Need second opinion on pesky gremlins

nodwick

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This weekend- I'll be diving into fixing my xs650. I need anyone's educated input, I have all weekend to wrench I'm just a dude who likes to wrench on bikes sometimes and new to owning an XS.



My Bike:

1981 xs650 (VIN id as "US spec XS-H special 2")
BS34 47.5 pilot 137.5 main
Pods & straight piped
TCI ignition from factory
No other mods (that I can think of/aware of)
Brief background:

I just bought this bike as a non-running incomplete project that is in good condition. Previous owners were about to start cafeing the bike out. They got as far as minimal aesthetic/annoying mods, then engine performance mods (pods and straight pipes) owner grew frustrated and elected to sell it as they had two other bikes that ran well. Before buying I had identified it just needs to be rejetted. Cleaned the carbs and rejetted myself and she's been running great for a about a month Been slowly working out the kinks. (To many to list in this post but some major eye rolls have been had)



4 days prior to issue-removed cheapo baffles from after market mufflers. Because they sounded cheap. And I got tired of it. (Will be doing fully custom exhaust later)



1 day before issue- refueled at same gas station as always. Using E5 from tesco. Every fill up has been from here in my 1.5 months of riding this particular bike (6-7 fillups)



Symptoms below:

intermittent LH side misfiring, and back firing in the exhaust pipe; occurs on accel when engine "8 cycles" on LH cylinder at low rpm
LH cylinder misses intermittently on idle causing stalling. And back fire upon any throttle application. Nearly stranded but was able to use higher than normal RPMs to take off from first
Backfiring on decel, could stem by turning mix screw out to 4-4.5 turns. And also by engaging enrichener to first position.
"Breaking up" on acceleration at all RPM. After period of high rpm, "hard" accelerations, and decelerations symptoms would subside.
Bike acted like this for 1.5 days and after driving it hard the issue subsided. For an entire day. But mix screws were still turned very far out (4.5 turns out) from nominal position (2.5 turns out) did not individually set mixes to compensated levels. Adjusted together for simplicity, but only to compensate for the LH side.



Weekend rolled around and these are my notes and fix actions I took:

[X] Goal: Diag fueling issue/lean condition

[X] Step 1 Clean/Rebuild carbs

• Removal of carbs from the engine revealed a severely kinked fuel line before the T on the right side. Kinked section is permanently deformed and will easily kink off again • Upon inspection of fuel drained from float bowls it's clear crumbling fuel line is the culprit as evident by sizeable black chunks in float bowls (figure 1.1 and 1.2) and kinked fuel line that now has a permanent weak spot.

• Carbs rebuilt and weak spot in fuel line eliminated.

• Kinked spot of fuel line was discolored on the inside and weaker where it had been stressed but I could not easily see any visual degradation.

• Checked spark plugs out of attempting to cover all bases and plugs seemed to be in expected condition. LH plug black, dry and sooty RH nominal plug creme/tan color. (Figure 1.3) To me seemed a secondary effect of having the uneven metering of fuel into the cylinder.

[X]step 2 test ride

• Rides went great, set idle once at operating temp & tweaked carbs to ballpark settings.

• Mix screws turned inwards by .5 turns and engine seems very happy. Not as many nice sounding pops on decel as when it's perfectly dialed in but very slight.

[X] step 3 If mix screws still far out go up pilot jet again

• Un-needed

[ ] If lean condition still exists on full accel at high rpm, up the main jet

• No obvious lean condition from full throttle acceleration but feels like it could be pulling harder. Requires investigation and will monitor during week for insight



Bike parked after 30ish minutes of riding around and tweaking. Feeling accomplished.



With issue seemingly resolved I swapped out spark plug caps for the same model of plug caps (existing ones on the bike were old and crusty. With one having previously un-attach off the wire)



Bike fired up and ran just fine after spark plug caps being swapped.



the next morning



Momentarily started as expected only at 1st notch on the enrichener



then when set to no enrichment after a bit of idling (15-45 seconds) engine totally stalled

Then would not start at normal enrichment setting (1st notch). Had to fully engage enrichener (2nd notch) and then had weak idle. "Solved" by increasing idle screw. Indeterminate amount of time before turning off enrichener. Was immediately suspicious and frustrated but had to get to work



Rode maybe 2-3 miles when the following issues cropped up and grew increasingly until I was left stranded.



LH misses intermittently on idle causing stalling. And back fire upon any throttle application. Making starting from a stop very difficult without stalling.



