No Top End Power (i think)...

My bike feels like it has top end power, i mean it pulls 1st,2nd,3rd and even 4th but in 5th it just falls flat on its face, after reading a couple of topics iv checked:

 

1. Brand new Top end.

2. Silencer needs repacking, but when i pulled it out none of the holes where plugged it was pretty clean actually.

3. Pv works, in all gears i can feel the kick in 5th (not actually the kick but the transition)

4. have 48, 3rd on a n3w and been playing between 175 and 178... i pulled the choke while wot and it felt on its face gurgling, so im pretty sure im close to the jetting for the main.

5. Clutch is fine not slipping, plenty of free play.

6.i can transition 3rd to 4th in a wheelie.

 

 

Only thing missing is check the pipe but it seemed pretty clean just a little bit of soth thats it..... im @ sea level and around 80f

 

I was thinking that maybe im not pushing the bike hard enough to climb into 5th , im shifting 2 to 3 seconds after the pv hits, should i let it rev untill it dies and then shift?

Edited by thieaux

What gearing are you running?

 

Does it pull at all in 5th gear?

 

At least the way you put it, it almost sounds like it's only a problem you experience in 5th gear only (which rules out actual engine issues if the power feels normal in all other gears) In that case you could just be geared high enough that 5th gear feels like it's lacking power because of the slightly slower acceleration.  Keep in mind too, you won't accelerate as hard in 5th as you will in say 2nd or 3rd so the power won't feel quite as snappy in the higher gears.

 

On the other hand, if it's an actual difference in power you've noticed since you've owned the bike, it could be another issue all together

14/49 i just saw a couple of videos of "yz250 top speed" and im definitly not pulling in 5th like those guys....also saw a cr250 wheeling in 5th that rattle my bones....

Edited by thieaux

Floats set correctly? make sure it is not starving for fuel..

Yep floats are set, the bike 1 through 4 its perfect... but 5th falls flat...i dont have a go pro , but ill make a video with mt cel tomorrow and post it.

Maybe perform a plug chop at almost full throttle, so you rule out the jetting. Other than that it sounds pretty normal.

BTW, maybe someone put a WR 5th gear in it?

The yz250 really doesn't have any top end power to begin with. It's really a low-mid set-up and the opposite of a 125. Can you ride another yz250 and compare it to yours?

Also does this only happen in 5th gear or no top end power in all gears?

Take a video of it when it happens. Usually you would have a problem through all gears and not just 5th. Have you ridden any other yz250's to compare it to?

Has anyone ever done a bottom end or crank on this bike? I'm aware you bought it used so you may now know.

A very popular mod is to use WR gears or even just a WR 5th. The WR ratios are very wide- especially 5th as I have one myself. 5th gear goes on forever and it will feel like it fell on its face.

It sounds like otherwise the bike is ok. Id just try to deal with it instead of selling the bike after doing work to it.

Take a video of it when it happens. Usually you would have a problem through all gears and not just 5th. Have you ridden any other yz250's to compare it to?

Has anyone ever done a bottom end or crank on this bike? I'm aware you bought it used so you may now know.

A very popular mod is to use WR gears or even just a WR 5th. The WR ratios are very wide- especially 5th as I have one myself. 5th gear goes on forever and it will feel like it fell on its face.

It sounds like otherwise the bike is ok. Id just try to deal with it instead of selling the bike after doing work to it.

 

 

 

Thats whats bothering me the bike pulls really hard and then flat.... I dont think the bike has the wr 5th in it, this bike wasnt owned by a mx or trails guy, it was more for riding in a farm...the bolts dont even have marks of being worked on...

 

And nope never ridden a yz before, all my references are from big bikes 750 and above... i know its a big difference but it doesnt feel right....

 

My thoughts were a plugged exhaust but its clean, top end is fresh, pipe doesnt look clogged just a bit of soth, the bike revs to the moon in all gears, like i can transition from 3rd to 4th while pulling a wheelie, mind you not balancing but actually pulling so thats got to put some kind of load on the clutch and would have slipped by now.

