[Dos50R]

What would cause this on the piston? Is this still usable? 86 tRX. I had it out a couple weeks back it was fine then after the ride It wouldn’t start and felt kind of weird when kicking it over. So I cleaned out the carb changes the plug and it started up I ran it down the street and if felt off no power, bogging out then just started revving wot and would shut off. I pulled the head and this is what the piston looks like. Any help of what should be done or what the cause and fox would be. Thank you.

 

[Sterling johnson]

Looks to me like it’s too lean…. That will cause the underside of the piston to overheat and cause the buildup on top. It’s hard to tell without a picture of the plug that was being run in it when you first pulled the head off. If it is super hot in there, that could’ve cause it to run like crap due decreased compression. If the bog feels like a hesitation and then cleans itself out and the runs then it is rich. If it bogs and feels like it’s stalling , it’s too lean. The part about it revving super high then stalling leads me to think it’s lean as well as the burnt carbon on top of the piston.

 

[Dos50R]

Thanks for the for the reply Sterling. I’ll grab some pics of the plug I had in there. I was running a 40/1 mix with 927 and 91 pump gas. I guess I’m going to pull the top end off and check the cylinder and replace the piston.

 

[Sterling johnson]

That ratio is good…. I’m thinking your main jet may be on the lean side. What jets are you running? And is the motor on stock bore?

 

[scrappy]

My guess is you had an air leak & you caught it just in time. You can see a chunk missing from the inner o-ring in some of the pics. Do you have a leakdown tester?

 

[bushwesl]

My guess is you had an air leak & you caught it just in time. You can see a chunk missing from the inner o-ring in some of the pics. Do you have a leakdown tester?

Agreed, that o-ring looks very suspicious.

 

[Dos50R]

That ratio is good…. I’m thinking your main jet may be on the lean side. What jets are you running? And is the motor on stock bore?

175 main and 52 pilot the top end was done a few months back bored to the next size.

 

[Dos50R]

My guess is you had an air leak & you caught it just in time. You can see a chunk missing from the inner o-ring in some of the pics. Do you have a leakdown tester?

Yeah that’s the first thing I noticed, a chunk was missing from that o-ring! I don’t have a leakdown tester. I’ll need to get one.

 

[Dos50R]

I believe this was the plug I had in at the time.

 

[bushwesl]

Did you notice if you were down on coolant? Or possibly smell coolant burning when you last rode it?

 

[Dos50R]

Did you notice if you were down on coolant? Or possibly smell coolant burning when you last rode it?

No, coolant levels were good I didn’t notice any smell.