What was done to my yz125?? (Pics included)

[xtactical]

Hey guys, i'm trying to figure out what was done to this yz125 I just bought. It was built by a Zambrana Performance out of Miami and does not appear to be stock.

All I know if it's history was it built for a race kart driver in 1999 and has been running on 110 race fuel, and running an oversized carb pj38. I've included some pics of engine to help identify what was done, any feedback is appreciated!

 

 

[Thtyzguy]

RUNNING 110!!!!! thats waaaaaaaay to much for any yz125. i run 40:1 93 octane anything else would blow up my motor(mine is a race bike being rebuilt rn)

 

[xtactical]

Maybe that's why it blew up? I'm not planning on running 110, i've got about half a gallon from the guy sold it to me i'll prob mix it with pump 93 just to use it up...

[Thtyzguy]

yea get best gas in you area and mix 40:1 if you plan on beating the snot out of it/racing run 93 octane. if your going to just ride it casually(no one does) run 85 octane

 

Edited September 19, 2017 by Thtyzguy

[mlatour]

Hey guys, the OP's application is for a racing kart.

With sustained high rpms, it is typical of these guys to run their premix in the 20:1 - 28:1 range and with

unknown engine work, who knows perhaps 110 was required. (squish band height reduced but compression dome CC's not corrected)

 

Nothing will break or blow up by using too high an octane rating than required but

there is also no gain to be had. If anything it will loose some throttle response.

Edited September 19, 2017 by mlatour

[Motox367]

Whoever did it didn't use the correct yamabond ? looks like crap for a shop very messy 

[xtactical]

4 minutes ago, Motox367 said:

Whoever did it didn't use the correct yamabond ? looks like crap for a shop very messy 

Yep, definitely a sloppy execution. Hopefully will run okay once I receive  cylinder and piston back from repair/replating. Guy I bought it from says it's been clocked at 139mph, the waiting to fire up the karts killing me ?

[turbo dan]

I don't think you could gear it tall enough to hit 139.  Even if it had the power, and theres no chance of that either.

It may require 110 octane if they built the motor for it.  Running pump gas in a high comp race motor will burn it down in less than a tank of fuel.  Start with a compression test.  If you're above the stock spec the engine will require race gas.

[2strokeYardSale]

Looks like the cylinder was ported.

[xtactical]

25 minutes ago, turbo dan said:

Start with a compression test.  If you're above the stock spec the engine will require race gas.

Once I put the engine back together i'll do a compression test. What would be a "normal" range for an older yz125?  

[turbo dan]

Would have to know exactly which year, then you would have some google searching to do.  I would expect 150-170 for a 125cc but you need to know exact numbers to determine stock vs modified.

[Rosehill Ryder]

I would never dare put anything less than 91oct preferably 93oct  in any two-stroke even if it was stock . Detonation kills ! It probably did require the 110 . 

[turbo dan]

Premium pump fuel is usually sufficient for a properly jetted stock two stroke.  They are tuned right up to the edge of pump fuel in stock form.  Doesn't take much to cross that line.

[mlatour]

Not sure about that generation engine but my 2010 YZ125 once got 187psi on a new / freshly broken in top end. (2nd piston, I'm on #4 now)

Now with about 80 or so hours on the original plating (starting to show wear), it still gets 180psi on a new piston & ring.

 

Everything is otherwise all stock except for the 0.20mm reduced squish band & un-corrected dome which increased compression by 5psi.

 

Never experimented much with fuel, always ran a mix of 94* octane 'preventatively' and never had issues.

(* 91 pump mixed with 110 race fuel) also as a safety margin since I tend to jet a tad on the lean side.

Edited September 20, 2017 by mlatour

[Smoking 2's]

2 hours ago, Rosehill Ryder said:

I would never dare put anything less than 91oct preferably 93oct  in any two-stroke even if it was stock . Detonation kills ! It probably did require the 110 . 

I ride trails, only run 87 and always have for years and years at a 50/1 mix, never any issues! Why does 87 do damage. Right one was last year's brushed up, left is now straight out

[mlatour]

Octane requirement not only depend on engine compression but also on the specific application,

a trail ridden bike won't see has much sustained high engine loads as a MX track ridden one.

 

Same principal for premix ratio, lower rpms can run less oil,

sustained use at 10 000rpms requires more. 

Maxima has a research document about this, something like '2-stroke oil migration time' 

Edited September 19, 2017 by mlatour

[MaybeMe]

31 minutes ago, Smoking 2's said:

I ride trails, only run 87 and always have for years and years at a 50/1 mix, never any issues! Why does 87 do damage. Right one was last year's brushed up, left is now straight out

Too low of an octane will cause detonation in higher-RPM applications.

[Smoking 2's]

5 minutes ago, MaybeMe said:

Too low of an octane will cause detonation in higher-RPM applications.

Look at mine please! I'm no professional, what am I looking for! What damage have I caused?

[mlatour]

Smoking 2's

Since you trail ride, as mentioned octane requirement is not as crucial for your application.

Your piston's crown (top) doesn't seem to have suffered from any detonation but,

the excessive combustion blow-by past the rings indicates you might have stretched the refurb interval too long.

(or were too easy during break in on the last refurb)

 

Post some pics of the cylinder head's combustion chamber.

Edited September 19, 2017 by mlatour

[MaybeMe]

1 hour ago, Smoking 2's said:

Look at mine please! I'm no professional, what am I looking for! What damage have I caused?

None, but if you were to modify your engine and increase compression, you would need to run higher octane.