YZ426f vs YZ250 race

[alex_naumov1]

My cousin has a 99 yz 250 and I kill him on my 426, he's a little faster off the line because of the weight but only a couple feet then I take him 2 seconds later

[grayracer513]

Assuming the ability of the bike to hit peak power in 5th, stock gearing and accounting for 6% tire slip, right at about 80 MPH.

[RockerYZWR]

With a 30 lb rider weight difference and close to 30 lb bike weight difference and the heavier rider on the heavier bike; assuming both bikes are in good mechanical condition with equal tire wear; assuming riders are of equal skill; and assuming the OP is drag racing his buddy, which is most likely here: I bet the 250 two stroke wins every time.

[grayracer513]

The problem is that the 250 will top out at about 60-65.  And any healthy 426 should pull much harder from about 45 onward.  Patience and a long enough straight is all you need. 

[RockerYZWR]

I guess we need to establish the physical parameters of this race also. Or not.

[dirtpaw12]

Rode is about a 1/4 mile long

[dirtpaw12]

But have access to a longer rode

[UncleLuke]

About three-fifty 

[dirtpaw12]

About three-fifty

??

[ratom98]

depends on whether or not you can get the 426 started

[dirtpaw12]

The bike starts fairly easy, but if cold, I have to bump start

[grayracer513]

You know that is has a "choke" on the carb, I assume.  You pull the black knob out for cold starts and it adds fuel to enrich the mixture for that situation.  Another thing that helps is to give the throttle from one to three half twists (before cold starting ONLY), as this primes the engine.

 

The cold metal and air inside the cold engine prevents the gasoline from vaporizing, and actually condenses fuel droplets back into liquid, which is why they need more fuel for cold starts. 

[dirtpaw12]

I know, the guy that we're getting it from said it was always a pain to start in the cold even with the choke out, might just need a good carb clean or rejetting, I've been looking at the BK but really couldent find information on it, probably not looking in the right places IDK, can anyone shed light??

[Garret88]

The problem is that the 250 will top out at about 60-65. And any healthy 426 should pull much harder from about 45 onward. Patience and a long enough straight is all you need.

. All depends on gearing. 250 2 smokes can hit alot higher speeds than 65 dude I've owned three of em over the years and none of em were that slow I also owned a 426 n it was deeecent but a royal pain to start even when maintained properly.

[RockerYZWR]

Another thing that helps is to give the throttle from one to three half twists (before cold starting ONLY), as this primes the engine.

That is true for carburetors with accelerator pumps, not true for the PWK. That said, I don't know which carb the '97 YZ250 came with, but I suspect it's at least as rudimentary as a PWK.

[grayracer513]

That is true for carburetors with accelerator pumps, not true for the PWK. That said, I don't know which carb the '97 YZ250 came with, but I suspect it's at least as rudimentary as a PWK.

 

I thought we were talking about starting the 426.  

 

 

. All depends on gearing. 250 2 smokes can hit alot higher speeds than 65 dude I've owned three of em over the years and none of em were that slow I also owned a 426 n it was deeecent but a royal pain to start even when maintained properly.

 

Well, let's see.  With everything stock or with an aftermarket pipe, at 9000 RPM a YZ250 is at 10 HP below it's peak and falling, so we're going to call that topped out in 5th.  With the gearing they come with, that's mathematically 71 MPH (almost).  Deduct 6% for wheel slip, and what have you got? 66.74 MPH.  At that speed, the 426 has another 1500 RPM in it at 8 MPH per thousand. 

[RockerYZWR]

I thought we were talking about starting the 426.

...there we go, I got my head out of my butt now - ready to rejoin the conversation.

[Garret88]

I thought we were talking about starting the 426.

Well, let's see. With everything stock or with an aftermarket pipe, at 9000 RPM a YZ250 is at 10 HP below it's peak and falling, so we're going to call that topped out in 5th. With the gearing they come with, that's mathematically 71 MPH (almost). Deduct 6% for wheel slip, and what have you got? 66.74 MPH. At that speed, the 426 has another 1500 RPM in it at 8 MPH per thousand.

I'm not trying to stir the pot I'm actually curious how 6% wheel slip is calculated wouldn't it depend on the compaction of the road?

[Monkeybutt2000]

I'll just leave this here. I had a new 01'CR125, Buddy had a 93'CR250. Whoever got a good start on the gravel road "won" the race,

[RockerYZWR]

I'm not trying to stir the pot I'm actually curious how 6% wheel slip is calculated wouldn't it depend on the compaction of the road?

By my numbers, it's actually only around 4.56% wheel slip, which puts the two stroke only a knobby-width behind the 426. Factor in the weight differences and boom goes the dynamite.