renegade master Posted June 21, 2015 Report Share Posted June 21, 2015 Hi Guys, I am not long after buying a few project bikes/parts cheep! and after a few hours in my bike shed I was able to build a 97 or 98 (forget again) gas gas JTX 270 from one pile of parts, and after it was built I clocked up about 12hrs of riding time on it! in this time it was very well behaved, started first time everytime! and a lovely bike to ride! but now after a few weeks parked up, when I start it, it wont start and keeps blowing spark plugs! I have checked the color of the plug a few days ago and it was carbon fouled, and when I place a new/other plug in it, it runs ok (well little rough at full throttle) but then next day same thing, kick it over it starts for a few seconds and dies away, check plug and no spark!........... think i will check needle settings next? but I thought id ask you experts your opinion first??? Cheers Guys Quote Link to comment Share on other sites More sharing options...
feetupfun Posted June 22, 2015 Report Share Posted June 22, 2015 Hi Guys, I am not long after buying a few project bikes/parts cheep! and after a few hours in my bike shed I was able to build a 97 or 98 (forget again) gas gas JTX 270 from one pile of parts, and after it was built I clocked up about 12hrs of riding time on it! in this time it was very well behaved, started first time everytime! and a lovely bike to ride! but now after a few weeks parked up, when I start it, it wont start and keeps blowing spark plugs! I have checked the color of the plug a few days ago and it was carbon fouled, and when I place a new/other plug in it, it runs ok (well little rough at full throttle) but then next day same thing, kick it over it starts for a few seconds and dies away, check plug and no spark!........... think i will check needle settings next? but I thought id ask you experts your opinion first??? Cheers Guys 20150606_124909.jpg When you say "....and dies away, check plug and no spark" do you mean that with a new plug there is no spark, or that there is no spark with the plug that came out? Quote Link to comment Share on other sites More sharing options...
lineaway Posted June 22, 2015 Report Share Posted June 22, 2015 Are you turning the petcock to off when parked Have you ever thought to pull off the flywheel cover and give the crank a good tug? Bad main bearings play hell with ignition timing. Quote Link to comment Share on other sites More sharing options...
renegade master Posted June 23, 2015 Author Report Share Posted June 23, 2015 When you say "....and dies away, check plug and no spark" do you mean that with a new plug there is no spark, or that there is no spark with the plug that came out? no spark from original pug! when I put new plug in, it works fine! last plug I blow (the other evening) was a number 5 which is a hot plug! well maybe better if it was a number 7 or 8? Quote Link to comment Share on other sites More sharing options...
renegade master Posted June 23, 2015 Author Report Share Posted June 23, 2015 Are you turning the petcock to off when parked Have you ever thought to pull off the flywheel cover and give the crank a good tug? Bad main bearings play hell with ignition timing. I never turn of the petcock! can you explain the reason one would do that? I know i hydrolocked me txt pro one time by fuel getting past the carb into the head caused by sticking carb floats or something! maybe thats a good reason to switch it off! Quote Link to comment Share on other sites More sharing options...
lineaway Posted June 23, 2015 Report Share Posted June 23, 2015 Really, this is how bikes get flooded with fuel. I used to see the same guys show up at events with non-running bikes, just because they left the fuel on. In transport the floats bounce letting fuel in even with everything working good. Quote Link to comment Share on other sites More sharing options...
suzuki250 Posted June 23, 2015 Report Share Posted June 23, 2015 (edited) I had a similar problem many years ago on a 1990 KTM, the plugs would only last one meeting (or less) then they wouldn’t work again I tried all sorts, timing, carb setting, plug caps, different make of plugs ect...... In the end I swapped all the ignition components, and it worked perfect after that I also retried the original ignition, and the problem returned!?!?! Edited June 23, 2015 by suzuki250 Quote Link to comment Share on other sites More sharing options...
crazybond700 Posted June 23, 2015 Report Share Posted June 23, 2015 (edited) Could be all kinds of stuff. Bad ignition parts (cap e.g.), very dirty airfilter/carbonned exhaust, wrong settings (but why did it run good earlier?), fuel overflow in the engine etc. Bad gasoline or too much oil? Edited June 23, 2015 by crazybond700 Quote Link to comment Share on other sites More sharing options...
