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78 yz400

14K views 20 replies 11 participants last post by  78YZ400 
#1 ·
Just looking for some info on this bike. I picked it up last year for $150 off Cl locally. I think it's a 78. I've always wanted one of these vintage yamies. The thing didn't run when I got it. After cleaning the carb the thing fired right up and runs good. I had the seat recovered, clutch cable, and throttle cable were replaced. It needs a new needle, seet, silencer, and rear tire.

So, my question was is the 400 a pretty reliable runner ? Are they rare? I never see to posts on the yz400. Always seems to be the 250 or 490. How does the 400 compare to the 250?




 
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#4 ·
Thanks, I was just wondering if it was worth throwing anther 500 dollars (tire, plastics, Powdercoat or paint frame, exhaust) at it. Curious if they were somewhat reliable.
 
#5 ·
Spend the dough on a crank re-build, and a new piston and it will be dead nuts reliable.
Ditch the mikuni and put on a 38mm Keihin PWK, that alone will make a big difference.
I wouldn't say it's particularly collectible without a ground up restore but the parts are available.
Lot's of stuff from the 76', 77', and 78' interchange so do your homework.
 
#7 ·
Thanks a lot. I'll keep an eye out for a good used keihin. The motor runs real strong. I really like the bike. Just wanted to see if it was a reliable bike if I'm gonna put the time and money into it. Looks like she's a keeper. Thanks!
 
#12 ·
Def a 1978 YZ400 or more specifically the YZ400E.
Some people consider the E model better then my 79' F.
The difference between the 2 is yours has a shorter stroke/larger bore then mine. In theory yours should rev out higher.
All the big bore 400's and even the 465 are very reliable if tuned correctly.
Why? Because they don't have to rev out to make power like a 250/125.
RPM's = wear. The big bore's make the same power and more at a lower rpm.
They also make more torque.
If you don't raise the compression a bunch or port it out for high rpm power it should go years between ring and piston changes.
 
#10 · (Edited)
im not sure about the 400 but the yz465 was excellent bike and was highly collectable and worth a good chunk of money if its still in good original condition. do some investigating before you start throwing any of the original parts in the trash. most of them older bikes are worth far more if theyre unmolested. if you know what i meen.
 
#11 ·
Paulie B's advice is sound, especially on these old Yamahammers. That 400 will give you every reason to love it and I imagine you will. Go ahead and throw some dough at it when it's a good time for you and like Paulie said, it should treat you well if you do the same to it.

I have seen a few of these in the northwest recently and they are not bringing any real money so as long as you don't think of this as an investment , which is absolutely IS NOT, you'll be fine :thumbsup:
 
#13 ·
Great info guys, thanks a lot! I'm leaving the motor stock and just gonna work on the little things it needs. I'll definitely be looking for a new carb also. I'm not looking at it as an investment. I just like to know if I put the time into it that I'm gonna end up with a somewhat reliable runner if done right. Thanks again fella's.
 
#16 ·
Bought a new tire and tube today. Also found new carb for it. All I need now is a rear fender and a new silencer for it. Thanks again for the comments fella's. I'm thinking this will be next years winter project (complete tear down).
 
#17 ·
Brings back memories I got one given to me when i was 14 said it was blown up pulled the head off and cleaned the cylinder, carbs and replaced the plug fired rite up I beat the hell outta of it for a good 3 years before it ever blow up and thats only because a rookie rider liked to way over rev so id say its worth a little time and money.
 
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