Hello Everyone,

I haven’t posted in over a year. I have however been riding and wrenching on my two Yamaha enduros. I had been posting to two different topics I started regarding my enduros. One was “AT-1 running after five years”, and the other was mistakenly titled “1969 AT1 MX woods racer build”. I say mistakenly because I discovered that the bike I bought was a 1973 ATMX, not the 1969 that I was told. In both of those topics I related my experiences and asked questions regarding my bikes. This site is a tremendous resource, I received excellent answers to my questions, and as a result, I was able to get both bikes running and in a reasonable state of tune. I appreciate you all.

Around the time of my last posts the engine in the ‘71 failed catastrophically due to a wrist pin clip that came out and ruined the piston and bore. At approximately the same time I was preparing to rebuild the engine that came with the ‘73 ATMX. I was debating on whether to rebuild either or both to 175cc. I ended up building the ‘71 at 175, and keeping the ‘73 at 125. During the decision making, I had acquired a number of cylinders and heads from eBay, and my decisions were to some degree influenced by the price and availability of these parts. 

The 175 build went well. I used a reed valve head however, and the extra length of the reed cage precluded the use of the original air box, so I made an air filter with Uni foam and hardware cloth. It’s a little goofy looking, but it seems to work okay. I ride it once in a while, it’s fun and quaint, and people dig it when they see it. I don’t ride it enough to justify keeping it, but my son likes it, so it’s in the barn for now.

I’ll post again shortly with an update regarding the ‘73 ATMX.

Thanks for reading
Jamie Galvin
 

Link to a pic of the ATMX at my first race:

imgur.com/a/yv2O4vT

1973 ATMX build. 

While I was deciding whether to build the ATMX engine at 125 or 175, I found a reasonably priced 125 MX reed valve jug on eBay. After receiving it, I measured and determined which oversize bore to use, got a matching wiseco piston and rings and brought it to the shop I use for boring. It’s an old school rural shop owned and run by a guy who has considerable experience with vintage bikes of all types, and Yamaha enduros in particular. He has been very generous with knowledge. The end play in the connecting rod was out of spec, so I ordered a new rod, bearings and washers. I split the cases and brought the crank and new rod to my guy for him to install the new rod. After watching Dale Sweger and Allen Milyard on YouTube, I’m gonna try doing that work myself, I’m pretty sure I can do it. 

My guy sold me a set of All Balls main bearings and seals. I cleaned the cases, installed the bearings and seals, got the crank and freshly bored jug back, and assembled the engine. Things seemed to go well. I got the engine in the frame, checked for spark, drizzled a little premix in the intake, and it lit up first kick. Feeling good. Over the next few days I got the bike to the point where I could test ride. The first test rides were very promising. With little tuning, the bike started, idled, and ran pretty well. I felt like the jetting wasn’t exactly right, so I started experimenting. I felt like it was going lean at the top, so I incrementally increased the main jet until it went rich, then went back one size figuring I had it. After going back one jet, it was way too rich, fouled plug after plug. For two weeks or so, I tried scores of combinations of idle jets, main jets and needle clip positions. Right when I thought I had it, it would go rich again. During these weeks, I would go my guy at the bike shop, describe the symptoms as best I could. He’d make suggestions, I’d try things, but couldn’t get it. I finally swallowed my pride and brought the bike to him. He called me the next day and told me it needed a new source coil. I found one on eBay and got it to him. He called the next day and said “bad news, I thought I had it running perfect, then it quit, I think something major happened, do you want me to take it apart, or do you want to?”. Dejected, I told him that I would pick it up and get it apart myself. 
  
To be continued…

Thanks for reading
Jamie Galvin


 

I’ll get some popcorn ready…

Ugh!

MX woods racer is great idea though. I hope that you can get there.

I get the bike home. I say to myself, let’s look at a few easy things before we start crying. Clutch cover off, hallelujah, the nut for the primary gear had backed off enough to scrub against the cover, I guess that was enough to stall the engine at idle. I must have neglected to torque it properly. I torqued the nut, kicked it, and it lit right up. Phew, nothing internal. However, while tightening the nut, I noticed end play in the crank. WTF, it’s a brand new bearing. Dejected again, I began thinking about what could’ve caused this. In not very long, it became clear that I would have to split the cases again. I dried my tears, got the motor out of the frame and started to disassemble the motor. During disassembly, I noticed that the nos source coil I had purchased at the behest of my guy had not been installed. The condenser had been replaced, but not the coil. At the time I was a little mad that I wasn’t given the coil back, but as it turns out, it was an oversight. I got the coil back later. After getting the cases apart the problem was revealed. I had installed an incorrect bearing on the clutch side. The seal was right, but the bearing had the same ID as the flywheel side. I’m pretty sure the All Balls bearing set I was sold had the wrong bearing in it, and I didn’t notice. At this point I remembered how easy it was getting the cases together. I ordered a new brarings, and started wondering if I had done any damage testing the bike for weeks with an incorrect main bearing. While waiting for the bearings, I inspected the engine and thought about things. One thing that became clear was I had been chasing fuel issues when it was likely an ignition problem. Another thing was that it was possible that the ignition problem may have been due to the crank being improperly supported which made the points malfunction. In any event, new bearings installed, engine reassembled, back in the frame, lights right up. I spent the next few days riding in my yard and up and down the road I live on. It’s running good, starts right up, idles nice, good throttle response, the plug is brown, a little rich maybe, but that’s ok, I don’t want to burn another piston (story in previous topic). At this point I’m satisfied and relieved that the rookie mistakes I made hadn’t caused major problems.

 To be continued…

The narrative thus far brings us to late spring 2024. I bought the ATMX to build it to be able to ride in AHRMA  Cross Country races in New York and Pennsylvania. A life long friend, who is a long time rider, has been racing for some years. I have only been riding for a couple years, but it seemed like it would be fun to join him. The bike wasn’t ready for the first few races, and the next few races were in my mind either too far away, or too big of an event for a fat old first time racer to participate in. It made sense to have my first race at the track right up the road from me owned by my guy that owns the bike shop I go to. It’s also the place where my son raced his first race on the other Yamaha Enduro that I own. This was around the middle of July and the race was the middle of August. There is another woods course near me that has hosted AHRMA races in the past. I coincidentally met the guy who owns it a couple summers ago, and he told me people ride the woods course on Wednesday evenings, and that I was welcome to come ride despite my inexperience and morbid obesity. So on a sunny Wednesday evening in late July I loaded the bike and headed to Geers farm for my first taste of woods riding.

To be continued…

Thanks for reading,
Jamie Galvin

Jamie hope that MX riding helps you keep and stay fit, amazing that you found the 'wrong' bearing, that was a close call. Sounds like you are set up to have fun and get out, great to hear that you are back on track.

I was enjoying reading all that. Now I'm out of popcorn but have some on order while waiting for the next episode. Thanks for posting.