I'm so sorry to hear that, after all that work to get it running. I'm sure you saw Tinkicker's "Holy Piston Batman" thread? Lots of advice there, and it seems that you could get lucky washing it out upside down, but splitting the case would be better.

Oh no, that's bad news. I've tipped one up on the handlebars & flushed it out with a petrol gun--i call it. Even put the water blaster up close on wide spray & turned it over, then oil it up. Got away with it.
That was many years ago with my RX125 twostroke late "70's so a similar motor.
I sent my boy down the road with a lawn mower plug. My bad!!.

Running again, my boy is gonna try racing in the woods again, just north of Ithaca NY. New OEM 3rd over piston, rings, wrist and small end bearing.  I brought the top end to my local cycle shop, the owner there is very experienced with Yamaha enduros, for evaluation. The bore was marginal, so we decided to go 3rd over. This was two weeks ago, so there was plenty of time to get back together before race day. Somebody ordered the wrong piston however, so we lost almost a week. I found a set of rings 90 minutes away, but no piston. I ordered the piston from a guy in Alabama. I didn’t have much hope of getting back together by race day, but the piston showed up yesterday (Friday), I picked it up at the PO, brought it to the cycle shop and went back to work. They called me an hour later and said it was done. Got the bike back together last night, test rode it at 9:30 last night in the rain and was fairly satisfied. Tied up some loose ends this morning, and put a few miles on it around the village. I gotta say, I love riding this thing, I had intentions of selling it, but I don’t think I can.

Ill report back after the race tomorrow,

Thanks for reading
Jamie Galvin

Race went well. The bike ran good, and James rode well. The winner completed four laps, James made three, lots of improvement for both bike and rider. The 19” front wheel spec’d by MarkT with knobby were an improvement, and the fresh top end and bigger main jet didn’t hurt either.

After I got it running with the the new piston and bore before the race,  I was worried about running lean and holing another piston. I don’t have a lot of experience with two strokes, so I’m not always sure about what I’m hearing or seeing. I didn’t detect the lean condition after I installed the pod style air filter that seems to have created the lean condition, so what to do? After we theorized that the pod air filter was likely the problem. I took another shot at getting the original air box to work. The rubber elbow was shrunk and hard so I had been unable to install it. With the carb off the bike, I heated the boot, slipped it on the carb, and left it to cool. I was then able to install it back on the bike. Saturday morning after getting running, I went to the cycle shop with the spark plug to get a replacement, and possibly a read on the plug. The plug was the one that was in the bike when the piston holed, and it had a silvery gray look. It was the only one I had, it made good spark, it was 8:00 pm, so I used it. Bike started right up with it, but I wanted a new one. The shop owner, who is the expert, wasn’t in yet, the guy behind the counter sold me some plugs, but couldn’t really read the plug because of the discoloration. He said to look for “chocolate brown”. I asked if he had jets for the carb, I wanted to get 3 or 4 that were bigger than stock, but I realized that I didn’t know if it was a stock jet that was in it. Back home to get the carb off and back to the shop. By the time I got back, the owner was there. He asked me a few questions regarding how it sounded and ran, but we were unable to reach a satisfactory conclusion. He installed a new jet, one size up from what was in the carb, and said if it’s blubbery, put the other one back in. In retrospect I shoulda got a number of jets and kept going up until it went too rich, but there it is. Back home with the new plugs, bigger jet, new gas can with non ethanol 90 gas, and hope that things would go well. Back together, up and down the road, felt good, called it good.

Sunday morning, race day, loading up, pitch black, pouring rain, dreading what was sure to be a day of misery. The group hosting the race posted on Facebook that the weather at the track was good, I doubted it. 30 minutes south of home the sun was out out and no rain. Ended up being a beautiful albeit windy morning. James started slow, but his lap times improved each lap. Really great experience again. 

The race season is over, so Friday, I started to put the bike bike to street able condition. I got everything done except the rear directionals. Got those on Saturday morning, and took a ride. I rode the back roads over to the cycle shop so the guys there could hear and ride it to evaluate. They both said it is in good tune.

I put 50 miles on it yesterday. I am gonna say it again, I love riding this thing. A certain part of the the joy I experience with it is how much work I’ve put into it, the knowledge gained, the interactions with this forum and the guys at the cycle shop, but there is something about the way the bike feels that I can’t quite describe properly. “Quaint” isn’t quite right, but it’s close.

I plan on doing some cosmetic things as well as a fork rebuild this winter. I’ll post with updates.

I appreciate you guys.
Thanks for reading
 

I had been riding the AT-1 everyday the weather was good enough until about a week ago. I took it out and got a couple miles out of town, I was almost to the trail head when I lost power, eventually no power. A Good Samaritan got me home. I thought I holed another piston, it had similar symptoms to the last failure. Got the head off, no hole in the piston. Got the jug off, friggen disaster. A wrist pin clip came out and got caught between the piston and bore, both ruined. I have another project going with a ‘73 ATMX. They are both gonna get 175 top ends. The AT1 is gonna get a 175 standard reed valve, and the ATMX is gonna get a 175 MX reed valve. I’ll post again with progress reports, I’m sure I’ll have questions.

Bad luck.  It is disheartening when things keep going wrong.  I have kept a T shirt factory running for years with that.

I may be preaching to the choir but just in case.. Never, ever reuse piston circlips, whether they are seeger types or wire types as with Yamaha.
They will often come adrift as once they have been used, they lose some of their strength due to hot and cold cycles.  When you remove them, they will not maintain the wall pressure they had when new on refitting.

I have seen it happen so many times..

I’ve been accumulating parts and knowledge for both he AT-1 and the ATMX for a couple weeks now. I think I have things straight. After some answers from MarkT, I ordered a piston and some other things last night. Hopefully back running in a couple weeks. I’ll report back with results.

Thanks everyone 
Jamie Galvin

Sorry to hear that. Hope you found the circlip.

About 1/3 of the clip was lying on top of the case, other parts are embedded in the piston. 

Also, best to install/rotate the new pin clip so that the gap is either at the top or at the bottom.  With the gap at the side, the insanely high acceleration/deceleration forces can actually collapse the clip and allow it to pop out of the groove.  This is especially true for the clips with the "tail" that can be grabbed with needle nose to remove it. 

Some high RPM/high stress engines use teflon buttons (4 stroke only) or "spirolox" retainers to retain the pin for this reason.