vfiend Posted April 11, 2009 Report Share Posted April 11, 2009 '97 VFR 750 41,000 miles Intermittent loss of power, front left cylinder not firing (checked exhaust temperatures). Had this prob few months back and put it down to poor fuel as it disappeared after running it down and refilling elsewhere. Now doing it again (for the last tank and a half) so; drained the carbs and fitted new plugs in (it appears the previous owner never changed the front plugs, only ever bothered with the back! The new plugs did however gave a noticeable performance change when running on all four.) Any experience on this problem? 2 routes are electrical or carbs. The problem is worse when the bikes warmed up and the problem has cleared itself if I bring the clutch in and red line it (carbs?). This could be coincidental and the performance can still dip even at constant high revs (140 in 5th). However, I do ride the bike every single day no-matter what the weather, so it could easily be some green wire or plugcap/HT giving up the ghost. Any help / info would be much appreciated. (Also I've checked the throttle / choke are operating correctly and smoothly, the fuel filter is squeaky clean) Link to comment Share on other sites More sharing options...
rc30rob Posted April 11, 2009 Report Share Posted April 11, 2009 have you checked the valve clearances ,reason being ,it cant be electrical as the corrosponding cylinder of that coil would also play up (unless its lead ,cap or plug )it may be carb .check for muck in it and float hight if it plays up when hot what little fuel is in the carb may be evaporating or running out .More likely the shims on that cylinder may be too big as the valve pockets into the head slightly which then means you are loosing compression as the valve andshim expand wih heat it will become worse hope that helps Link to comment Share on other sites More sharing options...
lorenzo Posted April 12, 2009 Report Share Posted April 12, 2009 it cant be electrical as the corrosponding cylinder of that coil would also play up I'm not sure about this: are coils shared on a vfr750? My 800 wasn't, it had 4 coils, I guess because the crank on a normal VFR isn't big bang like on an RC or NC30. If they do have 4 coils, I'd swap them round and see if it follows the coil or not. Link to comment Share on other sites More sharing options...
rc30rob Posted April 12, 2009 Report Share Posted April 12, 2009 I'm not sure about this: are coils shared on a vfr750? My 800 wasn't, it had 4 coils, I guess because the crank on a normal VFR isn't big bang like on an RC or NC30. If they do have 4 coils, I'd swap them round and see if it follows the coil or not. mmmm not sure how many coils they have you may have a point Link to comment Share on other sites More sharing options...
stretch Posted April 13, 2009 Report Share Posted April 13, 2009 individual plug/spark test? Link to comment Share on other sites More sharing options...
ssray Posted April 13, 2009 Report Share Posted April 13, 2009 It has 4 coils swap one over. Ray Link to comment Share on other sites More sharing options...
deviant Posted April 15, 2009 Report Share Posted April 15, 2009 750 running on three? Maybe it's got FI Link to comment Share on other sites More sharing options...
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