Hesitation 1980 with TCI

Texas XS

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Hello everyone, this is my first post. I've been lurking for about three months now and the collection of knowledge here is awesome! I have owned a 02' M2 Buell cyclone and chopped 78' honda 500 twin over the years, but this is my first venture into the world of yamaha.
Ok, so I have been working on a buddy's 80 with the TCI ignition, he left it at my place since he already has a sportster he rides all the time. I get to ride it and work the bugs out, cool I haven't had a bike in a couple years. Should just be a carb rebuild and thrash it to work and back...it has turned into a real adventure.
PO already bobbed it and the harness was a butt connector mess. So first thing I did was re wire it to this schematic. I ran new wires from the coil back, cleaned all the male/female blades and soldered almost all the butt conectors up. It's just headlight, taillight and kickstart. I Did the basic check over stuff, timing chain and valve adjustment checked the floats for holes and cleaned the carbs.
I finally got it running decent after I replaced the tank (old one was rust city), petcock, gas cap, new manifolds, butterfly seals and rebuilt the 1975 bs 38's (127.5 main, 45 pilot, needle clip at 4th position), running down pipes and no air filters (cheap pods were choking the venturies so I ditched them). I had it die at idle waiting for a traffic light a couple times, no big deal...right.
Finished putting the new intake manifolds on and put new mains in the carbs so I went for a ride to a buddies. Ran good 1-4th but the bike felt like it was hesitating, or some one was flicking the on and off switch when I would get going 65 (5th gear) under throttle. Stopped and lowered the carb needles, jump back on the highway, same hesitation. 45 minutes at my buddies, before I headed back I lower the needles again. I got about 15 minutes down the road, still hesitating everytime I get into the throttle. Gets progressively worse, bike dies doing 65. Won't start back up even when I was popping the clutch. Headlight and tailight work, No spark, can't get 12v to coil, tow it home.
Next day I hooked the timing light up. Disconnect the reg/rec kick, kick. No spark. Hook reg/rec back up wiggle some wires...kick, SPARK! Stupid butt connector for reg/rec didn't get replaced, soldered that up. Soldered all the crimp connectors and re did all the grounds (battery to frame, rec to frame, ignition box to frame, new engine ground to frame, paint free and greased).
It was eating taillight bulbs like nobody's business, I figured it was the T shape license plate holder PO had welded on the swingarm shaking bulbs to death. So I cut that off and built a proper license plate holder and welded it onto the frame, installed a new trailer light. Put the carbs back to 4th needle clip. Go for a 20 minute ride before work..
It goes great until you get into 5th gear. Gets some hesitation again, more of a stutter or stamer when you get up around 65/70 in 5th. Bike feels good, doesn't pop or backfire, pulls hard. I get back to the highway after 15 minutes, start to head for work, doing 70 flat out for about 2 miles and it starts doing the ol hesitation, stutter thing again then dies. I manage to get it off the highway about a 1/2 mile from work. No headlight or taillight, just dead. No fluke meter on me, grab a wrench and slap test it. Nothing. Alright at least were getting somewhere, unplug the rec/reg turn it on, nothing, still dead. Plug them back in. Push it for 12 minutes or so then take a break, figure I would give it another try. Key on and I got power! Turn it off, unplug the rec/reg kick it over and limp it to work, hesitating, bucking won't really rev over 3k, rec/reg makes no difference. Sits all day, plug the rec/reg in and fire it up to head home eight hours later. Same crap all the way home, bucks hesitates, can't go over 3k or 35mph I had to feather the clutch in second all the way home.
So I start tracing 12v when I get home. 1 volt drop from battery to the coil, drops off at the ignition so I put a new keyed ignition in it. I went through the charging system next.
Readings at 200k:
-Cleaned the rotor slip rings, ohms at 5.6 inner to outer ring, infinite to motor.
-Replaced brushes
-Stator ohms .5 from any three white wires in combination, Infinite to ground.
-Rectifier pases diode test off bike.
•Black lead on black wire, white wires read 0.
•Red lead on black wire, white wires read .560-.580.
-Pick up sensor ohms .780 and .790.
-Jumped the green - wire at brush and the voltage just walked away 14.v, 15.v, 16.v so I shut it down.
-Replaced voltage regulator with 12v Fiat regulator.
-Replaced rectifer with 35 amp 100v 3 phase bridge rectifier from wind river.
Get that stuff installed, jump my ground brush and it regulates, woo hoo! Fixed you say? Nope.
Go to ride it and I can't even get to the end of the block, still bucking and hesitating. Ok, gotta be fuel, pull the carbs for the 8th time and put them in the ultrasonic now with a cup of mean green and distilled water. Blow everything out reassemble, fuel to the carbs, no change.
Unplug the new rec/reg, no change, still won't rev past 3k. Pull the ignition box apart and reflow the board, no change. Start looking for a voltage drop again, unpluged the power to the rectifier and acidently grounded the battery, pop the main 20 amp fuse. Replace that and now I'm back to no spark.
Load test battery at O'Reilly's, it passes.I have power 12.volts to coil, I get spark if I manually ground the coil...coil ohms at 2.7 primary, 29000k secondaries and infinte to ground. Shit, I think I just smoked the ignition box. I picked up a box from a forum member. Go through the harness again this morning, make sure all the grounds are good everything is hooked up right. Fire the bike up, advances ok with the new box, still hesitates and misses when I ride it to the end of the street, twist the throttle and it's 1-2 second delayed response before it accelerates, then the throttles falls on its face then comes back on. Pull the carbs off again, double check floats are at 24mm. Reinstall carbs and dead cylinder tune it, ground coil to fin via extra plug. The right bank is really hard to get a smooth idle out of it, seems like it has a miss then would die at a low idle or you have to idle it at 1300rpm to keep it running. Finally got them both to settle in about 1100, went for a test ride and there's a lot of hesitation 1st through 3rd (didn't drive it too far).
Off idle, through wide open. It will just fall on its face then come back on and try to spin the clutch it hits so hard. I really don't know what to look at next. My gut says the coil is having a heat related failure. It's the original unit as far as I can tell, the plug caps and secondary wires are all one piece. Even with the floats adjusted and the petcock closed I'll get a burp of gas on the floor after an hour or two. I put the floats in a gasoline filled jar overnight and they were still floating. Anyone have any insight, or see something I missed? Carbs or coil? I'm kinda stumped.
Thanks for hanging in there if you read this whole thing, just trying to be thorough. 20190714_161419.jpg


