No spark TC250

doug rooney · Post by **doug rooney** » Thu Mar 11, 2010 8:11 am

Had this engine apart again for an issue I resolved. Ran fine before but now no spark on the right. Have tried 4 different plugs. Great on the left side. Even tried that plug on the right side. Checked and rechecked points and timing. Don't know if this is a proper test but have 12v at BOTH plug caps with the key on. Checked and rechecked wiring connections and seem ok. What am I missing? Thanks

I just checked and even have 12v at the plug end BUT, it's when the points are open?? Seems bassakwards??

rbond · Post by **rbond** » Thu Mar 11, 2010 9:41 am

Pull out an ohm meter. Check both coils on both sides(input from wiring harness and then sparkplug wires) quickest way to eliminate the coils as the problem. If both are OK, then start from that point on the frame and follow all the wires looking for a disconnected or shorted to frame wire. Having the right voltage is not the only test, the proper resistance also has to be there. Wiring problems are usually a PITA, but on these older bikes, they are very simple and fairly easy to fix. Also, if you have a spare condensor, swap it out or at least borrow the working one to see if it magically starts firing on the right side. While you are nosing around the points, check the connections there to see if a wire is not isolated from ground, compare it to the left side to see if connected EXACTLY like the working side. Test anyway with your meter to check for improper grounding.

Coyote · Post by **Coyote** » Thu Mar 11, 2010 9:45 am

Don't know anything about your bike but if you have 2 condensers, try swapping them out and see if the problem moves to the other side. Also check for a short at the points. With the ignition off, hook up a voltmeter. attach one lead to the moving point arm and the other to ground. Set the meter to check continuity. Manually open the pionts. You should see a reading of full continuity with the points closed and it should drop to zero with the points open. If doesn't change when the points are open, you have a short where the pigtails attach to the points.

doug rooney · Post by **doug rooney** » Thu Mar 11, 2010 10:33 am

Thanks guys. Will try those things. What should "full continuity" be?
Did find that the wire from the right condensor was not spliced well to the stator so I redone that and now have a constant but weak spark. Not enough to fire the cylinder though. But, before this I had none. Maybe I'm onto something??

doug rooney · Post by **doug rooney** » Thu Mar 11, 2010 11:05 am

OK, set my multimeter to 20K Ohms and have 18. something on the good side and 12. something on the left??? Coil Bad??

rbond · Post by **rbond** » Thu Mar 11, 2010 1:36 pm

Full continuity is when you get a near zero resistance reading. This is a simple quick means of determining that you have a solid connection or a partial, intermittent, etc. See if you can find out what the resistance readings should be for your coils. Getting some spark means your on the right track, but not quite there. Maybe you should pull the stator off and do an R and R to really be sure everything is mounted solidly and ALL connections are good, if you still have weak or no spark, move up the wiring harness. If you have a bad coil, with the known resistance values of a good coil, buy a pair of aftermarket and put them on. Keep the known good original as a spare. All this is a inconvenience now, but it is the best way to 'get to know' your bike and raise your overall mechanical knowledge. Especially if you can do all this at home and not out in the boonies!!!

doug rooney · Post by **doug rooney** » Thu Mar 11, 2010 2:00 pm

Super six site says resistance between + and - terminals should be 1-2 ohms. I think I know how to test that but it then says between primary and secondary should be between 5K and 11K ohms. Where would I put my meter probes to check that?

tz375 · Post by **tz375** » Thu Mar 11, 2010 3:34 pm

Resistance on teh primary is between the two LT connections or the + and -.

With point ignition, one side is switched 12v and the other side connects to the points and condensor. Typically points ignitions run 3 to 5 ohms across the primary and ET systems or CDI systems are typically 0.5 to 2.0 ohms across the primary side of the coil.

The secondary side is the side of the coil that sends the spark - AKA the HT side. So you are measuring between the HT lead and one side of teh ocil connections.

On old bikes connections tend to be corroded and wires frayed, but another frequent problem is putting the condensor led on the wrong way at the points. the connection to teh points and condensor typically connects to one side of the points and has to be insulated from the bolt/post. If teh lead is not insulated, the power from the coil is shorted to ground and the points are not in the circuit.

doug rooney · Post by **doug rooney** » Thu Mar 11, 2010 4:55 pm

Thanks fellas. All great info!

Partially solved and have isolated the problem I think. The plug wire was broken in the middle I could tell after closer exam it was not stiff in one spot. Cut the wire and spliced that and had both sides going for awhile. Put the tank back on and it quit. It is also loose where the wire enters the coil and now fear it is broken inside. That part's sealed and don't know if it's fixable???

Post by **Suzsmokeyallan** » Thu Mar 11, 2010 5:38 pm

Doug there is way to change the HT lead on the coil but it requires cutting across the top so a portion the extruded portion where the wire comes out is sawed off parallel to the coils body.
You are basically trying to get to the contact where the HT lead is affixed to the output terminal on the coil.
To do this you would cut the HT lead off the coil where it exits the plastic housing and then cut across the coil section about 2/3 of the way down into the cross section of the HT lead
Then you carefully pry out the old HT portion of wire left in the body to get at where it is attached.
IF you are neat and use a thin sawblade the piece you cut off can be reused with some epoxy sealant to attach it to the coil once the new HT lead is installed.

doug rooney · Post by **doug rooney** » Thu Mar 11, 2010 5:48 pm

Wow. Not sure I'm following you Suz. What is HT lead? Hack saw blade? Can you say it again in some different words? What I'm hearing is to make 2 parallel cuts the length of the coil (Don't see how I could do it part way?) Then cut across the coil at some point down to the connection (Wherever that is?)
Sorry I'm so dense

Post by **Suzsmokeyallan** » Thu Mar 11, 2010 5:56 pm

HT lead is the (plug wire) better known at a high tension lead.

Ok here we go

Place coil in vise and using a micro hacksaw, cut off the plug wire where it exits the coil body
Then take the saw and cut across the protuding part of the coil where the wire came out of as if you are cutting it off the coil.
However you will do this cut just above the copper core of the wire thats left inside the part of the coil body.

Ok sorry for the confusion and making it too long in words

doug rooney · Post by **doug rooney** » Thu Mar 11, 2010 6:24 pm

OK Suz, that is more understandable to this old guy. I'm fried right now with this bike and a bunch of stuff so will look at it in the morning. If it's still fuzzy I will let you know. Thanks so much! Doug

Post by **Suzsmokeyallan** » Thu Mar 11, 2010 7:39 pm

Doug I've searched for a site where I once saw how a person had done such a mod to their coils but i cant locate a link to it right now.
If anyone has that link please post it here as there were photos of how the coil was cut open for the new plug wire to be adapted.

TLRam1 · Post by **TLRam1** » Thu Mar 11, 2010 9:12 pm

Stu I think had photos and did this to his..