Spectra and TRM 231 - Tuning advice needed

[Racer944]

Hi Guys;

I'm new to gasser tuning so please bear with me. I have also searched and read all I could find but I'm still not 100% sure of how to go, and rather than damage an engine I thought I would post here....

Setup: Spectra G with Toxic 231 / Hatori muffer / MA open air filter /Amsoil and Coleman at 40-1 / NGK Iridium plug / Loop on vent line

I set both needles to 1- 3/8 to start and did my first flights on my new to me Spectra Gasser (Heli and TRM 231 broken in by previous owner). Using normal throttle curve at a setting of about 47% she lifts off into a hover and the headspeed settles at about 1800. I would like to get setup for a normal headpeed of 1550 and the governer will eventually handle idle 1 and idle 2 at 1650 and 1750. The problem is if I lower the throttle curve in an attempt to get the headspeed down, she sounds and appears to loose power and the headspeed then drops way down. I also think she is burning fuel pretty quick as my 16oz tank appears to only last about 10 minutes or so.

My questions are where do I need to start tuning to get the headspeed lower and still have the engine develop enough power to hover smoothly and not kick the tail? Is it the low needle that needs tweaking at this point (leaning) or does the main needle need adjusting (richening)?

There do not appear to be any large vibrations and when the heli is in a hover at 1800rpm she sounds very good to me and very short climb-outs seem to go well. Basically just before she lifts off the headspeed comes way up all of a sudden and the engine sounds like it comes alive almost like the effect you get on a tuned pipe glow engine when it "comes on the pipe".

Any advice is very much appreciated before I start to experiment with the needles...

Cheers;
Eric

P.S. From what I can tell, the sparkplug looks pretty clean and is not dark colored...

[bigrcr]

First you need to get the needles set correctly as it sounds as if the engine is very rich by your description.

If you are try to run at low head speed the engine may be on the low needle. A Spectra-G using the 7.15 ratio normally will hover on the high needle with the low needle just adding an input into the transition. Of course, if you are trying to hover at a very low RPM this wil not be the case.

First take the model out and fly it. Full throttle climbs will usually show the top needle mixture best. Land and richen the top needle more each time until the performance drops off, then go back to the last good needle setting. If the performance is off to begin with (obviously rich) take the needle in a bit until you once again can richen it. Hopefully this makes some sense. What you are trying to do is "see" where the top needle is set. Once you perform the described technique you should know where the top needle is.

Go back now and set the bottom needle (from the 1 3/8 start point) so that the engine idles slightly rough (very slightly) and you should be close.

If at any time the engine starts to overspeed, land and richen the high needle until this stops. You may tweek open the low needle as well to accomplish this if the overspeed seems to occur at hover.

Once the needles are done, you can lower the throttle curves fro the lower head speed. Be forewarned that at much below 1600, the Spectra-G will dance around like a drunk pirate as the head speed is too low for the head damping. You can put in softer damping but the model may boom strike if you then want to hammer it doing 3-D. You cannot have both schemes (Low head speed putting around and 3-D) using the same set-up. The Spectra-G ratio was meant to support 1650-1850 head speeds.

Hope this helps!

BIGRCR-John Garst