jhimboden Posted July 25, 2012 Report Share Posted July 25, 2012 Hello, my name is John and a first time poster. I've got an extensive post put will try to get to the point. I have purchased a 1968 sherpa T250(my first 2 stroke). Restored 2 years ago and has not been started in a year. I started the bike, fires up in 1 or 2 kicks, idles very well but as you come off the idle circuit it begins to miss(not backfiring) and misses through all throttle ranges. I have checked the amal carb and everything appears fine,good pilot jet and circiut,needle jet good(.106),needle good no grooves or wear, main jet good,no air leaks, slide is snug. Float is set at .080" below top of float bowl. I have several Triumphs, BSA's,Ariels,Matchless so I have worked on Amals and am convinced it is not the carb. So I checked the electrics and this is what I found. Spark plug was a KLG B8ES gapped at .030"(changed to KLG BP5ES gapped at .020"), points gapped at .010"(I have changed this to .016"). The timing points opening was set at TDC(I have changed to both .110" and .130" BTDC). I thought this would solve the problem but it changed nothing. So I checked the ohms and this is what I find. Yellow wire-0.3ohms,green wire-2.0ohms,black wire-1.9ohms,spark plug-3380ohms. I also replaced the HT coil with a new one for my Triumph cub ET ignition systems and no improvement. I also put a new condensor and no improvement. Having gone as far as I can go I contacted Hughs Bultaco and talked to Hugh. I went through my sequence of timing and he said not to move the backing plate,to put it back in its original place and don't mess with it?? If this is true it is very hard(if not impossible for me) to set the point gaps and then to set timing without moving the backing plate. Am I missing something here? There are a couple of areas(very small) on the coil windings that I can see where it is discolored. This is where I am and don't have any more ideas. So any help would be appreciated. I am not at a computer very often so it may take a bit of time to respond to questions. Regards. John Quote Link to comment Share on other sites More sharing options...
naichuff Posted July 25, 2012 Report Share Posted July 25, 2012 Ignition timing is 2.8 to3.0 mm before TDC Points are set at 0.013to 0.017(0.35to 0.45mm) I usally set mine with a guage in the plug hole. I do not tighten the fly up until it is set as you can get it off easier.then tighten when set. I also fit my condencers under the tank next to the coil Quote Link to comment Share on other sites More sharing options...
jhimboden Posted July 25, 2012 Author Report Share Posted July 25, 2012 Thank you for your reply. I have the timing and points set at your numbers. I have moved the condenser to under the gas tank. I also have set up a single point ground as I thought the system might not be grounded correctly. Still misfiring. I am wondering if it's the LT coil. Quote Link to comment Share on other sites More sharing options...
sherpa325 Posted July 25, 2012 Report Share Posted July 25, 2012 I have heard of some people having problems with brand new condensors, so I would replace that as it is cheap, also if you dont have a brand new needle jet [106] then I would replace that as well as both items can cause your problems, the needle jets wear just slightly and you will not be able to tune the bike at all, same with the faulty condensor. Cheers Greg Quote Link to comment Share on other sites More sharing options...
dadof2 Posted July 26, 2012 Report Share Posted July 26, 2012 I would find a garage with a PICOscope or similar. All they have to do is clip a sensor on the plug lead whilst the bike is running and they will easily be able to diagnose if its an ingnition problem, and if it is almost certainly which component is at fault. Cheers Quote Link to comment Share on other sites More sharing options...
cvgmmartin Posted July 26, 2012 Report Share Posted July 26, 2012 You seem to be sure that it is ignition, but have you tried both raising and lowering the needle by one notch just to see if it changes anything? It is such an easy thing to do and may help confirm that it is an electrical problem. Quote Link to comment Share on other sites More sharing options...
jhimboden Posted July 27, 2012 Author Report Share Posted July 27, 2012 Thanks for all the good tips guys. Hopefully I will get a chance to work on it in a day or two and let you know what happens. John Quote Link to comment Share on other sites More sharing options...
jhimboden Posted July 29, 2012 Author Report Share Posted July 29, 2012 Well, I have put a new condensor on and moved the needle up one notch and then down one notch with no improvement. I did check the AC volts going to the HT coil when runnning at 1/4 - 1/2 throttle and she reads a little over 6 volts. Seem a bit low to me. Could somebody verify if that reading is within specs. Regards. John Quote Link to comment Share on other sites More sharing options...
woody Posted July 29, 2012 Report Share Posted July 29, 2012 Assuming you have a good earth (green wire) and that you have the black wire from the stator connected to the HT coil (they have been known to run with the yellow connected to the HT coil but badly obviously...) and that you don't have any breaks in the black wire either in the stator or up to the HT coil so that it is earthing out:- as you've replaced points, plug, cap, condensor and HT coil, there is nothing left to go wrong but the LT coil. It's 45 years old - just put a new LT coil on it. Then you have all new electrics. It's rare for an LT coil to fail but they can. If it was me I'd replace the lot (most of which you have) As for readings, I've never understood electrics, so given the cheap replacement of all components. that is what I would do, only costs about £60 over here everything, cheap for peace of mind. . You could go on forever messing with voltmeters or whatever. New components with no frayed or cracked wiring and problem should be solved. Quote Link to comment Share on other sites More sharing options...
jhimboden Posted July 29, 2012 Author Report Share Posted July 29, 2012 That is what I have narrowed it down to is the LT coil. Owning several British iron pieces and dealing with their little quirks I tend to check as much as I can before throwing in the towel. Several people have said a bad LT coil is rare. I guess that is my reason for taking so much time with the machine plus I learn something along the way. Regards. John Quote Link to comment Share on other sites More sharing options...
triple_x Posted July 31, 2012 Report Share Posted July 31, 2012 Hi Go on the Elextrex world site and buy their stator kit (is you canafford it) for the Sherpa. Bought mine three years ago and the bike has been trouble free. Trying to sort one for my Montesa 1970 now. Regards Martin Quote Link to comment Share on other sites More sharing options...
jhimboden Posted August 3, 2012 Author Report Share Posted August 3, 2012 I am having the stator checked at this time but I might be headed that way if I don't get good results from the test. Since I am from the USA the Elextrex is a bit pricy considering the exchange rate. But that might be the way to go. Regards. John Quote Link to comment Share on other sites More sharing options...
325 Posted August 28, 2012 Report Share Posted August 28, 2012 if you have a kill button fitted remove it as this was the problem on my bike withn these symptoms. Also check your wiring to the points as when fitting new ones it is easy to trap wires and to earth out. Quote Link to comment Share on other sites More sharing options...
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