View Single Post
Old Oct 27, 2012, 11:44 AM
Brutus1967 is offline
Find More Posts by Brutus1967
I convince things to work
The Netherlands
Joined Nov 2009
4,604 Posts
Originally Posted by SrTelemaster View Post
Could the engine be making more power when below operating temperture be due to a rich mixture being more suited to the cooler operating temperture?.
I think not: it does it the same, whether I set it a few clicks fatter or leaner. The mixture does not really seem to change, and the motor does not really seem to need a different mixture when hot

Originally Posted by SrTelemaster View Post
Power loss can also be attributed to a higher intake charge temperture (less dense intake charge) as the engine compartment temperture heats up the induction components. (carburetor, manifold, port runner, etc).

While drag racing @ high temeprtures in Ohio, I once experinecd a .45 second ET reduction just by icing down the intake manifold & getting ECT @ staging down to 156*F from 179*F on the previous pass..

The point is, that a hot induction system can significantly reduce power output.
The engine is fitted with the crankshaft pointing vertical down. Air is flowing vertical down through the cooling duct.
The carburettor is sticking out vertical upwards, with a spoolpiece of appr 1" between head and carb. So the carb is drawing air from even before the entry into the cooling duct
The carb is literally icing up on the outside at anything below 10 degrees ambient (degrees centigrade that is).
Has done that always with both the original and the 7H carb, and this has never infuenced the needle settings.
I have flown it with the original FS carb for over 5 years, and approx 1 year with the 7H carb, in temperatures ranging from 30+ till subzero, and the biggest change I needed to make due weather conditions was 2 clicks....
The 7H carb is equipped with a "power bell", basically an aluminium cap that catches the blowback fuel. This fuel evaporates in this bell, effectively cooling down the charge air before it enters the carb, while at the same time re-introducing fuel that would otherwise have been lost.
The effect of this bell was clearly noticeable when I installed it.
I have no idea how fast the air heats up while underway from carb to cylinder, but it should be pretty cold when it leaves the carburettor. So personally, I don't think heating of the charge air is an issue here.

Brgds, Bert
Brutus1967 is offline Find More Posts by Brutus1967
Last edited by Brutus1967; Oct 27, 2012 at 02:36 PM.
Reply With Quote