busyeddie Posted June 8, 2009 Share Posted June 8, 2009 As in the title really, just bought a restored 1979 DT 175 off ebay for £400, it runs ok once warm, pulling quite smooth from 2-6000 rpm, but then it hits a brick wall and wont go any further, any ideas? Any pointers much appreciated Cheers Ed Link to comment Share on other sites More sharing options...
little dave Posted June 8, 2009 Share Posted June 8, 2009 it sounds like a jetting issue to me. since jets are one of the responsible components of fuel draw, I think maybe that you have it jetted too small. if your jet isnt letting in enough fuel, it would not have a full range. will it rev past 6k with the clutch in? there are more learned people here than me, so I expect that many here will be able to give you a more detailed explanation. Link to comment Share on other sites More sharing options...
Moderator Cynic Posted June 8, 2009 Moderator Share Posted June 8, 2009 As in the title really, just bought a restored 1979 DT 175 off ebay for £400, it runs ok once warm, pulling quite smooth from 2-6000 rpm, but then it hits a brick wall and wont go any further, any ideas? Any pointers much appreciated Cheers Ed I've known this before the most common cause is the cdi, the 79 model uses 2 source coils the later model uses 1. Count the wires into your cdi, and check if you have a red. The systems dont mix. You need the right coils for the right cdi. Link to comment Share on other sites More sharing options...
busyeddie Posted June 8, 2009 Author Share Posted June 8, 2009 I've known this before the most common cause is the cdi, the 79 model uses 2 source coils the later model uses 1. Count the wires into your cdi, and check if you have a red. The systems dont mix. You need the right coils for the right cdi. ok, where do i find the CDI? sorry ive never really pulled a 2 stroke apart as my RXS 100 ran lovely for the 9 months I had it. Link to comment Share on other sites More sharing options...
Moderator Airhead Posted June 8, 2009 Moderator Share Posted June 8, 2009 ok, where do i find the CDI? sorry ive never really pulled a 2 stroke apart as my RXS 100 ran lovely for the 9 months I had it. Its behind the Right hand side panel, towards the back, a black box with a rubber belt around it. its held on a thin steel bracket top and bottom. 7 wire CDI Also is there a number 2H5 00 on the carb? Right side just in front of the manifold Link to comment Share on other sites More sharing options...
TylerP Posted June 9, 2009 Share Posted June 9, 2009 I would make sure the crankcase is not to full of oil. Also,the silencer in the end of the pipe may be getting clogged up. You should be able to pull it out & check it. Make sure the air filter is in good condition to and that there are no obstructions in the intake. Link to comment Share on other sites More sharing options...
busyeddie Posted June 10, 2009 Author Share Posted June 10, 2009 the cdi is a 7 wire model and there is a red wire, and it has the 2H5 00 carb. Checked air filter, all ok I cleaned the carb, changed nothing I took out the baffle, took out the wadding, (brand new yamaha pipe by the looks of things) its louder, but no better Checked the spark the plug gap from 1.8mm to the 0.6 mm stated in the manual. Wahey!! it runs far more smoothly, and upto 7200 rpm But still will not get close to the red line May buy a new plug tomorrow as the gap made the difference Any other ideas?? Oh and how do i check the crankcase for being full of oil?? Ed Link to comment Share on other sites More sharing options...
busyeddie Posted June 11, 2009 Author Share Posted June 11, 2009 New spark plug changed nothing. any ideas? Link to comment Share on other sites More sharing options...
Moderator Cynic Posted June 11, 2009 Moderator Share Posted June 11, 2009 New spark plug changed nothing. any ideas? If it revs to 7200 the cases havent got any oil in them. Don't take this the wrong way but the carb is fully open when the throttle grip is full throttle. How does it rev in neutral, right out or does it still stop at 7200? A check on the resistances on the ignition primary coils may be prudent. Link to comment Share on other sites More sharing options...
busyeddie Posted June 11, 2009 Author Share Posted June 11, 2009 nah it stops at 7200 in gear or in neutral. seems weird that it hits that speed quickly and wont even crawl further up the rev range, its not unlike an modern engine would be when its hitting the limiter. checking the coils? will do, but how do i do that? Link to comment Share on other sites More sharing options...