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Does it run okay sometimes? A couple things about the carbs for your year. Make sure the float needles move freely in the brass seats. Some aftermarket rubber tips expand and stick from some gasolines. You can get oem ones still. Make sure the seat itself is firmly in there -- it should be hard or impossible to pull out with your fingers. There's an o-ring around it that deteriorates and lets gas flow in through there.

The original coil might still be okay but it got to be suspect. A coil can measure good but still be bad, because you aren't measuring it using high voltage. Thankfully if it does measure bad though, it is bad... I don't know what's a good coil you can just buy and put on. Somebody else might. I use a Honda MP08 coil that has to be adapted to fit. I have an '81, a lot like '80.

P.S. Just re-read and saw you have '75 carbs. They are different. Also saw it was running good for a bit at least in 1-4. I'd suspect carbs or tuning at this point first. Sounds like when you didn't have spark you fixed that.
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Xjwmx, thanks for the response!
-No, right now it misses and hesitates consistently under load and through the power band.
-Yes, the spark issue has been fixed. It idles fine, and revs good now. It just won't run through the gears under load without hesitating, falling on it's face and coming back on hard.

I keep thinking and wondering if the coil is starting to fail but ohming ok. I'm in Texas and we have been hovering around 100°F for weeks now (real feel is about 115°) and the overnight temps are still in the 80's. I thought about icing the coil down and riding it real quick and see if it runs better before it heats up. If the coil were failing would it just go all together or just under a load when demand increases?
I have been searching a lot of threads and found the Honda coil you are running. I'm seriously contemplating replacing it, it's the weak link in the equation. 29000k secondaries seems like it's the high end of +_10% of the 15000k limits. Primaries ohmed at 2.5 the other day, when I double checked some stuff last night and they read 2.7ohms, seems odd.
I had It running really good, unless you were into the throttle and wound up in 5th. Then it would still accelerate but breakup while it was picking up speed (it would feel like spark cut, flicking the ignition on and off), and if you ran it for more than 20 minutes it would die. Got worse to the point it wouldn't advance. Replaced the old box with the "new" used box, breaks up across the bottom and mid range now, forget 5th gear now! Hadn't messed with the carbs yet, becuase it ran good before the box died.
In essence the ocassional high end break up moved into the lower/midrange and it is very consistant, to the point where I don't dare get more than a couple blocks from the house or out of 3rd gear. It will do it when you keep the throttle in one place, also does it under slow acceleration or WOT.

