eden1

With the genuine Yamaha CDI, if I advance the ignition timing it doesn't improve the non running over 3000rpm. At max advance it starts to kick back during starting. I thought I would be creative and extend the slots in the stator to allow enough movement for the Taiwan CDI's to be timed to 1.8mm btdc. Unfortunately, it still only revs cleanly till 5000rpm and then only fires occasionally after that. I don't know if it will be connected, but with all the starting and stopping I have noticed I can hear the battery fizzing after the engine stops.

I have fashioned part of a micrometer into a depth gauge and checked the stamped timing mark on the casing and the rotor and is 1.8mm btdc and it is bang on. I made a couple of other temporary marks at the upper and lower timing tolerances of 1.65 & 1.95mm btdc for reference. Using a xenon strobe clipped on the HT, and with the engine at 3000rpm, I started with the stator mark aligned with the timing mark on the casing. With the genuine Yamaha CDI, the timing was bang on the timing mark. Swap to the Taiwan CDI's, the timing was too retarded, around 1.0mm btdc. I slid the stator round to the most advanced position in its slots and the timing is still too retarded at around 1.2mm btdc. In a nutshell, the CDI's are behaving differently to each other.

Hi Cynic, I think I will try and check the timing. The Haynes manual isn't to clear so if you have any pearls of wisdom on the subject, they would be appreciated. I did check the crankcase and stator marks were aligned before and after the engine strip down. I will try and compare the Taiwan CDI 's with the secondhand genuine Yamaha CDI. Have you had any experiences with the Taiwan CDI's in the past?

Hi, thanks for the pointers The silencer seems to blow through without restriction. I think it would mean drilling out rivets to dismantle the silencer and draw out the contents. Quite correct, my needle is a 4J6 not the 4JC I said it was. Several years ago I had to extend some wires in the harness to the magneto in the area below the petrol tap, as they had rubbed through on the frame, but they seem ok. Pilot jet is 20, which I think is right for my carb, plus it has run fine with it for over 20 years.

