Reply To: GD250N – Hanging Revs and Stalling when Throttle opened quickly
What’s up again Hyoriders!
Got an update and asking for thoughts
Been quite happy with the bike so far!
Still handles very nice in the twisties we’ve got here! Nice torque to pull you up through hairpin turns!
The idle did trend upwards over the course of weeks. Diagnosed that to be some hidden parameter pushing up the value I manually set. So finally I decided to make a manual IACV adjuster using an idle adjuster cable and the carcass of the old broken IAC. This worked really well, and I’ve been able to adjust the air amount when necessary, getting the bike to idle really well at about 1800 when cold in most weather.
I did however notice that the bike started having issues when it got hot (before and after I replaced the IAC)
The fault is misfiring, this time even at higher rpms, but especially noticeable at low throttle in the transition between idle and gas. The bike jerks a little bit when it misses once, and the frequency of the misses roughly increases with temperature. Riding fast (60-120kph) It has never happened unless the engine was really hot right before. I was able to ride without problems for an hour on country roads and then around a half hour on the highway at quarter to full throttle at high to relatively low rpm (4000).
In the city, the bike still idled fine for a few minutes in slower traffic, slowly starting to stutter until it ultimately refused to run at all. It would crank, fire a few times and die or die as I slowly brought it up with throttle. Had to pull over, wait for it to cool down (the temp gauge didn’t show overheat or high temp) and set the IAC to let in more air, after which it ran begrudgingly and at a high idle with some stuttering but very slowly getting better once I got on a more open road again. This has happened a few times before the IAC switch when I was doing maneuvers on a parking lot as well.
The starting difficulties sound like it’s running rich to me, but really only happens when the bike is really hot
I assume that the airbox gets really warm when standing or riding really slow and the bike isn’t compensating? (IAT? problems?)
I’ve heard of vapour lock, but was also told that it’s really rare on Injected systems
The misfiring when warmer is something I can’t explain to myself properly. The bike runs without misfiring for longer when it’s cold out or at night and not at all at higher speeds.
Could the ignition system also struggle with higher temps? (It is quite close to the radiator and engine)
I did report pretty high resistance on my spark plug cap (when cold) so it could be more grossly out of spec at temperature? is that something that would cause misfires every now and then?
Lastly, I did recently check my spark plug and it was matte grey looking like a more lean condition. Not sure why it would be lean and then run super rich other times.
Thanks again for any ideas!