terrywaker Posted March 20, 2015 Share Posted March 20, 2015 Hi! I'm new to the forum (literally just joined!) but have found the various posts here really useful for fixing bits on my Virago XV 125. I have one problem which I am struggling to solve however, and I can't seem to find much information on it, although please correct me if I am wrong. There's a few symptoms and all are pretty intermittent, worse on some days and better on others: When riding the bike and coming towards a junction/roundabout/etc I clutch in, change down a gear, give it some throttle...but there is suddenly no revs (this is even before letting the clutch out). It literally just does nothing for about a second, then it'll spring to life, however it is not smooth. Please note that the engine does not stall during this time, it just idles, as if I'm not on the throttle. On it's bad days I struggle to get the top speed over about 35/40mph. Regardless of gear. The acceleration is also quite jerky (not too much, but it's noticeable that it's getting some power, losing some power, getting some power again, etc). On it's good days I've had it up around the 60mph mark and it still wants to climb! (I've only recently bought the bike and haven't had a chance to actually find out the top speed yet, although I'm pretty sure that's close!) I have already put a new throttle cable on it. The bike seems to idle just fine and will rev up ok just sitting on the drive in neutral. I did notice that it takes a little while for revs to die down if I rev it up, about 2-3 seconds to return to idle revs after letting go of the throttle...I don't know if this is normal, just something I noticed. Any ideas as to a solution would be very much appreciated! I don't really know where to start with this one. Thanks so much in advanced. Terry Link to comment Share on other sites More sharing options...
iandouglas Posted March 20, 2015 Share Posted March 20, 2015 Well I am no mechanic but I would start with checking out the free movement of the throttle grip, on my bike I simply take off the bar end stop and loose the cable housing, it should run free and spring back - worth a bit of a greasing maybe. I guess nothing is sticking at the other end, injection or carb there should be unrestricted movement, you seem to have eliminated cable issues, cables do not like ties much unless they are a loose fit. Link to comment Share on other sites More sharing options...
slice Posted March 20, 2015 Share Posted March 20, 2015 Have you checked the inline filter to the carb from the tank, that can give you jerky throttle if it's blocked, some you can blow clear others you have to change. Sounds like a throttle come fuel problem to me, might also be a blockage in the carb body itself, when was it last cleaned? Link to comment Share on other sites More sharing options...
terrywaker Posted March 20, 2015 Author Share Posted March 20, 2015 Thank you both for your replies. Throttle grip is unrestricted and moving as should be. Cable is not tied and takes its own natural route so it is not obstructed in any way. I have not checked the inline filter, will make that my first move. Don't know when the carb was last cleaned, however will be removing this very soon to change jets and air/fuel mixture so will be able to tell if it needs cleaning then. Will let you know how I get on. Thanks again! Link to comment Share on other sites More sharing options...
iandouglas Posted March 20, 2015 Share Posted March 20, 2015 Do not suppose you are near me, 15 miles east of Oxford? I know a fab motorbike fixer guy who does not charge a lot. Link to comment Share on other sites More sharing options...
neversaydie Posted March 20, 2015 Share Posted March 20, 2015 Check that the choke cable is set and working ok Inspect the carb rubber for cracks/splits etc Check the spark plugs for gap and cleanliness, not loose in the threads 1 Link to comment Share on other sites More sharing options...
Variomatic Posted March 21, 2015 Share Posted March 21, 2015 Sounds like it's bogging and not climbing properly, maybe a dead air filter, maybe a blocked fuel line, green death (gunk that apears when petrol goes bad after sitting for a while) built up in the jets, worn out plugs. Lot's of possible things. Just methodically work through stuff people have listed that sound like possible causes. Or just pay out and take it to a mechanic. Link to comment Share on other sites More sharing options...
terrywaker Posted March 22, 2015 Author Share Posted March 22, 2015 I'm based in Basildon, Essex so a little too far from your guy, but thanks anyway! Choke cable is functional and behaving as should be. Spark plugs are brand new, but will check colour, cleanliness, etc. I'm going to have the tank off this week and pull out the carb. Will be able to assess the cleanliness of it and the others bits that were mentioned and most likely be taking it for an ultrasonic clean. Thank you all for the suggestion, it really helps! Will let you know how I get on. Terry Link to comment Share on other sites More sharing options...
