help i got problems

[andywright03]

Hi all new to the site so hello to every one

Right got 2 bikes a yamaha YZ250 1999Year
Honda CR250 around a 1998year

First of the honda cr250 bought it couple weeks ago just had new piston and gaskets, but took it out and it blew the head gasket with in half hour of takin it easy found that some head nuts were loose so any way new gasket and the same happened again but also noticed when it was running it is always pushing water out the over flow so stripped it right down and just carnt find anything wrong engine has been presure tested and has come back ok any ideas????

Right now the yamaha bit simpler i hope to fix when the fuel gets around half way in the tank it just bogs down totaly if i fill it up again its fine on and off , i have cleaned the tank out thinkin it would cure it with the amount of bits i got out of it . it sounds fuel related but just carnt think could it be the fuel mix ???

sorry for the long post just hope some one can help me Cheers in advance Andy

 

[Reesknight]

Hello and welcome to the site!
The CR sounds like the head is warped. The blown head gasket or warped head would cause pressure back thru the radiator, forcing coolant out the overflo.
Not sure about the YZ. I doubt its the mix. I would clean out the tank, petcock, carb and jets and make sure the float level is set correctly. And change the plug.
Good luck! :cool:

 

[Bodge]

check the gas tank vent tube on the yz

 

[rmc_olderthandirt]

The water out the overflow is a result of the blown head gasket. High pressure from the cylinder leaks into the water system, increasing its pressure until the cap vents. Very common symptom.

It is possible that the head was never torqued down properly and that the gasket leaked as a result. You need to have a torque wrench and the specifications from a repair manual to get the proper torque settings. Tightening down in the proper pattern, and a little bit at a time is also essential.

It is also a very good idea to re-torque the head after a short run. Start the bike, get it up to temperature but don't push it too hard. Run it for a few minutes, let it cool a bit, then check the torque settings again. You might want to check the settings again after the first full day of use.

If it fails again then there is definately something else wrong. Like reesknight said, a warped head could do that. It is also possible that the wrong piston was installed and the compression is too high.

On the Yamaha, something is interfering with gas getting to the carburetor. When the tank is full the pressure of the gas will be about double what it is with an empty tank. If there is an obstruction, such as a kinked fuel line or clogged filter, the greater pressure would be able to force more gas through.

Try taking the fuel line off at the carburetor and opening the gas valve. A good steady stream of gas should flow. If it dribbles out instead, check for an obstruction in the fuel line, the shut off valve, or in the tank itself. Try blowing air back into the tank, then clean the tank out (to remove any gunk that was just blown in).

If gas flows through the line okay then the problem is probably in the carburetor, probably in the float needle valve. You can try removing the carburetor, splitting the case (top from bottom), removing the float, then the needle then the seat. If there is any gunk around the needle clean it off. Blow through the gas inlet to push out any gunk in the lines (it should blow very easily with the needle seat removed.)

 

[Reesknight]

^^^^ Good info right there. :cool:

 

[andywright03]

cheers for the help i will hopefully have it rebuilt by the weekend so i will take it out for a run will keep you posted on how i get on thanks andy