I've lurked here for years - and have been impressed with the level of knowledge here.

I now have a major issue that could definitely benefit from the advice of some of you.

Our 05 YFZ450, ESR intake, stock exhaust, quiet core removed, has been a great machine. Some trail work but mostly in the dunes (Sand Mountain, Little Sahara, UT). The machine has been with my son in southern Utah and appears to have blown a gasket ? not sure which one.

After riding it for about 10-15 minutes, it starts to bog down real bad ? first thought was it may be a jetting issue. It runs great at 4500 ft ? it was bogging down after the 15 minutes of run time at 2500 ft altitude. After letting the machine cool for about an hour, the same sequence would repeat ? run good for 15 then bog down real bad and continue to get worse until it would not start.

It sat untouched in a garage for a couple of weeks ? when I pulled the plug to check for proper jetting ? the plug was wet ? not damp ? but wet. No strong smell of gas ? pretty sure it?s coolant.

Anyone have a similar experience ? any history of coolant leaks into the head or intake?

I usually do my own work and as soon as I can get my hands on a shop book ? I will tear it down to see what I can find.

I look forward to anyone?s thoughts. This 450 is a great machine.

Thanks in advance.

 

If you are leaking coolant into the head/valves then you will have a white exhaust instead of the normal greyish tint. It might of just been condensation buildup that was on the plug. If you are leaking coolant you prolly just need to replace the head gasket.

Hows the coolant level?

As for the jetting, if youve done those mods you should probably rejet. Do a plug chop to make sure its right.

 

Sparky - thanks for the input.

I wasn't there when this problem occured - I will ask my son if the exhaust was "whiteish"

He did add about a a small amount of coolant to the overflow tank - my first thought was he was being extra carful to restore the coolant level to the "stock" level since it has been "low" ever since I spilled some coolant when I stood it on the grab bar last summer.

The chopped throttle plug check is a good idea - I'll try it tomorrow.

With the stock jetting at 4500 ft altitude, and the mods - stock exhaust (quiet core removed), ESR intake - the thing runs like a raped ape. When racing up sand mountain, it beats most other machines with aftermarket exhausts. No extreme header glow, or stumbling.

If I go to the hassle of pulling the head - are there some upgrades I should consider - Hotcam, porting, perhaps even a oversize of the cyl?

Thanks again.