Jeremiah+Josh Posted June 16, 2011 Share Posted June 16, 2011 Hi I am very frustrated but i do see the funny side of this ... well i have built rebuilt a few bikes ever but this f****** is taken me to hell well two of em now cos i bought another will not run proper nor will the other will start on one cylinder then other wont run ... ahh you say .... no I say cos it could start on the opposite then the one that was running previously wont run so far checked points gap good timed and retimed and some more then fitten new conatcts timed timed again coils tried loads of different coils new condeser so i figured it the engine so i buy another basket case xs250 swap engine same thing contacts timed retimed take off check advance all good time retime check time a again Carbs been to cleaned with ultra sound have two other sets of carbs that do the same thing go figure as i type son is changing the exhaust system with air filters on it will not start at all take filters off and block pipes and she makes an effort .... thats the only significent data i can present HAS any One please got any ideas at all Jez going Mad Link to comment Share on other sites More sharing options...
Jeremiah+Josh Posted June 16, 2011 Author Share Posted June 16, 2011 Ohh forgot compression tested 100psi inlet and outlets done set... Link to comment Share on other sites More sharing options...
blackhat250 Posted June 16, 2011 Share Posted June 16, 2011 Well jermiah " you"l be the only thing an XS250 has ever beaten , ,,,,,, On a positive side Drewpy , the Y.O.C. Xs wizard will Be along with some suggestions, sounds like you"v covered everythin tho Link to comment Share on other sites More sharing options...
Moderator drewpy Posted June 16, 2011 Moderator Share Posted June 16, 2011 I'm here... well what do you mean by not running proper? that could mean anything if you can described exactly what the bike is doing/sounding and revs etc i will be able to help you! 100psi is not good, its usually 140 psi the xs's are bloody funny with carbs, if they are not really really clean, and I mean stripped down and ALL orifices blown through and clear you will have issues. float height need to be spot on (26mm) checked your idle mix tips? bet they are broken off in the carb body (lucky if not) Link to comment Share on other sites More sharing options...
Jeremiah+Josh Posted June 17, 2011 Author Share Posted June 17, 2011 Hi Bit more "un-frustrated" this morning late last night after posting we did notice that when she tried to start on the right it was not as strong as when she tried to start on the left we swapped coils and got same result so i tried another coil on right .. and now it does try and start on both cylinders Current status tries to start on both cylinders sound possibly missing wont respond to throttle best its run for with out starter turning is about 5 secs to start last night i had to remove air-box and block/restrict intakes once firing a bit i put air-boxes it the would continue to start ...choke on to start after a while it doesn't like it but still wont start .. Carbs they have been ultra sonicily cleaned ... it made little or no difference i have 2 other sets of carb's they have the same result ... same symptoms ... I have put a new condenser on made no diff Points I have gapped and timed using a light bulb timed to the first mark after LF ... I will say that i found this a bastard of a job as the timing wondered as re-tightening screws but they seem to be on the mark now I am thinking of the fag paper method but the hassle last time to get them spot on is putting me off atu bob weights seem too be free TODAY i will try putting old condenser back on some original exhausts and brand new coils if they arrive in the post Jez Link to comment Share on other sites More sharing options...
Jeremiah+Josh Posted June 17, 2011 Author Share Posted June 17, 2011 coils arrived ..... single wire wrong ones .... and i did tell the guy points in fact i ordered new points at the same time Link to comment Share on other sites More sharing options...
KirriePete Posted June 17, 2011 Share Posted June 17, 2011 Kill it! Kill it with fire! Then pour Holy Water on the ashes. I had an XS250 for just under a year many moons ago - I still get nightmares ... Safe to say it wasn't Yamaha's finest hour ..... Link to comment Share on other sites More sharing options...
Jeremiah+Josh Posted June 17, 2011 Author Share Posted June 17, 2011 tried other carbs back to one cylinder (right) unable to get left firing so took carbs off cleaned left one blew out pilot jets and airways examined needles (tips look to be there) set them at three turns out from full in now nothing will fire yes .. it has spark ... i have restored bsa's that people pulled apart in the fiftys and left outside ... and a sr500 that lay in a hedge for twenty years ... this pile of **** defies all logic Link to comment Share on other sites More sharing options...
Moderator drewpy Posted June 17, 2011 Moderator Share Posted June 17, 2011 tried other carbs back to one cylinder (right) unable to get left firing so took carbs off cleaned left one blew out pilot jets and airways examined needles (tips look to be there) set them at three turns out from full in now nothing will fire yes .. it has spark ... i have restored bsa's that people pulled apart in the fiftys and left outside ... and a sr500 that lay in a hedge for twenty years ... this pile of **** defies all logic vacuum barbs on manifold still got its cap on and the pipe to the pet cap ok? Link to comment Share on other sites More sharing options...
