Jump to content

06 yz250 pump or race gas?


Recommended Posts

Hey how many of you on here run race gas in your yz250?

bought my bike 2 months ago, checked piston when i got it..looked perfect.

have been running pump gas mixed @ 32:1 amsoil dominator... Plug was always tan color.

Last nite randomly crapped out (sure it has been for last few rides..but ran great)

piston is melted down near exhaust port side, actualy looks like a chunk broke off or just melted off..and a small part of the ring is missing.

Just trying to figure out if this is due to too low of octane. i always ran premium but dont think it was enough.. could hear it randomly spark knock sometimes when riding.

Link to comment
Share on other sites

Hey how many of you on here run race gas in your yz250?

bought my bike 2 months ago, checked piston when i got it..looked perfect.

have been running pump gas mixed @ 32:1 amsoil dominator... Plug was always tan color.

Last nite randomly crapped out (sure it has been for last few rides..but ran great)

piston is melted down near exhaust port side, actualy looks like a chunk broke off or just melted off..and a small part of the ring is missing.

Just trying to figure out if this is due to too low of octane. i always ran premium but dont think it was enough.. could hear it randomly spark knock sometimes when riding.

Same thing happen to me.

Its called detonation and its from pump fuel.

I ride sand tracks and pump fuel makes it run hot.

My 250 is a 265 now and will drink race gas. . .

Link to comment
Share on other sites

unless your compression ratio is modded (higher than stock) 91 octane pump gas is more than enough for the bike.

IF your detonating after that, then it's because your leaning the bike out too much, and/or improper ignition timing.

Only when you change the compression ratio do you require higher than 91 octane fuel.

91 AKI

is

95 RON (what the manual calls for)

Keep in mind that if you have bad timing or lean jetting, race fuel will help with detonation as the octane is higher and there sometimes is lead in the fuel which helps huge on detonation. However, this is not the proper solution for your problem on your bike.

Link to comment
Share on other sites

My 295 is built for 110. I run race gas just because it dosnt have corn in it and I olney put soo many hours on a bike id rater have them pulling my arms off. Pump gas seems to verry in jetting from tank to tank. Ethinol amounts can verry soo much in gas its hard to jet right before a race were you dont get practice. When I run vp 110 its mosty the same jetting just how old is the 110. Another reason I run 110 is my other bikes are built for 110 so i dont have to have soo many fuel cans. In winter I find 110 that much ezer to jet. When its below 0 its no fun changing brass unless you have to.

Link to comment
Share on other sites

I feel like the engine needs to be totally stock to get by with 100% pump gas. A pipe and silencer made mine ping worse. Now, that was at 4500 ft, so it would be worse at low altitudes.

I think we found easier (and cheaper) ways to deal with the issue, but I do think the bike has one. The more rich needle added in 07 covers it up as will a larger main.

Link to comment
Share on other sites

im running stock jetting with fmf pipe/silencer.. plug was always tan color, but i def heard it spark knocking a few times...

no biggie.. just goign to redo it

def going to try out that needle w/ the diff taper.. hopefully it helps, and maybe bump up the main.

Link to comment
Share on other sites

Which FMF pipe? I'll bet it's the SST.

The SST is very sensitive to jetting and timing because it raises the EGT and thus the piston crown temp goes up. I've seen several other guys on this board claim the same issue with their YZ250 and an SST pipe.

I use a 2005 OEM pipe on my YZ. I like the power curve better than the SST, and the jetting is pretty close to set and forget in warm weather.

Last year I switched to .045" squish and I run race gas with slightly advanced timing. That combo really works well and kills the SST lap times at every track.

Race gas is plain better you should run it if you can. Just don't switch back and forth all the time, you'll have to change brass each time.

Link to comment
Share on other sites

I mix 1 gal of Sunoco 110 with 4 gal of 93. I use an FMF SSt pipe with the stock silencer, and stock timing on my 07' 250. The bike WILL detonate, no ifs ands or buts about it, under a load with just 93 octane fuel. This is with the N3Ew needle top clip, 48 pilot, 178 main, AS 2 out and .5 mm cut from the slide. I've tried adding more 110 octane fuel and it makes no difference in the way the bike runs at all. It's just more expensive, $7.00 for a gallon of the 110 vs $3.00 for 93.