Backfiring on decel, could lessen by turning mix screws out again to 4-4.5 turns. And also by engaging enrichener to first position.



"Breaking up" on acceleration at all RPM. After period of high rpm, "hard" accelerations, and decelerations resulting in the symptoms subsiding temporarily.



LH cylinder missing at low RPMs causing jerking acceleration and bucking at low speeds.



Bike totally dies (2x before giving up and getting trailered home). Both times before dying all above symptoms occurred. These symptoms also are very similar and I believe to be more than likely the same issue from the previous weeks issues and cleaning the carb relieved the issue for enough time for a test ride and to get a false positive for a fix.



Moments before bike totally died

issues seemed to transition from LH side to both LH and RH. Started as "breaking up" while maintaining speed (sudden uneven power feel without moving throttle) approx 2-3k rpm.dropped down in gears to get engine up in rpm to try and clear the issue as before. I was able to accelerate briefly then after a couple moments it just turned into popping and banging, bike couldn't maintain speed. At low speed felt like someone was switching my key/kill switch on and off repeatedly and then gradually came to a stop with lots of jerking and popping.



This sequence was unchanged both times the bike to decide to totally not fire, with or without enrichener engaged at any position.



---First time bike totally gave up---



Left the bike in parking lot completed an appointment and came back 1.25hrs later. Drained fuel bowls and check for contaminants. LH sample had flecks of black but at very tiny near imperceivable size with 1 larger black fleck and 1 similar sized brownish contaminants (figure 2.1)and RH sample had slightly more black flecks of near imperceivable size and 1 larger black fleck contaminant(figure 2.2) Unable to do any actual fix action. Attempted to fire up bike. It started fine and would idle. but was totally gutless and easy to stall and with misfire on the left side with throttle application until rpms were higher.



Cruising at 30-40 bike would pop and bang and had to keep rpms up. Was trying to limp home.



---Second total stall out---



Symptoms moments before it totally died symptoms were exact same as first time. But difference being it would not fire up again approximately 2hrs later. Would crank strong but no fire, no signs of even trying to start at all. Also I verified fuel is flowing into bowls. But was unable to verify if fuel was entering the cylinders



Many hours later in the evening after a tow, it fired up cold, but left side was intermittent at idle. And idle was low/weak.



My thoughts

I think it's a fuel issue, I want to say the particulates keep clogging the carburetor. But I truthfully don't know. I've never had a run in with dirty or contaminated fuel so this is a first.



What I don't know is what size and concentration of particulate will start to cause issues, obviously the size being anything that will block the little holes in the jets. I have attached photos and would love others opinions because I have mixed feelings if contaminated fuel is what I'm dealing with here.



Since the issue returned after I eliminated the fuel line section that was bad, could this just be left over debris in the lines?



Is there an easy way to inspect a fuel tank with no endoscope/inspection camera? Visibly through the fuel filler hole I can't see anything but really fresh looking metal inside the gas tank.



Could the degradation be from inside the petcocks? My RH petcock Will drip once or twice on my finger when I turn it from "off" to "on" or "reserve"



I've seen that electronic ignition on these bikes, if failing, will usually happen at operational temperatures. but I don't know if that happens on the pamco and other brand aftermarket kits for adapted bikes from points, or if the factory TCI ignition will do the same?



with the jerkiness that happened occasionally I know that's also a symptom of electronic ignition failure?



My bet is still on fuel and I will update as I dig in this weekend. Does anybody have any resources on detailed troubleshooting of a TCI ignition system? I am okay with electronics and will have no problem troubleshooting analog circuits as long as I have a guide in nominal values.



Thanks!
 

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First, welcome aboard!!
Ignition... always ignition first. My greatest mentor was fond of saying "never underestimate an ignitions ability to fool you into blaming the carbs." .... and you'd get a boot in your ass if you didn't start there.

I've had 2 TCI ignitor boxes go south on me now. In both cases the bike would pop, sputter and generally pitch a fit when you tried to accelerate. If you worked through all the bucking and ear splitting pops, at around 3-4k revs it'd smooth out and run just fine... 'till you dropped down below them revs.
And all that was only after the box(es) warmed up for 10-15min. Prior to that they'd work as they should.

I'm not saying it's not the carbs. It very well could be.... but make sure your iggy system is solid first.
.... and you're likely way overjetted on the pilots. But maybe not... hard to say with straight pipes.

Anyway.... TCI boxes are like hens teeth. And when you do find one, it'll cost you your first born male. Do a forum search for the "gonzo" ignition. It's a Suzuki igniter box that you can pick up for about 20 bucks or so. Also, @jetmechmarty just finished a run of Gonzo pigtails to adapt the Suzuki box. I think he still has some left.

