Yamaha TRX850 Enthusiasts Forum

I've got a big problem here. My TRX started to leak fuel rom where the exhaust attaches to the engine. First it was only on 1 cylinder but the other started to leak soon after. I had a good look through the previous posts and it all looked like it was the emulsion tubes (needles / jets) So I've tried some new tubes and it made no difference (the old tubes diddn't look oval)I brought some other carbs ,told they were fro a 160000 mile bike so pretty fresh, anyway, I'm still getting leaking from one of the cylinders down the exhaust.
The bike was running / starting well before this leaking happend. Why would the bike empty is fule into the engine when it's not running? If I remove the tank the fule stays in there. it dosent leak out of the pipes, so why when it's all connected up to the bike.

So, any ideas? Has this happened to anyone else? I'll post a pic later.

sounds like the float valve in the carbs , (and 160,000 miles is not pretty fresh ) i would not run it until you have fixed this problem ,, the oil may now well be past its best ( full of petrol ) take the carbs off and give them a good clean and inspect them closely , pay attention to the float valve for wear or damage , check the floats are not full of petrol they may have a hole in them ,, make sure your fuel tap is not on prime although if the float valve is working this would not be a problem ,, does it leak when the bike is not running ?? are you sure its not water that's leaking ,, that's enough for now , get your tools out

the more i read your post the more i think its water from the head gasket

Hi Steve Speed. It should have read 16.000miles! It's definetly fuel. I just went to take a pic and it'd stopped leaking but a quick turn over of the engine started the leaking again. It'll leak long enough to leave a nice big pool of petrol under the bike. How does a float valve get damaged? Do they just stick? When i took the carbs apart to get the emulsion tubes everything looked fine. I've got a Haynes manual and there's some guff about float hights, i read that. I still dont get how one day it's fine then the next it's shagged. Anyway, here's the pic -

there may some shite jammed in the rubber part of the float valve , but how you would get that exhaust off !! its going to be tricky, any way if its leaking to that extent it has to be the float valve, and i urge you not to run it as there is a great risk of fire , take off the carbs and carefully inspect there innards , my moneys on the float valve , buy new valve and seat

Take the exhaust off? I'm gonna try not to, there's a lifetimes of rust on those studs and bolts. Appolgies for the filthy bike! So is that a float valve and seat? Forgive my ignorance but there seem to be alot of parts all called valve, seat, jet ect

when you take off the carbs and take off the float bowl, inside there is the float it pushes on the float needle its got a rubber point on one end this in turn seats in a brass seat ,,, ,,,download the manual from this site ,,, and half the the money you save doing it yourself send it to max the site boss , and on a personal note dont ever post a picture showing that much rust and dirt ,, i feel sick now

steve speed wrote:...dont ever post a picture showing that much rust and dirt ,, i feel sick now

Dirty bike!

WTF has been done to those exhaust flanges?
They look to be welded on and the springs,they do what exactly?
Poor old girl has had a bl**dy hard 16,000 miles has she not?
I`ve NEVER known of such a thing occuring on Japanese iron,seen it on big british singles with GP carbs,matchbox float chamber and sticking ticklers though.

"Poor old girl has had a bl**dy hard 16,000 miles has she not?"
It's the replacemnet carbs that are 16000 miles. The bike is aprox 30.000. Agreed it's not a pretty sight at the moment but there's some sick pleasure in me that's enjoying showing you lot such dirty pics. This'll piss you all off - That dirty exhaust is a full Ackrapovic 2-1! You should see what it's blue spots look like!!!

