danellie Posted October 4, 2018 Share Posted October 4, 2018 I have a 1981 XS250, the problem is the revs don't drop or drop very slowly when revved. It seems fine when first started but as soon as it starts to warm up the problem starts. I have thoroughly cleaned the carbs twice with air line without success, diaphragms are ok, it has good compression, timing good with good spark at the plugs. I fitted new manifold rubbers and can see no leaks elsewhere. Any suggestions will be much appreciated before I put a light to it. Cheers Link to comment Share on other sites More sharing options...
Moderator drewpy Posted October 4, 2018 Moderator Share Posted October 4, 2018 thoroughly cleaning carbs with air, is not thoroughly cleaning carbs. they need stripping completely and ultrasonic cleaning and poss replacing pilot jets if blocked. the issue is the galleries are so small, that air won't shift the fuel gunk collected over time 1 Link to comment Share on other sites More sharing options...
danellie Posted October 4, 2018 Author Share Posted October 4, 2018 Are you sure this is the problem?, the carbs have been completely stripped down, jets cleaned, settings checked. If I am sure ultrasonic cleaner would solve the problem I would buy one, which would you recommend?. Cheers Link to comment Share on other sites More sharing options...
NE0 Posted October 4, 2018 Share Posted October 4, 2018 Hi there, The trouble is with many DIY ultra sonic cleaners is their small size. You can get bigger ones but You'll need one to fit at least one carb if you want the internals cleaned properly so you would be looking at at least a 1 litre one. Having said that you might want to consider looking up ultrasonic cleaning services for motorbike carbs (often seen on ebay as a service). These guys can strip it down and reset them etc,I appreciate it won't be cheap but an industrial one will beat any home purchase one hands down. As drewpy says it's likely the internals which are blocked and often no amount of blowing with an airline will clear them. Petrol if left standing evaporates leaving behind a shelac like varnish which is unbelivably rock hard!! Link to comment Share on other sites More sharing options...
danellie Posted October 4, 2018 Author Share Posted October 4, 2018 (edited) Thanks for that, just can't understand why it runs fine until it gets warmed up??. When warm it takes probably 7-8 secs to die down, nearly stalls then settles to perfect idle. Edited October 4, 2018 by danellie Link to comment Share on other sites More sharing options...
NE0 Posted October 4, 2018 Share Posted October 4, 2018 (edited) I found this on our website....post no 8 states... ,when it is warm it still tends to be slow returning to idle. https://yamahaclub.com/forums/topic/26876-xs-250-running-issues/ may be of some help. Edited October 4, 2018 by NE0 Link to comment Share on other sites More sharing options...
danellie Posted October 5, 2018 Author Share Posted October 5, 2018 Yes I saw that post, didn't seem to get his problem sorted. I've been over everything I can think of over & over without result. very frustrating. Thanks. Link to comment Share on other sites More sharing options...
NE0 Posted October 5, 2018 Share Posted October 5, 2018 Just a thought but where abouts are you? (i dont mean publish your address) just the general area. Sometimes members are willing to come over and help. Link to comment Share on other sites More sharing options...
danellie Posted October 5, 2018 Author Share Posted October 5, 2018 Bridlington Link to comment Share on other sites More sharing options...
Moderator drewpy Posted October 6, 2018 Moderator Share Posted October 6, 2018 its usually the idle jets that get blocked. try opening up the mix screw which is near the manifold (anticlockwise) if it doesn't make a difference then professional cleaning is the way to go. I sent mine away to cornwall which cost £100 and i also sent new jets. this was back in 2006 so more expensive now. look in xs400.com and you can get an xs teeshirt with "clean them carbs", that's how notorious they are to get right 1 Link to comment Share on other sites More sharing options...
blackhat250 Posted October 9, 2018 Share Posted October 9, 2018 Brid" how does the XS250 pull up the Garroby Hill,,,, A166,,,,,,,,weve done it loads Link to comment Share on other sites More sharing options...
danellie Posted October 11, 2018 Author Share Posted October 11, 2018 Thanks for all your constructive replies. Have ordered a decent Ultrasonic cleaner & solution so hopefully it should be sorted. Link to comment Share on other sites More sharing options...
danellie Posted October 19, 2018 Author Share Posted October 19, 2018 Carbs have been ultrasonic cleaned repeatedly with heat and carb. solution, no difference. timing re-checked, auto advance checked. Any more suggestions guys?. Thanks Link to comment Share on other sites More sharing options...