Since the hesitation didn't go away I have done the following to the carbs yesterday thinking it is a fuel issue;
•Cleaned float pin,
•Checked pilots again (pilots look original, but orifices are clean).
•Bowls are nice and clean,
•Float jets are new but have some wear around the cone, assume it was scuffed from the rust in the old tank (old tank had a lot of sediment!).
•The float jet moves freely and have new washers in there.
•I didn't replace the needle during the rebuild because it looks good. •Needle jet is original but clean, I had replaced the o ring and it seems to be in there good, but I will re check it after reading this.
It also has new mains, the rubber diaphrams look good against a light, no visable holes. They take about ten seconds to drop when you cover the air inlet, so I didn't replace. Floats set at 24mm, fuel level sets just below the bowl lip with a tube in the drain hole. I just ultrasoniced the bodies, bowls, needles and everything last week thinking the upper rpm stumble was due to debris in the fuel system.

Gave her a spin after carb clean up last night. Dead cylinder adjusted them to 1100 rpm and It still stumbles through a throttle roll. Doesn't seem to matter if it's steady or hard acceleration, just gets more violent the harder you accelerate. So if you give her cruising speed she will still blip out and come back on. It doesn't backfire or pop though.

What do y'all think Break the carbs down again and ultrasonic one more time, maybe order a couple jet sizes? Or get a new coil, plugs and wires coming? Hate to tell my buddy to just throw money at it without having a sound answer. I would like to have a definite fix for him because I thought the box was gonna do it, but it is a 40 yo scooter.
In essence the ocassional high end break up moved into the lower/midrange and it is very consistant,
So... if I'm reading all that correctly, you changed the TCI box and the problem went from high end to low end... correct? That's telling me you changed something and the problem changed. I'd suspect the box you put in it. Did you put the old box back in and see if it went back to the high end as before?

On the coil... a wise man I learned a lot from used to say... "never underestimate the coils ability to fool you into blaming the carbs."
I've replaced coils before to fix breaking up under heavy throttle. Rare... but it's a definite possibility.
Thanks Jim. Yes, you are correct. The problem moved to high end with the original box, to low end with the replacement box. I stopped getting spark with the orginal box, but I'll put it back in and see what happens.

On the coil... a wise man I learned a lot from used to say... "never underestimate the coils ability to fool you into blaming the carbs."
I've replaced coils before to fix breaking up under heavy throttle. Rare... but it's a definite possibility.

That's wise advice really. The fuel system on this bike was in really poor shape, and I have fought it every step of the way. I just recently got it under control, then all the hesitation crap popped up. It doesn't feel like intake leak or debris in the jets. I had my fair share of that and I'm running out of stuff to replace ha ha.
I have worked on cars for a long time and usually have found either components work or fail completely. On ocassion there are intermittent failures, but it's fairly rare. Just blaming the coil doesn't seem like the right answer but not out of the question.
I have a hot date with the wife tonight. I'll swap boxes and report back tomorrow. Appreciate the help guys, I really needed some third party insight. Been fighting the gremlins for so long I feel like I'm not seeing the whole picture anymore.
Temporarily close your plug gaps to 0.015". If it runs better, suspect the coil...

Two ManyXS1Bs, sir last night I found a thread where you had told someone else the same thing. I cleaned the plugs up and re gapped them to .015 before I turned in. Didn't get a chance to ride it today. Going to run it in the morning, fingers crossed!