Last thought... there's resistor plugs and resistor plug caps. Run either/or, never both. Both is too much secondary resistance and causes screwy shit to happen. On the other end, no resistance added to the secondary causes screwy shit also. Either the plugs OR the caps need to be 5kΩ.

And pics!!! We love pics here!!
 
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Does anybody have any resources on detailed troubleshooting of a TCI ignition system? I am okay with electronics and will have no problem troubleshooting analog circuits as long as I have a guide in nominal values.
Sorry, forgot to answer. There's a procedure in the manual. It's pretty limited though. About the only sure fire way to isolate the box is to replace it with a known good one (or the Gonzo box).
 

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I had a somewhat similar trouble. One fuel line had shaved off a bit of rubber internally. sometimes it blocked line part way, sometimes not. The brass fitting was sharp and the puttin' together was by a man other than me, he was careless. I always chamfer the brass bits in lines, and blow them out. He did not. . It was a question of very careful physical examination. The "carbs" were btw flatslides. Mostly it ran, left cut in and out. If you can borrow a scope it might be nice to look at the spark. O scope software for computers maybe? Just my 2 bits, brother. Used electronics o scopes are actually pretty cheap. Good luck.
 
Thanks for the input everyone! I'll update y'all probably this Sunday or Monday if I don't get the bike running sooner. My other bike has a flat so I'm stuck at home so there's no getting away from one or the other! (No I don't have a car only motorcycles)

1. I didn't know about resistor plugs, only resistor plug caps, I'll go check what I have. And I didn't want to, because I really WANT it to be fueling because i don't have to wait for parts if it is the issue. The voltage across the battery should be strong, the starter was able to crank the engine easily, -i will verify with actual measurements-

2. I do have access to and O-scope so I'll hook her up, of I can call the favor in to use it.

3. I think I'm still gonna investigate the fuel anyway after I check the ignition. My instinct was to check fuel systems first, so thank you to all for the advice.
 
I concur with the others on the fuel.......................... Replace all fuel lines and install a good inline filter, may need to empty, clean and flush the tank. Do carbs again making sue to clean the pilot circuit and check the float valve for dirt embedded on the valve or seat.

Here is a secondery list that i would check and do in conjunction with the above.
Adjust Cam chain, set tappets and check timing.
Make sure the gas cap vent hole is clear.
Make sure the barb caps on the manifolds are sealing and the caps arn't cracked. I am guessing you have a manual petcock going of your description
 
I concur with the others on the fuel.......................... Replace all fuel lines and install a good inline filter, may need to empty, clean and flush the tank. Do carbs again making sue to clean the pilot circuit and check the float valve for dirt embedded on the valve or seat.

Here is a secondery list that i would check and do in conjunction with the above.
Adjust Cam chain, set tappets and check timing.
Make sure the gas cap vent hole is clear.
Make sure the barb caps on the manifolds are sealing and the caps arn't cracked. I am guessing you have a manual petcock going of your description
Thanks for the input! What fuel filters should I look into? I installed one previously but it was causing fuel starvation.

Valves I just checked and are in spec as of less than ~200 miles ago. And I have adjusted the cam chain. No rattle, and the plunger wiggles very slightly while idling. I would have liked to see more movement from the plunger, but if I loosened it at all I would start to get a chain like rattle at times.

Vacuum barb caps on carburetor boots and the boots themselves are indeed sealing well. Verified with carb cleaner while it was running.

I do indeed have manual petcocks.

I will investigate fuel tank breather! (Not as a root cause but just to cover all bases)


Thank you much!
 
Hey y'all a very minimal update!

Tested coil pack and readings are nominal enough I believe it's not my issue. (3.0 and 20k ohms for the primary and secondary)

New spark plug caps are the same resistance as old ones, connections on harness->tci box and TCI box -> primary are firm and without corrosion (outside just being old)

I didn't while I was in there but I will be cleaning the contacts just to get them super fresh once I diagnose what the actual root cause was. Until then I'm holding off because I only want to change one variable at a time.

I got the other bikes tire changed so I can at least get to work Monday (and so I can have more fun working on the xs) and when I did that I was able to talk to the mechanics and BS with them for a while.

In that said BSing I showed him the photos in this post and he believes that it looks like rust and -maybe- rubber.