feetupfun Posted June 23, 2015 Report Share Posted June 23, 2015 maybe wrong heat range plug maybe weak ignition system maybe sucking in gearbox oil when it runs maybe coolant leaking into the combustion chamber when it is parked maybe carbon deposits coming loose due to change of fuel type from previous use years ago Suggest you run it with a new plug then when it cuts out, have a really good look at the plug - strong light and magnifying glass - to work out what is happening to the plug. It will be either a fine (whisker) bridge made from carbon, or the nose coated with a layer of conductive carbon Quote Link to comment Share on other sites More sharing options...
renegade master Posted June 24, 2015 Author Report Share Posted June 24, 2015 Great ideas guys! thanks, I shall get to work on it in the next few evenings and try and eliminate this problem, kinda bugs me when the bike has been running fine prior to this! I will take on board all your suggestions and keep you all up to date with the progress Quote Link to comment Share on other sites More sharing options...
renegade master Posted June 24, 2015 Author Report Share Posted June 24, 2015 Really, this is how bikes get flooded with fuel. I used to see the same guys show up at events with non-running bikes, just because they left the fuel on. In transport the floats bounce letting fuel in even with everything working good. So is it best to turn off after every ride/spin or only when being tansported? Cheers lineaway Quote Link to comment Share on other sites More sharing options...
feetupfun Posted June 24, 2015 Report Share Posted June 24, 2015 Think about what might happen if your bike is leaning against a tree or on its stand and while you are off somewhere else, it falls over. If your fuel tap is off, then the only place it can get out of the tank is through the vent. If you have the fuel tap on, you could lose your fuel out the carby overflow pipe Lots of bikes have slightly dodgy float needles too, and if the bike is left parked with the fuel on, fuel will also be lost either out the overflow line or into the engine while parked. It's a good habit to turn the fuel before you walk away from your bike. However until you also develop the habit of turning it on again when you want to ride, you will probably get a few fives by riding sections with the fuel turned off. 1 Quote Link to comment Share on other sites More sharing options...
renegade master Posted June 24, 2015 Author Report Share Posted June 24, 2015 Ok went out to the bike shed today with the big happy head on me thinking I was going to sort the problem! yeah right! anyway i strpped carb, cleaned it! descoverd that the clip on the needle was at the top setting, I moved it down to one up from the bottom setting, I took off the fly wheel cover and checked for play in it, it was solid, so i put everything back and put another plug in it! it started fine! idled fine, ran fine, then took for a quick spin and after 2mins .......plug gone again! and thats quick! so later after that when my mate called around he put an idea into my head! This bike was built from a box! lots of gas gas parts, 3 bikes in total frist one a 96 jtx 250 (i think) engine gone, and 97 jtx 200 and a 97/98 jtx 270, so i had 3 carbs to choose from! could it be that i picked the 200cc carb! its the same as the 270 but probably jetted different? but if that was the case why did it run sweet for about 10or 11 hours prior to this? could this be the problem? I will check the jetting tomorrow, just thought I would up date you all frist! Thanks again Guys your input is much appreciated!!! Quote Link to comment Share on other sites More sharing options...
tony27 Posted June 25, 2015 Report Share Posted June 25, 2015 For some reason the jetting on trials bikes doesn't really seem to change between different engine sizes, 250 & 270 probably ran the same settings standard seeing as the bottom ends are the same, the 200 is only a 125 with a bigger bore - 164cc from memory, so jetting for that carb would be closer to the 125 Is it possible that some of the ignition components have been mixed up? Because you say it ran fine for 10 or so hours before this problem I'm leaning towards something in the ignition breaking down, first thing to try with a brand new plug gapped correctly is run it in a darkened garage to see if there is any cracks in the cap or lead jumping to earth, I had similar problems a few years ago & it turned out that the cap had a tiny crack that was arcing to the fan motor which was only visible in the dark After making sure there are no cracks in the lead or cap then you are going to need to find someone with the same bike who is prepared to allow you to swap ignition parts around to see if changing any part cures the problem, only do 1 part at a time & if no improvement put your part back on & move onto the next Quote Link to comment Share on other sites More sharing options...
crazybond700 Posted June 25, 2015 Report Share Posted June 25, 2015 Also because you did a ''build'' check maybe for corrosion on all the important wires and where they are attached to the frame. And if you have available change the ignition parts. Those are most likely to cause problems ''sometimes'' while first working perfectly. Other suggestion could be to check for air leaks, but you should be able to notice this. Maybe crank seal or something gone because of standing still for a while. Quote Link to comment Share on other sites More sharing options...
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