I'm pretty new to gas planes - former glider guy - and bought an Evolution .61 primarily because I don't want to mess with engines - I just want to go fly. Well, I'm stuck messing with the engine anyway. Right now it has the following symptom: if I idle for a few seconds and hit the gas to 1/2 throttle, it revs high, then drops a few hundred RPM. Kind of brpbrpbrpbrpbrp-BRRRRRRRR-BRRRRRRRRRRRRRRRRR if you get my drift. If I let it idle more than about 10 seconds, I never get to BRRRR - it starts to rev, then dies.

My limited experience tells me it's too rich on the low end. But it's all the way lean - at least as far as the needle valve limiters will allow. Should I just bag these limiters? Or is my diagnosis off, and should I look elsewhere? I found a thread that said these engines often have thread cuttings stuck in the needle valve area, which can cause this symptom - and sure enough I found and removed a bunch. But it didn't help. Any suggestions?

I had to loosen those retainers when it needed further adjustment on mine.It runs geat now but the evo 46 I have is a whole other story I'll buy os ,ys, or saito next time
good luck

Whenever I have a student show up at the field with a limiter on the high speed needle, the first thing I recommend is to take it off. Then with their approval, I help them remove it. Better to teach them how to properly tune the engine from the start.

Your problem sounds like you're setting the high end too lean. (you said it revs high for a few seconds then drops). The statement "If I let it idle more than about 10 seconds, I never get to BRRRR - it starts to rev, then dies." leads me to believe your low end is too LEAN. Just to be sure, are you sure you're adjusting the low speed needle? I don't want to seem insulting, but some first timers don't recognize the difference. This is different than the high speed needle. The low speed needle typically requires a very small (jewelers screw driver), and is located inside the ring around the throttle arm. I just looked at the Evolution manual on line, and it does show a limiter collar on the low speed needle. I'd get rid of it.

I had a Megatech engine I just finished breaking in that I actually had to modify the carb internals in order to get the low speed needle adjusted correctly. Its set up with a tube and sleeve arrangement. The low speed adjustment moved the sleeve to adjust the mix. The sleeve was a few thousandths too long. The engine was exhibiting similar characteristics as yours. The difference between rich and lean at the low end is difficult for the novice to determine. Rich, after 20 to 30 seconds, the engine will hesitate, and then rev up due to the excess fuel that builds up in the carb. Lean, the engine will hesitate, then die because there isn't sufficient fuel in the carb already to support the extra air being dumped into the carb when you punch the throttle. Its subtle.

To test, richen the LOW speed needle by 1/8 turn, start the engine, and reset the high speed needle to 200-500 rpm below peak to the rich side. Try the punch test. Keep trying this by making small adjustments in the LOW speed mixture until you're convinced (try up to a full turn) its not getting better. If its getting better, keep going until it doesn't get better, or you start to get the hesitation before the runup.

Good Luck.
Brad

I have three Evolution engines, a 40, a 61, and a 100. ALL of them have the same basic problem... the adjustments on the needles are not within the limiters that the factory put on there. Sooo... I removed them. I used the 100 on an Excelleron 90 pattern plane and finally took it off in favor of an OS 1.20 AX which is absolutely delighful after all the fuss and pain I had with the Evolution 100. But, I think that with the proper feel and enough time and patients, I could have gotten it to run much better. All symptoms you had, I had. I ended going way more lean on the low end just to get it to idle. It would run a while, I would carry it out to fly and it would die. There was not one day that I got more than two flights with that engine. It would die in the air for no reason that I could think of, but it all seemed to come down to proper setting of the low end needle valve which needs to be way more lean than factory limiters would allow, and a high end that needed to be a tad more rich than the factory would allow. It seemed to always run to lean on the high end.

Again, the OS 1.20 AX cured all that and, as far as I am concerned, is the absolutely best choice for these intermediate pattern type aircraft.

In your case, however, the OS 61 SF is a grand choice over the Evo 61. Only because of the reliability and AND the support you will not get from Horizon Hobbies with the Evo. I had one (an OS 61 SF) on a Tiger 60 and only removed it because it needed rear bearings (I bought it used). It always started and ran very well and had lots of power.

DS.

