leembarnes Posted December 9, 2018 Report Share Posted December 9, 2018 2017 Rr 300 has always run perfectly. Went out today and after ten minutes of 1st gear pottering around to warm up I got a big backfire. Started ok but wouldn't rev properly had loss of power and was knocking. Limped it back to the van and left it ten minutes whilst getting local opinion. Ten minutes later it started perfect and ran spot on for about 3 or 4 minutes including at half and three quarter throttle whilst static. Then it started to bog down again and lose power. Back to the van quick strip down...carb clean all ok put a new plug in which took 15 minutes. It then ran great for 15 minutes and same again started to bog down lose power and pop a bit so called it a day. 2nd and 3rd try there was no audible knocking. Only work done prior to riding was fresh oil. Also new tank of fuel but same stuff I always use. Any ideas welcome? Never done this before! Seems to be an issue as the bike gets hotter?? Fan working fine so overheating shouldn't be the issue. Bad batch of fuel? Or has the big backfire damaged something..... Quote Link to comment Share on other sites More sharing options...
lineaway Posted December 9, 2018 Report Share Posted December 9, 2018 (edited) Vent line plugged? Take the fuel cap off and run. During a 40 mile event, my son`s check ball in the fuel cap started to stick. We drilled it out. No more ball no more problem. He had to keep taking the cap off to ride the sections. Edited December 9, 2018 by lineaway Quote Link to comment Share on other sites More sharing options...
leembarnes Posted December 9, 2018 Author Report Share Posted December 9, 2018 Thanks will try that. Brought it home and washed it and again it's run perfect for ten mins on stand. I did have a thought....just because the fan is working doesn't mean it's not overheating....could it be an impeller problem? I've heard of the Trs melting impeller blades and had been planning to do the upgrade on it. If there is no circulation could that give same symptoms.... Quote Link to comment Share on other sites More sharing options...
mcman56 Posted December 9, 2018 Report Share Posted December 9, 2018 Water in gas can cause weird intermittent lean issues and be difficult to get out of system. I once pulled a carb and found a drop of water stuck in the main jet. Still, I can't see how that would cause a backfire. Quote Link to comment Share on other sites More sharing options...
leembarnes Posted December 9, 2018 Author Report Share Posted December 9, 2018 5 minutes ago, mcman56 said: Water in gas can cause weird intermittent lean issues and be difficult to get out of system. I once pulled a carb and found a drop of water stuck in the main jet. Still, I can't see how that would cause a backfire. Thanks I will drain everything off once more and get some new fuel to try. Intesting that when the bike is allowed to cool it runs fine for a while and then the issue returns Quote Link to comment Share on other sites More sharing options...
lineaway Posted December 9, 2018 Report Share Posted December 9, 2018 Careful, because that can be the same thing as fuel or electronic. Had the same issue with a guy with a 2018 Beta. He swore he had no spark issue. Turned out it was the replacement fuel cap not venting. Quote Link to comment Share on other sites More sharing options...
leembarnes Posted December 9, 2018 Author Report Share Posted December 9, 2018 8 minutes ago, lineaway said: Careful, because that can be the same thing as fuel or electronic. Had the same issue with a guy with a 2018 Beta. He swore he had no spark issue. Turned out it was the replacement fuel cap not venting. It's got an aftermarket csp cap and the ball is moving fine doesn't appear blocked... Quote Link to comment Share on other sites More sharing options...
nhuskys Posted December 9, 2018 Report Share Posted December 9, 2018 4 minutes ago, leembarnes said: It's got an aftermarket csp cap and the ball is moving fine doesn't appear blocked... Drill the ball out of your stock cap as lineaway suggests, put it back on the bike instead of the CSP cap, ride the bike and report back. Quote Link to comment Share on other sites More sharing options...
lineaway Posted December 9, 2018 Report Share Posted December 9, 2018 (edited) Too bad as it is the easiest problem to sort. Still could be the carb. The Keihin works fine, except that tower can get clogged up and or the oring leaks. My bikes float tab actually sticks and then bends the tab with a hard hit. Then it just floods. Pain in the rear. Good luck. Edited December 9, 2018 by lineaway Quote Link to comment Share on other sites More sharing options...
leembarnes Posted December 9, 2018 Author Report Share Posted December 9, 2018 Defo not the vent cap...just ran it again for ten mins with cap off and same result...perfect for a ten or twelve mins then bogs down won't rev and a few backfires this time too Quote Link to comment Share on other sites More sharing options...
nhuskys Posted December 9, 2018 Report Share Posted December 9, 2018 (edited) In my experience it's usually an ignition problem, when it occurs when bike gets "hot" after running a bit. That doesn't mean overheating.... Start with a new plug, then pull the plug cap, cut the HT lead and reinstall cap. Try a new plug cap if you have one. Run it in the dark and spray some water on it and see if you get any stray voltage. It could be anything... stator, coil, etc but start at the simple end.... Edited December 9, 2018 by nhuskys 1 Quote Link to comment Share on other sites More sharing options...
heffergm Posted December 9, 2018 Report Share Posted December 9, 2018 Had someone local with a similar problem I think, turned out to be ignition. If you could swap with someone that would be the cheapest way to confirm. Quote Link to comment Share on other sites More sharing options...
leembarnes Posted December 9, 2018 Author Report Share Posted December 9, 2018 1 hour ago, heffergm said: Had someone local with a similar problem I think, turned out to be ignition. If you could swap with someone that would be the cheapest way to confirm. Thanks going to try a new cap first and then work back towards the stator. A friend has a different cdi unit so that's useful! 1 Quote Link to comment Share on other sites More sharing options...
lineaway Posted December 9, 2018 Report Share Posted December 9, 2018 It could not hurt to unplug all connections and double check all grounds. Quote Link to comment Share on other sites More sharing options...
2stroke4stroke Posted December 9, 2018 Report Share Posted December 9, 2018 I'd be checking the Woodruff key. Quote Link to comment Share on other sites More sharing options...
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