 

She doesnt slip cause the engine doesnt rev up, she just feels like i have open a gas faucet on the carbs i dont think its my mains cause then she would have done the same thing in wot in 1234.....

 

Coils? again 4th wot symtomps would have appear.....

 

MOST OF ALL : I know its not fine, because of the sound.....a 2 stroke pinned has a very distinctive tune. I know its sounds ridiculous, but i've determined the conditions of the engines of my other bikes by the way the sound, once you've heard a tuned engine rev and clear its throath, anything less and you have a problem.

Edited by thieaux

I would start with trying to ride another yz250. The yz250 really doesn't have any top end compared to a 85 or 125. It's more of a low-mid bike and revs then out of power. If you look at a yz250 dyno you will see the drop around 9,000 rpm.

I wouldn't get bent out of shape until you rode another one. It would be tough to have a gear specific problem. I could see if its a bike with a Trans gear sensor, and the Cdi won't advance timing in that gear. But that's not the case with this bike.

UPDATE :

 

Here is the video... 

 

Today she ran perfect dont know why, didnt touch a thing in the engine..

Otherwise put a gallon of fuel in and recorded the video.

 

Note: I really pushed the bike, that was a concern i had, when i asked "maybe im not climbing high enough on the revs for 5th"

But today she really ripped for the past 2 months ive been chasing that falling to its face problem, today she just ran perfect....I was so scared thinking i need it to split the cases,   SORRY IF I WASTED ANYONES TIME.

 

Now Thinking about it, i did use a different brand of fuel.......

 

 

TIL:

 

1. Different brands of fuel can make you look like an AS************!

2.The harder you ride a stroke the better they get.

3.Never underestimate the smallest details in a two stroke

Edited by thieaux

I was riding at Unadilla once many years ago, and after the first session, I stopped for some Gatorade & a rest. When I went out for the next session, the bike ran like total crap! Then I remember topping off the fuel tank with some gas that I had just purchased that morning. Drained the tank and used some fuel from another container that already had fuel in it from the week before, and problem solved!!!

 

Today's fuel is pure crap! And that's when it's fresh!!! It only goes downhill from there!!!

I was riding at Unadilla once many years ago, and after the first session, I stopped for some Gatorade & a rest. When I went out for the next session, the bike ran like total crap! Then I remember topping off the fuel tank with some gas that I had just purchased that morning. Drained the tank and used some fuel from another container that already had fuel in it from the week before, and problem solved!!!

 

Today's fuel is pure crap! And that's when it's fresh!!! It only goes downhill from there!!!

Never in a million years i would've guest that fuel in a 2 stroke was so delicate

I can feel a huge difference between fresh fuel and week old fuel. Sometimes I'll have some left from a previous ride and use it up. I feel the bike pull harder with fresh gas.

A lot of people put those shorty vent hoses on their gas caps with the little breather on the end.  Those tend to plug up and any vacuum in the tank generated by a long full throttle run could starve the engine for fuel as well.

A lot of people put those shorty vent hoses on their gas caps with the little breather on the end.  Those tend to plug up and any vacuum in the tank generated by a long full throttle run could starve the engine for fuel as well.

They say that a 2 stroke is simpler yet the balance of air and fuel is so complicated .

Edited by thieaux

It is simpler for 2-strokes.  More frequent intake pulses from a 2-stroke engine eliminate the need for accelerator pumps and complicated pilot circuits making it much easier to tune the off idle snap where 4-strokes tend to hesitate.

 

How is your air filter, anyways?

Edited by 1987CR250R

It is simpler for 2-strokes.  More frequent intake pulses from a 2-stroke engine eliminate the need for accelerator pumps and complicated pilot circuits making it much easier to tune the off idle snap where 4-strokes tend to hesitate.

 

How is your air filter, anyways?

brand new uni, oiled and greased...

 

Im beginning to put things together... The fact that temp around here swings from 100 to 70 from mid day to afternoon plus motul 800 (high flash point) and different brand of fuels that have an ill effect on the bike, is the reason why the bike is pretty unstable.

It seems that this bike needs to be ran pretty hard to clean its throat with a specific brand of fuel .

Edited by thieaux

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