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Xt600 Misfires, then cuts out... Help Needed Xt600 Misfires, then cuts out... Help Needed
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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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  #1  
Old 19 Feb 2015
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Xt600 Misfires, then cuts out... Help Needed
Hi Everybody!


I recently bought myself a poor running 1984 XT600 34L.
The original symptoms was:

Won't run at full throttle
Idles bad when hot.

Thinking that this would be a doddle to fix I bought the bike.
Well, not it has turned in to quite a headache. So I need some of your wisdom.


The symptoms are now the same.
Here are two videos, one is when the bike is just started. Then it will run with no problems, when it gets to operating temperatures, it misfires, cuts out etc.
When it does this, it can be hard to start it again.

http://youtu.be/HGipgiK3Xj0
http://youtu.be/_FgNRz8LKdk

Well I have done the following.

Cleaned out the carbs
Measured Pickup
Measured Source Coil
Measured Ignition Coil
New rubber intake boots incl. o-rings
New sparkplug
New CDI
Checked the ground-connections for CDI, Coils etc.
Checked Valve clearences

After all this the symptoms are exactly the same..!


I am thinking that this is Ignition related since it gets hard to start after cutting out because it sucks in fuel while stumpeling and therefore drowns.

Please let me know if you have any good ideas to what this might be...


thank you
jonas
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  #2  
Old 19 Feb 2015
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Bad stator likely. Testing them does sometimes show them to be good but once hot they short out. Try doing the same tests, once cold, once hot and compare.
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  #3  
Old 19 Feb 2015
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Quote:
Originally Posted by jjrider View Post
Bad stator likely. Testing them does sometimes show them to be good but once hot they short out. Try doing the same tests, once cold, once hot and compare.
Hi -

I have done a test like that measuring the resistance in both pickup and stator both hot and cold.
And everything was within spec.

The ignition coil was within spec aswell
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  #4  
Old 19 Feb 2015
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Just because you've cleaned and tested something doesn't mean you should necessarily cross it off your list.


Any chance of getting another carb off another bike and trying it out ?

Cold engines and hot engines have VERY different fuel/air requirements.

It could be running very rich and at high temperatures, trips it up.

How is the choke and pilot curcuit ?? Do you need choke to start it ??
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Old 19 Feb 2015
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What jet sizes are you using? What altitude are you at? Could be waaaay too rich.THUMPTHUMP
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Old 19 Feb 2015
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Quote:
Originally Posted by *Touring Ted* View Post
Just because you've cleaned and tested something doesn't mean you should necessarily cross it off your list.


Any chance of getting another carb off another bike and trying it out ?

Cold engines and hot engines have VERY different fuel/air requirements.

It could be running very rich and at high temperatures, trips it up.

How is the choke and pilot curcuit ?? Do you need choke to start it ??

Hi Ted

It's true!
As it is right now it will start without choke. It did need it before.
The thing is, I havn't been able to adjust the air / fuel screw since I can't get it to idle.

Last time i cleaned out the carb I went through pilot / choke systems with a piece of piano wire and they were 100% clean.

I am thinking that this might be my ignition coil that is going wrong. It is afterall a momentary fault. So I guess I won't be able to measure it....
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Old 19 Feb 2015
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Quote:
Originally Posted by jonasp View Post
Hi Ted

It's true!
As it is right now it will start without choke. It did need it before.
The thing is, I havn't been able to adjust the air / fuel screw since I can't get it to idle.

Last time i cleaned out the carb I went through pilot / choke systems with a piece of piano wire and they were 100% clean.

I am thinking that this might be my ignition coil that is going wrong. It is afterall a momentary fault. So I guess I won't be able to measure it....

FYI, dragging steel wire through aluminium carbs isn't a great idea. You can do damage and make things worse. However, lets assume you were super careful and everything is okay.

Well, In my experience a big 600cc air-cooled single usually always needs a decent amount of choke to get it going. Even in hot countries. If it starts without any choke in a bleak, cold British winter then I think your jetting is out.

Take it all back to standard book settings with the jet sizes and pilot screw and see how it goes from there.

Do you know what your screw setting and jets are at the moment ??
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  #8  
Old 19 Feb 2015
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I sent this to a few mates who had XT or similar in the past.. one of them just emailed this..

Have you changed the air filter or is the one fitted a cheap after market one? Once had a Honda with a similar issue - as you ran towards full throttle the foam compressed making it run rich to the point of misfire and cutting out.
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  #9  
Old 16 Sep 2015
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Xt600 Misfires, then cuts out... Help Needed
Is this thread still active? I'm trying to tune the carbs on my 1989 xt600 and I'm not sure what the stock main jet size is. Can someone please enlighten me?

Thanks!

Pk


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  #10  
Old 17 Sep 2015
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1989 Yamaha XT600W Carburetor | Yamaha Sports Plaza
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  #11  
Old 17 Sep 2015
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I think my stock ones are 120 main left carb, 125 right carb,
#46 pilot and 2 turns out on the mixture screw.
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  #12  
Old 18 Sep 2015
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My 86 came with 130 in the left and 125 in the right. TTs had 135 in both. THUMPTHUMP
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