TTR600R carb pipe
 

Hi all - this is ref a TTR600 but am sure will be similar for other Yamaha thumpers.

My 2003 kick start TTR600 has been parked up a while in the garage and the other day i went in and there was a puddle of petrol underneath it.

I had a look and one of the pipes coming off the bottom of the carb had perished, but more to the point the small outlet on the bottom of the carb it was attached to, was dripping fuel. However, I'm unclear how fuel was getting through it so I hope someone can help?

On this handy diagram: https://www.motorcyclespareparts.eu/...or-346464.aspx you'll see part 20 - which is a small screw on the bottom of the carb - is it a jet or a drain screw?
In any case the small nub in front of that on the diagram is where its leaking from. Turning off the fuel stops it.

Any idea why it would be leaking / what I need to fix to stop it leaking?

Thanks!

Phil

That overflow valve is doing what it is supposed to be doing... It's leaking to prevent excess fuel mixture into the cylinder, preventing it from doing a hydraulic combustion... You shouldn't be focusing on that... Your real problem is inside the carburetor... If it could guess I would say it has to with the floating device inside the carburetor... It always on a downward position so it would keep adding more fuel inside, thus causing the overall overflow... But this is just a quick guess since we can't see what's going on inside there...

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Your problem would be on 4 or 42 according to your diagram...

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TTR600 - got to love them
 

When I owned one of these bikes, it did much the same thing i.e. overflowing from the carb.

When you are finished riding the bike, turn off the fuel tap and run the engine until it dies on you i.e. until the float bowl has run out of fuel. This does deal, to some extent, with the problem you describe and, more long term, it limits the tendency for the fuel to evaporate from the carb and leave gummy deposits in those "hard to get at" small bits inside the carb.
It's not exactly vital to practice this procedure for short term stops but it is a great procedure to use when the bike is to be laying around for a while without the engine being run.
But, some people say that if the float is left "not floating" for a long time then it can jam in that position, so you have to make a decision on that point for yourself.

Regarding your precise current problem, it is probably caused by an issue with the float bowl - if out of adjustment it allows fuel to overflow.

There is an o-ring underneath the brass part(seat) that the float needle goes in and seals off the flow of gas coming in when the float is at the set level . Those o-ring get hard and crack , usually from age and certain gas formulas . They will allow gas to bypass the needle and overfill the bowl . That would be first go-to item to replace , even if it "looks" ok , and install a Viton version that can handle fuel , especially ethanol , better than the std , Buna-N o-ring that is in there now .



.

Thanks all - thats a great help. Sounds like I'd better get the carb off and investigate those two items you mention.

Actually, there are differences which is why this sub-section was broadened a few years ago (I suppose the other option was to have a stack of sub-sections related to each of the vast range of yamaha products - of which I have owned a few!!).

"Originally the Yamaha XT600 Tech Forum, due to demand it now includes all Yamaha's technical / mechanical / repair / preparation questions"

Sure enough it was the float valve - the ring had hardened. While I was at it I found the pilot jet to be partially blocked and also a fair bit of crap above the little gauze filter as well - so gave it all a good clean and service. Thank you everyone for your help - now I've read about carburettors it was all pretty obvious!