Jeremiah+Josh Posted June 17, 2011 Author Share Posted June 17, 2011 yeah 1 has cap other goes to petcock whilst turning engine over with petcock in postion on or reserve petrol comes out prime just dumps fuel so all ok and fuel cap open closed make no difference i have even tried swapping cap and line about ... from one intake rubber t' other re done compression test ... its not a very great tester its a cheapo am-tech i have borrowed and its hard to deduce the fast flickering needle but its hitting 125 psi as best i can see ... Jez Link to comment Share on other sites More sharing options...
JimR Posted June 17, 2011 Share Posted June 17, 2011 Hi Bit more "un-frustrated" this morning late last night after posting we did notice that when she tried to start on the right it was not as strong as when she tried to start on the left we swapped coils and got same result so i tried another coil on right .. and now it does try and start on both cylinders Current status tries to start on both cylinders sound possibly missing wont respond to throttle best its run for with out starter turning is about 5 secs to start last night i had to remove air-box and block/restrict intakes once firing a bit i put air-boxes it the would continue to start ...choke on to start after a while it doesn't like it but still wont start .. Carbs they have been ultra sonicily cleaned ... it made little or no difference i have 2 other sets of carb's they have the same result ... same symptoms ... I have put a new condenser on made no diff Points I have gapped and timed using a light bulb timed to the first mark after LF ... I will say that i found this a bastard of a job as the timing wondered as re-tightening screws but they seem to be on the mark now I am thinking of the fag paper method but the hassle last time to get them spot on is putting me off atu bob weights seem too be free TODAY i will try putting old condenser back on some original exhausts and brand new coils if they arrive in the post Jez hmm had loads of XS250's do this with various causes from the training I received in the early 80's I'll give you the diagnosis path Compression check wet/dry out of spec Remove Cylinder head check valves for leakage check bores pistons & rings for wear in spec adjust valve clearances to the correct values set the dwell angle to 22.5 % set the ignition timing (with strobe) to LF (left cylinder) RF (right cylinder) Always start with the L/H cylinder when sat on the bike Ignition timing & dwell are set at the same time you may set the dwell correct then adjust the timing which will then set the dwell to an incorrect value.... reset the dwell then recheck the timing keep doing this until you have the dwell and timing right check the advance for both cylinders (between the | | marks) adjust the mixture screws for a steady idle (some engines require the mixture screws to be set well away from the default 1.5 turns out) check/adjust carb balance Still running badly check inlet manifolds for leakage the rubber o ring within the paper gasket can fail (you will see the 'gas track' across the paper section of the gasket) if OK check the diaphrams for splits. with a diaphram split this can give you a false reading when balancing the carbs so if you have a split you will have to do a re balance if this doesn't fix it post up again Link to comment Share on other sites More sharing options...
Jeremiah+Josh Posted June 17, 2011 Author Share Posted June 17, 2011 hmm had loads of XS250's do this with various causes from the training I received in the early 80's I'll give you the diagnosis path Compression check wet/dry out of spec Remove Cylinder head check valves for leakage check bores pistons & rings for wear in spec adjust valve clearances to the correct values set the dwell angle to 22.5 % set the ignition timing (with strobe) to LF (left cylinder) RF (right cylinder) Always start with the L/H cylinder when sat on the bike Ignition timing & dwell are set at the same time you may set the dwell correct then adjust the timing which will then set the dwell to an incorrect value.... reset the dwell then recheck the timing keep doing this until you have the dwell and timing right check the advance for both cylinders (between the | | marks) adjust the mixture screws for a steady idle (some engines require the mixture screws to be set well away from the default 1.5 turns out) check/adjust carb balance Still running badly check inlet manifolds for leakage the rubber o ring within the paper gasket can fail (you will see the 'gas track' across the paper section of the gasket) if OK check the diaphrams for splits. with a diaphram split this can give you a false reading when balancing the carbs so if you have a split you will have to do a re balance if this doesn't fix it post up again Ok right whats the ?? dwell ?? and whats the compression spec Thanks for the input Link to comment Share on other sites More sharing options...
Jeremiah+Josh Posted June 17, 2011 Author Share Posted June 17, 2011 Ok out of intrest today (and the fact i cant seem to leaver the ****** alone we slapped a mikuni vm34 round slide carb jetted for sr500 single on mr left cylinder no throttle cable just carb choke fired after three seconds started to splutter & run on one cylinder choke off adjusting throttle stop i managed various degrees of succses and run on one cylinder for around 30 secs didnt have time after to try right cylinder .... carbs stripped again will rebuild next week off for the week end Jez Link to comment Share on other sites More sharing options...
