General Information

[drgriffi1]

I am a newbie to everything dirtbike. I just had a 1983 Yamaha YZ400 given to me. I know nothing about it. I noticed there are 2 spark plugs, but only one wire. What is the 2nd plug for, or is there supposed to be 2 wires? The bike seems to start after one kick if I gun it as I am kicking it over. It seems to have a lot of power and runs good, I guess I am just wondering what the second plug is for. Also, do I need to mix oil and gas? There is a spot on the right side of bike to add oil, what oil do I use? Do I just put regular 2 stroke oil in there and not mix with gas? How do I change the oil? I'm sure I will have more questions, but let's start with these. Thanks.

 

[76GMC1500]

The 2nd plug is in case the first fouls. You simply switch the wire. Yes, you need to mix oil in the gas. 32:1 seems to be universally safe for all bikes. You mix it with the gas prior to adding it to the tank. The oil fill on the right side of the bike is for the transmission. That oil needs to be changed often. I do mine every other ride. It will come out gray from metal powder. This is normal, it's debris from the clutch. To change it, the drain is a large bolt under the crankcase. There may or may not be a dipstick. If not, there is usually a bolt you remove on the right side of the crankcase and you fill it until the oil comes out the hole. This bolt usually has a copper washer. You may also have a glass window for sighting the oil level. If this is the case, fill it until it's in the middle of the window. The bike needs to be upright and level, not on a side stand.

If you feel the bike is running lean at any time, do not ride it until you fix it. These old air-coolers will melt a piston down in a heartbeat if you lean it out. I had some friends who found out the hard way on a similar YZ490.

 

[drgriffi1]

What oil do I use for the tranny? Do I put the 2-stroke oil in there or is there somthing else that goes there? Thanks.

 

[mox69]

80w gear oil or 10w-40 will work. If you get a "synthetic oil" make sure it is safe for motorcycles (specifically wet clutches).


If your not gonna be racing, regular old 10w-40 works fine.


Also, there is like 800 different opinions regarding this subject, don't be surprised if you get a lot of different answers.

 

[76GMC1500]

Use 4-stroke motorcycle oil for your 2-stroke tranny. It's a little weird, but that's how you do it. The 2-stroke oil is for mixing in the gas only.

 

[drgriffi1]

Ok, so I stripped the bike down (pulled off all the plastics, tank, seat, etc...) trying to look for a VIN plate. There isn't one that I could find. I went to the Yamaha dealer and told him that the guy I got the bike from said it was a 1983 YZ400. The dealer looked in his book and said there is no YZ400, IT400, or any 400 that he could find in that year. Is it a different year bike? The only numbers I found on the thing are 2X8-001316 stamped on the neck, 2X500 396cc stamped on the engine, and 2x500 Y-1 stamped on the tranny. Can anyone identify the bike by these numbers? The parts guy sure couldn't figure it out, but I think he was a little mentally challenged. I am going to look on the internet too, just figured I would try here first. Thanks in advance. -DrGRIFFI

 

[drgriffi1]

After much searching, I think I have identified it as a 1979 IT400. The original color was blue and from the pics I found on internet, they are very similar. Still would be nice to know how to identify it without finding a VIN plate.

 

[76GMC1500]

The engine should also have a serial number that the dealer should be able to trace. The VIN isn't necessarily on a plate, it's usually stamped into the metal of the steering head. It should be visible unless the bike has been painted or someone ground it off.

 

[drgriffi1]

Where is the serial number on the engine? As I stated previously, those were the only numbers I could find.

 

[76GMC1500]

Well, the only Yamaha I have has the serial number behind the cylinder on the top of the crankcase. My Honda has it above the shifter. Look around, you should be able to find it.

 

[MOgle80]

you say the frame has 2x8-****** that is a 79 IT400 frame
according to the Yamaha corporate web parts pages.. 2x5 is 79 YZ400

 

[drgriffi1]

So the engine and tranny are YZ400, but the frame is an IT400. That's what I got out of it. Thanks. Hey, more help needed...
There are 4 places for a hose to connect on the carb, one towards the center on the left side as you are sitting on the bike has the hose from the petcock, the other three are not being used. One is on the right side and is plugged with a small piece of hose and a screw, the other two are on the left side, one on bottom one on top with nothing connected to them at all. Should something be connected there? Thanks.

 

[whenfoxforks-ruled]

Nice work on the pics!I am fairly certain all them areas of concern are overflows and vents that should have hoses on them and draining under the bike.The one with the screw in it is priceless!Bet fuel runs out consistently,clean the carb throughly,replace the float needle,check the float height.Try this and id your carb,http://www.sudco.com/

 

[drgriffi1]

So, from looking at various carb diagrams, (thanks whenfoxforks-ruled) it seems that there are two air vents, one overflow, and one fuel intake. Assuming the fuel intake is hooked to the currect one, everything else should just vent under the bike as you stated. I am going to pull the carb off today and go through it. I'm sure I will have more q's later. Thanks for the help.

 

[drgriffi1]

Ok, so I pulled the carb off and cleaned it. It wasn't all that dirty. I pulled the jet out, pulled the air adjust out, cleaned everything out, should be good. But, how do I readjust everything? Mainly the air adjust and idle adjust. It has new premixed fuel in the tank, hopefully after I get the carb on and adjusted it will run like a raped ape. I also put new plugs in and changed the oil. Let me know about adjusting and if I should put the carb back on before or after adjusting it. Thanks for the help.

 

[whenfoxforks-ruled]

You touched on about half of the crucial areas inside the carb.Your manual will have model specific information for your bike.You do not know where you live and neither do I,elevation and temperature.

 

[drgriffi1]

I'm in Oregon. Ride at elevation anywhere from 2,000 feeet to 5,000 feet above sea level. Temp is usually around 45-75 degrees. Mostly around 60 though. That wasn't a complete list of things I did in carb, was just trying to keep it short. I DL'd a list of things to go through when cleaning a carb, and followed it. But, it didn't say anything about adjustments. I do not have a manual, and yes, I know I should get one.

 

[drgriffi1]

Sometimes ride at sea level too. (Dunes on coast)

 

[drgriffi1]

Correction, anywhere from sea level to 5,000 feet.

 

[drgriffi1]

The crank case has the same 2x8-********* as the frame. The tranny has the 2x5-*******, from what I read, the IT and YZ use some of the same parts, but now that I found two of the same number, I am certain it is an IT400. Also from looking at pictures and other reading, the IT's were all mostly blue, but the YZ's were made in Yellow and White probably other colors too. Anyways, I got the carb back on and now waiting for air filter to come from UNI, then I will try to tune the carb. From what I read, I should get the bike running, which I did without the filter, and turn the air and fuel adjusters out 2 and 1/2 turns to begin with. Then adjust in or out until idling corectly. Not exactly what procedure says, but I'm trying to keep it brief. Anyways, I think I got it figured out. Will install filter, put covers back on and adjust as needed.