I would like to note that the b5 was very easy to run too lean on the top for me, and it really seemed to be working well. If you're losing compression or performance after a gallon, it could very well be a hidden tuning problem that doesn't show up as a major issue.

The only indication for me was that it tended to be too fat in the low/mid range at times. I continued to get better performance by leaning out the main needle, but I was probably being tricked by an increase in acceleration, not top speed. When my motor was too lean on the main, and idling at the correct mixture on the LSN, it was boggy down low if let it load up at all, but other than that it worked very well and temps were stable. Additionally, a long high speed run on the street took my motor to 280F after I had just temped it at 220, and THAT was the real wake-up call that I had something going on for sure.

I have noticeably less compression now than I did just weeks ago when I started really running this motor lean. When you run lean, even if you don't overheat, that period where there is little fuel there is also little oil, and that does lots of wear. I cannot realistically expect to get the full 6+ gallons out of this motor before a refresh is needed now, and it's my own doing. It still is just nuts on the bottom end though, so it's not like it's done, or even close, it still has *plenty* of good 'kick' in the compression for sure.

Needle imbalance is a bitch. Since temperature takes time to develop, you really can have it starving in one place and rich/cooling in another and not see an issue because the overall temperature has gravitated to a safe place. Unfortunately, when you were lean and starving, excessive wear is being done, and it adds up.

Keep in mind that I raced my motor with the main needle set a full 8-9 hours leaner that my recent re-tune for multiple club racing events. EIGHT TO NINE HOURS! After my races, when I'd pull into the pits, the motor would be in the 200 - 220 range always. Same tune on the street produced 280F in one pull. If I hadn't kept coming in here and reporting very slight strangeness, strangeness that was NOT keeping me from doing very well, I would have had no motivation to keep addressing the tune on the motor and my motor would surely have been done in very short order and it would have looked as if I had tuned it right, it ran well, and crapped out in 2 gallons.

It is almost a curse that the b5 runs so well with a bad tune because running well doesn't mean lasting long.

Wayne