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Yamaha Xt600


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#1 cobi

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Posted 30 November 2018 - 08:17 pm

I have a 1998 XT600 that has lost a lot of power. It starts and rides fine but runs out of steam at 70mph. I suspected a fuel issue and checked for a vacuum leak with carb cleaner and the revs remain constant. Checked the diaphragm which is good. Carbs are clean with no signs of wear. Fuel flow from the tank is good. Think I am missing something obvious and installing and removing the carbs is difficult so any thoughts would be much appreciated.

I will never complain about access to parts on the TDM again :rolleyes:



#2 Muppdog

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Posted 30 November 2018 - 09:56 pm

Stating the obvious. Air filter? Fuel level in carb bowl? There is a small filter in there that can block over time not supplying enough fuel to the secondary carb. You probably checked if you say carb is clean?
There is not a lot else that can go wrong on the old XTs. If it got fuel and it sparks it will go.

Rob

#3 cobi

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Posted 01 December 2018 - 01:41 pm

Thanks for the reply Rob.

Air filters new

Fuel level is correct

Small filter I did not see so will check that out.

 

Mark



#4 bopster

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Posted 01 December 2018 - 07:57 pm

Have you checked your valve clearances? 


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#5 cobi

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Posted 01 December 2018 - 09:19 pm

Valve clearances were done 2000 miles ago. But will check them again while its apart and access is easy.



#6 Muppdog

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Posted 01 December 2018 - 10:08 pm

If all the physical stuff is good there is a chance the electronics are playing up. Not sure yours still got a CDI but whatever it is its not very clever for today's standards. It can go wrong and not change your ignition points correctly. Replacement the only option.
Worse case this is.
I take it your Carb still got a choke? Does the cable run freely? Does the choke open properly and not overrich the mixture? Got that from the german XT forum, by the way.
Is the membrane in your secondary Carb a Yamaha item or an EBay replacement?

Rob

#7 cobi

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Posted 01 December 2018 - 10:36 pm

Choke is a knob on the side of the carb and works well. Membrane is original but appears in very good condition. I have considered the CDI but it would have to be breaking down under load so I would expect a misfire. Could be wrong about the misfire and happy to take advice? I have arranged to have the carb stripped and sonically cleaned by a mate who is a HGV specialist and biker.

I am going to replace the inlet rubbers while its apart as they are a known weak spot.

I will update when the carb is refitted.

Thanks for the help.


Edited by cobi, 01 December 2018 - 10:38 pm.


#8 bopster

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Posted 02 December 2018 - 04:46 pm

also possible is the de-compressor cable sticking or fouling and stopping the valve fully seating.


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#9 cobi

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Posted 13 December 2018 - 02:13 pm

Finally got round to putting the bike together. Main problem was the inlet rubbers, They looked in good condition and spraying carb cleaner around the joints had no effect but once off the bike they fell apart in my hands. Idle jet and the small filter were also partially blocked. I'm surprised it ran at all!

Thanks for the input I wouldn't have noticed the small filter. 




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