Need Help With yz400 project

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MrYz400

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Apr 23, 2015
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Just picked up a Yamaha Blaster with a 1979 yz400 engine.
not currently running. ive cleaned the carb, changed the plug changed the
coil, new gas. dont know anything about the wiring, only thing left on the quad is the stator ,coil, cdi 6 wires total. the guy i bought it from claimed it was only a carb problem. i can see the carb is only opening about half way. so i bought a pro motion twist throttle and cable for a yz400 didn't work the cable at carb side was not right. even tried a 400ex thumb throttle with yz400 cable. to much slack. jumping head a little back to getting it started checked the ground looks fine. i am getting spark not sure if im getting enough spark thus changing the coil. any ideas???
 
Last edited:
If it has spark,fuel,compression, it should at least make some noise.One step at a time,verify everything.Have you put a squirt of fuel in the sparkplug hole and tried to give it a kick?
 
Jimmer said:
If it has spark,fuel,compression, it should at least make some noise.One step at a time,verify everything.Have you put a squirt of fuel in the sparkplug hole and tried to give it a kick?
Click to expand...
no i haven't but im assuming thats fuel blowing out the spark plug hole when i tested for spark?
 
If its blowing that much visible fuel out kicking it over with the plug out,you may have it flooded.
 
Do not listen to anyone who tells you to put fuel in the plug hole!

It washes oil from the cylinder walls and the rings run un lubricated.

If it is flooded,take the plug out, turn off the fuel, drain the carb, open the throttle wide and kick till your leg hurts.

Put in a new plug and start it.
 
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Oh come on,premixed fuel of course.Just a splash to tell you if its a fuel starvation issue.But now that he posted it was huffing fuel out, I too say he has it flooded.
 
Probably the needle seat or float height. My buddies wr500 carb was letting fuel dump into the motor. It sat overnight and filled the bottom end. Took a good hour to kick all the gas out of it.
 
Pre mixed fuel has no lubrication properties at all.

Never put anything in the cylinder that will remove lubrication!

A very poor practice and advice should never be given to do it!
 
Okay im assuming, it's not flooded like i said just got it none running. Cleaned the carb meaning i had the carb off tank disconnected. Mixed new gas put everything. Back together and gave 2 pumps of the gas to prime and kicked about 6 times. It didnt really sound like it was trying to start to me. So i then removed the plug while holding it to the head and kicking i felt a drop of gas hit finger. Im guessing this is not out of the ordinary. Did not add fuel to the head. I would all so like to add i am runing an open carb no hose no filter. Waiting on hose piecing it back together. But again im guessing this sould not stop it from trying to start but effect running properly?
 
Im going out now amd i am going to remove the foot peg to see if it helps. Probably not but i noticed the kicker is meeting up with the peg. But they meet a 6 o'clock so thays wjy i dont think its going to make a difference.
 
Got a milky goo comming out now that ive been kicking a while. Comming out where head and pipe meet.
 
Bad crank seals are common with the old Yz400
I rebuilt my yz400 twice with new crank, rod , bearings and seals and within a few rides it got very hard to start again.
leak down test showed it leakin into the crank case again.
 
Okay i pulled the pipe off and that required me to pull the motor so its taken me a while. i was thinking maybe water in the pipe, But instead there was a good amount of gas? is this normal or could this be cause of all the kicking that has been done to start the quad. In any case i replaced the reeds. I did figure out the float clip was in upside down. Switched back to old coil seemed to put out more spark. I tried to do a compression test don't really know what im looking for but this is what i got. About 6 kicks puts it a 60lbs waited about 20mins no loss of pressure. id also like to add i have a lt230 and it takes quite a bit of force to kick it over. this motor kick's really easy. BTW i am MrYz400
 
pipe is not fitting tight to head is there a gasket i need to get? also any idea's on a kick starter swap this thing is dangerous. the guy i bought it from broke his leg trying to kick this thing over. i hate that i half to pull off the rear plastics to kick it over. thanx for the help!!!!
 
UPDATE.... i got it running, running strong. waiting on a few parts to finish it off. but for now is there anybody that can tell me how to hook up this kill switch. i bought a oem replacement switch for the 79 yz400f motor installed it now the motor will only start when i have it pushed. what am i doing wrong here?
 
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