airtourer

Hi Everyone,

Just after some advice please.

I have owned and operated a 3w 70i for about 12months. I have been running it a bit on the rich side with no problems at all. Recently I adjusted the top end needle a fraction leaner which gave a boost in performance. I made no adjustment to the low range needle.

Now the engine misses a little when the throttle is opened (only in the air).
The plug colour indicates it is quite rich ie a darkish brown but quite dry. I have measured the temperature of the cylinder head and it is operating around 80 degrees C (sorry dont know what that converts exactly to in degrees F). The ignition battery is a six volt nicad and is in good condition. It starts very easily and never quits until asked to. I am running a 24x10 prop. The muffler is a Johnson. Fuel is mixed 50:1

What adjustment do I need to make on the low needle? Any other suggestions??

Regards,

Paul.

pe reivers

The idle needle also supplies fuel at full throttle. You probably have to set the idle needle slightly richer to allow a better transition. Check if in flight transition gets worse, or becomes better.Then maybe lean the H needle a bit more. It is not clear if the engine sputters (idle too rich) or gasps (idle too lean) when you apply throttle in flight.
How and when did you measure CHT? 80°C seems very low for in flight air cooled operating temperature.

airtourer

Hi Pe reivers,

Thanks for the info.

At the moment the transition is good. It almost sounds like the plug is fowling then clearing, neither a splutter nor a gasp. Like a sharp miss.

I have an non-contact thermometer, point the laser light where you want to measure and it gives a measure. Tested on boiling water gives a temperature of 102 degree C so I believe its reasonably accurate. The ambient temperature (middle winter) is around 15-20 degrees C. The temperature was measured after a flight short taxi to the pits followed by a high power run.

I will try your recommendations and get back to you.

Cheers

airtourer

Hi Pe reivers,

Tried your recommendations, problem sorted.

Thanks for your help.

pe reivers

I am glad you solved the problem. Yet I would like to comment on temp measurement.
After a landing with taxi run, head temperatures are way down again, and have no meaning for engine adjustment or cooling problems. Temperatures should be measured in flight. This can be done with a venom temp gauge, which has a peak temp hold function, so you can read it after you get the plane landed safely. You then know, if you can lean out the engine further, If cooling flow baffles are called for etc.

airtourer

Thanks will try to purchase one.
Cheers.