Just bought a 1975 Yamaha MX 250

[giggyhurdle]

And I've got a few questions..

Is there anywhere I can get information on dirt bikes made that year? From what I've found is that it's the YZ and MX models, but I've seen the only difference being the shocks in the back. Also, my bike has 250 Motocross on the tank, I haven't found any other pictures with this game tank, is it original? Thank you.

 

[dirt bike dave]

From what I've found is that it's the YZ and MX models, but I've seen the only difference being the shocks in the back. Also, my bike has 250 Motocross on the tank,

The '75 MX and YZ were monoshocks. If yours has two shocks in the back it is not a '75.

From what I've seen, the '75 MX250 has a white tank and it says 250 in big letters with Yamaha below it.

 

[giggyhurdle]

That's exactly what my bike looks like.. As well as what the title says.
With all that being said, why are there two spark plugs? Is one a spare kept on the bike in case the first gets fouled?

 

[gwcrim]

Is one a spare kept on the bike in case the first gets fouled?

Give the man a ceegar!

If yours is as clean as the one in that pic, you have one SWEET ride.

 

[dirt bike dave]

Give the man a ceegar!

If yours is as clean as the one in that pic, you have one SWEET ride.

That one came up on google as listed for sale on a vintage bike site. The asking price was $2,900. Not sure if that was current listing and price or not.

There was one listed at $800 that was not nearly so pretty. ;)

Lots of old bikes had two plugs in the head. For some reason, the plug that is not firing does not foul as quickly as the plug that was being used, even if you put them in at the same time.

 

[giggyhurdle]

My bike almost as clean as that one..
Here's the kicker though.. I only paid 225. It doesn't run, but it ran 4 years ago when they parked it. The pecock smells like vinegar though. I don't think know it its from them trying to clean the engine or what. I'll have pictures this afternoon. Hopefully, it'll stay nice..

Also, can you point me to where I can buy the front hand brake? The one I have is broken at the joint on the handle, so it looks like I may need a new handle/lever was well as connector. Thank you.

 

[giggyhurdle]

So, looks like my clutch is out.. it's not engaging (disengaging??) when i squeez the lever.. anyone point me to a place where I can get it replaced? Or can someone tell me how much it cost to have repaired?

 

[Vintagesplash]

I have one that is just as clean also. I also have a couple tanks and an engine.

A little history. People will tell you that the MX was just a trail bike. I say rubbish. If you went to any pro races back then there was always at least two or three MX models racing. They were more available then and are getting hard to find now.

The '76 YZ was nothing more than a '75 MX with a yellow tank, different swingarm and air cannisters on the forks. The frame and engine numbers on both models started with the same number, 509. To me the '75 swingarm looks stronger, having a rectangular top bar.

If anyone knows where a good '75 MX400 is in the southeast, I need one.

 

[giggyhurdle]

Here are a few pictures of my bike.. I guess it does look sort of rough..


Edited because I figured out how to add photos..

 

[dirt bike dave]

For $225, I would say you did very well! The tank is in very good shape, and it looks like it is all there except the stock silencer. Someone probably added the SuperTrapp to get a spark arrestor on it.

That bike should clean up real nice with a little elbow grease. FWIW, I would certainly take the yellow boots and bar pad off.

Pretty small airbox on those old monoshocks. I had a '76 YZ125X (with the air forks) and seeing your old bike brings back a lot of memories. Sure helps me appreciate modern suspension too, lol.

Looks like you have Preston Petty fenders on there.

 

[giggyhurdle]

The tank is in amazing shape. I opened it up yesterday, and there is no rust or fouling of any sort. It's a nice silver. It looks brand new.
Now.. to just fix the GD clutch and clean the carbs.. and I think I'll have a steal.

 

[Vintagesplash]

Your tank is made from aluminum, so will not have rust.

You can get original style fenders and side number plates from DC Plastics. They have pretty good quality and have an E-Bay store.

Mine came with a Skyway spark arrester/silencer from the factory. I know this because I am the 2nd owner and have had it for many, many years.

If your ignition goes out, pick up a PVL and all will be well.

 

[giggyhurdle]

Thanks for that information.. good news, though, I have both side plates, I just took that one off to take a look at the air box.

