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Old 05-06-2012, 07:13 PM   #1
Droz88 OP
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Not getting spark on a Yamaha CT3

After determining that the engine is not getting spark, I decided today to tear into the bike and see if I could find the problem. After some extensive research about how ignition systems and magnetos work I feel pretty comfortable. However, at this point all the parts seem to be there but I still can't get spark to get to the spark plug. Below I have posted pictures of what my coils look like so hopefully someone will be able to tell if there is an obvious problem somewhere. Other than that I think my best move now is to get some sort of volt meter and find out if there is a problem with the condensor or ignition coil. I'm pretty sure that the wiring is done correctly so as to give spark to the plug as long as all the components are working.

Here is how I have it wired: From the magneto there is a green/red wire which is connected to a black wire (black wire is coming out of the ignition coil). From there there is simply a spark plug wire going to the spark plug. I am testing for spark by holding the spark plug against the engine block while kicking the engine over with my hand. I am just visually watching the gap in the plug to see if there is any arc.










Other than this one problem I took the carbeurator apart and cleaned it today too. It sounds like it has good compression and as long as the timing is right I feel this engine should start up. Can anyone suggest how I could properly diagnose this to find where exactly the problem is?

Droz88 screwed with this post 05-07-2012 at 01:27 PM
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Old 05-08-2012, 09:39 AM   #2
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After carefully reviewing the factory service manual, I believe that the green/red wire is NOT the ignition wire. The only other wires are the green, yellow, and black wires. The green and yellow are also not ignition so that only leaves the black wire. This makes sense but I wonder why the previous owner had it hooked up to the green/red? Maybe they just didn't know what they were doing?

Also, from reading it appears there is supposed to be some type of cam lobe which opens and closes the contact breaker but I didn't notice anything like that on this bike. Perhaps that is missing?
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Old 05-08-2012, 02:58 PM   #3
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Two outta three of those coils dont look good.

Its sounding like you have alot of wire tracing and electrical diagnosis ahead.

The cam lobe that opens the points is on the inside of the flywheel thats off that was covering the points and coils.
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Old 05-08-2012, 03:35 PM   #4
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Took the ignition system off today and took it to a local yamaha service/parts shop. The grizzly old guy who owned the store tested things out for me, told me which is the ignition wire, sold me a new contact breaker, and gave me instructions on how to install and set the new one. He even greased the cam lobe for me.

I replaced the contact breaker, set the point gap to about .0014. The green/red wire was NOT the ignition wire; instead it was the black wire. IT NOW HAS SPARK!!!!

However, the service manual say that the arc should jump when the spark plug is around 7mm away from the head but that is not the case here. I have to hold the electrode pretty much right up against the cylinder head in order for it to spark. Not sure if this is an issue because the spark plug gap is supposed to be 0.5-0.6mm so at those measurements the spark is fine.
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Old 05-08-2012, 03:46 PM   #5
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Houstan we have Ignition , you are getting close
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Old 05-08-2012, 05:18 PM   #6
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Ok well now the spark is jumping the 7mm so not problems there!

I put some fuel in the gas tank and tried starting it but no go...it sounded like it was very close at one point when I sprayed carb cleaner in it (backfired). I don't have an air filter for this thing and I know that sometimes that can cause them to run funny. Otherwise I think the only thing I have to do is to tune the carburetor but there is no mention of how to do that in the service manual.

Anyone happen to know the right settings for the air/fuel and idle screws?

So close I can already smell the 2 stroke exhaust........
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Old 05-10-2012, 07:42 PM   #7
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No luck getting it to start or run. When I spray carb cleaner in it and kick it over it sounds like it's on the brink of firing but the carb cleaner evaporates so it doesn't start. I put fresh fuel in there and mixed it with fresh yamaha 2 stroke oil for a 20:1 ratio but still didn't start. So i've narrowed it down to being either a fuel delivery problem or weak spark.

I already took the carb apart and cleaned it. I am missing the pilot jet o-ring so possibly that is causing the fuel delivery problem but i have doubts. Otherwise since I don't have an air filter on the bike maybe that is also causing the problem.

Any suggestions?
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Old 05-11-2012, 05:33 AM   #8
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First things first.

You need to do a real compression test. If its under 80 pounds, its very low. It might run if its around 95 pounds.

If its 120 pounds your good.
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Old 05-11-2012, 06:15 AM   #9
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Don't have a compression tester. I've already dumped enough $ into this bike and really don't feel like spending any more. I'll try a few more things today and if I can't get it to start I'll probably just sell it....turning into a money pit.
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Old 05-11-2012, 01:11 PM   #10
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Ok got the compression tested and it was like 20psi. The i checked the head bolts and they were finger tight! So I took the head off, cleaned the surfaces and gasket and put it back on and tightened the head bolts good. Now it has 120psi!!!

I kicked it and it fired up on the first kick and ran for about 5 seconds and then died. I've kicked it about 100 more times and haven't been able to get it to start again. Tested compression again and it was still at 120. Checked the spark and it is there but it may be a weak spark; I don't know how to tell. The fuel petcock is leaking and there is air in the fuel line but I don't think that's a problem. I am also missing an o-ring inside the carburetor but I don't know if that could be causing this problem. Otherwise the only thing left is the timing but I don't have anything to check it with. There are no marks or anything on the flywheel/case.

PLEASE HELP!!
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