Running lean will not pull past 7800 rpm


Running Hayabusa in a NASA Super Touring race car. Engine ran perfect last year after rebuild. The engine is running very lean and will not pull past 7800 rpm. We made no changes to engine for this season, except to use Lithium battery to save weight. Did a few easy laps in first 20 min session, ran OK. Did another full second 20 min session and ran OK. In third session ran harder and ran good for 15 min and then started to run lean and will not rev past 7800 rpm. I did change battery back, so far checked fuel system, we have adjustable pressure reg with gage and can see we have good fuel pressure to rail so would think could rule out fuel supply. We did experiment with raising fuel pressure the next week. Started cold and did a few laps and was able to pull red line. Took into pits and after heat sinking for about 15 minuets went out to verify if fixed and again will not pull past 7500 rpm so we called it a day. This week I am going to do a leak down test to make sure nothing damaged from lean running. But at a loss as where to start checking systems to determine the problem. Was hoping someone on this site may have had similar issue. Could use some guidance where to start diagnostics. Should add this is a gen 1 2004 bike. Was professionally tuned on dyno previously, we are not running stock map. Not using a power commander.
If the stator is intermittently shorting or rectifier failing when hot, it might still run but affect the ECU or limit the injectors. Try the standard electrical tests when the system is hot.

I am ignorant on fuel so I will throw out a dumb question: Does the fuel gauge catch all vapor situations?


I would think a check of the CKP( crank position sensor) should be on the short list. I do have the max voltage tool to do this. And will need to test hot, but any other possible causes is most appreciated. Yes the fuel gage is positioned to catch vapor and ran fine with same set up all last year and using same fuel. We also have a lambda sensor and reads 15 plus when starts to run lean.

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