Sudden loss of power and heavy vibration

[Phare Est]

It sounds like the bike was running on all four when you checked it.
One other thing to remember is that coils sometimes get inoperative after they get warm. The coils expand, and the cracked wire opens up, and they quit. They cool down, contract, and work again. So ride the bike with an ohm meter and the tools necessary to get to the primary and secondary coil circuits in your pocket, and go ride around the block till you get tired of it, or the miss starts.
Then measure the continuity through both internal coils of both coils.

Hi CaptonZap,

Cylinders 2 ou 3 are definitely not firing. I rode the bike a couple more times over the weekend and it still would not go faster than 50 mph. I didn't get the chance to do the coil swap yet.

[speedlimit85]

Pinch the vacuum advance hose with a wire tie. Then ride for a while. If it keeps working, your pick up wires are intermittently disconnecting.

[Phare Est]

The easy check is to move the plug wires so 1&4 now go to 2&3, and then swap the connections at the coils. Then firs the bike and see if 2&3 are now hot. If not, you have a bad coil. If they are now hot, you have pickup coil/wire problems.

Hi DiverRay,

I did exactly as you suggested by swapping the plugs wires AND the connections to the coils. Here are the results:

Cylinders 1 and 4 were hot; cylinders 2 and 3 were cold. Wouldn't that be indicative of a WIRING issue? The coil that was previously plugged on cylinders 2 and 3 would not be working on cylinders 1 and 4 if it were bad. And the coil that was working on cylinders 1 and 4 is not working on cylinders 2 and 3.

Should I replace the two (light blue and white) wires I haven't touched yet? https://lh3.googleusercontent.com/k6...5-w955-h716-no

[jetmechmarty]

Kurt gave you the answer. You no doubt have a pick-up coil wire issue.

[Phare Est]

Update − All cylinders are firing

The problem has been solved ☺. I had a spare ignition unit (taken off a '79 XS11 Special) lying around and decided to swap it with my existing unit. Lo and behold, all four cylinders are now working as they should and the bike sounds beautiful! For the past year, it had been difficult to start and was backfiring more and more. I had pretty much convinced myself the carbs were out of synch, but the ignition unit was no doubt starting to fail. Is this a common issue with XS11s?

[DiverRay]

Age is what caused the problems. If you take the cover off the unit, and you know what to look for, you will probably find some of the solder joints have cracks. You should be able to fix the old box by re-flowing the solder on all the joints.

[Phare Est]

Age is what caused the problems. If you take the cover off the unit, and you know what to look for, you will probably find some of the solder joints have cracks. You should be able to fix the old box by re-flowing the solder on all the joints.

I thought I had resolved the issue... Although all cylinders are running, it turns out the bike delivers barely more power than it did when the faulty ignition unit was plugged in. There is also a strange sound coming from the engine when I rev it. I noticed that the IU on the '79 Special isn't the same type (TID14-01) as the one on my '81 Midnight Special (TID14-04). Would this explain the fact that the engine isn't running properly?

[skids]

I thought I had resolved the issue... Although all cylinders are running, it turns out the bike delivers barely more power than it did when the faulty ignition unit was plugged in. There is also a strange sound coming from the engine when I rev it. I noticed that the IU on the '79 Special isn't the same type (TID14-01) as the one on my '81 Midnight Special (TID14-04). Would this explain the fact that the engine isn't running properly?

Yes, it certainly would!

[Phare Est]

Bad news : I tried to get a look behind the circuit board in the ignition unit by first removing the two screws underneath the box, but I ended up damaging the circuit board anyway: https://lh3.googleusercontent.com/fs...U=w971-h728-no.

Can this IU be saved? I don't even know if it was salvageable in the first place, so I'm probably just gonna go ahead and buy another one and save myself a headache in the process.

[dansmith65]

That link doesn't work for me. Make sure you use the "share" feature to get a shareable link as the url to the file as you're viewing it only works when logged into your google account.

This is for a different bike, but I still think there is relevant info, like it says to cut a hole in the plastic rather than trying to remove the circuit board. Sounds like it's too late for that, though! http://www.jetav8r.com/Vision/IgnitionFAQ.html

Here's another option, if you do need to get a new TCI: http://www.xs11.com/xs11-info/tech-t...-gm-parts.html

[motoman]

I thought I had resolved the issue... Although all cylinders are running, it turns out the bike delivers barely more power than it did when the faulty ignition unit was plugged in. There is also a strange sound coming from the engine when I rev it. I noticed that the IU on the '79 Special isn't the same type (TID14-01) as the one on my '81 Midnight Special (TID14-04). Would this explain the fact that the engine isn't running properly?

TCI unit for 81 models has mechanical advance incorporated into it. 78-80 models has actual mechanical advance unit mounted under left side ignition cover, underneath advance unit is centrifical springs etc. TCI unit has 2H7 embossed on it for 78-80 models and 81 models have 4RO embossed on it. In other words, using a 78-80 TCI on an intended 81model with 81 ignition, you will NOT have any mechanical advance resulting in serious power loss.

[Phare Est]

That link doesn't work for me. Make sure you use the "share" feature to get a shareable link as the url to the file as you're viewing it only works when logged into your google account.

This is for a different bike, but I still think there is relevant info, like it says to cut a hole in the plastic rather than trying to remove the circuit board. Sounds like it's too late for that, though! http://www.jetav8r.com/Vision/IgnitionFAQ.html

Here's another option, if you do need to get a new TCI: http://www.xs11.com/xs11-info/tech-t...-gm-parts.html

Thanks dansmith65 and motoman for the info and the links! Here's my damaged TID14-04 4RO-10 ignition unit: https://www.flickr.com/photos/143801...posted-public/. Is it actually reparable?

[DiverRay]

That's a multi layer board. Your better off getting a different unit. Like almost anything, it COULD be repaired, but may cost hundreds of dollars to do so.

[Phare Est]

That's a multi layer board. Your better off getting a different unit. Like almost anything, it COULD be repaired, but may cost hundreds of dollars to do so.

Hi DiverRay,

Precisely what I was thinking. The circuit board would absolutely not budge on the end where it ended up braking. I'll start shopping around for a new unit.

[Phare Est]

TCI unit for 81 models has mechanical advance incorporated into it. 78-80 models has actual mechanical advance unit mounted under left side ignition cover, underneath advance unit is centrifical springs etc. TCI unit has 2H7 embossed on it for 78-80 models and 81 models have 4RO embossed on it. In other words, using a 78-80 TCI on an intended 81model with 81 ignition, you will NOT have any mechanical advance resulting in serious power loss.

Hi motoman,

Would it be possible to install a mechanical advance mechanism on a '81 model and use a 2H7-10 ignition unit?