Bad Coil??

[Tonup76]

I think my coils went bad today.  Let me preface this by saying that this is only the 2nd time this spring I ran the bike, I was waiting on my new tank, I'll post a pic.  Ran the bike for about 20 min took it around the block, it seemed to be a bit jumpy and cut out on me a few times....thought it was the gas so I filled it up, definately don't think it's a fuel problem.  When I got it home, well, when I pushed it home, I started checking things.  Pulled the coil/plug wire and it had no spark.  Pulled the tank and put a tester on the coils, they didn't work, tried it again and got some juice and it started and ran for about 10 seconds, tried it again no juice.  Put tank back on and it wont start, still no spark from the wires.  IS MY COIL BAD?  If so or if not where do I start?  What do I check first, second and so on to make sure it's my coil or and not something else.  Thanks in advance for the help and advice.

S
 
1973 CB750

[CB750Winger]

  Kind of unusual for both coils to go bad at the same time. Try unscrewing the spark plug caps off the wires and check spark there first, then back together with the plugs in the caps. Did you recently install new spark plugs and if so, what brand. Autolites, Champions, etc don't work, only NGKs. Also check to see if your point connections are grounded out on the plate.

[Tonup76]

I haven't changed the plugs recently, well, last summer.  Don't think it's the plugs.  Now that you bring it up I think I only tested one of the coils, I'll check them both tomorrow.  Hopefully just one of them went bad and it was the one I checked.  Thanks.

[woodsrider250-2]

Nice bike.  Check points.  The dyna electronic ign for the SOHC's is cheap.  

[Tonup76]

What am I looking for when I check them?  I was told to look at the condensor, but what am I looking for?  Also, should I be able to see the spark in the points?

[Re-run]

the condenser does nothing really. It prevents arcing on the points mainly. I do not think it is possible for a condenser to PREVENT spark.
Try this. Start the bike and run it a bit. Shut it off and then when it doesn't start, spray some carb cleaner in the carbs and see if it starts. If it does, then I would speculate a fuel issue. If still no start, then you can concentrate on ignition.

I have seen it where the fuel filter is plugged and when you run for a bit and shut down, the bike will not start right away.

The issue you seem to have though seems more like a loose connection issue though. I mean, if you run and then dont run and then run again, a loose connection is usually the culprit. OR a wire that is grounding.

[brcree]

  Great looken motorbike!!!!! Mine is almost there as well. Waiting on bumbstop seat and tank painted. Yes, there should be spark at the points.  My coils went bad awhile back...got some on ebay at a good price.  Pull a plug out and put the wire back on. Place the plug close to a good ground and crank it up. If spark is weak or not there...bad coil mate! Check all plugs to see if both coils bad. Hope this helps.

[Tonup76]

I think it's my coil.  I pulled the #1 and #4 plugs, one at a time, put the plug back on the coil wire, grounded it on motor, tried to crank and nothing, no spark.  What is really making me crazy is 15 min b4 that I actually started the bike and it ran for a few min.  I shut it off, waited a few min and then nothing.  Is that what happens when coils go?  I mean are they real tempermental like that and inconsistant?  If so, I'm gonna go get some coils.  Actually, I'm gonna clean the connections to them first, see if maybe there's a bad ground there.  If that don't do it, guess I'm gonna have to spring for coils. (sorry, couldn't help myself) I wanted to upgrade to a dyna system anyway so might as well do the coils and ignition.  

One more thing, what sends the current to the coils?  Could that be bad?

One One more thing, when I pulled my plugs they were black as hell, I just replaced them last year, what's that all about and how do I fix that.  

Yinz guys rock, thanks for all the help.  Hopefully I'll be able to do the same someday.

[Re-run]

Does 2-3 do this as well? I mean I suppose it IS possible for heat to make a coil not work but since it works for a while and then does not shortly after, I just do not feel it is a coil issue.
I certainly advocate new coils and a dyna but I still suggest checking the connections for your ignition system, ESPECIALLY the kill switch.

[woodsrider250-2]

what sends the current to the coils?

  The points.  Replace points and condensor together.  What you are looking for is clean points.  Points are like a switch.  They wear out fairly quickly.  Note that they need adjusted too.  WHen you turn the motor over while looking at the points you'll see them move.  Don't know what the spec is for that bike but the thickness of a matchbook will work.

Get a shop manual if none of this makes sense.

Dyna system replaces points with a fully electronic unit.

[Re-run]

it may be possible it is the points but read what he said happens. He CAN start the bike and run it for a bit. If he tries to re-start when warm, it does not go. now points are not that touchy. I have had pits and points on the points face and they worked without starting issues. However, maybe he has a points plate that is NOT stock. If so, then the plate might be warping when it gets warm and not allowing the points to move right.

I have been saying to check wires and connections as many times, that is the source. The kill switch is a common problem area. I have also seen a plug wire that was grounding, work fine when the engine was cold and then cause the cylinder to misfire when the engine was hot.

He can start checking whatever he wants but my idea does not require cash being thrown at the problem to test it.

he may just have a simple poor ground that does not manifest till the connection gets hot.
Heck, it could be his coil. All that heat gets trapped under the tank and the coils sit up in there and heat raises the resistance of wire and maybe be causing some issue.

I just do not believe that throwing parts at the bike is the answer. Points are very durable and take a lot of abuse. Which is the primary reason why so many like them. File the points smooth, gap them and see if that does it. If not, move on to something else.

not trying to start a piss match just saying to start at the bottom first.

[Tonup76]

I stopped at thee honda garage today in my area.  The owner is a good guy who is willing to give free advice.  Here's where he told me to start.  He was saying that the Kill switch could be bad, just like most of you are saying.  He told me to run a wire directly from the battery to the common wire on the coils.  He said this will basically bypass the kill switch, if it starts and runs there's my problem.  I'm going to try this on Thursday and I'll let you guys know what happens.  

Now the next question is that if it is the kill switch do I have to replace the whole unit or can I just purchase the internal parts.

Also, I posted above that my plugs were black when I pulled them.  I know this means that I'm running "rich", but what exactly does rich mean and how do I fix that?  

[brcree]

  Hey man, my old coils that were bad, had white powdery stuff on them....I've seen this on other electrical parts that have gone bad.

[Re-run]

Did you clean the powder off or just replace the coils?
Just wondering. See I am cheap!  I do not mind buying parts but only when I have to or there is a real plus. If I can recondition a part to work well, I do that instead of new parts.

[Re-run]

It may be possible that the internals are just dirty. You can actually pull the right hand controls apart and clean things up pretty well in most cases. Sometimes you have to replace but the parts themselves are generally durable. Just do it over a clean surface carefully as there is a spring in there that could fly out and disappear for 10 years!

[Tonup76]

THANK YOU THANK YOU THANK YOU!!!!!!!!!!!!!!!!!

IT WAS...............................(drum roll)


The Kill Switch!  Fixed.  Just got back from riding for about 3 hours.  I used the tip my mechanic gave me, ran a wire from the battery directly to the common wire that goes into the coils and BAM, she started right up.  I would have NEVER tried that if you guys didn't point me in that direction.  Got a new switch for 60 bucks.  Thanks so much I am happy as a pig in shit.

Ton Up.

[Re-run]

Always start with the simple stuff first!

ESPECIALLY with electrics!  

[Half-Caf]

Good advice. Wondering if my kill switch is bad. Will have to try the wire trick to see if that helps...

[Lucky 1]

Coils almost NEVER go bad. Very rare.

[TOOLS1]

I just had to replace one the other night, but I will agree. They hardly ever do go bad.
TOOLS