Jeremiah+Josh Posted June 22, 2011 Author Share Posted June 22, 2011 Just some of the latest here Dwell is Points Gap (new one on me) any way that's all good I chucked a Mikuni vm34 (Jetted for a SR 500) on the left cylinder and with some fiddling it runs well and starts easily it will tick over very nice and not cut out miss or fart at all running one cylinder the plug looks nice too nice tan color repeated the process on right cylinder all good runs ticks over nice looking plug so its the CARBS back too them stripped again blew out pilot holes and set floats (they were previously ultra-sonicly cleaned back on same shit fires up now on two cylinders wont run for long it is missing and generally running very rough wont respond to throttle what i have noticed is no matter where i put the mixture screws it makes no differance (I have even removed them) i cant work out where the problem could be could it be between the float bowls and and main body there is a gasket there that looks very good the tips of the mixture screws look ok under scope seriously considering getting some 42 mm copper pipe and fabricating a 2:1 manifold Jez Link to comment Share on other sites More sharing options...
Moderator drewpy Posted June 22, 2011 Moderator Share Posted June 22, 2011 Dwell is Points Gap (new one on me) any way that's all good Not quite, dwell is the time the points are closed,so its the opposite. so its the CARBS back too them stripped again blew out pilot holes and set floats (they were previously ultra-sonicly cleaned back on same shit fires up now on two cylinders wont run for long it is missing and generally running very rough wont respond to throttle what i have noticed is no matter where i put the mixture screws it makes no differance (I have even removed them) i cant work out where the problem could be told you these carbs are finicky, are you really sure those tips have not broken off, can you see daylight with the carbs off and mix screw out? the only other thing is the float bowl has a fuel run and it did take me a while to ungunge it using compressed air, solvents etc. drewps Link to comment Share on other sites More sharing options...
Jeremiah+Josh Posted June 22, 2011 Author Share Posted June 22, 2011 Not quite, dwell is the time the points are closed,so its the opposite. Ahh yes sorry when i researched "Dwell" i came away thinking it meant the time closed ... but the smaller the gap the less time closed = less power charged in the coil .. ????? told you these carbs are finicky, are you really sure those tips have not broken off, can you see daylight with the carbs off and mix screw out? Yes you did i did believe but cant see how to get them cleaner but it will be somewhere something ... The crux is three sets of carbs with the same or similar symptons . However we now know ignition is tip top .. Personaly when i have a doubt i keep going back. I looked at mix screw through a jewelers eye piece had blunt end but we concluded that should be the case however ... Ive only seen old ones Ill take em off tonight and have a look see for daylight and get back on that one. the only other thing is the float bowl has a fuel run and it did take me a while to ungunge it using compressed air, solvents etc. drewps bowl is deffo ok but will check again Thanks for replying Jez Link to comment Share on other sites More sharing options...
Moderator drewpy Posted June 22, 2011 Moderator Share Posted June 22, 2011 Ahh yes sorry when i researched "Dwell" i came away thinking it meant the time closed ... but the smaller the gap the less time closed = less power charged in the coil .. ????? it is the amount of "time" ie degrees angle over the circumference of the shaft the contacts are closed. This charges up the primary coil and when the points open, the electricity has built up so much in there that is inducts into the seconary and through the spark plug jumping the gap. the more the coils are energised the fatter the spark. Link to comment Share on other sites More sharing options...
Jeremiah+Josh Posted June 22, 2011 Author Share Posted June 22, 2011 some weird shit tonight started mixing up carbs made up a new set slapped em on it was running a treat on the right cylinder made up a new left no luck made last left no luck right going well though split carbs put right carb on left left ran fine put a left carb on left left ran fine ??? put these together no right put a marked good right on right no right got totaly mixed up now suspect we burning plugs out but i think we are close Link to comment Share on other sites More sharing options...
Moderator drewpy Posted June 23, 2011 Moderator Share Posted June 23, 2011 thank god for that, can't wait to see this problem sorted Link to comment Share on other sites More sharing options...
Jeremiah+Josh Posted June 23, 2011 Author Share Posted June 23, 2011 it is the amount of "time" ie degrees angle over the circumference of the shaft the contacts are closed. This charges up the primary coil and when the points open, the electricity has built up so much in there that is inducts into the seconary and through the spark plug jumping the gap. the more the coils are energised the fatter the spark. VERY well put and now easily understandable I wonder if it is connected to today's anomaly XS 250 now starts well and ticks over well tick over ATM a little fast but sounds a lot better and it stays alive it does try and respond to throttle but it ain't great but well .... Hey one thing at a time Now the plugs that came with the bike(s) all six in fact were set to or near to what it says in the Haynes 0.7 mm last night i thought i was getting close but all the plugs seemed to need constant attention apart from one when i examined it this morning it had a smaller gap (possibly dropped) i measured it at 0.4 mm set the others to that and hey presto ... intial prob's gone and bike starts and ticks over well.. Is Haynes wrong >>>>AGAIN.. or is there something more sinister ... Possibly related to dwell ...gap set to smallest in Haynes book 'O' lies 0.3 thanks for the input Drew look forward to your thoughts Jez Link to comment Share on other sites More sharing options...
Recommended Posts