neversaydie Posted March 22, 2015 Share Posted March 22, 2015 Always eliminate the cheapest and easiest options first. Carb work is not the easiest stuff to undertake for a beginner Link to comment Share on other sites More sharing options...
pignapper Posted March 23, 2015 Share Posted March 23, 2015 Hi. Id favour the idea of the carb. Look how the throttle works inside the carb. What happens inside the carb when you twist the throttle and then make sure that all is clean and not sticking. Dont forget to tell us when you find out. We love to know and learn. Stay safe. Link to comment Share on other sites More sharing options...
terrywaker Posted March 23, 2015 Author Share Posted March 23, 2015 I had the carb out yesterday and I think we've found the potential problem. The big rubber seal connecting the frame (air box) to the carb intake has gone hard, wasn't sitting very well at all and is missing it's jubilee clip. Came to the conclusion that this may be the cause as it would make the bike run very lean (something that someone had already suggested it sounded like). Have ordered a replacement rubber seal and clip which is on special order so will take a couple of weeks to get this and put on the bike. I have also sent the carb away for an ultrasonic clean and to be fitted with new jets. It didn't look too bad in there, but it can only help. Throttle valve seems to be functioning properly. I can't actually get into the inline fuel filter at the moment, the screws are like cheese (due to age) and just round off no matter how skilled with a screwdriver you are, will see if the above solves the problem before fiddling around trying to open it. I'll let you know how I get on with the replacement parts and carb cleaning/new jets. Thank you all for your suggestions! 1 Link to comment Share on other sites More sharing options...
terrywaker Posted April 15, 2015 Author Share Posted April 15, 2015 UPDATE So a lot of things have been changed on the bike and as a whole she seems to be running a lot sweeter, but I still have a problem. The bike starts really quickly and idles great, but when I twist the throttle the bike hesitates and struggle to get past a certain RPM (Unknown as there is no RPM dial!) and will either stall or can take up to 30 seconds for it to give me a window to get the revs up and past that point. When I'm past that point and going forward in gear then it runs absolutely beautifully. It has loads of pulling power, gearing is great and the plugs are a perfect beige colour. It's quick in accelerating and has a pretty decent top speed on it too. It's just this hesitant RPM spot that is causing me big issues. When I pull up to a roundabout or junction it's pot luck whether it'll rev up or give me nothing and want to stall. Things I have changed: New exhaust (a lot more freeflowing, but still silenced/baffled) Super sonic cleaned and re-jetted carb Slightly harder (I think?) piston spring Modified (opened up) air box Oil flush/change and new oil filter New throttle cable New rubber seal between airbox/frame to carb (as old one was brittle, had shrunk and wasn't making a good connection) I'm really struggling to find the solution. As I've said before when it's past that hesitant spot it rides perfectly, air/fuel mixture seems just right, idle screw is set nicely, things are clean and pipes are clear.... Has anyone had this problem? I will surrender and take it to an engineer very soon, but just wanted to put one last feeler out there to see if anyone had any last suggestions? Thanks so much everyone! Link to comment Share on other sites More sharing options...
KevtheRev Posted April 16, 2015 Share Posted April 16, 2015 Try un-modifying the airbox and make sure the jetting is back to standard before you go shelling out any dosh . From what I've read this seems to be a fuelling problem . Link to comment Share on other sites More sharing options...
terrywaker Posted April 16, 2015 Author Share Posted April 16, 2015 Thanks for your reply. Taking the air box back to standard makes the bike run very rich and makes no difference to the hesitant throttle. I have however found what seems to be the problem. The accelerator pump plunger is very sticky and is getting stuck after it's been pressed down. This would indeed cause the problem that I have detailed. My next question is what is causing it and how to fix it? I have copper greased the plunger inside and out which made it much better, however fuel enter the plunger chamber and cleared the copper grease away (don't worry I checked to see if it's ok to use on engines before doing this!) and got stuck again. Momentarily the problem seemed to be improving however. The plunger/rod itself is in good condition and the carb has been cleaned and all passageways are clear. Next step we filed down the end of the plunger ever so slightly as it only gets stuck right at the very end of its push and it seems to be functioning better but I haven't had chance to run it yet. What would be causing this to stick? Has anyone had this problem? Do you think a replacement plunger would solve this? Thanks! So neatly there with it! Link to comment Share on other sites More sharing options...
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