Hi VFR worlders, I have this problem with my VFR 750 1993 model that is driving me crazy. It started about 2 months ago, the bike was running fine but as I had never changed the spark plugs I thought that it would a good idea to do this. I decided on using Iridium plugs. So me and a mate put these plugs. From that moment I have had this problem that I would describe as a missfire......it feels like the bike is running out of petrol but only when you have it on a steady throttle....5800 to 6100 is the worst spot. Under hard acceleration the bike revs out fine and it also idles perfectly. In fact if you are running around town and constantly changing throttle positions the bike is perfect but as soon as you are on a perfectly steady throttle it shows up. It also shows up at each gear change when you are revving it out.....there is just this moment of hesitation after the gear change. OK to help solve it we thought of the obvious things first. That being tension leads. These have been replaced. No difference. THen we thought that the 5 ohm resistor in the caps of the spark plugs may have broken.....especially on the front as these may have not come of in years......so I replaced the caps......still the problem is there. OK what about coils. Can coils go of just a bit??? Either way I was reluctant to replace all 4.....so I bought 2 new coils. I replaced the easiest ones to get at first, the ones that you can easily see when you remove the side covers, no change in the problem......so then I put the news on the most arkward ones.....so in other words each piston has had a go at having a new coil.
You threw alot of parts at the problem, but seems you never tried switching back to original plugs, which were running fine. BTW, the resistor caps are 25,000 ohms, not 5.
I'm very unqualified to chime in but I would buy another set of plugs and replace the plugs. Even new parts can be defective.
Yes I forgot to mention that I went back to original plugs after putting in the high tension leads, but the problem is still there. thanks for replying. anymore ideas. regards Dex
This one's tough. Following an air filter inspection, how about seeing if a good carb clean and adjustment solves the problem?
The symptom does sound more likely fuel than ignition. Spark plug change may just have been coincidence?