BKDavy, yes I'm adjusting the correct needles. And no offense taken, for sure. The way you characterize my transition problems is right on - after a long idle, if I punch it it will die; after a short idle, if I punch it, it over-revs then settles down. My theory was that it was building up fuel as it was idling - idle too long and it builds up so much fuel that it chokes off, idle a shorter time and it burns it off then settles down to its high-speed setting. But your description makes sense too. Like you say, "it's subtle." Amen to that. Electric is looking better and better.

CGRetired, I'd have bought an OS but I'm trying to save the bucks. Since you never got your Evo 1.00 to run right, could it be that you were mistaken and were actually too lean all that time, not rich, as BKDavy suggests?

(this is vwalton's son) I'd be curious to know if anyone else has any input on this problem. We've pretty much decided to take the low speed limiter off since it is acting like it is running too rich and it spits oil like crazy at idle, but if anyone has heard of this problem and knows of a sollution to it we'd like to know. Thanks.

Hi Guys, I have 6 EVO motors 4x46 2x61. Some have pitts mufflers on them some are stock standard. I have never had a tuning problem with any of them.
They like to run on the rich side and seem to produce more power this way and with a beautiful reliable idle to boot.
The first thing I do when I get a new Evo is replace the Hangar 9 Plug with a OS F plug,they always run better with more reliable transitioning from idle to peak revs.
I leave the low end adjuster in the middle of its range and only ever so finely adjust the top end to produce a nice smoke trail from the exhaust.
I have never had to take off the limiters in the past 2 years I have been using these motors.
If you have removed them I can explain a sure fire way to set up any 2 stroke glow motor to run near perfectly first time every time.
I learnt this from Mr Brian Winch who is the Australian Guru on model engines and writes a coloumn in Airborne Magazine called Airborne Engineer.
With your radio on and motor off and in a nice quiet spot ,open the throttle just enough to place a T pin or similar into the carby opening,then with your radio,adjust the throttle to close firmly onto the pin.
Remove the fuel line from the needle valve and replace it with a foot long piece of clean fuel tube.
Using a small screwdriver,turn in your low end screw until it stops.
Blow into the clean fuel line with a constant breath while unscrewing the lowend needle,keep going until you can hear the air escape from the carby where the pin is.As soon as you can hear it come through stop turning the screw. Your low end is now set as close to perfect as you will get it. Now just remove the pin and put your fuel line back on .
All you have to do now is set your high/top end needle to about 2-3 turns out ,start your motor and adjust to peak revs then back off the needle a couple of clicks.
Try this it works..
Good luck..

That explains why you need to be rich. Not a bad idea though. OS-F plugs are for four strokes and are a hot plug. The need to be hot since a four stroke fires every other stroke of the piston.

In every Evo glow engine I have ever looked at, I have always had to remove or loosen the limiters to get the adjustment I need. Some of the guys not having to do this. I also found that most like to run on a fuel mix of 15% nitro and 20% oil. Castor/synthentic blend seems best such as what Byron's sells

These are pretty reliable engines and take allot of abuse, getting them tuned can be a bit tricky.

I finally got my evo .46 to run right.The clunk was stuck forward and after repositioning it and some adj it's perfect now I take back my previous statement.A little patience goes a long way I guess.

Thank you for your input, we are going to our flying field tomorrow morning and we will get a chance to mess with the engine a little more. We have an os f plug lying around so we might try that and if it doesn't have an affect I guess we will take the limiters off and see if we can get it to run properly. Thank you for all your help and we will keep you updated on our progress.

Shocker, I had an Evo TPS that wasn't running right, so I Checked with the factory.

Their recomendation was to open the carb 1mm. Then, with the low end limiter removed, close the low end adjustment and open it 1 1/5 turns (one and one fifth). That is where it was supposed to be set - mine was wrong, but once I put it where it was supposed to be, it ran great.

Now my engine was smaller than yours, but that's something you could try.

Have you done the pinch test. With the plane at an idle, pinch the fuel line and see if it picks up RPM for about 4 seconds the starts to rev up and quit or if it just quits when you pinch it. If it just quits, you are too lean. If it revs up for 7 to 10 seconds before it dies then you are too rich. That will fix your low end.

well we went flying yesterday and we managed to get the engine running great. We couldn't get the limiter on the low end off all the way but we changed it so we could go quite a bit leaner with it. Once we got the low end leaned out and the high end set correctly the engine ran great, so I guess the limiter was set wrong from the factory. I'm very happy with the engine right now and thanks for all your input.