Hi guys anyone any pointers on this, had the bike a few years now doesn't get used a great deal but she's never missed a beat but Wednesday night ended up being stuck in traffic and she got very hot ( 2 o'clock on the dial) almost immediately she started to misfire what seemed like 1 pot cutting in & out. With no load on the motor she revved up fine but as soon as I'd set off she'd judder and stutter pretty much unridable. Let her cool down for an hour and she was fine until temp got back up to 12 o'clock and then it would start again. Checked the plugs they looked fine replaced them anyway but it hasn't cured it, went on the run to Buxton today all was ok till she got up to temperature and it started again
I see you are having as much success getting a sensible answer as I did with the 916 misfire. :Sour: I'd suggest you might have a failing coil stick with the internal insulation breaking down under load once it gets warm.
Cheers Derek, I haven't got a wiring diagram for the 748 just this rear loom image, do you mean #29 the HT part after the coil or the feed to the coil & does this come directly from the ECU. On the 998 it comes directly from the ECU but it's completely different.
Sorry I was thinking 749 for some reason Either way it still seems like a an ignition problem. It could be a coil (#7) or a plug lead (#27) or even possibly a plug. If you can identify which cylinder is going off, try swapping the coils round and see if the fault changes to the other cylinder. Similarly, try swapping the plug leads. Only change one thing at a time so that here is no confusion about what's happening.
Yeah suppose it's just a process of elimination she's been cast to the back of the garage under a sheet for a couple of weeks to reason over her bad behaviour :Grumpy:
?? I never got an answer from my reply containing a relevant and sensible question.. "I'd suggest you might have a failing coil stick with the internal insulation breaking down under load once it gets warm." pot?.. kettle?...
Sorry Chris got asked the same question on the other forum & forgot to answer both, yeah tested the fan and it kicks in exactly as expected, gonna swap a few cables around, I've got another coolant sensor I can put in & stick the standard chip back in as I've heard the foreign aftermarket ones can fail. Also got the chance of borrowing another ECU
It's worth a careful study of spark plugs and even checking colour at exhaust exit in case it's running weak. As you said, the chip plays an important part here if you have free-er flowing air filter plus cored/unbaffled exhausts. I have heard of partially failing water pump causing overheating usually only showing up in hot weather but would be better to research this for more accuracy. Many other reasons possible but it's worth exploring all options of course.
Plugs were the first thing I checked, they looked fine but changed them anyway didn't make a difference, open Termis JHP filter & aftermarket chip & she'd been running perfectly for 18 months or so. She isn't overheating as such just starts missing/bogging down/running on one cylinder when she does get hot.
Had a near identical scenario on a SPS a few years ago. It was the TPS unit suffering from heat soak and causing it to short out. Cooled the bike down and all was well again.
I get it now, i'd taken the title literally. I don't know what 2 oclock on the dial equates to but if the fan cuts in and importantly also turns off during running particularly while idling then it's generally ok temperature-wise.
I don't get that Chris I'm not in the habit of posting unnecessary garbage which is pointless and annoying to the person asking the question and looking for some help. I'd mistakenly thought the bike was a 749 which uses coil sticks on each head. In fact it's a 748 with separate coils but the same could apply as I posted subsequently.
Toby, I had a similar problem, it only occured in town on hot days. Started by missing on one cylinder, then dropped both within 1/2 a mile and would not pull on restart until it had cooled down. Turned out to be the atmospheric pressure sensor (next the steering damper). The rubber plug cover had perished where it is folded back on itself allowing water into the the sensor connector socket. When the bike is on the side stand the water sits in the socket and causes the contacts on two of the three pins to corrode. Cleaning the pins fixed it but I had a new one fitted during a Louigi Moto service as the ecu recorded a fault and I wanted piece of mind. Pull the plug and look for white on the contacts. High resistance on the contacts has quite an effect on the mixture and when sensor gets hot the sensor can go out of range and drastically effect the duration of the injection pulse. It does not necessarily flag a fault in the ecu
