out in the lip (see photo), this is where your ruler will sit and thats why there is a cut out there, spring un compressed as has been said Hi, checked the Clymer manual and it didn't make reference to measuring from the base, in fact the diagram showed it being measured from the lip! But I will bow to your greater knowledge of these things. Did it my way with the 125 jet and top notch on the needle and it is getting better but still stumbling around 5,000 revs, so will go with your method of measure to see what happens. I suspect the exhaust leak may be having some influence as we get nearer to spot on. What speed can I expect, i have been getting 55 to nudging 60 top wack? Phil ps needle jet didn't want to come out easily so have left it hoping its ok. Link to comment Share on other sites More sharing options...
philhill Posted April 13, 2009 Author Share Posted April 13, 2009 Hi, have remeasured and adjusted the float height according to your instructions, still got a problem at 5,000 revs. Not sure what to do next other than wait for the exhaust gasket to come through the post. Does it matter what 2 stroke oil I use, I have gone for the most expensive synthetic. Are you able to use less oil when using synthetic, I believe i have read somewhere that you can use a lesser concentration with this stuff and if so are you able to alter the amount that is pumped out into the carb? Thanks Phil Link to comment Share on other sites More sharing options...
Moderator Airhead Posted April 13, 2009 Moderator Share Posted April 13, 2009 dont be tempted to mess with the oil pump, it involves adding or removing shims, IMO a recipe for disaster and a heat seized motor. maybe your problem lies in the carb and fuelling , maybe it is a misfire points/condenser? or is it a CDI. why wouldnt the needle jet come out? its got a fairly big hexagon on it, is it jammed and in danger of breaking? the thing is theres lots of little holes in the side of it that usually block up with gunge a compression test would be good also as blowby will cause erratic running because you will have a polluted fuel/air charge, one last thing, to eliminate float height as a problem, switch off the fuel tap when bogging occurs and see if things get better as the fuel level in the carb drops lower. ok thats me out of ideas Link to comment Share on other sites More sharing options...
philhill Posted April 13, 2009 Author Share Posted April 13, 2009 Hi again, CDI i think, the main jet and holder unscrew (hexagonal pieces) then there is a rubber 'O' ring and then the needle jet tube. It would probably knock out with a smart tap, I tried a light tap and nothing happened and didn't want to risk breaking/bending the top, U shaped looking from the top i.e it has a cut away. looking up from the bottom of the carb there appears to be a brass peg and possibly a grove/cut away in the jet tube to ensure it is fitted the correct way round. No holes are apparent in the tube but then it is very difficult to see without taking it out. The flat spot is definately improved now but not gone, dropping a gear and keeping the revs high it will whizz through the flat spot without much notice but still want it right if possible. What about the speed, I seem to remember that my old one went faster but I may be wrong. If converted to 175cc what can you expect? Thanks Phil Link to comment Share on other sites More sharing options...
Moderator Airhead Posted April 13, 2009 Moderator Share Posted April 13, 2009 ok your carb is different from my 175 version, on mine the needle jet screws out and there is a series of small holes drilled into the side which need to be kept clean, I can no loger advise on yours as its different but I would guess it knocks out, whether it has holes in that too i dunno so perhaps best left alone pending further investigation. As for speed dont expect a lot, that wasnt what they were designed for, the 175 will do around 69 mph if you wring its neck, this can be increased with sprocket sizes and tailwinds or reduced with headwinds etc, dunno what the 125 will do but the 175 will be quicker off the mark Link to comment Share on other sites More sharing options...
philhill Posted April 13, 2009 Author Share Posted April 13, 2009 hi Paul, speed not that important to me other than a guide to how well it's performing in comparison, though i would like to be able to take it on the motorway for short hops on my way to visit a mate in Sheffield. The 125 prob not up to that but there are other routes I can use. Your probably not that far from me, are there any green lanes, off road areas out your way? Phil Link to comment Share on other sites More sharing options...