Anyway back to topic - I've found this blub on the MCN web site -

"You are right in saying that early TDMs where supposed to have trouble with wear in the emulsifying tubes but over the many years of stripping and rebuilding these carbs i myself have not found this to be true.Your carb is a Mikuni down draft type and is the same one used by lots of other manufacturers not least ducati.So why is it we dont hear the same of them if they too are using the same carburettor ie with different jet sizes?.In all high milage bikes this carb wear can be expected but you say your bike has only 26,000 on the clock.Which i find incredible but i suppose not impossible so i think this wear factoid is a bit premature.So i will tell you two real facts about early TDMs and not myths.One the fuel pump on the early bikes is a diaphragm type and as TIME goes by the rubberize canvas type cloth gets perforated allowing fuel to cross over to the vacuum pipe and then straight into the intake bypassing the carb.Two the choke needles corrode and wear and then do not seat properly, as they leak they will allow fuel past just like the coke is still slightly on.Check theys things out first.I have found that if the fuel pump problem is not addressed it will start washing the cylinders and you will end up with a sump full of petrol and severe wear.Also at the age of the bike check the slides are not sticking and are fully lifting as this to will make the bike run rich.And check needle slide diaphragms for perforations this to will stop the slids lifting."

So being as it's gushing fuel into my engine and my float valve heights are good could it be a vacuum leak letting the fule in? Do the trx's have that same type of pump as the tdm?

yes they have the same pump

Right, i've removed the vacume lines that go from the pump to the inlet. Turned the engine over and no fuel comes out of the pipes. I guess the pump is fine. When I turned the engine over I still got some fuel comming through the exhaust (as in the pic earlier)
I quickly took the carbs off to see where the fule had been coming from and the only wet part was by the hole under the butterfly - see the pics.






This hole looks like it connects to the float chamber in the area that has the jets boted to it. Does this point to anything at all? Why do both my sets of carbs throw up the same problem? Why is fuel getting dumped into my engine? Has anyone ever seen this type of thing before?

Ok,well in answer to the Motor `comic` News blub,the choke ends(like a needle and made of plastic)do indeed wear but are clipped into the carb bodies and easily replaced although they aint cheap!One of mine was worn when I stripped my stock carbs but it`ll not give the symptoms you`ve got as the choke can only deliver too much fuel while the bike is running not while stopped.
I do however feel that his diaphragm explanation could indeed be true in some cases but I`ll bet not on a bike with around 20,000 miles on the clock!
I`m concerned that he poo-pooed the `issues` around the emulsion tube/needle wear,I would say that he`s not considering quite a few things.

1) Ducati`s are not often used as commuters through traffic every day.(low engine speed/high gears rattles the needles a treat)
2) The position of TDM/TRX carbs relative to the horizontal(Needles are not rigidly fixed in the slides,there`s a fair bit of lateral movement,as there needs to be).Therfore the needles are again more likely to be in intermittant contact with the emulsion tube.
3) This is a TRX forum,if the owners don`t know best living with the beast,who the fook does?

Anyway,needle valves under the floats or the pump diaphragm for this problem,can`t be anything else really.
First thing to do?
Change those float needle valves and clean the carbs fully.
Of course,it could always be those damn petrol gnomes up to no good again.

666mph wrote: This hole looks like it connects to the float chamber in the area that has the jets boted to it. Does this point to anything at all? Why do both my sets of carbs throw up the same problem? Why is fuel getting dumped into my engine? Has anyone ever seen this type of thing before?

Yup,me.

Picking up on the fuel pump bit, my TDM850 would flood its cylinders if I left the fuel tap "on" when the motor was stopped, turned out to be a pinprick sized hole in the diaphragm in the fuel pump. The weight of the fuel in the tank was sufficent to push the fuel through the pump and back along the vaccum line into the carb inlet stub, fill the cylinder head up behind the inlet valve if I was lucky, if unlucky, the valves would be open, so the cylinder would fill up with fuel and then I couldn't crank the thing over. It took a lot of delving around to discover this, because as others have indicated, the carb floats should have switched off any fuel flow, but the vaccum line bypasses the carbs completly, so the fuel was not shutoff by the floats.

With the TRX, with the engine canted forward slightly more than the TDM setup, the fuel is most likely running straight across the head and out of the exhaust valves, and weeping past the exhaust to head joint.

My suggestion is to strip the pump, and see if there is a hole in the diaphragm, shown here by the pen sticking out of my old pump....




Ya never know.

Mike.

Ahaaaaaaaaaaaaa,yes of course the vacuum pipe to the diaphragm pump,yep that`ll likely be your boy then 666mph.
And of course gravity will allow fuel to flow past the diaphragm,especially if the tank is well topped up.