Posts
459
Joined
9/23/2014
Location
Katy, TX
US
Edited Date/Time
5/17/2015 11:52am
Ok guys, I'm about to pull the head off my YZ250 tonight to inspect the cylinder and remove the Namura piston that the PO installed before it has a chance to grenade on me.
1. Can I use the Namura piston to measure the squish band tonight or should I wait on the new Wiseco that I'll be ordering to replace the Namura to do the squish measuring?
2. Who are some reputable shops that can set the squish band for C12? I'm running stock porting to my knowledge and at this time it's fine for my purposes but I wouldn't mind getting a little power all throughout. Suggestions and reasoning as to why I should go with them please.
Obligatory pictures of bike below....
1. Can I use the Namura piston to measure the squish band tonight or should I wait on the new Wiseco that I'll be ordering to replace the Namura to do the squish measuring?
2. Who are some reputable shops that can set the squish band for C12? I'm running stock porting to my knowledge and at this time it's fine for my purposes but I wouldn't mind getting a little power all throughout. Suggestions and reasoning as to why I should go with them please.
Obligatory pictures of bike below....
www.tdc2strokeperformance
Jake #719 2006 YZ250 450 C Fl. Winter Am's at Gatorback.
All cad designed with rider factors considered for proper setup.
Remember, octane does not add power, but rather slows down the burn to help with detonation. This engine will run better and last longer if set up for pump fuel.
Paw Paw
The Shop
100LL (Avgas) - $3.99 / gal
Sunoco 260 GT Plus (104 Octane unleaded) - $10 / gal (Highly oxygenated producing more power)
Sunoco Standard (110 Octane) - $10 / gal
Sunoco Supreme (112 Octane) - $10.50 / gal
Sunoco Maximal (116 Octane) - $12 / gal
VP C12 - ~$13 / gal (5 gal pail)
CP U4.4 - ~16 / gal (5 gal pail) for fuel injected 4 strokes so it's out.
I was running 100LL without any issues until I discovered the dealership next to my house had C12. I like the smell of race gas and I'm able to afford to pony up a little bit so I bought 10 gallons. Today I found out I have Bumbera's Performance next to me that will sell me the Sunoco fuels at the prices listed above. Instead of C12 I'll swap over to any of the others as it'll end up being cheaper. I now have the two 5 gallon pails to store it in and mix my oil which will be handy.
If 100LL is sufficient I'll run it. The added lead pleases me as well as the cost. Much cheaper than C12 or Sunoco Standard. From what I'm reading the GT Plus may also be a contender if I remove it from my carb after every ride (not a huge deal) but will it, with proper porting and head rework, make more power than 93 pump?
I blew up a RM144 running it, its a silent detonator and burnt through the top of the cylinder until the o-ring was compromised.
The Sunoco supreme is a really good choice, its 112 octane and runs very similar to VP C12; compared to the other 110 leaded fuels, it has a much more superior distillation curve and the extra 50 cents a gallon is totally worth it.
Bottom line, the best place for ethanol is in your cocktail, not your dirtbike fuel tank!
Lots of people run Avgas, but the compromise is that it is designed to be operated thousands of feet in the air, so the physical properties are different than surface fuels.
I drain the tank and carb back in to a metal container if the bike isn't going to be ridden the next day. By doing so, the fuel will last for months and there's no chance the carb will get gummed up.
but at the end of the day, if its leaded and ethanol free, just go ahead and run it- nothing bad will happen.
I'll probably end up running the Supreme after I use all this C12. I bought that built motor CRF to flip and need the fuel for it anyway.
Johnboy
Any knowledgeable tuner knows to make the combustion chamber bowl deeper to compensate for the cc:s lost when tightening up the squish clearance.
And no tuner worth his salt would rework a cylinder head without access to accurate squish measurements from the engine to be tuned. Variations in manufacturing means there are no two identical engines, even in 2015.
/Lasse
http://www.klemmvintage.com/deto.htm
I was telling the OP that he would be wasting his time and money to try and get any more power out of a motor that is going to grenade regardless of whatever you do to it. My solution to the problem was to get a Vertex piston with the stock squish setting which I believe Yamaha calls for right around 1.2mm?!
With the forged vertex piston, and I recommend vertex because of the inconsistency at wiseco, run 100 octane fuel and this will give you the most longevity. 25 hours MAX on a top end!! I've seen these yamahas do some weird stuff. Skirts breaking off the back of the piston, holes in the middle of the piston!! I've seen brand new 2014 yamahas come with missing stator plate bolts (only one bolt installed from factory) and on that same bike the clutch basket was cracked on 3 of the fingers and the bike only had 3 hours on it!! They are just not the fit and finish of any other manufacturer's 250 two strokes.. It amazes me because the same basic motor has been in the works for 10+ years! And it still sucks!!!!!!
So to the original poster, save your money! Save your time and frustration! Don't get crazy inside your motor!
Pit Row
Would you say that a vertex piston is more consistent than a wiseco or OEM?
That pic looks like from Rio..
The engine will become more responsive, easier to jet properly, less prone to detonate and have a better gas mileage. As a bonus, you can pick and choose a compression ratio to suit the kind of fuel you'll be using.
If Yamaha has been delivering bikes with quality issues, well that's bad on their part, but don't write off the YZ250 engine as a bad design because of it. In my view it's an amazing power source.
By the way, I have never used a piston in a 250 for more than 20 hours. Read the manual, follow the service intervals, and in many cases avoid stuff like broken skirts and so on.
Stretching the service life of a two stroke piston is just not very smart, performance will suffer and sooner or later so will your bank account.
/Lasse
However, I am currently having my transmission gone through for the second time. Third gear went out AGAIN. So, yeah, I'm a little disappointed with Yamaha. Next new bike I buy will be a KTM 250 smoker.
Send the head to RB Designs. Last cyl head I had done, total turn around time was one week using Priority Mail.
http://rb-designs.com/rb_designs_llc_025.htm
Measure the squish with the piston and base gasket you plan on using and try stick with them for consistency.
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