engine will not rev passed 5000 rpm why

[advinnie]

Stock exhaust with flared tail pipes and a rusty 4 into 1 header with a single quite pack

[Copbait73]

I'm new to this site and my experience is old working my way through school rebuilding Type 1s in the late 60s but here goes: I had a friend with similar symptoms after he rebuilt his motor. We were stumped until I noticed his crankshaft had excess end play. As the engine reved it progressively bound the rods and limited revs. Chech your end play.

[Piledriver]

I have seen weak coils, badly adjusted points, condensers, and ignition modules cause a "rev limiter" like effect, but it's usually load variable.
Will rev freely no load, and fall on its face when you punch it (I assume its lack of dwell time related in most cases)

1st is far less loaded than any other forward gear.