It's only run a very short time, I shut it down when I spotted the exhaust connection leak. I'm not concerned about the smoke coming out of the end of the pipe, it looks like what I'd expect for 32:1

Once I get it all back together, I'll post some pics. It's in kinda rough shape. It's been rattle canned Prince Purple, the windshield is cracked and zip-tied, a few dents in the tank, etc.

Please correct me if I misread your OP.
To recap.
Customer's bike was "rebuilt" (what? top end? bottom end? carb cleaned? what?) then quit on the way home years ago and parked.

You did a top end O/H and got it running but stopped because a exhaust leak concerns you?
Right so far?

The exhaust leak is at worst a annoyance but it's easily fixed with a new gasket or (yes) red RTV on the old (or the new) gasket.
It may be leaking because the non stock expansion chamber's ex flange in thinner but why is moot.

What's the history on this bike?
Did it run well before it quit the first time?
Or the 2nd?
When did it get a chamber? What else? When it was overhauled for his birthday?

What I'm getting at is has it ran well for a while in the configuration it's in now? (i.e.,expansion chamber etc.).
Does it have the OEM air box?
The fact that the oil injection's gone and it's got a pipe makes me suspect it's someones pocket rocket project and no one can know whats been done to it. (let's go in thar and port and polish that thing while its apart!)

Fix or ignore the exhaust leak and proceed with caution, WECSOG's exist in all forms of life.

I would be tempted (with the exhaust off, of course) to put a stud socket on the exhaust studs to make sure they are in all the way.

Large round threaded collar on cylinder with nut on expansion chamber, round gasket in between.
Tighten nut onto cylinder. No studs.
Flange on aftermarket pipe might be thin.
Still a non issue no matter what.

Not a single person with half a fucking brain has run 2 stroke oil at 32:1 for almost 30 years so why the fuck would you think it's a good idea.  

Also known as a “Johnson Shot”….. It’s a safe ratio to play with on most oils, but it comes from a time when oils weren’t what they are now-there are lot of modern 2-stroke oils that can go much higher, I’ve seen 50:1 in aircraft 2-stroke and 80:1 in some lawn equipment

LoL, the Dale Carnegie way to Win Friends and Influence People!

I see you have read the bottle of Amsoil. Congrats.

So anyway, run the oil at the manufacturer recommendation. They built the engine, not the oil company. Oil has not advanced so much in 30 years that you can half the oil and expect good results. 32:1 is still recommend to this day on some bikes.

Wow, OP! The original Pic looks shitty for a new piston. Did you try red rtv on the exhaust pipe?

You'd save a ton of time with this powerful Guangdong bicycle engine.



I'm being a clown. Best wishes, pal. Godspeed.

Youll never keep your driveway properly lubed with that. Just do a milwaukee eight vtwin swap

I’d recommend a fat ratio if I were on the hook for warranty claims and wanted a reputation for making reliable bikes…

Seriously though, if two stroke aircraft engines that run for extended times at full power and then cruise at 70% throttle can run 50:1 and even higher, oils have definitely improved in the last 30 years.

I'm well aware of the advances in oil technology.

Team Calamari has been the ARFCOM of these modding these pit bikes since 1996, they recommend 32:1 with the manufacturers specified oil when the autolube system is deleted. I'll stick with their recommendation.

You sir, can go suck a fart.

If the owner wants to dick around with the oil ratio after he gets it back that's his decision AND his responsibility.

That's the old piston I took out. (If you were being sarcastic about the piston:)

LOL on the Guangdong

Just busting your balls.  

For the record not only are Autolube pumps are extremely (as in never saw one, ever, in over 50 years of keeping them going) unlikely to fail. Running them dry, cable breaking, pulley rusted to wide open pumping, sure.

IF the oil seal at the back (which is NOT part of the pump, but on the clutch cover the pump bolts to) were to fail "gravity" would pull the oil into the transmission/clutch portion of the crankcases, not the crankshaft's.
But it didn't because they don't do that.
Even if the oil pump failed somehow and allowed the oil to bypass the pump, the outlet from the oil pump to the engine is on top the reed cage.
The odds are 99. repeating 9's there's nothing wrong with your poor misunderstood oil pump.
But I'm certain that's a no go for you.

Massive amounts of people delete the injection "just to be safe" only to introduce the possibility of mixing the oil wrong EVERY single time they do it .
Forever.

