[Hotrodjohn]

So my CDI died, All of my numbers check out good on the charging stator and trigger, so I found a used CDI on ebay. I put it on and it is getting a spark but its putting out a spark on every stroke, not just the power stroke, basically a constant spark as the engine turns over. As you can imagine this doesnt work. Any possiblity the trigger is causing this? It checks good on resistance, I cant imagine how it could constantly send a signal. seems like this CDI is bad too, it is a used 87 CDI. anybody?

 

[lizrdbrth]

TW's use a`wasted spark system. It fires every revolution.

 

[Hotrodjohn]

TW's use a`wasted spark system. It fires every revolution.

So it fires constantly?

 

[lizrdbrth]

Every rev, rain or shine, intake or exhaust stroke. Spark isn't your problem.

 

[Hotrodjohn]

Every rev, rain or shine, intake or exhaust stroke. Spark isn't your problem.

This thing is driving me nutty. I got it, rebuilt carb, ran perfect then cdi started acting up until no spark, no it has this constant spark which you are telling me is normal and it fires and sputters. Took carb off again and neither jet is clogged.. Mixture screw is either one two or two and half out.. anyway, it ran near 70 mph before the cdi went out . puzzling.

 

[operose]

They seem to get some extra "pep" when the CDI is about to let out its magic smoke.



Sounds like it is sparking fine... you say it fires and sputters, but won't start?



Don't have any immediate advice, but keep digging. It is probably something small that has been overlooked, happens all the time

 

[Hotrodjohn]

They seem to get some extra "pep" when the CDI is about to let out its magic smoke.



Sounds like it is sparking fine... you say it fires and sputters, but won't start?



Don't have any immediate advice, but keep digging. It is probably something small that has been overlooked, happens all the time

when I ground a plug and crank it, that plug looks like a sparkler on july 4th, just a constant spark.

 

[operose]

http://en.wikipedia.org/wiki/Wasted_spark



"The wasted spark system is an ignition system used with some four-stroke cycle internal combustion engines. In a wasted spark system, the spark plugs fire in pairs even though one is on its compression stroke and one is on its exhaust stroke. The extra spark on the exhaust stroke has no effect and is thus "wasted". This design halves the number of components in a typical ignition system, while the extra spark, against much reduced dielectric resistance, barely impacts on the lifespan of modern ignition components."





That example is for a 2cyl engine, but the principle is the same. The spark plug fires on both power and exhaust stroke, but the firing on exhaust doesn't matter. As long as it is actually firing once at the right time in the stroke and is getting fuel and air, the bike should run (but perhaps poorly depending on other issues...)



Is it literally sparking "constantly" ?? It should not fire on the intake stroke which might be your sputtering issue.



Did you have the rotor off? Are you sure the "pulser coil" (trigger as you call it) checks out spec wise?



Keep feeding us info and we can help you figure this out. Don't get too discouraged

 

[Hotrodjohn]

http://en.wikipedia.org/wiki/Wasted_spark



"The wasted spark system is an ignition system used with some four-stroke cycle internal combustion engines. In a wasted spark system, the spark plugs fire in pairs even though one is on its compression stroke and one is on its exhaust stroke. The extra spark on the exhaust stroke has no effect and is thus "wasted". This design halves the number of components in a typical ignition system, while the extra spark, against much reduced dielectric resistance, barely impacts on the lifespan of modern ignition components."





That example is for a 2cyl engine, but the principle is the same. The spark plug fires on both power and exhaust stroke, but the firing on exhaust doesn't matter. As long as it is actually firing once at the right time in the stroke and is getting fuel and air, the bike should run (but perhaps poorly depending on other issues...)



Is it literally sparking "constantly" ?? It should not fire on the intake stroke which might be your sputtering issue.



Did you have the rotor off? Are you sure the "pulser coil" (trigger as you call it) checks out spec wise?



Keep feeding us info and we can help you figure this out. Don't get too discouraged

Took it back off, checked the charge coil, the pulse coil, the coil, all within yamaha spec. It starts and sputters, as you move it or squeeze it, it will run perfect intermittently, sounds like cdi failure to me.

 

[Jon H]

I ordered a new cdi for my 1987 from Power Sports Plus about a week ago. Put it in, but could only manage a few miles since it isn't much over 20 today. So far, so good. This after the usual chasing of a carb issue for some time.

 

[Hotrodjohn]

I ordered a new cdi for my 1987 from Power Sports Plus about a week ago. Put it in, but could only manage a few miles since it isn't much over 20 today. So far, so good. This after the usual chasing of a carb issue for some time.

Well, it damn sure was the CDI that was bad even though it sparked. I ordered a new one, also from Powersportsplus, and plugged it in. It runs perfect now. When I first bought the bike I too went thru the carb ten times thinking that was it. It would run perfect one day and barely run the next.. It will drive you crazy. Hopefully this will keep on running now for a while.

 

[Hotrodjohn]

Bought a new CDI, Powersportsplus, 241.00 dollars., runs great now........ Never buy used 87 cdi, lol, they all go bad, its just a matter of time. Ive owned over 30 bikes and up until now have never had a CDI go bad.

 

[Jon H]

Glad you are on your way Hotrod. Mine seems to be running great too with the new CDI. Just a weakness with this particular year TW. Cheers.

 

[operose]

Can I have your bad CDI? Will pay shipping