[Jason Pittenger]

I've been having some strange symptoms.

With the warmer weather (maybe coincidence), I've noticed some off-idle hesitation, and a feeling of being down in power at the top end.

On Saturday, I rode in some fog and mist and ran out of gas on the ON position. I switched over to reserve and it seemed to run on one cylinder for a LOT longer than usual. It normally recovers in 10 seconds or so, but this felt more like 30-45 seconds.

Today I had it idling on the kickstand and the off-idle response was pretty bad. Grabbing full throttle, the RPMs never dropped, but it caughed and spit it's way to about 3500 before shooting up in revs. At least once it backfired up the intake. I was reaching for the idle adjustment screw and felt it on the carb intake boot.

Strangely enough, as soon as I sat on the bike and held it upright, the off-idle issues went away. Almost like the angle was causing running issues.

My first thought (until today) was plug wires. AFAIK, they are original 2005 wires. But could it be carb/fuel issues instead?

It rode fine after that idle session, but I also didn't get into the throttle much today.

Something just feels off, like the early stages of a pending problem.

 

[mmart]

I've been having some strange symptoms.

With the warmer weather (maybe coincidence), I've noticed some off-idle hesitation, and a feeling of being down in power at the top end.

On Saturday, I rode in some fog and mist and ran out of gas on the ON position. I switched over to reserve and it seemed to run on one cylinder for a LOT longer than usual. It normally recovers in 10 seconds or so, but this felt more like 30-45 seconds.

Today I had it idling on the kickstand and the off-idle response was pretty bad. Grabbing full throttle, the RPMs never dropped, but it caughed and spit it's way to about 3500 before shooting up in revs. At least once it backfired up the intake. I was reaching for the idle adjustment screw and felt it on the carb intake boot.

Strangely enough, as soon as I sat on the bike and held it upright, the off-idle issues went away. Almost like the angle was causing running issues.

My first thought (until today) was plug wires. AFAIK, they are original 2005 wires. But could it be carb/fuel issues instead?

It rode fine after that idle session, but I also didn't get into the throttle much today.

Something just feels off, like the early stages of a pending problem.

standing the bike upright may have something to do with flow, I posted this video a while back because the bike was running high on the side-stand. Since then I’ve done a fair amount to the bike but I did not change the plug wires.

July 30, 2019

VN750 rpms are weird

youtube.com

 

[Spockster]

Happen to notice the voltage when the problems occurred?

You can look for spark, in a dark area, and even mist water onto each wire/boot.

Ohm reading can identify a dead wire.

The stock throttle cables usually rub on the front right spark plug boot, mine was arcing there on my last ride. It chug-a-lugged at low rpm and sneezed through the intake.

 

[Jason Pittenger]

standing the bike upright may have something to do with flow, I posted this video a while back because the bike was running high on the side-stand. Since then I’ve done a fair amount to the bike but I did not change the plug wires.

July 30, 2019

VN750 rpms are weird

youtube.com

I can't tell from the video, was that due to straightening the front wheel, or pulling it upright from the sidestand? I know sometimes the throttle can get pulled when the wheel turns. Did you find the problem?

Happen to notice the voltage when the problems occurred?

You can look for spark, in a dark area, and even mist water onto each wire/boot.

Ohm reading can identify a dead wire.

The stock throttle cables usually rub on the front right spark plug boot, mine was arcing there on my last ride. It chug-a-lugged at low rpm and sneezed through the intake.

I happened to log that idle session, because my goal was to set my warm idle speed. On my ride on Saturday, I accidentally bumped the switch that pulls 10 degrees of timing and my idle speed was VERY low at the next stop. (I really need to disable that switch!). I reset the idle without realizing why it was so low. Later after correcting the switch I set the idle back by hand. However, I have noticed that 1100 RPM (according to the ignition module) shows up as about 950 on the tach. Fun fact, it's off the other direction by redline with 8500 showing as about 8700.

I set the idle to 1100 and tried messing with the throttle a bit. When I get home, I can look at the voltage, dwell time, advance, engine vacuum, ambient air pressure etc. Obviously, fuel flow, engine temp and ambient temp won't show up in the data.

 

[mmart]

It was shifting the bike from the side stand to upright that caused it to settle down. All I’ve done to the fuel system is religiously used Seafoam. This video was not too long after I had my stator replaced at a local kaw dealer, they took forever to get the job done so it could have been a result of the bike sitting dead for the better part of a couple months. But to say I definitively identified the cause would be false.

 

[Spockster]

It was shifting the bike from the side stand to upright that caused it to settle down. All I’ve done to the fuel system is religiously used Seafoam. This video was not too long after I had my stator replaced at a local kaw dealer, they took forever to get the job done so it could have been a result of the bike sitting dead for the better part of a couple months. But to say I definitively identified the cause would be false.

I've noticed my idle improving like that when I stood the bike up. Probably after a week or so off too. Not always, but at least once.

