I need some advice, please bear with me on this long story.
Over time, my ’91 200 had developed a flat spot from off idle to perhaps 2000 rpm. Above that it would be strong. The transition always occurs at the same rpm, like someone hit a switch. (not fun in the rocks!). Not sure what I dinked with to perpetuate this, but it was not as detectable until I tried improving the rich stock jetting last year after consulting JustKDX. I had tried the pilot from 48 to 45, 1173N vs 1172N needle, airbox mod, Main 150 summer, 152 spring and fall. KIPS was operating and assembled correctly. AS (.5-.75 typ) had some effect of course, but no setting resolved the symptom. Overall the bike was running much better with jetting, but off-idle didn’t keep pace.
Over the last few years I added a DG pipe and Delta-V reed block, I think the low and midrange came up significantly, but the Off–idle stayed flat, exaggerating the rough transition. All attempts at jetting improved low, mid and top, improved plug color, but this only accentuated the lackluster off-idle.
This symptom is also independent of throttle position (cracked to WOT), off-idle remains blah; no bog or gurgle, just bland. I was beginning to doubt jetting was the cure nor cause.
I discovered a blown out crank seal on the mag side (Ah-HA! I thought), so I recently had it torn down at the local dealer (they did a nice job) new top end, crank bearings and seals. But the same symptom persisted, despite more attempts at jetting and AS adjustments.
I remembered that while installing the flywheel, although there was no visible damage to the keyway nor slot, there was about 1 to 2 degrees slop where the flywheel could settle on the crank and key but still be seated.
I reinstalled the flywheel but let it settle where it could be more advanced, then noticed marked improvement off-idle. It even sounded different the first time I started it. Encouraged, I gave the stator a nudge more advanced; only halfway between the middle line and the adjacent ‘advanced’ mark.
It runs really great now, really strong off idle, and then gets stronger and stays crisp with more RPM and throttle. Front tire comes up in first 3 gears, w/ 13:48 ratio. In two words, just right. Rockcrawling control is great.
I suspect the CDI advance is minimal at idle and I felt it kick in at a certain low RPM, resulting in the ‘switch-like’ change in performance I observed at 2000 rpm or so? But I’m just guessing.
So, do you think this a sign the CDI or coil is suspect, or just manufacturing tolerance? Know of any timing light procedure? I am hoping the factory may have been as conservative with the timing as they are with the jetting.
Before I put more time on the engine, I wanted to hear what you think or any related experience, as to whether this solution is viable or risky before I damage something.
Thanks!
G. Gearloose