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Dave_VanBrocklin

YZ ignition box?

23 posts in this topic

I heard something today that interested me. I was told by an independent repair shop tech that the YZ cam timing is only half of the difference between the WR and YZ 400 engine.He was under the impression that the YZ has different ignition mapping, and a higher rev limit. Has anybody heard the same,and if so, have you tried the YZ ignition box? I don't know if different spark curves are used,but it does make sense. I rode a bike with YZ timing and personally didn't care for it. I ride mainly heavy woods and prefer the snappy low end. It seems that the YZ was kind of soft down low.Maybe different ignition curve would change this?

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There WILL be different mapping for the different cam timing.

Its prob cheaper to buy a Dual curve Votex ignition! :) (from me!)

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**Ride it like you Stole it!**

Matt Porritt

99 YZ400F

Vist the Rubber Chicken Racing Online Shop

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Matt

can we be clear about this, the YZ has a different ignition curve, correct?

folks have been changing their WR's to YZ cam timing & they say that the bikes are weaker off the bottom?

ok so has anyone gone between the two ignition system/curves?

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YES the WR DEFFINATELY has a different CDI

99 WR part starts with 5BF

99 YZ part starts with 5GR

The YZ is slightly advanced at the mid-top compared to the WR and the WR is slightly retarted on the bottom-mid.

**Anyone played with the TPS to advance the timing in relation to the carb opening?**

This explains the WR different feel when YZ timed and also the YZ timed to WR timing doesnt have the same 'ummmph' as the WR.

***NOTE***

I have recently been told the WR cams are 'slightly' different to the YZs.

There are listed as a different part number and are also cheaper for some reason.

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**Ride it like you Stole it!**

Matt Porritt

99 YZ400F

Vist the Rubber Chicken Racing Online Shop

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Matt

part numbers. could it be that Yamaha put different part numbers to each model, but that the parts are the same?

if you give me the lift of the cams from the service manual i can at least check if that much is the same.

as someone recently posted, nobody on this web site appears to have the official cam timing of the two models.

all i'm trying to do is build a picture in my own mind.

i had no idea the two models behaved differently-with YZ timing-off the bottom. ummmmm!

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So has anyone tried the YZ box on a WR with YZ timing? I'd be interested to know how it feels at low revs. I cant compare the 2 b

ikes because the gearing is a bit different.I have a hunch that this would make the bike a bit more responsive down low, and still have that midrange punch. Also the cam timing might be fully realized if you had a few more RPM's to play with.

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A WR with YZ timing and a YZ box will have less bottom and basically be a YZ with a flywheel weight.

Picture this as the cam end on (its crude but hey! :) )

SNIP Pic that didn't turn out.. refer to WR manual for A,B,C..

99 YZ400F specs

INTAKE:

A= 31.7-31.8mm

B= 22.95-23.05mm

C= 8.65-8.85

EXHUAST:

A= 31.2-31.3mm

B= 22.95-23.05mm

C= 8.15-8.35mm

As you can see there is quite a variantion in some of the standard specs (wide tolerances)

I can't get any info into the actual timing as such at the moment but the WR is 1 tooth different on the exhuast.

The difference is the part numbers (if no difference in cams) could be because the WRs exhaust cam will be marked 1 tooth different to the YZs.

Anyone able to refer to their WR manual and compare these specs?

I expect them to be the same (dimentional) but the ramp angles etc 'may' be different.

Anyone know a way of getting the angles and duration from a source?

------------------

--

**Ride it like you Stole it!**

Matt Porritt

99 YZ400F

Vist the Rubber Chicken Racing Online Shop

Discounts for ThumperTalk members.

[This message has been edited by Matt Porritt (edited 07-20-2000).]

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Has anybody considered flywheel weight, this is probably more significant than a different ignition curve.

My observations on YZ timing for my 2000WR with DSP pipe and header... It rips of the bottom. From idle to wheelspin in no time flat.

Maybe the 2000 carb w/accel pump (does the 99 have one?) has something to do with it as well.

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Matt

the valve lifts in the WR manual are identical. the tolerance levels will be for wear don't forget & not loose manufacturing.

i'll bet a pound to a pinch o' salt that these are identical cams.

it's always interested me that the WR cam timing gives more bottom end than the YZ. so what would half way be like etc using slotted camwheels? anyway all a bit technical.

it would be argued john, that first you get the cam timing you want, then you get the ignition to match. in that order, the flywheel is a side issue.

technically that means a 'WZ' with YZ ignition is the correct way to go. but first i think someone may like to check that there is a valid difference. it could for instance put a halt to all that stalling people talk of.

these things light up so quickly on my 13 x 50 gearing that i guess you won't notice much except on a climb or rolling over a hump in third etc.

if the ignition curve is controlled in a box & it's that easy i guess someone has got a chance to have a bit of back to back fun.

the area we are on about is where 90% of us use the bike. the racers won't be hanging around to see if the bike lugs or not.

the reason for retarding the ignition right at the top of the WR is to stop people thrashing their bikes in that rev range. if the cam timing is such that the show is over by those, heady revs then it's best to put the customer off & retard it. we are all treated as dangerous idiots don't forget!

the 00 YZ had a new ignition i believe. i wouldn't bring the TPS into the equation. just test bits back to back r-e-a-l slow. even jetting will need to alter slightly.