And when I showed him the fuel line that I took off the bike, he said that they often get old bikes with this style of fuel line and it's not ethanol rated, so it -could- be the issue (it is the issue if the mysterious fuel line on the bike was not in fact ethanol rated, but I don't know that for a fact or not yet)

I have also come to realize no matter what, I will ,in fact, have to clean the carbs and replace the fuel line and inspect the tank. So instead of doing ignition system first I will be doing the fuel system first. And seeing how the bike responds.

I'm waiting a paycheck and then ordering a borescope because I'm on a meager budget. I do have new ethanol fuel line and an inline fuel filter that the shop through my way for 10 bucks.

I was going to dig in in a bigger way this weekend, but without the other bike running it just wasn't going to be fun, and I like working on the XS when it's fun and not an obligation.

But I will be getting it running this weekend because it's too pretty to keep this bike inside! I'm new to this forum etiquette stuff. I want to post pics of the bike and also an update when the time comes (eta 1.5 weeks) do I update this current thread/post or do I make a new one?? I've only ever been a lurker before.
 
An update:

Had some energy after work today and I could help myself but tinker. Especially now that I have the other bike ridable again (nail in tire)

Attached are some photos of the tank after I shook around like CRAZY for 5 ish minutes .5 liters of fuel.

The fuel looks very clean to me and there's the slightest little bit of crud. MUCH less than I found in the carbs when I had issues initially


Is that enough to worry about? Is this my source? Or was this just the tank and the the potentially non ethanol rated fuel lines getting to know each other after I park each day.


Update to the update:
Found a very significant amount of debris in the float bowls which would track with previous trends. Feeling good because now I feel less crazy! (Photos attached)

Gonna clean out the carbs and see how she rides this weekend.

More to follow. I'm cleaning the carbs currently but may not finish until the weekend if I run out of brain juice.

Thanks in advance
 

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I just read through this post and I don't see anywhere in it that you verified the engine to be mechanically sound. Compression test, valve adjustment, leak down, head bolt retorque, timing chain adjustment, check intake boots for leaks. I agree it sounds like it may be carburetion, and also agree ignition problems may appear to be carburetion. I also don't see where you have balanced the carbs. If you've already checked all this, don't roast me too badly! :bow2:
 
I just read through this post and I don't see anywhere in it that you verified the engine to be mechanically sound. Compression test, valve adjustment, leak down, head bolt retorque, timing chain adjustment, check intake boots for leaks. I agree it sounds like it may be carburetion, and also agree ignition problems may appear to be carburetion. I also don't see where you have balanced the carbs. If you've already checked all this, don't roast me too badly! :bow2:


Oh yeah! I forgot I had to remove that originally because I hit the character limit.

Compression check with a cold engine was 126 on both sides with the same gauge (+- .5psi).

Boots are not leaky

Valves are within tolerances

Unfamiliar with leak down?
And head bolts have not been retorqued

And I've put a couple hundred miles on the bike before these issues started cropping up.

I'm starting to think when I added a filter then removed the filter (it was starving the carbs at high rpm) almost 2 weeks later is when things started going chaotic
 
Oh yeah! I forgot I had to remove that originally because I hit the character limit.

Compression check with a cold engine was 126 on both sides with the same gauge (+- .5psi).

Boots are not leaky

Valves are within tolerances

Unfamiliar with leak down?
And head bolts have not been retorqued

I'm starting to think when I added a filter then removed the filter (it was starving the carbs at high rpm) almost 2 weeks later is when things started going chaotic
Refer to this video for a leakdown test quick explanation:


I have a 1978 XS I'm overhauling and I had low compression one one cylinder. The leakdown test revealed it was a leaky exhaust valve from a bit of gunk - I blew out the gunk and the compression matched the other side. 126 psi seems a little low - I usually get north of 150 psi on a good engine.
 
Refer to this video for a leakdown test quick explanation:


I have a 1978 XS I'm overhauling and I had low compression one one cylinder. The leakdown test revealed it was a leaky exhaust valve from a bit of gunk - I blew out the gunk and the compression matched the other side. 126 psi seems a little low - I usually get north of 150 psi on a good engine.

Thanks! I'll check out the video when I'm not at work 😅.

126psi did seem low when I ran the test, but it was taken when it was dead cold and had been sitting a few days. I'll do it again once everything is fired up and warm
 
Compression was the same on both cylinders. Good indication it isn't an issue. Very uncommon for both to b the same, (even low), if rings are worn. Good chance it will rise when hot and running
Im glad to hear this sentiment, my gut didn't feel like it was much of an issue really because *when it is running* it runs great!
 
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