Ignition skip/misfire

[gaps]

Hola, hoping to get some input with my XS project bike, having some trouble...
I've been chasing my tail with a weak spark problem. This is a 1980 TCI bike that will start first kick when stone cold and run great until warmed up a bit, then it will begin to skip under load.
Battery is holding a nice 12.5 volts at rest and my volt meter shows a good charging system when running.
I replaced the coil, wires and plug caps after finding high resistance on the secondaries but that didn't fix it.
Also noticed that when the bike gets warm I can get it to skip by beeping the horn, this takes away almost all spark almost like a kill button...hoping this might be a clue...but I don't have a clue why.
Any thoughts???

 

[CDNTX650]

clean all your connections well. Secondaries on Coils should have high resistance. If you can't fix it try using a relay with a fused + right from the battery for the + to the coil. Then see if you get any cutting out.

 

[gaps]

CDNTX, thank you for your help. I'm a bit confused, how is the spark timing controlled if not thru the positive coil lead? I thought the positive feed for the coil comes from the TCI unit and handled ignition timing...or is the ignition timing controlled by the negative?
If I hook up the coils positive terminal to the battery thru a relay it seems something is needed to make the spark happen at the right time.......
Oh yeah, my oem coils had over 30k ohms across secys, isn't that out of spec?

 

[pamcopete]

gaps,

Try riding the bike briefly with the reg/rect unplugged. It's possible that the magnet in the rotor that is used to trigger the TCI pickups has lost some of it strength after 35 years. (like all of us!) and the magnetic field in the rotor is interfering with the magnet and the pickups.

If this is the case, then you can buy a rare earth magnet at Radio Shack and epoxy it on top of the little magnet in the rotor to restore like new performance.

 

[gaps]

pamcopete,
Thanks for your help.....here come the dumb questions.......What should I be looking for with the reg/rec unplugged?
Also, where is the rotor with magnet that triggers TCI located?

 

[xjwmx]

What should I be looking for with the reg/rec unplugged?

You should be looking for the absence of the symptoms....

Under the left side case cover.

 

[pamcopete]

pamcopete,
Thanks for your help.....here come the dumb questions.......What should I be looking for with the reg/rec unplugged?
Also, where is the rotor with magnet that triggers TCI located?

Here is a picture of the rotor and the trigger magnet (TCI Magnet in the pic):

It's located under this cover;

 

[gaps]

thanks again pamcopete, I have some good stuff to go on here, bit of luck I'll have her humming soon.

 

[CDNTX650]

ahh, sorry. forgot you have TCI. For points thats a quick fixer. yeh, 30k ohms seems higher...i thought it was only like 12k or so...

 

[XSLeo]

Depends on how you measure. spec for just the coil is 10500-15500 ohms, if you add the caps then another 10000 ohms for them. 15500+ 10000= 25500, most specs are +or- 10% so 25500+ 10% = 28050 So 30000 is stilll a bit high.
You say your "meter shows good charging system when running" What voltages are you getting at 2500 rpm? Should be 14.5 volts. Much less than that and your not charging as well as it could. The TCI doesn't like low voltage.
Check the voltage when the bikes wrmed up to the point you are having trouble. I have a rotor that charges fine cold but after it warms up it stops charging.

 

[gaps]

XSLeo, I'm getting about 14.2V at aprox 3k rpm but that is when I first start it. I'll have to give it a check when it's hot then, great idea.
I'm still trying to figure out what's up with the horn... today again when I operated the horn I got misfiring, but only when the bike is reved above idle. I can operate the horn at idle rpms and she sits there purring nice. Bring up the revs to about 3k rpm and the horn takes the spark strenth down to where you get a misfire....So, if the horn is on a seperate circuit but pulling power from my coil, what does that mean? And only as revs climb?

 

[XSLeo]

Every thing runs off the battery, the charging system recharges the battery. Anything that draws the battery down works the charging system harder. If the charging system can't keep up then when you draw more than the system has something is going to not get what it needs. The TCI box can be very fussy about voltage.
It may be partly caused by several things. Those that Pamcopete mentioned as well as those I mentioned.
Just another thought, the horn push button can be dirty and drawing more current to work the horn or the horn is going bad and drawing more current.
How well do the turn signals work? They often won't work well if the voltage is low.
Check the grounds.
I'm running low on ideas.
How old is the battery? If it's not up to snuff that can be part of it.

 

[pamcopete]

gaps,

Have you investigated the weak rotor magnet issue?

If the magnet is weak, then any disturbance in the electrical system, such as blowing the horn, could cause erratic operation of the TCI. The TCI electronically advances the spark at higher RPM but not at idle, so it's possible that the weak magnet is interfering with the TCI's ability to properly advance the timing when there is a disturbance in the electrical system.

The TCI uses the time difference between the two sensors to work it's magic. That's right at the heart of the problem. Please check the weak magnet theory so I can sleep tonight.....

 

[gaps]

First, let me just say thanks again for all the input. You guys have been great and this site in general is just terrific.

Next up is the weak pickup magnet test, I'll unplug that rec/reg and give er a go. I think I spotted that connector last night under left side cover near the rear of airbox.
Hope to get to it tonight, I'll post up soon as I do.

I do have signals that operate nice, horn is bright and loud. I get a bit of lighting dip at idle but they come bright with a few revs.. I can't wait to get this puppy running right, sure is fun for those first few minutes before she gets to wheezin.

 

[gggGary]

A possibility is a failing TCI There are several how to's on TCI R&R there are a few diodes in there that are prone to failure and a transistor that can act up as well. The TCI is not potted so replacement of components is not difficult. Getting the TCI out of it's hiding place under the battery may be a different story if you live in the rust belt.

 

[gaps]

PAMCOPETE, may I call you Pete? Sir, you are a real gentleman, perhaps a genius and certainly respected around here.
A few minutes ago I went out to the garage and fired her up as usual on the first kick. Up and down the road (rainy, windy and dark but with a headlight) I go until she starts skipping. Pull into the garage, unplug the rectifier/regulator, and back out into the rain...this time no lights and the damn thing just pulls clean, NO SKIP. Slow down and try it again beeping horn, just keeps on pulling Just for fun I plugged it back in and bingo, she's a skkipper!!
Now to locate a rare earth magnet and some epoxy, any specifics in that regard? Special epoxy, JB Quick perhaps?
Dude, you are on my Xmas list, I need an address.

 

[pamcopete]

gaps,

Well, the magnet is available from Radio Shack. Use JB Weld (not JB Quick) to attach on top of the existing magnet with the same polarity, that is, in the direction that the magnet is attracted to the existing magnet.

Be sure to clean the surface completely before attaching the magnet and wait overnight for the epoxy to cure.

The rare earth magnets are part # 64-1895. A two pack, 4.8 mm/ 3/16 ". $1.99 a pack. Check to see if I am correct on this. The important thing is that there is enough clearance between the rotor and the stator frame for the magnet.

 

[gaps]

Pete,
Great, I'll pick up the JB Weld and magnets tomorrow. I haven't looked behind that cover yet, do I need to pull the rotor or is the magnet right there under the cover?
thanks again,
Eric

 

[pamcopete]

gaps,

No need to pull the rotor. Just remove the round cover as illustrated above and the TCI Magnet is exposed if you just rotate the crank with a 17mm ratchet on the rotor nut.

Just make sure that there is clearance between the magnet and the stator frame.

 

[xjwmx]

Is the original magnet removable? I know of a magnet recharging service....