Jim I was thinking about your first question again tonight, and wanted to clarify some. I realized my posts are long winded and some what confusing.
The night I limped it home on the original box it idled but wouldn't rev past 3k and had no power (felt like it wasn't advancing spark). I had to give it gas then clutch and coast to make it home, wouldn't power out of second. Prior to that it had plenty of power but a hesitation in 5th, then died when hot, no power, no start.
Replaced the box. Now it idles good, revs past 3k with out popping and missing. Has good power now but hesitates, falls on its face and comes back on under load 1st-3rd (haven't gotten it up past 3rd due to poor running).
So yes, the problem moved with the box, to an extent. The issue of it breaking up and hesitating still exists but it got the power band back.

P.S. I took a look in the original box and found a leg on a capacitor broke. I'll have to re read the TCI repair threads and see if I can find sources on these and the diodes.20190716_215038.jpg
Thanks for clarifying. Sounds like the box fixed part of the problem. Waiting to see what happens with the closer plug gap.
I took a look in the original box and found a leg on a capacitor broke. I'll have to re read the TCI repair threads and see if I can find sources on these and the diodes.
Saving the pic and zooming in, you should be able to save the cap using a blob of solder to connect the two halves of the lead. Then squirt hot melt or Shoe Goo under it for vibration damping they left off of that one. The four diodes together that are those fragile glass eggs can be replaced with 1N400x from Radio Shack. Check an old one with a meter to make sure you turn them the right way if there's no symbol on the board. Give them the damping treatment too.
Of the (3) TCI circuit board pics I have, this one seems to match your pic.


The broken black electrolytic capacitor is just below C1. Can't see its designator, but guess that it could be C2.

Member Sleddog83 did a reverse-engineer of his TCI, and posted his schematic, from this thread.


C2 in his schematic feeds into pin 1 of the IC.


I couldn't tell you what purpose C2 serves in this circuit...
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Wow! Ok I downloaded sleddog83's schematic from a link I found the other night. Looks like I have some more reading to do. Thank you gentlemen. I will give her a dab of solder and glue tonight and see if she gets spark back on this box.

Ran her about a quarter mile from the house round trip this morning. About 20 yards out from the house I chopped the plugs, grabbed clutch and coasted in..
Right cylinder.
Left cylinder (a little wet)

It ran a little bit better, idled faster and felt like the timing was advanced with the smaller .015 gap. Symptoms didn't completely dissapear.

I stopped down the road to put a couple of O-rings between the plugs and caps (the caps have been ratteling around, making sure they arn't losing contact). The left carb had burped out the overflow during this procedure (over the course of two mintues). Needle tube is sealed, I watched it this morning while it idled.

Been chasing my tail for about a week now and feel like the definition of crazy, ha ha! Is it not getting good combustion or flooding out?

P.S. Here's what the plugs looked like last time it flat out died on the highway, before this whole rig-a-moral started. I actually ultrasoniced the carbs since this reading.
Yes sir that's the one I'm working on. My buddy was running those cheap pods but the lip was hanging over the ports and choking it. I've been running them with a piece of panty hose zip tied over the throat but took those off and it hasn't changed anything. I wear regular straight leg jeans any time I ride it. I'll look and make sure they arn't jamming the throats up next time I'm on it.
The pods were not on the bike when it died and no started on me, they have been off for a while. I drilled and vented the gas cap a couple months ago. It has a clean sporty (sorry guys) tank on it and new petcock. I get plenty of flow when I take the lines off. All this hesitation coincided with the bike dieing on the highway and then not having power with the key on. After a 15 minute cool down power came back on and it has run like crap since.

I thought maybe the pick up or rotor magnet...but the pick up ohms good and it doesn't change how it runs if the rec/reg are unplugged. How much of a driveability change would I see in shortening the plug gap? Issue gone completely or just run a little better or worse?
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What was your method of getting into the TCI box?

Mini flathead, got between the side and cover then popped the cover off. I did reflow the original board again tonight and fixed the broken leg on the cap. Put some epoxy on it, I'll drop it in and see if it gets spark again in the morning.
Looking forward to it. I’m about to fire up my TCI motor for the first time this weekend and want to be prepared if something goes south. Thanks for the info!
...How much of a driveability change would I see in shortening the plug gap?

An improvement if the coil is weak or failing.
An improvement if it's fuel or oil fouling.
A mild decrease in power otherwise.
Too much fuel/oil fouling will eventually bridge the narrow gap.
It's just a diagnostic tool.
Return gaps to normal after fixing...