560sl fuel issue
 

Hi guys and gals. I have a 1989 560sl with 19,000 miles. Nothing has been done to it as far as replacing anything (nothing needs to be) But i am noticing it has a little attitude problem every once in a while (fits me perfect im told by friends ha) Here is the issue, I fill it up FULL of the premium gas and it runs great...everything works. BUT when it reaches half to just below half it gets an attitude. Example: its a rough start up, the gas gauge is not acurate for the first 10 mins of driving then comes to an acurate display. What is the problem? Thanks for the help...