Can't get 109E3 to roll fast enough for takeoff (but E4 no problem)

[Walrus1]

I can start the E3 engine fine, max the throttle and roll across the tarmac, but my speed never gets near high enough to takeoff.

E4 I can takeoff and land just fine. Either model I can start the engine no problem.

I tried to follow instructions on Fleas reference although obviously I missed something.

Is there some kind of brake that needs to be released, or some other switch to be toggled or lever moved that I am unaware of?

I am sure the problem is quite simple and is right in front of me somewhere but for the life of me I haven't been able to solve it.