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**Fixer** · 13-12-2007, 12:38 AM

This is the best info I’ve fund on the net about the 231, hope it helps.

How to tune the 231 Pgasser

Fine tuning, one has to learn what changes one makes, and what effect it had.. For this, its important to make one change at a time to see the results..
The guide lines that I give, gets you pretty close.... While I give these guide-lines, it is hoped that you conform to the same equipment to what is recommended as possible, in order to produce the same results. Any deviation lessons the chance...
For the most part, I've wondered how to put the tuning method into words, and it is very difficult to do for as sounds, and unexplained vibrations, and such.. I can tell you if you have reach the rotor rpm, with the reasonable mount of throttle at hover, and you made all the mechanical setups as required, and then you are basically there...
To understand the beast further requires going to fly-ins, and getting a personal education, which I have done many times....
Nevertheless, we will try to help

>1. When should I start to adjust the needles.

I really would rather you not adjust the needles unless you see vibration coming, and staying during break-in. If it comes and goes, then don't chase it with the needles
Don't ever adjust the needles until the engine has flown around a while...
When was the last time you tuned your weed blower? Never? Well, the same thing here , the diaphragm will make up the difference to a certain extent, unless you see a big change in pressure

>2. Which needle and how much should I start adjusting.

I consider the low-end the hover needle, it handles 60 % of the fuel flow feeding 3 orfices...You adjust it with very small movements, it is very sensitive, about 1 /32 movements...Never tune for idle, just hover. Put the trim where ever it needs to be to make the engine idle.

How do I know I'm correct with the low needle?
Since I've been doing this for a long time, I go by how much the throttle is open for hover. If I'm between 40, and 50%, I know I'm pretty close for high rpm operation. I also look for vibration, if I see a buzz anywhere, I richen the low needle, IF I'm not over speeding, if I am, I first get the rpms or load corrected first. If its still there, then I richen the needle 1/32, sometimes, 1/64th See where we're going?

What if I'm hovering at say 28%?
On a 231, there would be two things, 1, you're to lean on the low needle, or you have differential in your atvs on the throttle which would screw up the timing effect between the engine, and collective movement. Plus give you the wrong throttle position relative to your butterfly inlet. You would have a vibe you can 't get rid of no matter where you put the throttle curve. I say this to help you understand how important setup really is on a gasser...Why? because the torque band is so wide.

How can I understand that last statement?
To see this, consider yourself in a hover at a good rpm on the gasser. Without the throttle moving, just raise the hover pitch, you can raise the hover pitch pretty good before you see a change in rpm...On a glow, it would drop off much sooner. The longer it takes to make a change, the wider the torque band for that amount of throttle. Since the gasser is so strong, the throttle has to be in the right place, at the right time, in order to keep everything in balance for as timing between the throttle, and collective movement to maintain a constant rpm without the vibes..

Adjusting the high needle:
Like I said before those nifty positions 1 3/8 's on both needles took a long time to find, so the hard work is mostly done. The high needle comes into effect about 50 %, it handles the other 40 % of the fuel flow, but I consider it for wide open only...Yes, it can effect the hover, but its best not to look at it that way..Only for wide open throttle is the way I do it for novice. Once you get more experience, you'll learn the little stuff like just tuning from idle, and effecting the hover with the high needle...For now, just do what I tell ya
You can move this needle at 1/8 increment, so that means it not as sensitive....

How do you know you have the high needle to lean?
It will get real smooth, and not climb out as fast, and if you continue, it was just quit, all of a sudden. If you don't know, then always adjust rich first to see if the climb improved. Most 231's near sea level with air filter, and 643 series run 1 3/8's on the low, and 1 1/4 on the high.. With these new engines, I've never run any leaner than 1 1/4 on the high, and no leaner than 1 3/8 on the low..
I haven't touch my needles on the 231 since I first adjusted them.

3. What should I be listening for from the engine?
When first starting the engine, you want to hear a steady idle, but, your not going to get it till it warms up, so just add trim till it does., let the engine warm up a little before you take off.
When you go to 1/4 throttle, its should kind of miss a little from being rich but reach operating rpm fairly easy, and stabilize (this is without a gov)
It will have a Evenrude sound to 1/4 throttle From 1/4 throttle to half, it will have a low tone, and pretty well be trying to clear out. Once you get to hover, if you hear a slight hesitancy miss, but see it in the tail wagging slow, back, and forth. That will be a sign that your fat in the hover. Don’t be so quick to run and lean it, this is a good thing on a gasser, you just minimize it ..If it goes away after your warmed up, then your on the money...I let mine pulse the tail, about once every 10 seconds to let me know I'm rich, when I'm flying real hard
Don't worry about engine temps so much. So long as you run a good rpm, and the suggested needle settings, you'll do fine...I don't even check temps now. If its to lean in a hover, you'll see it vibrating, and sounding real raspy, and get real smelly..
Now, to really learn the needles, and the effect they have, go buy you a cheap leaf blower, and practice on it, using the same oil, and amount you use in the heli...
BTW, I run all my weed eater engines on this stuff...
Hope this helps,
To be continued

Regards,
Bill Meador
Century Helicopters

**Fixer** · 13-12-2007, 01:22 AM

stephenk99
I'm no expert but this is what I would do for starters
Start by using a full synthetic oil mixed at 33.1, the more oil content means the needle settings aren’t as critical, I would start by turning both needles out to 1 1/2 and don’t go below 1 3/8 or you will fry the engine.
Remove the air filter and with the throttle off set the trim so the butterfly is just open a fraction and at full throttle the butterfly should be half open, any more than halfway is closing the throttle off again.
If it still wont start or run properly try a new isolator block between the carb and engine, these are renowned for splitting and drawing air, I had the same problems with my gassers until I fitted the new alloy isolator blocks with Teflon gaskets and I haven’t looked back since.

http://www.z-rc.com/?action=displayP...e&viewItemID=6

Don’t use a throttle curve like you would on a nitro it just wont work. to give you some idea mine is set at 15 28 36 55 100 with the pitch set at -5 +10

Good Luck
Fixer

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