Calling all DT experts, I have joined up YOC after I stumbled upon it while googling for ideas what may be wrong with my '81 DT175MX which has done 50,000 miles. I have had it for the last 24 years. I have a picture loaded on my profile. It looks like the knowledge in the workshop forum is a pretty vast resource, whereas my knowledge is pretty much exhausted with this particular fault. It is a pretty epic story, and goes back over a year, I struggle to recall the exact sequence, but as far as I remember it goes something like this...... The bike had been parked up over winter and refused to go in the spring - a surprise as it is usually a great starter. Initial thought was stale petrol, so drained tank and tried fresh. Not starting. Had a look in the airbox and found the foam filter cone was disintegrated. Cleaned out the airbox and the carb, replaced the foam air filter, new NGK spark plug. Good fuel supply to carb - full bore of pipe. Engine now starting well, idling well, revving cleanly to around 4500rpm, after that it fires intermittently & backfires occasionally. Drop it below 4500rpm and it is fine again. The ignition switch was worn out - the barrel lifted in and out with the key sometimes. I had read that a faulty ignition switch can fry the CDI unit so I resorted to a made in Taiwan CDI off ebay. Advertised as fitting an ,81 DT175 MX it is a 6 wire type from Yuniworld in Derby, 18G-85540-00 I replaced the ignition switch with a pattern part at the same time. Still, above 4500rpm it fires intermittently, backfires occasionally, drop it below 4500rpm and it is fine again. Still thinking it was CDI related, I armed myself with the Haynes manual and did some testing with a multimeter. The bike is the type with F3T251 4 slot flywheel, single source coil and 6 wire CDI. The resistance for the source coil looked below spec so I sourced a made in Taiwan one off ebay - Yuniworld again. No better. Tried the rest of the resistance test at the CDI wires. All ok, except I was getting minus18 ohms at the black/white kill switch wire. I decided to run a new wire up the frame and plugged it direct to the kill switch at the connector in the headlight, thus bypassing the ignition switch. As I expected, the engine now starts and runs with ignition switch turned off, and the kill switch can be used to stop the engine. Thinking I may well have fried the Taiwan CDI, I ordered another one off ebay Yuniworld - no better. I decided I couldn't be that unlucky with CDI's so I looked elsewhere. The reeds didn't quite seem to sit fully closed on the reed block, so I tried some new reeds - no better. I then thought it could be air leaks at the crank seals or the crankcase gasket. Engine out, strip down. Bore ok, rings a bit gummed up. New main bearings, oil seals all round. Freed off rings, cleaned piston grooves. Reset autolube pump setting. Renew autolube pipes & clips with clear pipe and spring clips. Woodruff key OK. Checked exhaust clear. Clean up engine mount earthing positions. Start and run - just the same. At least splitting the engine allowed me to cure a longstanding oil leak by the sump plug with some liquid metal in a hairline crack. For good measure new pattern part ignition coil, HT lead, NGK plug cap. Also replaced pulser coil with pattern part, then removed it again as resistance was higher than tolerance. Refitted original pulser coil. Thought maybe the Taiwan CDi's were no good, so I bought a second hand Yamaha one off ebay marked 3J0-20 1.9.24. This significantly changed the characteristic of the engine. It starts and idles, but will not rev above 3000pm at all. Reverted back to one of my the Taiwan CDI's, back to 4500rpm then intermittent firing, occasional backfire. Electrical tests carried out results (spec):- Ignition coil & HT Resistor plug cap 5230 ohms (5000) Ignition coil primary 0.9 ohms (1 +/-10%) Ignition coil secondary 5920 ohms (5900 +/-20%) At the loom connectors to the CDI Orange HT primary 1 ohm (1 +/-10%) Brown magneto charge coil 279 ohms (300) White/red magneto pulser coil 10 ohms (10) Black female 0.1 ohms (0) Black male 0 ohms (0) Black/white ignition on/kill switch run position - open circuit (open circuit) Black/white ignition on/kill switch kill position - minus 19 ohms (0) If I touch the multimeter leads together I get either 0 or 0.1 ohms. Carburettor Mikuni VM24SS 3U500 Main jet 160 Main nozzle 267 10-8 Pilot jet 20 Float height 21mm measured with carb upside down - gasket mating face on carb body to top of float. Throttle valve 1.5 Jet needle 4-JC Needle clip always used to run fine with it in top groove, have also tried it in middle and bottom groove. All standard I think, and unchanged since it used to run fine. Decided to strip the carb and give it a few goes in my little ultrasonic cleaner from Aldi with some washing up liquid. No surprise, but no better. Other info, it does seep a drip of blackish oil out at the exhaust gasket. Spark plug is generally slightly wet oily black rather than biscuit coloured. So here I am, with a box full of spare parts that probably were not needed, and a bike much the same as it was over a year ago, apart from curing the sump plug oil leak. On the plus side I am now much more familiar with almost every engine, fuel and electrical component on the bike!! Does anyone now if CDI's can be tested, or is it a case of plugging it into a "good bike" to try it? Why am I getting minus ohms reading at the black/white kill wire and is this killing my CDI's? (I have tried not connecting the kill wire at the CDI and just contacting the black/white from the CDI to earth to stop the engine) Does anyone have any other ideas or suggestions I should be looking at? Sorry it is such a long post, I said it was an epic. Please help, wife is now saying it might be kindest thing to let the DT slip quietly away - unbelievable!!!!!!!!!!!! eden1 (David)

I have added a couple of pictures in my garage area of the RD I used to have and the DT I still have. I have been trying to change my profile picture to the DT, but so far I have been defeated!! I will keep trying as I am sure it will be me doing something wrong.

Name: Yamaha RD350 LC (1982) Date Added: 21 June 2015 - 03:40 PM Owner: eden1 Short Description: Picture taken 1985 View Vehicle

Hi everyone I am a 40 something from the Eden valley in Cumbria, UK with a 1981 DT175 MX in white, which I have had since 1991. It is quite a high miler with just over 50,000 on the clock (dry miles only for the last 20 years or so). I don't use it that often now, and I usually have a bit of a laugh with the MOT tester about the pitifully low increase in miles since the previous years test. Previous bikes include a 1974 FS1-E in purple, a 1983 Kawasaki AR50 in black, a 1980 Suzuki GP100, a 1982 RD350LC in black, a road legal TY175 in white, can't remember the year of the TY. Wish I still had most of them, especially the FS1-E and the RD350LC. When I got my current DT175MX 24 years ago, that is the last time I bought or sold a bike! Now I have joined YOC, I will probably be trawling through the workshop forums because after 24 years of almost faultless service, the DT is giving me some running headaches at the moment. She is way to good to scrap and I have the sort of attachment to her that steadily grows as the years roll on by. I am pretty sure the DT will see me out!!! eden1