XS11 Off Idle Stumble

[DEEBS11]

Bike has been running great for many years. I was on a typical 300 mile Sunday ride with my wife in a nearby state. It started with a small stumble from time to time when the RPMs were just off idle. As the revs increased to 3 - 4K it runs great. I was able to get all the way home like this. It now starts easily from cold and has a rough idle. #4 cylinder seems to pop a little which it never did. Get the RPMs up to 3k on the road and it then runs great.

My first thought: Advance unit broken wire(s). Had this happen a few years back and it was an easy diagnosis and fix. But no. I really got in there and pulled on all the wires while the bike was running and it still idled.

Here is a list of what I did to diagnose this issue so far:

✔ Removed and check advance unit and all of its functions.

✔ Checked advance unit sensors with ohm meter 740 ohms (good) at the connector in back of the fuse panel.

✔ Cleaned connector (which was clean) and then checked back at the TCI ignition unit. 745 ohms (all while pulling and moving the sensor wires).

✔ Checked harness with ohm meter from TCI ignition unit to coils. Perfect.

✔ Checked Dyna coils. Perfect 3 ohms each.

✔ Checked ballast jumper.

✔ Checked spark plugs. All good burning clean.

✔ Checked spark plug high tension wires all good.

✔ Drained gas tank and carbs. And installed fresh known good fuel.

✔ Removed carbs and cleaned each pilot circuit. They were clean.

✔ Checked for diaphragm tearing. All good.

✔ Checked carb sync. Perfect.

✔ Checked for vacuum leaks. Manifolds & throttle plate seals. No leaks.

✔ Tried a spare (tested & known good) TCI ignition unit. No change.

✔ Set the engine to "C" and reset the cam chain tensioner. All seemed good.

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Wow. This one is a head scratcher. I guess I need to check the cam timing marks next (did it jump?). I am still wondering about the advance unit. I have a good spare that I will install and try after I check the cam timing. I have read here in the forum about the neutral wire interfering with the sensor wires but the sensors did read 740 ohms. I will try new spark plugs as well. Will also check for a cracked coil. This is a tough one.

[LoftCol]

I am sure you have thought of this, but have you changed the exhaust since your last ride.

[LAB3]

Spark plug cap resistance? How about coil voltage?

[bikerphil]

Maybe one of the enrichment plungers not shutting off, richening mixture off idle.

[DEEBS11]

LoftCol - No, same exhaust for years.

LAB3 - 0 ohm plug caps. Wires are mint. I made them myself. I will check the coil voltage. However, I have a Geezer voltage regulator that charges rather high and my volt meter sometimes reads as high as 15v (possible meter inaccuracy). One of the coils (possibly 1&4) could be defective under load because of overheating. I had this happen on another bike.

[DEEBS11]

Maybe one of the enrichment plungers not shutting off, richening mixture off idle.

I will check that Phil. However the plugs all look very clean burning. Also, this came up suddenly in the middle of a ride with about 150 trouble free morning miles. It sure seems electrical but at this point anything is on the table.

[LAB3]

The "off idle" part is where I came to the conclusion of checking the voltage going to the coil, system voltage in general is going to be lower at that RPM and just a little resistance is going to go further under those conditions.

[DEEBS11]

LAB3 I have this aftermarket fuse holder and I will check to see if the fuses are possibly corroded. Especially the one that feeds the coils. I will also check the ignition switch for any voltage drop.

[bikerphil]

Might be time for the voodoo ignition mod, run power direct to the coils thru a relay.

[DiverRay]

I know it's probably electrical, but one thing I didn't read you checked. When was the valve lash last checked? Also, did you use one of the Chinese shims? I've had the Chinese shims break while in use, and threw them all out after that.

[DEEBS11]

Phil, that might be the fix if I have low coil primary voltage. I had made that mod in the past to other bikes with good results. Especially with starter solenoids (Motoguzzi common issue). However, I think I may have an over voltage issue with the Geezer regulator as it charges close to 15 volts @ 3,500 RPMs. Yikes. Coils might be overheated. Maybe. I had this happen on a 1980 KZ1000 with 3 ohm coils. It needed 5 ohm (black not green) coils to slow down the current that the Dyna S electronic ignition provides. Result: Cooler coils. Never had another issue. I rode that bike to Alaska.


Ray, I had checked the shims a few weeks back and they were all in spec. Didn't need to replace any. I would not ever use a Chinese part on any bike or tractor (knowingly anyhow) I always use OEM if possible.


I am also going to spray the coils with water once the bike is warmed up to see if one is cracked. If it has a breech, it should have a huge impact on the idle if it is cracked.


If all this checks out I will try installing the spare advance unit and see it anything changes. I will take a look at the cam timing also.

[bikerphil]

I wouldn't think 15V would hurt the dynatek, and no way you'd be getting that much thru the old factory red/wht wire. My Special has an overcharging problem too, 14.5+ with dynatek/geezer with the relay mod and no issues.

[LAB3]

Checking your basics is always good, a VOM at the coils will let you know whether to look elsewhere. Sounds like you're on track and far as checking for cracks. Keep us posted!