1997 YZ250 New-To-Me: Coolent at Cylinder Head

Related:
Create New Tag

10/17/2021 6:54 PM

I recently acquired a 1997 YZ250 and after completing a laundry list of items on the bike, I finally took it out today for the first time. I have not opened the engine up yet, but intend to this winter.

So here is my question...the bike starts and idles well, runs good, but has a big, choke sensation midway through the power. Air screw didn’t have an effect on this bog type issue, and my jet settings I believe were good for temps today, etc. Reeds are good, clean filter, C12 with Supertechniplate @ 40:1. When I got home I found the below on the head. It’s Yamalube Blue coolent about 1/2 way around. Coolent in radiator is only down maybe 1/2- 3/4” from top. I’ll drain oil tomorrow and pull and inspect head/O rings. Was this related to my bog while riding today? Plug looks nice brown color, nothing out of ordinary. Photo

|

10/18/2021 4:07 AM

Looks like pretty minor seepage from outer oring, I would definitely get new orings & pull head, check form warpage, inspect top end & powervalves. If it’s a stock engine the straight c12 likely overkill.

|

10/18/2021 4:50 AM

sandman768 wrote:

Looks like pretty minor seepage from outer oring, I would definitely get new orings & pull head, check form warpage, ...more

Thanks sandman, any chance this would cause the bog situation I was having? Like you said, outer o ring is likely the culprit, as the plug looks good with no sign of coolent, and starts easily. I will spray with WD and see if I have an air leak somewhere else as well.

|

10/18/2021 4:57 AM

JB500 wrote:

Thanks sandman, any chance this would cause the bog situation I was having? Like you said, outer o ring is likely the culprit, ...more

I don’t think minor seepage from the outer oring would cause a bog, but have to eliminate a possible coolant leak with inner oring going into cylinder. Was carb cleaned/ rebuilt? Are the powervalves operating correctly? Inspect exhaust for blockages? Was bike sitting a long time? New plug? Process of elimination….

|

10/22/2021 11:59 AM

sandman768 wrote:

Looks like pretty minor seepage from outer oring, I would definitely get new orings & pull head, check form warpage, ...more

JB500 wrote:

Thanks sandman, any chance this would cause the bog situation I was having? Like you said, outer o ring is likely the culprit, ...more

sandman768 wrote:

I don’t think minor seepage from the outer oring would cause a bog, but have to eliminate a possible coolant leak with inner ...more

X2. The outer o-ring won't be responsible for a bog, but the condition of the inner o-ring is now suspect. Check them both.

|

Braaapin' aint easy.

10/23/2021 6:58 AM

Do a leak test.
Do a compression test.
Then replace the head gasket and repeat test.

Paw Paw

|

10/30/2021 4:08 PM

there are 2 rings so if outside is leaking odds are the other is also leaking so replace them both.

|