[This message has been edited by Taffy (edited 07-20-2000).]

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Hello

the cams are exactly the same. I was on a mechanic course in germany only about the WR and they told us about the difference between

the WR and YZ .The cam wheels are pressed thats the reason why changing the exhaust cam is not exactly the same like the YZ timing ! Also the CDI is different,the curve also the rev limit. Diferent carburators ,needles,air box system ,exhaust etc .

the most guys (and i hope also girls ,Hi sonia) on this side no this differencesand working on it to change their stock bikes in real DOUG HENRY and JIMMY BUTTON replicas.!!!!!?!!!!

Stay on having fun.

--------------------------------------------- WR 99 applied triple clamps ,all blue acerbis plastics .black excel /talon wheels,

IMS gas tank,YZ seat ,tecnosel seat cover ,

open air box,spes moto cross exhaust and alot

of other funny thinks like öhlins shock ,pölished skid plate from france

bye bye EDE from Germany

etc

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Well, that's just great. I was told the two boxes were the same and put a WR one on my 426 for lighting purposes. Fortunately, for me I'm oblivious to the difference. However, I might like to do the WR gearbox change as I no longer care to entertain my riding buddies with death defying wheel stands when climbing rocks and technical hills. -Ahhhh what the heck, I'm on a bad boy thumper! :)

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Sorry about my english !

I don t know teh exact english word for it , bur it does mean that there are no screws

on the cams and wheels to hold them together,like on yamahas tt or hondas xr. So you can take them of from the cam with a hydraulic " PRESS" ? and put them together on the exyct YZ timing . I hope you understand my german english

Tschüss EDE

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Originally posted by Taffy:

Matt

the valve lifts in the WR manual are identical. the tolerance levels will be for wear don't forget & not loose manufacturing.

Nope.. the spec i listed are the standard (manufacturing tolerances).. the wear tolerances are different.

i'll bet a pound to a pinch o' salt that these are identical cams.

Yip and as I said the difference in part numbers is that the WRs cams hav different markings for the cam timing.

the reason for retarding the ignition right at the top of the WR is to stop people thrashing their bikes in that rev range. if the cam timing is such that the show is over by those, heady revs then it's best to put the customer off & retard it. we are all treated as dangerous idiots don't forget!

But the YZ has a more advanced igniton up the mid-top range.

I think the WRs boost in bottom and slight lack on top is a compromise between the 2 (bottom and top)

Why not just say &%$#@!it and get a dual curve and have more bottom than the WR on the torque curve and more screaming top than the YZ?

The revlimiter is a 'safety'.. its to cause you overrevving the bike and getting valve bounce etc.

The bikes have been proven to be reliable at high rpm use.. 1/2 the reason I brought one was because I rev the living snot out of bikes/cars etc.. thats just the way I ride! :)

------------------

--

**Ride it like you Stole it!**

Matt Porritt

99 YZ400F

Vist the Rubber Chicken Racing Online Shop

Discounts for ThumperTalk members.

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I've been following this discussion, but please forgive me for asking what might sound like a stupid question, do you need a yz box to get the benefit of changing the wr timing to yz spec? I have heard lots of people also say that they won't change their cam timing to yz spec as they loose that bottom end pull , but isn't it supossed to be that an advantage that a four stroke has over a two stroke is its tractable power delivery, and if you do loose that bottom end pull its still going to be better than a two stroke?

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Matt

i stand corrected on those tolerances. we are agreed that each ignition has it's benefits (wr best at bottom & yz at top). so the vortex covers it all hey!!!!

plug! plug! plug! (you've more teeth with that salesmans smile than james coburn!)

clark used to have a steady throttle stutter which was, in his case, not cured i believe. the ignition was modified to 'ISDE'. also why have two curves when one is never used.

how much!!!

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Originally posted by splint:

I have heard lots of people also say that they won't change their cam timing to yz spec as they loose that bottom end pull , but isn't it supossed to be that an advantage that a four stroke has over a two stroke is its tractable power delivery, and if you do loose that bottom end pull its still going to be better than a two stroke?

Good question..

The WR has MORE bottom than the YZ.. while they both have more than a 2st..

You don't loose that bottom (infact a YZ timed WR has more than a stock YZ)

You reduce the 'excess' bottom inorder to trade it for some mid-top! :)

------------------

--

**Ride it like you Stole it!**

Matt Porritt

99 YZ400F

Vist the Rubber Chicken Racing Online Shop

Discounts for ThumperTalk members.

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