I recently got a gas gas txt pro 250 07..

First of all the crank base gasket needs replacing as it is leaking and also sucking in air so the bike is running like crap I have ordered the parts required including all o rings ect...

My main problem is my gearbox breather pipe is syphoning out oil from the gear box as if it has pressure in it. I know this because when I loosen off the top filler bolt to the gearbox it then doesn't rise anymore.. What's strange too is the crank base seal doesn't seem to spit as much black fuel and carbon out and the exhaust smoke is clear and runs better.... Could just be coinsedence as I did change the fuel and mix today etc..

I should say also I did take into consideration of the head gasket etc but she's not loosing coolent and the oil would also be very milky and foamy like I have been told and it was not. The oil I replaced today was a little dark in colour almost a light brown colour. I should also mention when I open the cap no air is coming out nor does it smell etc...

Any help given would be really appreciated.. Me and my dad are going to strip it down on weekend and take a look at the piston rings and the clutch basket bolt..

Strip it and sort the base gasket, It could be the water pump seal pressurizing the gearbox, More common than a head o ring problem.

Hi steve I don't think its the waterpump seal as usually this makes the oil milky like and mine is not it is staying golden...

And there is also no bubbles coming from radiator fill pipe

 And you started a second thread on the same problem. You pull the bolt out of the middle of the clutch assembly yet?

Yes I have deleted the other thread.. That was to more just diagnose what that little tap was the gearbox breather..

I now know a number of things it's not.. We are stripping it this weekend but someone may have had the exact same problem and make it much easier for me.

The first thing I will be checking is that bolt when I strip it down.... Cheers

375cc is all this case takes. If you have 450-500 it spit oil out of the breather.

There is no oil in the cylinder nor is there water in the block other than the water pump. Leaking base gasket will cause all sorts of fuel mixture issues. Fix the base gasket and make sure you have 375cc of oil in the lower end.

--biff

Cheers biff the base gasket is getting done this weekend.. The guy at gas gas UK says 400 cc's my dad said 360 so I went with around 380 in end. There was around 350cc before I dropped it as I dropped it into a measure jug.

It basiclly rises out the breather pipe almost like being slowly pumped with pressure. When I loosen off the top filler bolt it doesn't rise out the breather pipe which would say it is pressure in there

Well the vent is there to release pressure. The oil level shouldn't be at the level of the vent but when you get a bit too much oil in there it is at that vent level and as pressure builds oil gets pushed out and not air. Of course you know that if you release the pressure at the fill plug it no longer pumps the oil out of the vent. If the oil level is growing then you have a water pump seal going bad but as you have said its not getting milky its staying proper colors. If you had a lower end crank seal or crank seal o-ring bad it generally would suck the oil from the case rather than pressurize the case. 

 

One thing you can do if you want to get tricky. Add florescent dye to your crank case oil then run the bike hot. When you have your cylinder off use a black light to see if any dye shows up on your crank shaft. It shouldn't if your crank seal is good. 

 

Another thing i wouldn't do is remove your cylinder head from the jug. Its no worth the hassle to get the o-rings back on your head if they aren't bad. Its a bit harder to remove the cylinder with the head on in the bike but it will come. Good luck.

 

--Biff

Edited August 11, 201511 yr by biffsgasgas

Thanks biff, I'll update when we take it apart on the weekend...

Anyone ever had this same problem please share what it was lol...

Cheers

Could it be the piston rings?

Or even the main head gasket need replacing

If you are confident it isnt the water pump and it isnt over filled, there are only two things it can be, clutch side crank seal, or centre crankcase gasket.

 

What's strange too is the crank base seal doesn't seem to spit as much black fuel and carbon out and the exhaust smoke is clear and runs better

 

 

You are drawing oil into the combustion chamber as well as pumping it out of the gearbox/clutch.

 

Other than that, if unscrewing the filler cap solves your problem, why not drill a hole in it and attach a breather?

Edited August 11, 201511 yr by faussy

Hi faussy, I spoke to a very helpful guy at gasgas UK and he said igsact same thing as you. For some reason my dad has piston rings in his head... But as I say this guy from gasgas says igsact same 2 things if it's not water pump seal. The oil is staying nice and golden you see.