Vintage motor mods, YZ400

I have this old 79' YZ400 that i'm building. Does anybody remember any motor mods or what the hot ticket was back in the day?

BTW I'm building this motor because I love the big vintage 2 smokers AND I want to whip all my friends on their new 4 strokers.

For some extra power, throttle response, and better all 'round performance, try and swap on a newer carb. A 38mm PJ would work fine. New, or aftermarket reeds, ported cylinder, mill head for higher compression, aftermarket pipe.

A better bet for your cash would be suspension and brakes. It's the suspension that makes you faster, not the power output of the engine.

Currently it's @ 426cc, V-force 3 reeds, milled head, DG pipe.

I am running the stock 28 year old 38mm Mikuni. A 38mm PJ would really help? I'll look into that, thanks!

What about lightening the flywheel, is there any benefit in that?

I have to add the motor came out of my quad.

hi

if it is a gen 1979 yz400 it is the most powerfull 400 yamaha made.it was called the update model.pistons are very hard to come by as the only ones i know that fit are the gen yamaha ones no one makes aftermarket ones.the barrel is different and also the ignition.i havent checked about the 1980 and beond parts yet but i do know not much fits from earlier yamahas.some it400f parts fit as i have a it converted to yz.if you can get a yz490 disk brake front it should bolt straight in as they still use the same steering head bearings.

ps mine whips the arse of a 2006 wr450.my mate cant keep up with me even on a gravel road.:applause:

hi

if it is a gen 1979 yz400 it is the most powerfull 400 yamaha made.it was called the update model.pistons are very hard to come by as the only ones i know that fit are the gen yamaha ones no one makes aftermarket ones.the barrel is different and also the ignition.i havent checked about the 1980 and beond parts yet but i do know not much fits from earlier yamahas.some it400f parts fit as i have a it converted to yz.if you can get a yz490 disk brake front it should bolt straight in as they still use the same steering head bearings.

ps mine whips the arse of a 2006 wr450.my mate cant keep up with me even on a gravel road.:applause:

It is a 79'. Through some top secret resources I can get pistons in any size I want. I have it out of my hybrid 4 wheeler and want to build it up as strong as possible. Thanks for the info, keep whippin that wr450!

Behold brand new 426 'OW' kit complete

IM000688.jpg

I remember the PDQ team and what they did.

If I remember the PDQ team used OW426 kits because I saw some of their "old" parts in a boneyard about 10 years ago. There was a few keystone shock kits and complete shocks, OW kits, transmission gears, cranks, cylinders and Simons forks/kits and tank/seat graphics.

Don't bother to ask where this place is because it's not accessable anymore, sorry. IF I coud I would have got out the parts.

MY 79 was done by RPM in Toledo, Ohio. long out of business.

They did stage 4 porting, turbo balanced crank and coating of the piston and cylinder, modded the cylinder head and decked the cylinder.

I had a fox airshock and simons forks, Answer silencer and stock pipe. (its the bike in my avatar shot at Mid Ohio)

My frame broke at the downtubes by the pipe mount. The cylinder base gaskets were always blowing till RPM decked the base.

That was a good bike.

Must have been a real hand full! What kind of HP do you think you were pushing?

Forgive my ignorance but what does the 'OW' in 426OW stand for??

OW were the Yamaha designation for works factory bikes.

IE. OW31's were what Kenny Roberts road raced

Thanks Shawn! I always wondered what it meant...PB

Hello! I was wondering if you can tell me what parts crossover from 80 it425 to yz 400 < I Have an IT and hope to find bottom end seals and gaskets bearings etc ..thanks for any help with this ! Leon

The It425 is identical to the 79' It400 except the bore is 85mm instead of 82mm.

You can bolt the 79' YZ400 top-end (cylinder and head) directly on the IT425 bottom end without any modifications.

In fact the 79' YZ400, 79' IT400, and 80' IT425 top and bottom ends are all interchangeable.

The sad part is that the 80' IT425 the hardest to find pistons for followed by the 79' IT/YZ 400.

The hot ticket back in the day would be the 80' IT425 top on the 79' YZ400 bottom.

Leave it stock and give 'em a whipping, I'm rebuilding an IT425G and am riding my recently finished reed valved XR 500 complete with little wee carby and it's fast enough to keep my mates under control, only problem so far is lack of ground clearance in tough stuff.

The It425 is identical to the 79' It400 except the bore is 85mm instead of 82mm.

You can bolt the 79' YZ400 top-end (cylinder and head) directly on the IT425 bottom end without any modifications.

In fact the 79' YZ400, 79' IT400, and 80' IT425 top and bottom ends are all interchangeable.

The sad part is that the 80' IT425 the hardest to find pistons for followed by the 79' IT/YZ 400.

The hot ticket back in the day would be the 80' IT425 top on the 79' YZ400 bottom.

Thats really cool !! glad to hear you are in the know on these classics ..I have a 425 I bought on ebay fully restored ..turns out that second gear was pooched so parked it and started gathering parts..I have 3 xtra engines now and a carb.etc but yet to put it back togeather for lack of gasket kits ...Last week I scored an IT 400 with 1500 orig k from orig owner even has orig tires ..as well he threw in a dt400 in really nice shape and looks to be the same engine ...but im reluctant to part this baby poo brown puppy out because its so complete and every thing works ..only thing it needs is fork seals ..these bikes are classics for sure with a nice low center of gravity.. not to mention good low end grunt and low gearing please keep posting about your bikes its great hear good news..:thumbsup:

leon in alberta canada

I have a guy that prints and cuts all my gaskets out on a machine.

He has all the gaskets for an IT425, IT/YZ400 on file.

C&M Cycles #301-343-7005

It is a 79'. Through some top secret resources I can get pistons in any size I want. I have it out of my hybrid 4 wheeler and want to build it up as strong as possible. Thanks for the info, keep whippin that wr450!

Behold brand new 426 'OW' kit complete

IM000688.jpg

RICK HORVAT!:thumbsup:

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