Link to comment
Share on other sites

If you can get some....I highly suggest race fuel on this bike.

I also agree on a stock motor 1 gallon to 4 is perfect...

When running pure race gas...jetting can go leaner across the board (needle...pilot...main etc.) as the stock yz is pretty rich on the needle IMHO...it just detonates too easily to really jet it spot on.

Link to comment
Share on other sites

Have run my 07 Yz250 on 93 octane for four seasons of racing and trail riding. Platimun II pipe and Lucas two stroke have put two pistons in it in four years no detonation pits or any problems at all. Melting parts your too lean

Link to comment
Share on other sites

If you can get some....I highly suggest race fuel on this bike.

I also agree on a stock motor 1 gallon to 4 is perfect...

When running pure race gas...jetting can go leaner across the board (needle...pilot...main etc.) as the stock yz is pretty rich on the needle IMHO...it just detonates too easily to really jet it spot on.

Yeah seriously. Mine pings a little even with avgas mixed in. Right now it does pretty well with 1 gallon av to 3 pump. But jetting isn't close. I was 2 clips from the top on the needle and running rich so I went to the top. Result, instant detonation. I need to get the squish set. I don't know how anyone runs these bikes on pump. I have a pretty keen ear for it so possibly they just don't notice it?

Link to comment
Share on other sites

Have run my 07 Yz250 on 93 octane for four seasons of racing and trail riding. Platimun II pipe and Lucas two stroke have put two pistons in it in four years no detonation pits or any problems at all. Melting parts your too lean

where are you getting 93 around here?

Link to comment
Share on other sites

It will never hurt running at least part race gas. All it will do is add a good margin of safety. It keeps cylinder temps much lower and there really is no negative with using it.

I blend Sunaco 110 octane with 93 pump 4 to 1 so I end up with roughly 104 octane.

All it takes is to get a bad batch of pump gas.

Link to comment
Share on other sites

the pipe im running is the fatty with fmf silencer.

another guy around here has same issue with same bike and same track.. said he had to run race gas.

not a big deal really, just sucks that i have to get it replated now.. it wore a spot right above the exhst port.

Link to comment
Share on other sites

Guys that know fuel better than I do, a question please. As s142510 (odd name???) said the fuel has corn in it. Is there a possibility of getting in trouble mixing 4x1 race gas with the ethanol pump gas, oil, and race gas?

I am starting to think seriously about switching to the AV gas since I have a municipal airport close by and wonder if that might be a good solution?.

Link to comment
Share on other sites

In theory Ethenol degrades seals and rubber lines and in general is corrosive to certain metals.

If you look around, some stations do still have ethonol free premium unleaded which certainly would be preferable.

But as to your original question mixing race gas with a 10% blend of ethonol pump gas will not effect anything withen the gas itself.

AV fuel is 100 octane if memory serves, so really you dont even have to mix any pump gas with it I would suspect. I have never used AV fuel before, just actual leaded race gas like VP and Sunaco.

Hopefully more will chime in with AV fuel experiance

Link to comment
Share on other sites

In theory Ethenol degrades seals and rubber lines and in general is corrosive to certain metals.

If you look around, some stations do still have ethonol free premium unleaded which certainly would be preferable.

But as to your original question mixing race gas with a 10% blend of ethonol pump gas will not effect anything withen the gas itself.

AV fuel is 100 octane if memory serves, so really you dont even have to mix any pump gas with it I would suspect. I have never used AV fuel before, just actual leaded race gas like VP and Sunaco.

Hopefully more will chime in with AV fuel experiance

Last year I coudl shop around and find gas without ethanol. However,a law was passed a few months back that mandated 10% be sold. I THINK the airport might be exempt, but I'll have to see.

Link to comment
Share on other sites

avgas has been used forever...and it works well.

Often times people need to lean their jetting to get best power results.

It's not an ideal race fuel...but it's much better than pump for tuneability...and frankly on par with almost any race fuel for power when tuned in well.

I HIGHLY suggest putting in just a TAD pump to the avgas. I mean barely any...say quarter gallon to every 5. For some reason it helps the premix to actually mix in better...couldn't tell you why.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

×
×
  • Create New...