BadHarry1942 Posted September 5, 2016 Share Posted September 5, 2016 Hi all names Brian and new here. 4 weeks I bought my bike which ran fine for some time and then suddenly I have this strange issue, Hope you can help with my problem. My Neos 50cc YN50 has started to bog down and go around 10-20mph when it use to top 40. I went out one day then on the way back bog down. I thought this may be rollers so changed the variator and snapped the crankshaft, so total engine rebuild but problem is still there. So new engine, crankshaft, piston, head, variator, clutch, springs all good as is the belt. Engine pressure 170psi. Carbs cleaned and also swapped to be sure. Fuel supply good, no air leaks as best I can tell, also checked the fuel cap breather. Plug is good also swapped that still Good. Put the bike on the stand and it will start with one kick and tick over nicely. Turn the throttle and it will go like hell, no problem there. Get on and ride it,,, 10-20mph,!!!! Tried removing exhaust, checked air filter all good. All I can now think of is HT lead\coil, did a resistance test and seems ok, as I say runs like hell in the stand. Then there's the Stator and the CDI.. not sure what to do here. What am I missing? Any pointers please because this it driving me nuts. Thanks, PS. Bike is 2015. Just to add, if you have a long straight the bike will get to 20mph ok and then slowly slowly will make its way to about 35mph, but I do mean slowly. Link to comment Share on other sites More sharing options...
slice Posted September 5, 2016 Share Posted September 5, 2016 Hi Harry, welcome to the YOC. Sorry to hear about your problem mate, just a suggestion tho, you have no electrical problems as it starts and runs so it's almost certainly a fuel air mix problem, you seem to have fixed all the other things it might be so that only really leaves the fuel. Not sure with these bikes if they have crank seals cos some of the lads on here say that crank seals can give this type of problem, usually when they bog down like this it's to much air so check for leaks around the whole of the inlet side of the fuel system, good luck mate. Link to comment Share on other sites More sharing options...
blackhat250 Posted September 5, 2016 Share Posted September 5, 2016 you"ve 170 psi , well that's good compression , I would try another carb, just to eliminate this, ,as it sounds lik fuel related , , Also, start a thread in workshop, as replies to this will domineer the newbee section , Link to comment Share on other sites More sharing options...
BadHarry1942 Posted September 5, 2016 Author Share Posted September 5, 2016 Black hat. Thanks for the reply but I have already tried another carb from another bike. They both have the same effect and both work in the other bike so I have ruled that out. Link to comment Share on other sites More sharing options...
BadHarry1942 Posted September 5, 2016 Author Share Posted September 5, 2016 Slice, thanks for your input. Will do a thorough air leak test and maybe change that tapcock. It will be a new bike by then. Plenty of spares, lol. Link to comment Share on other sites More sharing options...
BadHarry1942 Posted September 10, 2016 Author Share Posted September 10, 2016 Guys, thanks for the help so far. Checked for leaks can't find any that I can tell. Sprayed carb cleaner around and listened for engine change, no joy. Plan to change belt and spring next week. However one thing I just picked up on. When it's on the stand it appears to run full belt BUT if I open the throttle fully the bike revs to say 3000 rpm and the is defo a pause for a second or so before it fly's on up the revs. Any further thoughts. Cheers Sent from my SHIELD Tablet using Tapatalk Link to comment Share on other sites More sharing options...
anyoldiron Posted September 11, 2016 Share Posted September 11, 2016 When you said ''tried moving exhaust'' what exactly did you do? lf there is a removable baffle try running it briefly without, sometimes the exhausts can get fouled up wont run right with way too much backpressure. Link to comment Share on other sites More sharing options...
BadHarry1942 Posted September 11, 2016 Author Share Posted September 11, 2016 I removed the exhaust from the engine, no joy also removed the final part of the exhaust again no joy. I do think it's something to do with the mixture. Took it out today after belt change and still doing the same. Took it on a long road and when it eventually got to 30 it shot up to 40 and cut out as if cutting the fuel line. Pulled over and started again with one kick. Got to be the mixture. Will have another look on Tuesday. Link to comment Share on other sites More sharing options...
slice Posted September 12, 2016 Share Posted September 12, 2016 It does sound like a fuel blockage or something to do with fuel, that sudden surge might suggest that the fuel filter is blocked or the tank filter is bunged up, might be worth cleaning all the pipes and filters out just to be sure. Just remembered something that happened on the XJ, it would run fine till it got hot then spit and fart till it stopped then when it cooled down it was fine, it was the rubber fuel pipe collapsing with the pressure from the heat and draw from the carb. Just a thought? Link to comment Share on other sites More sharing options...
BadHarry1942 Posted October 9, 2016 Author Share Posted October 9, 2016 **** Update - it was the Bloody Vacuum pipe. Can sleep now...... Sent from my SHIELD Tablet using Tapatalk 1 Link to comment Share on other sites More sharing options...
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