2stroke4stroke Posted June 22, 2014 Report Share Posted June 22, 2014 (edited) I wonder if anyone else has experienced this one and knows the cure. Bike is a 2003 200 which has run perfectly all its days. I took it to a trial three months ago and it started and ran fine on putting about but when I tried to rev it it developed a really bad misfire. This both in neutral and under load. After draining the carb in case of water in the petrol I put in an old plug and this immediately sorted it and it ran fine all day. I put it down to some reason caused by the lack of use. It hadn’t been used since until this Saturday when the same thing happened. The plug which had been fine last time out had to be changed to get rid of the misfire and the bike ran fine all day thereafter on a worn plug. Come day two of the trial and same again, the perfect yesterday plug had to be changed. After checking the Woodruff key, I tried two or three plugs with no effect and had to scrounge a new one, which still had a slight misfire but that disappeared after about a minute. Bike ran fine so, in order to try a “hot” experiment, I put yesterday’s plug back in after the first lap which reintroduced the bad misfire. Put the new one lap old plug back in and a slight misfire occurred but disappeared after about half a minute and the thing then did two long laps absolutely fine. I had wondered about coolant getting in to the combustion chamber (there is avery slight loss of coolant) but it had a new head gasket and pump seal a couple of trials before all this started. Any ideas? Edited June 22, 2014 by 2stroke4stroke Quote Link to comment Share on other sites More sharing options...
lineaway Posted June 22, 2014 Report Share Posted June 22, 2014 You are fouling plugs, quit playing with the old ones just put a new one in. Have you changed oil or mixture? Cleaned the filter or cleaned out the exhaust. Check the grounds, or you might be needing a stator. Quote Link to comment Share on other sites More sharing options...
dan williams Posted June 22, 2014 Report Share Posted June 22, 2014 (edited) Hopefully just a need for a couple mm cut off the spark plug wire and a new plug cap. It sounds like it's not the plug but the removal and replace of the cap that is repairing the bad contact in the wire/cap junction. Try removing the plug cap and nipping off the end of the wire and screwing the old plug cap back on. Note: I don't remember if the stock cap unscrews. If not pardon my ignorance. Edited June 22, 2014 by dan williams Quote Link to comment Share on other sites More sharing options...
dan williams Posted June 22, 2014 Report Share Posted June 22, 2014 ... as lineaway says this could be a stator starting to go but try the cheap stuff first. Quote Link to comment Share on other sites More sharing options...
suzuki250 Posted June 23, 2014 Report Share Posted June 23, 2014 Don’t bother with old plugs, you’ll just waste your time Buy a couple of new ones & make sure you set the gap correctly Quote Link to comment Share on other sites More sharing options...
lineaway Posted June 23, 2014 Report Share Posted June 23, 2014 Dan is very correct. Unscrew the cap and clean back the wire. It`s easy, fast and costs nothing to try. Quote Link to comment Share on other sites More sharing options...
thats_a_five Posted June 23, 2014 Report Share Posted June 23, 2014 Agree with others - fouled plugs. In addition to what others said, be careful to not leave the choke on for too long when starting. That can foul even a new plug. Brand new plugs are best but it is possible to clean them well when they foul. Search Youtube and you will find some clever guys who clean plugs with a torch! That is a flame torch, not a flashlight. I always carry a spare plug on my 2 stroke bikes. Quote Link to comment Share on other sites More sharing options...
0007 Posted June 23, 2014 Report Share Posted June 23, 2014 Hopefully just a need for a couple mm cut off the spark plug wire and a new plug cap. It sounds like it's not the plug but the removal and replace of the cap that is repairing the bad contact in the wire/cap junction. Try removing the plug cap and nipping off the end of the wire and screwing the old plug cap back on. Note: I don't remember if the stock cap unscrews. If not pardon my ignorance. I agree with Dan, remove the plug cap and measure resistance, it should be 10k or less Causes the resistor in the plug to fail, puts a severe load on the rest of the system Quote Link to comment Share on other sites More sharing options...
dan williams Posted June 27, 2014 Report Share Posted June 27, 2014 Any results yet? Quote Link to comment Share on other sites More sharing options...
2stroke4stroke Posted June 27, 2014 Author Report Share Posted June 27, 2014 Thanks for the enquiry Dan. I had intended to give an update to all who offered the helpful replies but have not yet been able to get to the bike – should do so this weekend. Of the suggestions made I’m inclined towards the HT lead answer as the plugs don’t appear to be fouled and the bike runs perfectly up to a certain point in the rev range. And I’m not that tight - previously used (not worn out) plugs were employed as that was what I had in the toolbox having just used up the new ones on my twinshock. Will report later. Quote Link to comment Share on other sites More sharing options...
dan williams Posted June 27, 2014 Report Share Posted June 27, 2014 Here's hoping. Cheaper is better. Quote Link to comment Share on other sites More sharing options...
dadof2 Posted June 28, 2014 Report Share Posted June 28, 2014 Try running your bike in darkness and look for stray electrical sparks on any of the electric parts or wires, take flywheel cover off so you can see inside there as well. Quote Link to comment Share on other sites More sharing options...
2stroke4stroke Posted December 1, 2014 Author Report Share Posted December 1, 2014 The Beta has been neglected over the last few months while I did things twinshock but, as I have just got the Beta sorted, I thought I should update those who were good enough to respond. Turns out the triggers needed to be replaced, though why that was cured intermittently by changing the plug i don't know. Quote Link to comment Share on other sites More sharing options...
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