I have a 400 running lean in mid range rpm's causing piston melting. I have a pipe and silencer on it has anyone ran into them causing problems. Its a Aaen pipe and DG silencer. It has the recomended main jet of 260 and a clutch kit. If someone could help I'd appreciate it. Thanks ahead.

 

Try installing a jet kit.

 

It has a 260 jet in it 230 was stock. Aaen said they use anything from 240-260. It is more lean in mid range than wide ope though. I tried to richen the mid-range and it would hardly run and the plug was black, so that was too rich. Any other ideas? Thanks

 

have you tried moving the e-clip on the neddle jet?

 

Yep thats when it ran too rich. Do you think I should just go back to the stock pipe? Its driven me nuts everything is new and runs great, but it will get so hot it will die in 15min and it started to burn a hole in the new piston already. This is all before the temp light will come on.

 

My dad burnt his 400 up doing the same mods. He blocked his oiler off and started manually mixing the fuel and never had a problem after that.

 

I already did that too. What was he mixing his gas at. I have been doing 40:1 I have also heard 32:1 can that make a big differance? Did he burn premium only? Thanks!

 

He was using 32:1 and used golden spectro. We raced 250r's for years and that was all we ever ran. Once you start mixing oil with one don't switch to a different brand. That can cause problems also.

 

Thank you, I will try that. I have been using Klotz so I will keep using that. I will switch to 32:1 though.

 

Did you race Honda's or Suzuki's in the 250R class?