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99 XT600 Severe popping under acceleration 99 XT600 Severe popping under acceleration
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Yamaha Tech Originally the Yamaha XT600 Tech Forum, due to demand it now includes all Yamaha's technical / mechanical / repair / preparation questions.
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  #16  
Old 15 Jul 2013
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So with your numbers, are you actually getting spark to your plug when it is under compression? O.O when the speck is 10K sounds like that setup isn't quite right. Sometimes even though a plug is sparking when out of the head, it doesn't or has sporadic spark under compression. Do you have another plug wire and cap to try?
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  #17  
Old 19 Jul 2013
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No there's no spark at all, I tried another plug wire and cap from a set of automotive wires I had in the shop, they don't have the copper wire like the original but still I thought it would do if the plug wire/cap were the problem, still no spark.
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  #18  
Old 19 Jul 2013
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You'll have to check for juice getting to the coil and see if the cdi is sending it in the first place. Start from there and work back.

Did you take the coil off the frame and scuff up the mount surface plus shine up the ground wire and all touching surfaces. You want good grounding to start with. Not just clean but physically sanded and made positive contacts.
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  #19  
Old 2 Aug 2013
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Just an FYI. Your decel valve looks like it has been replaced already. The 3 little marks are factory marks. Mine had that too. I just grabbed the lip on the brass and rocked it a little and it came out easily. Might be worth a try. Normally this circuit is held open with the spring behind the cover of the diaphram. High vacuum from the secondary in front of the butterfly valve over rides the diaphram spring and closes the air off of the pilot jet causing a richer condition.

You mentioned popping under acceleration. I don't believe this circuit will cause this as it is to enrichen the mixture to the point it will not burn in the muffler and cause a backfire.

Is your spark good and robust? Really snap? If not, if it is a weak spindly spark your CDI could be dying. I had that happen to me, then it quit altogether.

Steve
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  #20  
Old 13 Aug 2013
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Quote:
Originally Posted by jjrider View Post
You'll have to check for juice getting to the coil and see if the cdi is sending it in the first place. Start from there and work back.

Did you take the coil off the frame and scuff up the mount surface plus shine up the ground wire and all touching surfaces. You want good grounding to start with. Not just clean but physically sanded and made positive contacts.
I pulled the coil off and scuffed up the mounting surfaces but still no go, can you explain the procedure for checking for juice to the coil ? I set my tester to 200 AC and placed one of each lead to each of the wires going to the coil, turned the engine over but the meter remained at zero, I've searched all over for stator output numbers going to the coil but nothing is coming up, can't find anything in the various XT600 service manuals I have on pdf files either, I'm probably not testing it right.
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  #21  
Old 13 Aug 2013
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Quote:
Originally Posted by steveloomis View Post
Just an FYI. Your decel valve looks like it has been replaced already. The 3 little marks are factory marks. Mine had that too. I just grabbed the lip on the brass and rocked it a little and it came out easily. Might be worth a try. Normally this circuit is held open with the spring behind the cover of the diaphram. High vacuum from the secondary in front of the butterfly valve over rides the diaphram spring and closes the air off of the pilot jet causing a richer condition.

You mentioned popping under acceleration. I don't believe this circuit will cause this as it is to enrichen the mixture to the point it will not burn in the muffler and cause a backfire.

Is your spark good and robust? Really snap? If not, if it is a weak spindly spark your CDI could be dying. I had that happen to me, then it quit altogether.

Steve
Thanks for the info Steve I appreciate that, except for the extreme popping under acceleration the bike has been running excellent, starts right up runs great right up to 3500 when the popping starts, then suddenly no more spark.
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  #22  
Old 13 Aug 2013
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Before my CDI quit altogether the bike got to be hard to start and backfired quite often. I think the CDI "CAN" die a slow death. Since yours starts and runs ok up to a certain RPM may be an indicator of CDI problems.

I did test my stator output and trigger coils for output. I did not measure the actual output values as I have a digital meter that is not a good indicator of short burst of voltage. I just wanted to see if there was AC output when spinning over to verify my stator and trigger was working.

A better meter to use if you are concerned about the amount of stator output is an analog meter or an oscilloscope.
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  #23  
Old 14 Aug 2013
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Steve brings up a good point, can very well be cdi or the trigger coils. There is two signals a 12 degree and a 34-36ish. It may be that only the 12 degree signal is being sent or received. I have a spare cdi if it is compatible your welcome to try to see if it's you cdi. I don't have a pulse generator yet so no help there.

I doubt if the coil itself is bad, those don't fail very much plus it would probably effect low rpm also, but you can pick up new ones for relatively cheap.
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  #24  
Old 14 Aug 2013
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Since we are on the subject of CDI's, I have been in communications with the engineer for the new CDI he is making for the XT. He is working on a starting function that MAY have an anti kickback function. He is measuring the starting RPM and adjusting the function from that. It would be adjustable as some bikes could be harder to spin over due to the rider's strength or very high compression or perhaps the decompression cable has broken. I have asked for a bypass of this function that can be done in the field if you have a decompression cable break and you cannot kick it as fast as normal. This is still in testing phase so could change or not be implemented at all. The stock ignition does retard during starting so this is being looked at and made adjustable so it could be customized by you or eliminated.

I am very excited to see this manufacturer take such an interest in these old bikes. Hopefully there is a market for a programmable and reliable CDI so he can recoup his development costs.

Stay tuned...

Steve
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  #25  
Old 18 Aug 2013
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Problem solved ! a guy by the name of webmonstro over at ADV suggested I check for broken wires at the connector for the TCI where sure enough I found a broken green/white.

This photo was taken before I started testing components, the
green/white wire looks perfectly intact.



After pulling the connector from the TCI the wire popped out.



Broke clean off at the spade connector.



Lengthened the wire by an inch and installed another spade connector, the bike fired up immediately and ran perfect with no popping at all, my thanks to Mezo, xtrock, Bandit, jjrider, Walkabout, becardi and steveloomis for all your help and suggestions, thanks also jj for the offer of your spare CDI, the beast is back !

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  #26  
Old 18 Aug 2013
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A happy ending is always good news.

You might as well take a look at the other connectors while you are there.
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