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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 Post By steveloomis
  • 1 Post By *Touring Ted*
  • 1 Post By theoneandonlymin

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  #1  
Old 7 Feb 2015
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Dying opening throttle
When the 3TB is warm and changing up from say 4th to 5th maybe 50 mph the engine will lose power then backfire and carry on as normal. Not every time mind you but reasonably often.
This is the worst to diagnose I appreciate. We like consistency in our faults.
So.......

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Min
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Old 8 Feb 2015
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I think gears and speed are irrelevant here. Probably just coincidence.


Sounds like a bit of a fuelling problem. Give the carb a good clean and service. Check your fuel filter and fuel hose etc. Make sure tank is vented.

Popping is usually because there is a mis-match in fuel/air ratio. When you have either too much fuel or not enough it end up detonating in the heat of your exhaust causing the 'pop'.


Your description of "suddenly losing power" sounds like a bit of a fuel blockage.


If can also be caused by a faulty ignition system but it's far more likely to be fueling.


Also, are you using good fuel ??
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  #3  
Old 8 Feb 2015
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Check the fuel valve to see if it is passing a steady stream of gas and not clogged with rust. Rust in the tank could possibly be a problem. Normally there is a screen on the main pipe that should keep rust out, but fine grained rust can get through. Also in the carb, there is a screen that sits on top the the brass valve the float needle sit in. You have to remove 1 small phillips screw and carefully rock the brass valve out. It has an O-Ring that holds it snug. Once out you'll see the screen fitted to the brass valve.
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  #4  
Old 9 Feb 2015
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Also I know it sounds easy but check your Air filter I agree with the problem sounds like fuel air mixture also check the airbox snorkel thing is it collapsing blocking the air flow.
Have you changed anything on the bike lately?
Also check the fuel tank breather that can cause issue's not common but isn't unkown.
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Old 9 Feb 2015
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Thanks people, it will be Saturday before I can give it a once over so I'll get back to you with any findings.
Nothing in particular done that would affect it. She says it doesn't have the get up and go it used to have. I think the 2nd carb is CV on this model so if so how would a torn diaphragm react ?

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Min
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  #6  
Old 10 Feb 2015
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Quote:
Originally Posted by theoneandonlymin View Post
Thanks people, it will be Saturday before I can give it a once over so I'll get back to you with any findings.
Nothing in particular done that would affect it. She says it doesn't have the get up and go it used to have. I think the 2nd carb is CV on this model so if so how would a torn diaphragm react ?

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Min
Lack of power, feels like you have 30hp.
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Old 10 Feb 2015
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Ooooo 30 Hp, now we're talking.

Min
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Old 10 Feb 2015
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Quote:
Originally Posted by theoneandonlymin View Post
how would a torn diaphragm react ?

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Min
It would be consistently crap. Not just occasionally. It would feel sluggish and hesitant.

However, with most carburation problems. It's witch craft. Not science
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  #9  
Old 15 Feb 2015
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Inlet rubbers were pretty bad so have a pair ordered See how that goes.
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Min
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Old 26 Feb 2015
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Ha har that sorted it. Didn't realise the rubbers were supposed to be bonded to the stubs until the new ones arrived.
Rockin again

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Min
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  #11  
Old 26 Feb 2015
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Originally Posted by theoneandonlymin View Post
Didn't realise the rubbers were supposed to be bonded to the stubs until the new ones arrived.
That`s right, people say "yeah they are in good condition" just by looking??

Its not until you remove the rubbers & they separate that you realise they are knackered, i did this last week, on looking i thought they was in good nick & when i removed the carb they just fell to pieces.

I think it must be the ethanol in the fuel that`s melting the bond?

Mezo.
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  #12  
Old 26 Feb 2015
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That`s right, people say "yeah they are in good condition" just by looking??

I think it must be the ethanol in the fuel that`s melting the bond?

Mezo.
I think it's the weight of the carb. Supported both sides by just 'Rubber' manifolds. The manifolds are chemical resistant but I guess nothing is fully immune. Everything degrades in time.

That carb is bouncing up and down hundreds of times a minute. Not enough that you can see but enough to cause fatigue on it's mounts. Those mounts being the manifolds.
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Old 26 Feb 2015
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Intakeboots have gone bad way before ethanol, its a wellknown problem on xt350 aswell.
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  #14  
Old 26 Feb 2015
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My newly rebuilt SRX600 is in need of some boots as well. They are hard to find apparently. Different angle than the XT due to carb packaging.

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Min
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