Anyone know anything about getting a new clutch for this? As far as cost of the clutch goes? (not work, so far, I've seen it for for around 100 bucks..)

 

[zoommx]

That air box is not a lot different from the one on my 78 YZ100!! (top end off for bore)

I have an 75 MX400 at my nephews. Mostly complete, but I think it needs a new rod and the shock is blown. Lots of spray paint too. It never has ran since I got it, been about 3 years now. I did put LOTS of oil everywhere before storing though.

 

[giggyhurdle]

Things are looking bleak...

1. Bike will not run. I've got spark and sprayed some starter fluid into the Carbs.. no go. Next step is to start taking the thing apart.
2. Clutch does not work. I've checked the cable, and it's pulling on the lever on the bottom of the bike. Still not disengaging the gears.

I found a clutch hub basket on Ebay.. The listing says it's the complete clutch.. will this work to replace my clutch? I can't post the listing.. but.. I'm unsure if I should just buy it.. before knowing if my clutch just needs oil.

 

[schmanman]

it might need new rings. check the compression.

and your clutch might just need to be broke loose, when I got my bike, which had sat for 18 years, all I needed to do was pull in the clutch and ride it around until it freed up.

when a bike sits for a while, the clutch will often stick together.

zoommx, where did you get the graphics for your yz 100? i have been looking for a set of those for forever!

 

[giggyhurdle]

I have compression, so we are good there. I'm going to switch the spark plug wire to the other spark plug (since there are two in the head, I didn't switch it first). I'm also going to purchase some new spark plugs.

 

[Shaw520]

The smell that you noticed from the petcock is the old gas that has turned into shellack. That will be consistent through out the entire fuel system. You will need to remove the carb, clean the bowl, the jets, needle and needle valve. Check that the float still floats, and that it and the needle valve move freely up and down. May also want to check that the reeds arent gummed up as well. Also change the bottom end oil, Im sure its contaminated from sitting
The clutch will most likely free itself once you get er running. good luck

 

[giggyhurdle]

The smell that you noticed from the petcock is the old gas that has turned into shellack. That will be consistent through out the entire fuel system. You will need to remove the carb, clean the bowl, the jets, needle and needle valve. Check that the float still floats, and that it and the needle valve move freely up and down. May also want to check that the reeds arent gummed up as well. Also change the bottom end oil, Im sure its contaminated from sitting
The clutch will most likely free itself once you get er running. good luck

thanks for the info.. quick question.. does my bike have a wet or dry clutch?

 

[Vintagesplash]

The Yamaha clutch is wet.

 

[Shaw520]

your clutch is submersed in oil,... another reason to get that old oil out and replace with a good quality oil.
Very important to get the carb clean, it will not run/run properly with clogged jets and needle valve. When you get the carb off, remove bowl (bottom) remove two jets and blow clean with compressed air ,check visually for clean passages. Same with float/needle valve. post here if you need help.

 

[zoommx]

zoommx, where did you get the graphics for your yz 100? i have been looking for a set of those for forever!

It was just a couple perforated sheets with the yamaha logo, I had to trim to size, they look good, but that was about 4 years ago when I got them from these guys:
http://yzworks.tripod.com/index.htm

 

[giggyhurdle]

I've got the carb off. one of the floats had trouble moving up and down. I got some soap and water and I'm cleaning them now.. Just realized I can't leave them in soap and water.. or they'll rust. Where are the jets at? I'll go have another look. on a side note, the carb looked really clean inside, but where the floats were.. very dirty.

Also, how do you drain the oil from the clutch?

 

[Shaw520]

I've got the carb off. one of the floats had trouble moving up and down. I got some soap and water and I'm cleaning them now.. Just realized I can't leave them in soap and water.. or they'll rust. Where are the jets at? I'll go have another look. on a side note, the carb looked really clean inside, but where the floats were.. very dirty.

Also, how do you drain the oil from the clutch?

Better to clean with carb cleaner, or if you dont have that wd-40, water is not good idea. When you remove the floats the needle will drop down with them, look up into the belly you will see two brass jets and a brass seat that the needle was in, one of the jets is larger than the other (main/pilot). remove and blow clean.

The bottom end oil is drained via oil plug at the bottom of the engine, large bolt usally 14-15mm

 

[giggyhurdle]

Heres a picture of the carbs..