High RPM missing on FB
 

I was running my Spec-7 at the Lowe's motor speedway road course this weekend, and I had problem with the engine missing really badly at high rpm in 4th.

At first I was running about 1/2 tank of gas, and I had momentary (1-2 second) power loss at about 5800 RPM when coming out of the high banking in turn 2, then no problem anywhere else on the track. I would see about 7000-7500 RPM in 4th sustained on the oval section.

Next, I ran with 3/4 tank and had no problems.

In my race, I started with a little more than 3/4 tank - no problems for 4 laps, then horrible problems starting at same part of track but never recovering. The engine would not rev past 6000 in fourth - period. No problems reving to 7500 in third in the infield section.

Seems like a fuel delivery problem, right? Any idea what would come on so suddenly? I'm running a facet pump with no regulator. Had zero problems at Nelson Ledges with this setup. I did notice that the tank was much more pressurized after a run with the higher fuel level.

Any help would be greatly appreciated.

Maybe the banking let some crud in the tank collect near the fuel pickup? You said it got worse and then worse and never recovered? Sounds like a progressive failure type of thing. Your sock at the pickup may have junk blocking it now.

Thanks for the suggestion, I was hoping not to have to drop the tank as a first step.

I'm not really sure that the two problems are related. The first problem I had seemed to be lack of fuel due to cornering which basically went away with higher fuel level. The top speed problem came on suddenly after 4 laps and then stayed - still could very well be the pickup.

I was wondering if it is normal for the tank to get pressurized, and if this has any benefit or drawback.