Light popping/burble on acceleration

[Lbxpdx]

I’m trying to figure this out.  For a while I have noticed that at speeds roughly 40 and above I get this feeling, as if the wind resistance is higher, then it disappears.  It happens relatively rhythmically.  I changed the fuel filter, the plugs, checked the temp gauge, has the injectors cleaned by a shop, adjusted the TPS, replaced the fuel lines, the Z hose, cleaned/rebuilt the ignition, and ran Techron and non-ethanol fuel for a few tanks. 

Earlier today I decided to check to see if the symptoms were present when in neutral, and there is a burble/popping that happens from 2K and up.  I tried carb cleared around the TB’s and nothing happens when I press the starter button when running. 

The hall sensor is lined up to the factory notch.  I’m leaning toward plug wires, but as far as I know the only way to check them is to replace them. 

Any ideas or items for me to check?

[The Mighty Gryphon]

Would you describe what the engine is doing a bogging down for a moment when the throttle is opened? 

Have you checked the valve clearances and balanced the throttle bodies? 

Also, what is the resistance between pins #10 and #13 on the big connector that goes to the Jetronic unit?  Measure when the engine is cold(~2500 ohms) and again at operating temperature(~250 ohms).

What is the fuel pressure in the rail?  Should be approximately 35psi.

[Laitch]

I changed . . . the plugs, checked the temp gauge, cleaned/rebuilt the ignition . . ..

Does "temp gauge" = coolant temperature sensor? "What is meant by "rebuilt the ignition?"
Have you done the basic clutch adjustment including 4mm freeplay at the joint of the clutch hand lever and its housing?

[Lbxpdx]

I have not checked the valves yet nor fuel pressure. I’m going to grab feeler gauges shortly and a manometer. 

It might say it feels bogged down, but ever so slightly and only above 40mph. 

Temp switch resistance has been verified both hot and cold. 

Throttle bodies were synced 2k ago at a dealer, prior to my ownership.  I double checked them with my carbtune.

Temp gauge does mean temperature switch.  Rebuilt ignition means I took the ignition switch apart, cleaned it with DeOxit and put it back together. 

I have done the clutch adjustment, but I did not do 4mm of free play.  The clymers calls for 1.5-2mm of free play for the k75. 

[Laitch]

. . . I did not do 4mm of free play.  The clymers calls for 1.5-2mm of free play for the k75. 

You're right about that. The 1994 K75 Rider's Handbook shows 4mm for the adjustment. Maybe specs changed; maybe accuracy took a holiday when it was realized that the K100/K75 line was going the way of the passenger pigeon one year or so after the handbook was printed.  Regardless of which measurement value is chosen, the intent of free play is to completely engage the clutch when the lever is released and completely disengage it when the lever is pulled.

If there is too much free play, shifting could become stubborn. If there's not enough free play, the clutch is not fully engaged when the lever is released, can prematurely wear, and can slip at speed. To some riders, it could seem like a headwind is interfering with acceleration. It can be a subtle feeling. Often, that subtle clutch slipping can be detected by goosing the throttle when cruising. Slippage will be apparent because the tach needle will move but corresponding acceleration won't be felt. The sensation of slippage won't necessarily be permanently felt but the corresponding excessive wear will continue.

I adjust free play while using a light pull with one finger on the lever. If the finger can move the lever to the required set distance but no further, it's good to go. 

[Lbxpdx]

I’ll check the clutch adjustment again then. 

I followed the process in the clymer, 75mm from nipple to housing, adjust bolt until resistance and tighten locknut on rear of tranny while holding the 10mm bolt, then adjusting the free play at the adjuster on lever. 

[Laitch]

Road test it by goosing at speed in top gear. If it slips, you'll know it.

[Lbxpdx]

No slippage. 

I got some new clamps for the FPR, new vacuum hose for the VPR and still no change. 

[Laitch]

What is a VPR in this context?

It could be that desensitization therapy is in order. If you could just find an 883 Sportster with a Bassani or Cobra exhaust and ride it for a thousand miles or so, that might cure your Brick. 

[Lbxpdx]

That would be fat fingers on a phone keyboard.  VPR is meant to be FPR.

[Lbxpdx]

I will say the plugs look much nicer after changing the FPR clamp and vacuum line. 

They were way leaner previously.  These look about perfect to me.

I did go for a 70 mile ride earlier today.  It felt great, despite the odd bogging/hesitation that was still present.   

[Laitch]

I will say the plugs look much nicer after changing the FPR clamp and vacuum line.. . . . These look about perfect to me.

Nothing is more unsettling than ugliness in the combustion chamber. Latte is a perennially popular electrode insulator color. 
Check resistance from the main ground attachment screw on the frame backbone under the tank to the battery ground cable attached to the transmission. It should be <0.05Ω. Verify that all battery and ground connections are clean and tight.

[The Mighty Gryphon]

Here is a link to a thread on the K100 forum that discusses connecting the vacuum ports on the throttle bodies together. 

It helps with some of the throttle response issues that seem to be especially prominent on the K75 engine.

https://www.k100-forum.com/t15212-vacuum-modification

[Lbxpdx]

Well, I don’t think it’ll solve my problem. I will try creating a vacuum hose that attaches to all three throttlebodies.  I couldn’t find the vacuum T’s anywhere, so I went down to the wrecking yard and pulled some off of newer Volvos wiper fluid hoses.