Moderator Cynic Posted June 11, 2009 Moderator Share Posted June 11, 2009 nah it stops at 7200 in gear or in neutral. seems weird that it hits that speed quickly and wont even crawl further up the rev range, its not unlike an modern engine would be when its hitting the limiter. checking the coils? will do, but how do i do that? Funny it stops. How fast are you going in top when your flat out? To check the resistances you need an ohm meter/multimeter and then at the generator connections (RH side behind sidepanel next to the frame )check the resistance of.... Red to ground 13.6ohm+-10% Brown to ground 420ohm +-10% and White/red to ground 12.4ohm +-10% Ground can be any GOOD earthing point on the engine. They should be separate bullet connectors next to the multiplug. The white/red is the pulse coil or ignition trigger (modern replacement for the points) these can cause problems if they are worn. Link to comment Share on other sites More sharing options...
busyeddie Posted June 12, 2009 Author Share Posted June 12, 2009 will check resistances later on, but as for top speed i dont know, the speedo drive from the front wheel appears to to broken, or square taper on the end of the cable is too short?? I will be overhauling the front brakes soon so will be looking at the speedo drive then Link to comment Share on other sites More sharing options...
Moderator Cynic Posted June 12, 2009 Moderator Share Posted June 12, 2009 will check resistances later on, but as for top speed i dont know, the speedo drive from the front wheel appears to to broken, or square taper on the end of the cable is too short?? I will be overhauling the front brakes soon so will be looking at the speedo drive then Its only a thought but i just wonderd if the revcounter was reading slow thats all. Got to cover all the bases eh. Link to comment Share on other sites More sharing options...
busyeddie Posted June 13, 2009 Author Share Posted June 13, 2009 Its only a thought but i just wonderd if the revcounter was reading slow thats all. Got to cover all the bases eh. nah im pretty sure its reading ok, as all the gears feel far too short if its revving ok. will get out to the garage soon and have a look with the multi meter Link to comment Share on other sites More sharing options...
busyeddie Posted June 15, 2009 Author Share Posted June 15, 2009 well i dont know what to make of this; i checked the resisantances of the coils with my multi meter and they dont tally with the ones in the manual, not even close, with im sure means ive measured it wrong, because surely with these results it wouldnt run whatsoever? Pulser (white/red) - 1 ohm charge coil (brown) - 24.4 ohms charge coil (black) - 1 ohm what does this mean? am i incompetent at taking readings, or is this feasible? Link to comment Share on other sites More sharing options...
Moderator Cynic Posted June 15, 2009 Moderator Share Posted June 15, 2009 well i dont know what to make of this; i checked the resisantances of the coils with my multi meter and they dont tally with the ones in the manual, not even close, with im sure means ive measured it wrong, because surely with these results it wouldnt run whatsoever? Pulser (white/red) - 1 ohm charge coil (brown) - 24.4 ohms charge coil (black) - 1 ohm what does this mean? am i incompetent at taking readings, or is this feasible? yes those readings are way out, i don't think it would run with those figures either. As for the black er? Get a nice clean point on the engine to use as an earth, the neutral switch is a good one as you can easily prove it first. If the neutral light is on the earth is good and just pop the little plasticy cover up and there you go. Make sure you have the metre on the correct range 0-20 for the white/red and the red wires and the 1000 range for the brown and then leaving the black probe on the earth point for all tests check the red wire then the white/red and after re setting the range on the meter check the brown. Link to comment Share on other sites More sharing options...
busyeddie Posted June 15, 2009 Author Share Posted June 15, 2009 yes those readings are way out, i don't think it would run with those figures either. As for the black er? Get a nice clean point on the engine to use as an earth, the neutral switch is a good one as you can easily prove it first. If the neutral light is on the earth is good and just pop the little plasticy cover up and there you go. Make sure you have the metre on the correct range 0-20 for the white/red and the red wires and the 1000 range for the brown and then leaving the black probe on the earth point for all tests check the red wire then the white/red and after re setting the range on the meter check the brown. hmm, my meter only goes down to 200 ohms as a minimum scale, and i used an earth under the seat, or the black cable in the loom, both gave the same readings, will have to have a better look later, or maybe try another meter. Link to comment Share on other sites More sharing options...
Moderator Cynic Posted June 15, 2009 Moderator Share Posted June 15, 2009 hmm, my meter only goes down to 200 ohms as a minimum scale, and i used an earth under the seat, or the black cable in the loom, both gave the same readings, will have to have a better look later, or maybe try another meter. No you really need the engine earth and a more accurate meter although if its digital it should be ok, you will be ok with the brown test tho (fnarrr). The black wire to the cdi is actually the earth return to the magneto/generator/whatever. The ignition system generates its own electricity so you must use the engine as the earth or the readings will be off as there is NO connection whatsoever direct to the battery. Link to comment Share on other sites More sharing options...
busyeddie Posted June 17, 2009 Author Share Posted June 17, 2009 I redid the test and got 140 ohms on the brown one, 0.5 ohms on the red one, and 20 ohms on the red and white one. Am i doing this wrong, or is this feasible? Link to comment Share on other sites More sharing options...
Moderator Airhead Posted June 18, 2009 Moderator Share Posted June 18, 2009 No its not ok, the specs have been given earlier. You are checking the connector that goes back to the magneto arent you? Link to comment Share on other sites More sharing options...
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