turrican64

I'm stumped! Not usual for a crank to just bend like that. Maybe someone has some insight?

Either the crank was bent before, or something was not put together right. If you split the cases and weren't careful, that would explain the bent crank. Do you have pictures? A bent crank is a difficult fix...and the bike won't run at all like that.

From that serial, it looks like you have a YDS3 as previously mentioned. It was also called a Catalina in some areas. http://cyclerestorer.com/pages/show_man_serial_num.php?sort_field=4&manufacturer=Yamaha

If that doesn't solve your problem, I'd suspect the crank seals...especially if the bike hasn't been run for a long time. What tends to happen is that they harden up with age and don't seal as well. When someone takes a bike out with hardened crank seals and attempts to start it, they can tear, creating the problem you describe. There are two seals, one on the magneto side, and one on the clutch side. You'll know if the clutch side one is bad if you see a ton of white smoke, otherwise assume it's the magneto side (or better yet not assume and replace both of them ). Just so you know, a good way to check for leaks is to get the motor running and spray WD-40 wherever there is a gasket. You'll see bubbles if there is a leak.

Welcome to the forum! I believe the points are on the outside of this bike...which means you are removing the points assembly and then the rotor. You need a slide hammer, and not a flywheel puller, if this is the case. Pictures?

If it's revving to red line without any throttle input, then you have an air leak somewhere. Could be crank seals, head gasket, base gasket or a leak in the carb.

Anyone have some of these, or any magazine articles of the 60's Yamaha twins in high resolution? I'm itching to read all I can about these bikes, and I find them interesting to look at.

Epay would be a good start. Other members will have better suggestions.

Magic. Find Harry Potter and ask him to stop that crap. Right now. ...in all seriousness, are you sure it was off? You might have a short in your wiring harness, or it might have been modified at one point in time. Try starting the bike normally, and shutting it off with just the ignition.

Looking forward to it! Hopefully you get that bike running...Yamaha's bikes will last forever when they are taken care of properly.

What 400 is this? If it's a two stroke RD400, and you got it started with straight gas, you have an air leak or your carb slide is backwards. My guess would be your crank seals (tranny side would result in lots of white smoke, mag side the condition you are describing), but could also be the cylinder head gasket, base gasket, or the reed valve gasket.

My scanner is busted, so I took a picture instead. Anyway, you can make your own, and modify the pistons and ports for maximum performance. Make sure to read it very very carefully. http://bayimg.com/image/aaeigaack.jpg Have fun!

I have the measurements to modify the existing cylinders and pistons, as well as the measurements to make the pipes from scratch for the old two stroke twins. What motor do you need it for specifically? If I have something, I can post it up.

On my '75 DT175 I had a 4.1-18 on the rear, but I wouldn't recommend it.

There is a shock preload adjuster on the bottom if they are stock. Check that out. If the preload is maxed out, your shocks are done and you need new ones. Oil seals don't seal as well after a while and they lose their oil, which is likely your problem.

Get the number off of that jet, and take it to a bike shop nearby. They should be able to match something up....Mikuni VM20 carb with x number jet.

Stock was 175cc of 10w-30 oil. You might want to take 15cc off of that or something.

To upload pics, you need to find a image hosting site (imageshack) and upload it there. There is a little image of a picture in the menu above when you make a post. Click that, place the image URL (www.xxxxxxxx.com or whatever) into the box and it's placed in the post. Like you said, phoning around would be a good option. You could also ask the guys here: http://64.234.201.42/YamahaForum/index.php They know tons about Yamaha enduro bikes and post quite often. Hope this helps.

Get me a carb number. It will be stamped somewhere on the carb body and it can be difficult to find. It might be here: ...or somewhere else. I'll take a look and see if it matches up in my book. Your best bet for parts would be a wrecker or ebay. By the way, if you can't find parts, don't just trash it! There are some who restore these and you could make some cash by parting it out.

I'm guessing that ebay would be your best bet for parts for this bike, or a local bike wrecker/salvage. I'm not sure if the parts will interchange between those bikes...your best bet would be to take the old part and compare it.

You have a 1974 TX500A. Search the first three digits and you will find it. http://cyclerestorer.com/pages/show_man_serial_num.php?sort_field=4&manufacturer=Yamaha

Cool! I'll have a look when I don't have a whole bunch of crap to do...I just got a hold of a couple other bikes and they have most of my attention right now.

That's OK. What you do is lightly tap the exhaust port with a rubber or plastic mallet (NOT THE FINS!!) to free it from the gasket on the bottom of the cylinder. It should come free and slide off, leaving the studs sticking up from the cylinder. You don't need to remove the studs. I provided a picture of a different motor, but the process is still the same. If the studs came off, no big worries. Since it's apart, you may want to remove any carbon from the cylinder head. Also, when you place the piston and rings back inside the cylinder, make sure to use lots of oil so you don't score anything. The torque values for the head nuts are 14.5 ft.lb.; make sure to tighten slowly and in a criss-cross direction. Hope this helps.

To find neutral, press down on the lever several times until you feel that it won't go down any more gears. From there, it's half a click up into neutral. If you were to click up past the "half click point", then you would find yourself in second. Basically you click down from neutral to first, click up from first to second, click up second to third...so on so forth. I suggest you search youtube to see it visually. It helps sometimes.

Your float height needs to be set, that will stop the fuel flow. There is a little tang that makes contact with the valve; bend it slightly (to spec...helps to have a clymer) and that should fix your problem. If not, maybe you have the valve in backward? The gears on that bike should be 1 down, 4 up. To go into neutral, shift down to first, and go up a half click. Try it first without running to get a feel for it. Unfortunately, I can't really help with anything else. Ask these guys when they open up registration again...they should know: