weak spark

[MAX]

Hi
I'm Max I have a 78 yamaha xs 1100 e. I had no spark so I replaced the ign. unit now I have weak spark. I have checked the pick up coil and the coil.
NEED HELP .
THANKS max

[CatatonicBug]

Just a stab in the dark here, but how about trimming the plug wires back from the end? I know there have been some threads on that recently. Something about pulling the caps back, trimming the wires 1/2", and putting the caps back, and re-installing on the plugs. I'm sure there will be better advice from someone else too.

[DGXSER]

Bug has a good suggestion. You pull the boot off the plug. Hold the wire and turn the boot to pull it off. Basically the boot has a screw thread like a wood or sheet metal screw in the middle of it that threads into the wire. Unthread the boot from the wire. Trim about 1/4" or so off so you have fresh wire to thread into. Push the wire in while turning the boot to let that screw thread into the wire.

Typically the way I understand it, the TCI does not effect the strength of the spark, just if one is there. For strength I'd start where you are plug ends, wires, coils, work back from there to the alternator perhaps? Have you replaced plugs recently, how old are they?

[dbeardslee]

Might try cleaning the handlebar stop switch too. All the power to the coils runs through that switch, and they get pretty grungy. Be careful when you remove the circlip that holds the switch together - there's a ball-bearing and three small springs in there that like to fly. Clean all your electrical connections and lube with wd40 or dielectric grease, and don't forget the ones that are hiding behind your fuse block. Pay particular attention to your grounds - there's a bunch of them hiding around the bike.

Might check your voltages with a multitester too. You should be getting 14.2 volts at the battery @2k rpms. If you get a reading that is significantly different than that you may want to check the charging system. You can also check your voltages at the TCI - with everything connected and the ignition turned on but not running put the red test probe on the orange wire and the black to ground. Should get a reading of 12 volts plus or minus. Repeat for the grey, red/white, and white/red (IIRC) and voltages should be about the same. The black/wht should show 6v. Check your resistance to the coils by running a continuity test on the 4-wire connector at the TCI (disconnected, power off) wht/red to wht/grn, and yellow to yellow/red. Should get 720 ohms plus or minus 20%.

[Silent]

I had a weak spark on my '79. I replaced the coils, wires, and caps. Even after all that, I still had weak spark. It turned out that the battery was very old and not holding a complete charge even after being on a Battery Tender overnight. I replaced the battery and the spark is now strong. Might not be the cure for you, but it is something to check.