I'm hoping someone may have some thoughts for me on an engine issue I have....which in fact may not even be an issue with the engine...read on...

I have an Enya 1.20 4-stroke (not the '1.20R') in a Top Flite P47 and I have just gone completely through the engine and got everything working nice and smooth, even replaced 2 ailing bearings up front. The engine is hard mounted in the model and runs extremely well while holding it still on the ground. Peaks nice and has a lot of pull. I'm running a 15x6 APC Prop with Omega 4-stroke fuel and everything seems great. I have fuel running through a Perry Oscillating pump (as the tank is slightly above the carb when the plane is right way up) and an onboard glow for reliable idle. Like I said everything seems great on the ground, however the problem is when I start my take off run the engine doesn't seem to come back to that 'peak' and doesn't have that same authority. I'm not sure if it is the pump arrangement as I would think that running it up while holding it still would also result in issues if this were the case. I should also add that I have plenty of inlet and exit areas for airflow over the engine.

OK, now the part that isn't related to the engine...I think the plane is having physical difficulty coming up to speed that isn't engine related. When I first flew the airplane with the ailing motor it seemed tailheavy. I rebalanced and added some extra nose weight. It still seemed to require more down elevator and as it turns out it may be a slight incidence problem as adding further nose weight didn't change much. Slight down elevator is req'd to maintain straight and level flight. Now, adding to this I'm using Robart scale tires without any foam inserts and apart from not running totally smooth on the axels they seem very soft. What I picture happening is that as the plane starts to roll on our grass strip the tail wants to lift very quickly like the brakes are on due to (a) the wheels not being totall free running on the axels, (b) the soft wheels wanting to compress into the ground, (c) the added nose weight, and (d) the slight down elevator when the servo is at neutral to create trimmed straight and level flight.

So, do you think that this mechanical issue that the plane has with rollout on take off is not letting the engine really pull the plane? Like it's trying to overcome this added drag? Or do I have 2 totally separate issues here?

Sorry to be so long winded, but I wanted to cover as many bases as I could with the current configuration. Thanks for any constructive thoughts!!