Now this is a curly one, after issues with faulty bottom end bearings, for some reason my the brass pressure relief valve beside the screw in radiator filler has started weeping, stops when fan comes on, i took cap off and it had like a carbon build up on the base and a bit of the thread of the main cap, also the relief valve was covered with gunk, not bad but a bit.

I know its two stroke, BUT could the o'ring on the head be allowing pressure into the cooling system ?This is only recently happened, and it seems to coincide with a bit of detonation under throttle. I have dropped the needle 1 to lean it a bit, and will run in comp tomorrow. I did not when idling bike there seemed to be fine bubbles under a bit of throttle, just like a head gasket on a 4stroke car engine.

Any thoughts anyone ? the level was down to the top of the internal fins, it was full after bearing surgery.

HELP, thanking you in anticipation of some clever person knowing whats going on.

So did the head come off during the rebuild? ( The head never really has to come off)

To be fair i don't know, it was a pretty testy time getting dealer to realize that my concerns on bottom end had been present for 5-6 months and getting worse, tried to fob off as rattly clutch, but clutches dont rattle when riding or under load !.

If you have some detonation under load, then it is lean and you should be going richer. To make it richer Lift the needle not drop it. (or conversely drop the needle circlip).

Some of those early small pressure relief valves were troublesome and could "jam". New ones are better. Your after part# BT701553013.

 

Why thank you kind sir! I'll reset tomorrow before trial and try it out.

And a leaking head gasket could indeed cause too much pressure in the system. Usually you can also spot this by having dirty coolant.

Ahaa. it does have that, judging by the crud on the relief valve and carbon type coating on the filler cap.

i have cleaned them both so will check after comp tomorrow. Thank you for the replies.

 

Sounds like they re used the o rings and barely pinched one. Keeps one busy.

Sadly you won't know without pulling it apart and them you might as well do a proper repair by replacing gaskets/o-rings anyway. Yeah a leaky head gasket will pressurize the coolant system (more than normal, coolant is usually under some pressure) you may also notice oil in the coolant.

Out of curiosity, what does oily coolant look like?

Out of curiosity, what does oily coolant look like?

Take an once of anti freeze and add a few drops of oil.

What Paul said.

And remember, there is no expansion tank. So, if you fill the radiator to the top, when the coolant expands when hot, it will go past the check valve as it has no place else to go. There needs to be a little bit of air-space in the top of the radiator to allow for expansion and contraction of the coolant.

 

 

Doesn t it have an overflow like the older bikes?

I think the TYZ was the only bike with an expansion tank - partly why they were so well suited to the Scottish.

Every bike in `93 had a coolant reservoir.

TYZ had a pressure cap like an old fashioned car radiator but didn't have an expansion tank