jones2007 Posted August 6, 2008 Share Posted August 6, 2008 i have a 1995 yamaha yzf750r, i have taken off the head to do the valve stem seals i put it back together with it timed up to the marks and i couldnt get to run so i moved the timing 180 degrees (thought i might have timed it wrong) and it run ok when cold but when i tried to ride it wouldnt run and when restarted wouldnt rev past 1500 rpm once it cooled down i restarted it and it sat and ticked over fine for half an hour or so (reved up fine) then i tried to ride and it died again then when restarted it repeated the previous symptoms what do you think the problem is ? thanks in advance Link to comment Share on other sites More sharing options...
billa65t Posted August 7, 2008 Share Posted August 7, 2008 Hi there, I take it that when you changed the timing your talking about the valve timing have you checked the ignition timing to make sure its firing on the compression stroke ? Link to comment Share on other sites More sharing options...
jones2007 Posted August 7, 2008 Author Share Posted August 7, 2008 Hi there, I take it that when you changed the timing your talking about the valve timing have you checked the ignition timing to make sure its firing on the compression stroke ? the ignition timing is unadjustable on it (i think) i have double checked the plug caps are in the right order so they are spot on, sorry i didnt say valve timing, still no further with it i have never come across a problem like it Link to comment Share on other sites More sharing options...
markf Posted August 28, 2008 Share Posted August 28, 2008 If the bike starts, idles, and revs then there is prob nothing much wrong with the valve timings. If it refuses to rev above a certain range but only under load, then it sounds more like a fuelling problem. I had similar problem with Suzuki GSX250 - it was a tiny tiny hole in a carb diaphragm. This causes the mixture to become too lean under load. It's less noticeable when cold as the choke compensates. However, can also be caused by lots of other things, such as blocked or kinked fuel pipe, dodgy fuel tap, blocked tank breather, etc. Link to comment Share on other sites More sharing options...
jones2007 Posted August 28, 2008 Author Share Posted August 28, 2008 If the bike starts, idles, and revs then there is prob nothing much wrong with the valve timings. If it refuses to rev above a certain range but only under load, then it sounds more like a fuelling problem. I had similar problem with Suzuki GSX250 - it was a tiny tiny hole in a carb diaphragm. This causes the mixture to become too lean under load. It's less noticeable when cold as the choke compensates. However, can also be caused by lots of other things, such as blocked or kinked fuel pipe, dodgy fuel tap, blocked tank breather, etc. thanks for the advice mate will strip the carbs and reinvestigate Link to comment Share on other sites More sharing options...
markf Posted August 28, 2008 Share Posted August 28, 2008 thanks for the advice mate will strip the carbs and reinvestigate Good luck. Suggest you check the other bits first simply because they're easier- open the tank cap to check there is no vacuum; make sure no fuel line kinks. If you have a vacuum gauge, this will give a clue as it won't be possible to get the affected carb balanced with the others, the symptom is similar to having an air leak in the inlet (which is another possibility, of course....). Make sure the carbs are mounted correctly and the inlet tract all the way from air filter to cyl head is airtight. If it is the diaphragm, I managed to repair mine, at least temporarily, by using a small dab of superglue. Link to comment Share on other sites More sharing options...
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