 

[Jason Pittenger]

I found the issue, but don't know yet how to correct it.
I have insufficient spark when I crack the throttle.
Below is a graph of the ignition coil dwell time (gray) over time.
It's normally in the 12-15mS range, but it drops to 5-6mS whenever I crack the throttle.

I had issues with this last year and thought I had resolved it.
The ignition module has a mode where it can automatically calculate the dwell time on the coils.
It also has a feature allowing the spark to advance beyond the starting edge of the protrusion (or lobe) on the stator.
When the feature is enabled that allows it to spark before the lobe, it will calculate the timing based on the previous revolution and the current RPM.
Thus timings before the lobe are best guesses and it can be a bit inaccurate at lower RPMs.
FYI the lobe is good for timings between 5 and 27 degrees on my bike.
I'm running as high as 31 degrees at part throttle.

Well apparently that feature can cause issues with the automatic dwell time feature at low RPMs.
In an email from Ignitech:
"This setting allows more advance (before pulse lobe), but it can to cause problems at sharp acceleration (mainly at low RPM). Try it without this choice."
At the time, I was seeing dwell times drop as low as 1.3mS when cracking the throttle.

I changed over to manual dwell times (based on measurements of the stock system) and I thought that had resolved the issue.
The dwell time still dropped (as seen above) but not down to 1.3mS anymore so it seemed to be fixed.
FYI, the stock system ran 25 mS during cranking, 15mS at idle and 2.5mS at redline.
However, it appears the dwell time is still misbehaving near idle.
I'm asking them what they recommend to fix the problem.

As I'm thinking about it now, I did increase my spark gap from stock settings late last year.
I figured the ignition system was stronger than stock and the plugs were iridium, so they could handle a larger gap.
I bet the colder temperatures masked the problem I recreated for myself and now it's showing up again as the weather gets hot.
Depending on what they recommend, I might regap my plugs back to stock.
I probably should do that anyways.

 

[Jason Pittenger]

Happen to notice the voltage when the problems occurred?

The voltage after starting was 11.45 volts, climbing to 12.45 volts after it's been running a bit.
I realized I never corrected a wiring issue from when I first installed the new ignition system.
I have the ignition ground connected through the safety interlock system (Kickstand/Neutral/Clutch).
Thus, it's not at true ground, but at 0.7 volts above ground (1 diode drop).
My actual battery voltage is therefore 12.15 volts climbing to 13.15 volts, but I'm loosing 0.7 volts through the interlock system.
That accounts for about 10% of the ignition system's power.
Every little bit helps I suppose.

Lastly, the start up behavior has been a little funny as well, and I think it's for the same reason: dwell time.
It starts fine, then hesitates before the RPM climbs further. See the flat spot at 1000 RPM before going up to 2500? It's very brief, but it's noticeable.
I've been ignoring it, but the graph shows the cause....again, the dwell time is kind of weird.
I have it set to not spark for the first two revolutions to allow the engine RPM to come up a bit before sparking.
The idea is to prevent backfire from sparking right away on a cylinder that's partway through the compression stroke already.
That explains the very low dwell time at the beginning.
Then after 2 revolutions, I have the dwell time set to be equal to the physical length of the lobe below 600 RPM.
This gives the ignition system an extra long dwell time to compensate for low system voltage during cranking.
(BTW, this GREATLY improves the hot start issues).
After it passes 600 RPM, it switches over to calculating the dwell time, and the dwell time dropped to 0 briefly!
I need to set that changeover point to 900 or 1000 RPM to try to eliminate that kink in the start up.
NOTE: This was a no-choke warm start after sitting 10-15 minutes or so.

 

[Jason Pittenger]

Since this issue is all related to the Ignitech ignition unit, I'm not going to continue this thread after this post. Any further updates, I'll add to my long thread on the Ignitech unit as I adjust settings to try to fix the issue.

If there's any good news, I correctly identified it as a spark issue! It behaved a lot like my old bike when the stator connector became so corroded that the running voltage dropped to 11 volts at idle and it would stumble coming off idle.

Thanks for your help!

 

[OminousDarkness]

Since this issue is all related to the Ignitech ignition unit, I'm not going to continue this thread after this post. Any further updates, I'll add to my long thread on the Ignitech unit as I adjust settings to try to fix the issue.

If there's any good news, I correctly identified it as a spark issue! It behaved a lot like my old bike when the stator connector became so corroded that the running voltage dropped to 11 volts at idle and it would stumble coming off idle.

Thanks for your help!

I've read every word of what you wrote above, and I've come to two conclusions.
1. I have no grasp of any of it.
2. I need to learn it.

This is fascinating stuff, man! I love to ride, and I don't mind trying to tackle intermediate level servicing issues, but this is the kind of next level stuff that just leaves me baffled. Kudos to you for sharing this with everyone!