Design error.  Worked great for off idle, but sucked in real world scenario.

I wasn’t thinking about the overall amount of vacuum, I had already envisioned the end build.

[Lbxpdx]

Nothing is more unsettling than ugliness in the combustion chamber. Latte is a perennially popular electrode insulator color. 
Check resistance from the main ground attachment screw on the frame backbone under the tank to the battery ground cable attached to the transmission. It should be <0.05Ω. Verify that all battery and ground connections are clean and tight.

I measure 0.03K Ohm, not 0.03 Ohm.  Did you mean less than 0.05 K ohm?


EDIT: I cleaned the bolt and connectors at the tranny ground and now I have .1ohm resistance. 

[Lbxpdx]

Feels better, but still has the hesitation.

[Laitch]

I measure 0.03K Ohm, not 0.03 Ohm.  Did you mean less than 0.05 K ohm?It feels better . . .

That is a symbol found in math, science, mechanics, and the BMW shop manual. It means less than. Others are ≤ equal to or less than, > greater than, ≥ equal to or greater than and ≈ approximately.

Your main ground connection is okay if it was measured as described. In what way does the ride "feel better."

[Lbxpdx]

I am well aware what the less than symbol means.  I do the majority of my responses on my phone and I rarely look for symbols. 

If it helps, I am a middle school math teacher. 

How does it feel better you ask?  Well, I did DeOxit a fair amount of connectors under the tank, such as the FICU all the way down the ground cable. 

It feels zippier above 5k.  Better throttle response.

One thing of note, the temperature here,PNW, has dropped dramatically in the last week, close to 20 degrees. 

My line of thinking at the moment is this: since my plugs are uniformly tan, then the odds I have a single bars HT lead is low.  This leads me to believe that if it is electrical, it is either HES related or FICU. 

If it is sire related, it would either need to be between the air box and the plenum as all plugs are evenly colored or it is a dirty connection at the MAS/AIR MASS METER, whatever the unit is called in the air box. 

[Laitch]

If it helps, . . .
One thing of note, the temperature here,PNW, has dropped dramatically in the last week, close to 20 degrees. 
My line of thinking at the moment is this: since my plugs are uniformly tan, then the odds I have a single bars HT lead is low.  This leads me to believe that if it is electrical, it is either HES related or FICU. 
If it is sire related, .  . .

At this juncture, I'm uncertain what can help. 
 
A drop in temperature should only effect warmup time, and that would be measured in seconds or a couple of minutes—depending on the degree of temperature change—until it was resolved on a moving moto in a decent state of tune.
Please rephrase "a single bars of HT lead is low". I can't comprehend that.
Sire related? You aren't referring to a progenitor issue there, are you? 

[Lbxpdx]

At this juncture, I'm uncertain what can help. 
 
A drop in temperature should only effect warmup time, and that would be measured in seconds or a couple of minutes—depending on the degree of temperature change—until it was resolved on a moving moto in a decent state of tune.
Please rephrase "a single bars of HT lead is low". I can't comprehend that.
Sire related? You aren't referring to a progenitor issue there, are you? 

The odds that I have a single bad HT lead is low.

I will admit that I generally respond right when I wake up if a response was posted overnight, which means I have not had coffee or I am not fully awake yet.

[Laitch]

I agree with those odds.
I'm not fully awake until midnight; by then I should be back in bed. 

Regardless, your description of this fault makes it seem a minor and transitory one, to me anyway. My tolerance for imperfection in machinery is a high one, especially if I'm enjoying myself when it's happening.  If you installed new spark plugs right out of the box without checking the electrode gap, I suggest you recheck them and set them if they aren't to spec. They are often variable from the factory.

Maybe one of the Brick whisperers here like Scott_, frankenduck, Mighty Gryphon, daveyson et al. would like to deep dive with you on this one. Without a sound recording of your engine's presumed flaw, my advice is to devote a few minutes of spare time regularly to cleaning all electrical connectors with DeoxIT D5 if you haven't done that already.
 
If your Brick keeps up with traffic and gets somewhere in the neighborhood of 40-50 mpg on the road, enjoy it while you have the physical strength and time because those can be fleeting when we least expect them to be.

[daveson]

My first thought was maybe check the fuel pressure, but that question was already asked.

One thing of note, the temperature here,PNW, has dropped dramatically in the last week, close to 20 degrees. 
 

You might have excessive condensation in the fuel tank, especially if it was stored for a while with a low fuel level, and if you never use ethanol blended fuel. Water in the tank might have caused your replced filter to swell and partially block. If it's hard to blow through, that might be why. If stored for a while, I think it's good to keep the tank full. Sometimes I use ethanol blend to absorb any water that might be in the tank.

Condensation probably isn't a problem where the weather is always good, but your latitude is like cold, sunny, cold Victoria.

[daveson]

  I’m leaning toward plug wires, but as far as I know the only way to check them is to replace them. 

If they're leaking a bit, it would make a snapping sound. I don't thinks it matches your symptoms though. Not the first time it's been said, but if you look at them under acceleration on a dark night, you might see sparks, a very dark night, darker than a black steer's bumhole on a moonless prairie night.

[Laitch]

. . . darker than a black steer's bumhole on a moonless prairie night.

It gets lonely at night out on the prairie, or so I've heard. 

[daveson]

Darkness warshed over him when he went to the dark side.