And that's the same pump used on literally dozens of Yamahas, sourcing a good one (any used one will be a good one) would be simple.
Partszilla says YSR's and RX's are direct fit but GT1,DT/GT 80's, DT100's perhaps some DT125's would all work.

This what I do, keep these classics running, bring them back to life.

Not knowing the history between picking it up and that dead piston, I would be afraid of a lean situation due to the combination of the  expansion chamber, air box mod (not so much there, maybe 5-10%, but leaner's leaner)  and the kajillion RPM it takes to get these things down the road. (they really live around red line)

Thus my question how long did it run in this configuration, hours or years?
If it needed and got rejetted properly years ago, great.
If not it's gonna bite you.

Plus your crank seals are almost 50 years old and they don't get softer.
Transmission side sucks oil. mag side air leaks.
It will be painfully obviously if they're bad.

edirt for puncsashun.

Responses in the quote tree in red.

What IS painfully obvious, is that you failed to read and/or comprehend all of the info I've posted in the OP and my replies before you typed up your response.

While autolube pumps are UNLIKELY to fail, some do, or they would NEVER fail.

Your opinion on premixing is

FWIW, as a teenager I ran the autolube system on my stock engine with a Team Calamari pipe, jet kit, and reeds without issue.  Later, I had them build a 60cc “superbike” motor on a different YSR and ran the pump on that as well. If you are worried about it, just don’t do long periods of deceleration on a closed throttle-but again, I didn’t see any problems with it and had almost 11,000 miles on my first YSR.

I know I had to check and adjust the oil pumps a few times when I was a wrench at a Yamaha/Suzuki/Arctic Cat shop in the 1980s (it was part of the standard "Tune & Service"), but I'll be damned if I can remember much about it now that we're 40 years down the road. I always went from the factory service manual and the customers were happy. I bet if I had a pump-equipped bike in front of me and a FSM, it would all come back to me. I hadn't thought about that in a long time, and enjoyed thinking back to a much simpler time in my life.  

I was mostly given 4-strokes to work on because the touring guys and the sportbike guys wanted me to be the one working on their bikes. 2-stroked were on the decline, although we still sold RZ350s brand new.

To the OP:  Yes, I understand that you are going the pre-mix route, but it's kind of too bad, because not having to mix oil and fuel is so much nicer.

I totally agree with you.

Unfortunately the only place the 2-stroke oil in the crankcase could come from is the oil tank and thru the pump. When I got the bike and removed the top end, the pipe was full of an oil/gas mix, at least it smelled like it (old gas smell), and the crankcase was full of the same. I thought "That's odd". Then, when I disassembled the carb it was severely gunked up from sitting 20 years, so I attributed the fuel in the crankcase to the needle being displaced from all of the gunk and oxidation, letting the fuel drain into the carb, but that still didn't account for the 2-stroke oil in the crankcase. I put a tight fitting vacuum cap on the end of the oil line that went to the carb, and marked the oil tank level with a sharpie for reference purposes.

Once I cleaned the carb and got the cylinder and piston back and reassembled everything except the oil pump cable (I wanted to be absolutely sure there was nothing actuating the pump), the oil was still at the sharpie mark on the oil tank. The bike got put on the back burner for quite awhile due to more important tasks. When I pulled the bike back to the front of the projects, the oil was considerably lower than the sharpie mark I had put on the tank previously. First time I started it was when I noticed the puffing of the smoke out of the leak and 2-stroke oil dripping out of the same spot. Just seems to make sense the pump was bad.

Full disclosure: I've never had one of these autolube pumps apart, so I have absolutely no idea whats inside of one. Maybe the owner of this bike will give me permission to take it apart....

Little update:

Even though I cleaned the flange before reassembly, I decided to double back on my prep in case I missed anything.

I broke out the dremel with a scotchbrite pad and gave the exhaust pipe flange a deep cleaning. Found a blonde hairline crack about an inch long in the radius for the flange that seals the gasket, most likely opening more when torqued down and flexing the flange.

It's at the machine shop for tig welding.

One of the reasons I don't default to stuff like RTV. The crack would have continued to grow, potentially cracking more, to the point the pipe would have broken off creating more issues and or damage.

If it wasn't used as OEM, I won't use it.

Unlike the other poster, I don't have an opinion about the longevity of the pumps or what their failure mode(s) might be, if they do go bad. In this case, gravity won, I guess we might say. that's the oil tank up by the steering head, right?




Good catch! Also, the vibration of the engine running would probably make the crack open and close in time with it.

You are correct, Sir!

That's quite the funnel!