philhill Posted May 4, 2009 Author Share Posted May 4, 2009 Hi, just to update and round of. I fixed the leaky exhaust which entailed a trip to my local engineer to remake the flange on the front of the exhaust as there was just a fraction remaining! With the exhaust now sealed into the barrel I worked my way down from a 130 main jet (book setting) to eventually a 115 where it is now working great. I was amazed at how sensitive the engine is to air restiction. With no filter I could run a 125, with a K&N type it runs as set up but with a standard oiled foam filter I would have to go lower again. I have a new problem now, the engine is very loud and attracts unwanted attention. I have an old Fresco end can fitted, can anyone recommend something quieter for road use or can the Fresco be made quieter ?, it has fiberglass cloth wrapped round the removeable tube at present. Also does anyone have the original paint code for a 1982 DT125MX red. I am also having the graffix re made, if anyone is interested I could get some extra made up. Phil Link to comment Share on other sites More sharing options...
Moderator Cynic Posted May 4, 2009 Moderator Share Posted May 4, 2009 Hi, just to update and round of. I fixed the leaky exhaust which entailed a trip to my local engineer to remake the flange on the front of the exhaust as there was just a fraction remaining! With the exhaust now sealed into the barrel I worked my way down from a 130 main jet (book setting) to eventually a 115 where it is now working great. I was amazed at how sensitive the engine is to air restiction. With no filter I could run a 125, with a K&N type it runs as set up but with a standard oiled foam filter I would have to go lower again. I have a new problem now, the engine is very loud and attracts unwanted attention. I have an old Fresco end can fitted, can anyone recommend something quieter for road use or can the Fresco be made quieter ?, it has fiberglass cloth wrapped round the removeable tube at present. Also does anyone have the original paint code for a 1982 DT125MX red. I am also having the graffix re made, if anyone is interested I could get some extra made up. Phil Not a lot you can do about the noise apart from putting a complete std exhaust on, and that wont make it quiet in comp to modern stuff. Noise wasn't the sensitive subject it is now in the late seventies. Link to comment Share on other sites More sharing options...
Moderator Airhead Posted May 4, 2009 Moderator Share Posted May 4, 2009 Hi, just to update and round of. I fixed the leaky exhaust which entailed a trip to my local engineer to remake the flange on the front of the exhaust as there was just a fraction remaining! With the exhaust now sealed into the barrel I worked my way down from a 130 main jet (book setting) to eventually a 115 where it is now working great. I was amazed at how sensitive the engine is to air restiction. With no filter I could run a 125, with a K&N type it runs as set up but with a standard oiled foam filter I would have to go lower again. I have a new problem now, the engine is very loud and attracts unwanted attention. I have an old Fresco end can fitted, can anyone recommend something quieter for road use or can the Fresco be made quieter ?, it has fiberglass cloth wrapped round the removeable tube at present. Also does anyone have the original paint code for a 1982 DT125MX red. I am also having the graffix re made, if anyone is interested I could get some extra made up. Phil First point is to keep an eye on the plug colour but 115 jet would be about right in the 125MX. As for the noisy silencer, is it the type that is fitted to my bike These silencers need re-packing occasionally, you can buy new packing material, see picture, you need to pack it tightly around the central baffle tube and you will notice quite a reduction in the noise output... Link to comment Share on other sites More sharing options...
col68 Posted May 4, 2009 Share Posted May 4, 2009 Try the BIG ONE rear silencer got mine from ebay £50ish not to noisy sounds the nuts Link to comment Share on other sites More sharing options...
philhill Posted May 5, 2009 Author Share Posted May 5, 2009 Hi, my silencer is about the same size but has a different end cap and double hole fixing, only one used, and is not as shiney. I will look for some packing and perhaps try a 'big one' if I can find one at the right price. Any idea about the paint colour or where to look, I have got the decals sorted. Phil Link to comment Share on other sites More sharing options...
Moderator Airhead Posted May 5, 2009 Moderator Share Posted May 5, 2009 Hi, my silencer is about the same size but has a different end cap and double hole fixing, only one used, and is not as shiney. I will look for some packing and perhaps try a 'big one' if I can find one at the right price. Any idea about the paint colour or where to look, I have got the decals sorted. Phil I dont know if there is a paint code colour, myself i took my tank in to a motorspares shop and ploughed through their catalogues for a match, then got them to mix the colour for me, I didnt paint the tank but did the side panels and mudguards and its a close match, unlike the one tonight... Link to comment Share on other sites More sharing options...
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