NE0 Posted October 20, 2018 Share Posted October 20, 2018 (edited) Very frustrating for you indeed. Bear in mind the bottom line is it's likely to be either fuel/air or timing. That's all it can be. Afterall it's only a collection of moving parts which do nothing until they are moving! Effort is required to get them going and fuel/air and timing keep them going until you turn it off by stopping. Simplistic view yes but in essence that's all it is!! Having said that my ramblings here might help guide you ......or not! Fuel/air mixture: making it lean or rich effects speed and whilst the carb is set up to deliver that correct mixture leaks on the induction side can screw it up too. When things get hot they expand so what's air tight when cold can get exposed when hot!, and conversely the same happens when cold. Leaks occur when cold making it difficult to start until hot when the expansion swells and everything closes! Which is why it becomes difficult to trace any faults! You test when cold only to reveal the problem when hot OR you test when hot and miss it when it was cold.The same Tests need to be done both hot and cold. Checking for air leaks is tricky, you can't hear them like an air leak on a punctured tyre. Mix up some washing up liquid in warm water making it as bubbly as possible (cold water doesnt make bubbles so well) then with a 1/2 inch paint brush paint it quickly around any joints of the induction side, paying attention to any rubber connector, they can leak at the interface or anywhere along its rubber length. Paint it on around the head gasket and on two strokes, especially around the base gaskets of the engine. Work quickly because the heat of the engine will rapidly evaporate it all even more so when hot. Listen out for changes in the engine speed not so much for the sound of air leaks although you get a nice reaction in the bubbles when you stumble across the leak. And before anyone says don't spread soapy water around it could get in the engine, it's likely to be a pin hole not a bloody great crack! Timing: A collection of bits which controls the high voltage to ignite the aforementioned fuel air mixture! Opening contacts too big or too small effects the timing and a few thousands of an inch can change it dramatically as many of you old dinosaurs like me will know. Equally wear and tear can also play it's part and have the same effect. Points should be checked when cold because when hot everything expands and the reading might not be so accurate. Equally when hot, things can stick! and also stop things working efficiently, don't spread it all in grease thinking you're making things better; it could have the opposite effect. Minimal oil works best here. One area often neglected is any spring loaded advance and retard mechanism found behind the contact sets. The goveners (weights on springs) move with the engine speed and advance the ignition automatically and can stick when hot, especially when covered in grease and crap over time. Pay particular attention to keeping these clean and maintained especially the pivot points. If it all sticks here it may take a little time for the springs to pull everything back and return the timing to normal. Replace the springs for example if they are suspected to be worn (springs do wear out!) Some vehicles have a vacuum mechanism attached to the goveners( I'm talking old classic cars here)but these are connected to the carb which influences the fuel/air mixture. Leaks and blockages here will also effect the performance. You might already know a lot of this but there again it might help others who stumble on this thread in the distant future! Hopefully of some help. Edited October 20, 2018 by NE0 Link to comment Share on other sites More sharing options...
NE0 Posted October 20, 2018 Share Posted October 20, 2018 It's not something simple like the throttle slide sticking and not returning to its idle position is it? or the cable binding at a 'hot spot'? just a thought! Link to comment Share on other sites More sharing options...
danellie Posted October 20, 2018 Author Share Posted October 20, 2018 Thanks so much for your reply, it is so frustrating, I have checked over & over all the points you raised, timing, a/r system etc.. Just at a loss now, back to the drawing board. Regards Link to comment Share on other sites More sharing options...
NE0 Posted October 20, 2018 Share Posted October 20, 2018 Have you ruled out the throttle cable? Disconnect it at the carb and manually operate the throttle at the carb. Does it still have trouble returning to idle? At least that way it would rule out the cable completely. It doesn't rule out the throttle slide , just the cable. Link to comment Share on other sites More sharing options...
danellie Posted October 20, 2018 Author Share Posted October 20, 2018 Cable's fine, slides close correctly, I've had enough, at my age life's to short to waste on this. I will put it on classifieds for any member here before it goes on the bay. Link to comment Share on other sites More sharing options...
jimmy Posted October 20, 2018 Share Posted October 20, 2018 Just burn the fekker, in the end thats what you'll want to do anyway..................... Sorry mate, I had an xs250cw back in 1981 and I'm still hurting 1 Link to comment Share on other sites More sharing options...
danellie Posted October 21, 2018 Author Share Posted October 21, 2018 Yes it's a shame the bike is sound, recent tyres & battery. Just lost patience with it, needs a fresh mind. Cheers Link to comment Share on other sites More sharing options...
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