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1978 YZ400E 450 Killer


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Hello, it's finally come time for me to build my YZ400E. I have a 250 of the same year that's going to be turned into my everyday bike so I've decided to build this bike into a modern 450 killer. I know it's never going to be as fast around a track, the suspention, frame, and brakes will never let me do that. But if I line up against one of my friends on a brand new 450 on a streight gravel road I want to destroy them. I'm gonna keep the bike looking old and beat up but I'm gonna fully rebuild the engine and chassis. My question for you guys is how do I make rediculous power out of this thing? How do I get a high top speed and quick acceleration? I have about 1k to spend on this thing so give me your suggestions. Thanks.

20190615_171249.jpg

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U wouldn't need to do a whole lot to have that complete in a drag race with 450's. A 400 two stroke is a very powerful engine perhaps all u need is the right sprockets to achieve what u want.. make it mechanically sound, look nice n hang on with both hands 😁 

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2 hours ago, FPMXer said:

Port and polish the cylinder, head and carb. Get it jetted properly and gear it for top speed. Also get the suspension done too. All that power and piss poor suspension and you will lose every time.

I'm only 17 and very new to this game, how do I go about porting and polishing? Do I sent the cylinder and head somewhere? Do I do it myself? What kind of porting needs to be done?

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42 minutes ago, Nicholas Sibley said:

I'm only 17 and very new to this game, how do I go about porting and polishing? Do I sent the cylinder and head somewhere? Do I do it myself? What kind of porting needs to be done?

Google is your best friend! There are plenty of places that can do the work. But only a few know exactly what to do. There are vintage forums for that bike. Eric Gorr is another resource.

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I owned a 79 YZ 400. Great engine, very rideable. I've seen the dyno reports. They made a hair over 36 hp. Your a long ways away from beating any 450 and there are probably 250Fs would beat you in a drag race. IMO enjoy the bike as is or look for a CR or KX 500. 

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4 hours ago, M E T A L A C I D said:

Ya wanna beat your buddies 450's in a drag race? Find and purchase one of these.image.png.af512380db790160c20923396ca126ab.png

But even those won't tho lol unless it's modded. Stock 450s are hard to beat nowdays in straight line

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Contact eric gorr, im sure he knows something about these big bore two smokers. With a port job, pipe and good jetting it has a chance against a 450. These old air cooled ones also have a terribly narrow squish clearance and as a result can't rev high enough to out run a 450. Eric Gorr can also fix that by milling your head out a bit... Oh yeah and that suspension can fly off into the woods and get lost, every yamaha that old i tried was terrifying at high speed. 

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14 hours ago, Nicholas Sibley said:

Hello, it's finally come time for me to build my YZ400E. I have a 250 of the same year that's going to be turned into my everyday bike so I've decided to build this bike into a modern 450 killer. I know it's never going to be as fast around a track, the suspention, frame, and brakes will never let me do that. But if I line up against one of my friends on a brand new 450 on a streight gravel road I want to destroy them. I'm gonna keep the bike looking old and beat up but I'm gonna fully rebuild the engine and chassis. My question for you guys is how do I make rediculous power out of this thing? How do I get a high top speed and quick acceleration? I have about 1k to spend on this thing so give me your suggestions. Thanks.

20190615_171249.jpg

$2000 more for what you expect outta it.😀where are you trespassing there? cemetery? park? be sure to get a dmv title,to prove you own it.🤔

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5 hours ago, Motox367 said:

But even those won't tho lol unless it's modded. Stock 450s are hard to beat nowdays in straight line

Gear it right, and the 4fiddy will be left in the dust. I raced my 84 500r vs a 750 ninga, he was on the street, on was off road, I smoked him no problem. Gearing is the key. An 85' 500R will completely wollop a 4 fiddy. Yee-haw!

deliverance_190pyxurz.jpg

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Just now, JustinXR said:

The limit these big bores have is they often don’t rev real high, but they make loads and loads of torque. Gearing is the key to unlocking the beast. My ‘85 500R blows every modern Mx bike out of the water I’ve ever raced against or ridden.

Bro, I think its safe to say that 85 might be the Holy grail of open bikes. I rode one back in 86, and I wanted to keep it for my self, the dude said noooo. I said, "Oh well, nice try" lol! Take care of your Red Dragon, she'll run for a very long time. Honda quality!

you-da-man.jpg

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10 minutes ago, JustinXR said:

The limit these big bores have is they often don’t rev real high, but they make loads and loads of torque. Gearing is the key to unlocking the beast. My ‘85 500R blows every modern Mx bike out of the water I’ve ever raced against or ridden.

Justin, ya got a picture of your 85 500r? I wanna seee, pweeese!😃

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3 minutes ago, M E T A L A C I D said:

Bro, I think its safe to say that 85 might be the Holy grail of open bikes. I rode one back in 86, and I wanted to keep it for my self, the dude said noooo. I said, "Oh well, nice try" lol! Take care of your Red Dragon, she'll run for a very long time. Honda quality!

you-da-man.jpg

Right on, my favorite bike so far, its like the perfect dirt bike for me. Best 1700 bucks i ever spent so far. 

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