Jetting and prop setting

[Good old number 29 158]

Put your prop info and jetting here. There is a lot of mixed info on props and static rpm. Please put down the raw data, then expand on it if you care to. 

Rotax 503 DCSI

Powerfin “B” blade 

68” three blade

Set .025” from finest pitch

STATIC RPM and TEMPS

6,500 rpm max, down to 6,300 

EGT 1,025

CHT 425

Ambient temp 30° f

Main jets 158

Idler jets 45

Needle jets 2.74

Needle 8L2 in position 1 (top notch)

Air screw out 2 turns

I haven’t yet put a protractor on the prop to measure the pitch. Powerfin set it up to be adjustable using feeler gauges to measure the pitch, and that is how I set it up. This is the initial setup on my plane, which I intended to be more toward climb performance than cruise. The plane had 145 main jets installed when I bought it. I honestly didn’t see much difference in EGT with 150, 155, or 158 main jets. It never exceeded 1,100°. CHT was pushing 450° with prolonged pulls on the 150 jets, so I worked back up to the factory recommended 158s, and saw a minor decrease in CHT. Keep in mind that this is all static pulls, so it should drop with increased airflow when it’s actually moving. Plugs look nice and tan. I got the lowest CHT, about 400°, at 6,100 rpms and .040” on the prop pitch. I’ve seen a mix of opinions on redline, varying from 6,200 to 6,800. CPS quoted 6,800 max rpm for up to 5 minutes. Being that they’re a licensed retailer, I believe that’s accurate. Other information suggests 6,500 rpm as the continuous redline. I have no intention of running it continuously at 6,500. I do want to be able to reach 6,800. Snowmachines with the 503 revved to 8,000. With the plane locked down and the engine warm, at this prop setting, the rpms jumped as high as 6,500, then quickly settled at 6,300, fairly steady. I did notice that the engine would do that at full throttle, regardless of pitch or jetting. I’d see an initial high rpm, then a drop of about 200 rpm over the course of a minute, in correlation with the rise in CHT. EGT remained the same. All the carb setting are factory recommendations, except the air idle screw. I got the highest idle at 2.5 turns out, and turned it back in 1/2 a turn. 

Edited 16 Dec 2019 by Good old number 29

[akflyer 1427]

Running too lean will show as soon as you get it in the air and unload the engine a little bit.  Static runs are sort of a base point but you will be doing more tweaking once you fly it.  I would much rather start off a little bit on the fat side and not have to be in a panic trying to ease it around the pattern and get back on the ground with EGT's that are bumping 1200+ .  On the ground wide open my EGT's are around 1050, but in the air I have to bump in a little more pitch or fatten up the mid range 1 turn to keep them under 1200 in cruise.

Most props will unload when you start rolling.  Setting my prop at 61-6200 static will give me around 6500 on take off.  Anything over about 6500 on take off and performance actually suffers as you are just beating the air with a flat prop and not really moving much.  

I am not sure on the 503, but the 582 has max tq at around 6500 and that is the one I shoot for. 

I would also be careful having the needle in the top notch.  You will be pretty lean in the midrange which is where you will be doing most of your flying.  On the 582 its pretty much a given that you will be starting out n the 3rd notch from the top fattening it up a bit.

If your sled is running lean and you melt a piston, you can tow it home.  On the plane its not that easy.  First flights I would much rather have a little stumble in the engine from it being too fat than to burn it down.

 

[Good old number 29 158]

The 503 makes peak torque at 6250 and peak hp at 6500. I tried the needle on the second setting. Temps were low and plugs were black, so I took it back to the top notch, which was the recommended setting. The picture above was taken during a run with the 150 jets. At partial throttle, the smaller main was having an effect. With the colder, denser air, I might want to move the needle up or go to a bigger main jet. Like you said, I need to actually get it up in the air and see what it does. Today was beautiful, but I'm in fisheries meetings through the end of the week. I think it's close, but having colder air flowing freely through the cowling will probably prove you right on every point. It was flying previously with 145 main jets, so I'm not too worried about being too lean right now. It's probably a bit skinny on the pitch, but I wanted to be reasonably sure it could run up to redline, if needed. I first pitched it for 6,000 static, but I didn't want to be behind the power curve, unable to call up peak power on demand. If temps are high the first time around the pattern, the enrichener might actually become useful. I believe that the loss of rpms on static runs was because it was breathing the increasingly hot air inside the cowling, but that won't be the same issue when it's moving. The fan is quite close to the firewall. I might add a vent to the upper cowling to feed the cooling fan. It pulls air from the back of the engine compartment and blows it out the top of the motor, and out of the cowling, through the square vent on the top cowl. I know, there's not much reason to run it past the top of the torque curve, except that it's better to be above it than under it. 

[Allen Sutphin 705]

I pitched my 503 for 6350-6400 static. E-clip in 2nd notch and standard recommend jets. I did have to drop down one jet size for summer weather and go back to standard jets for cold weather. Any 503 I ever set up for someone, I always reset everything to factory specs before starting to fine tune it. I ran 158 jets in winter and 155 jets in summer. This was at an average 3000' MSL.  Usually a main jet change for OAT was and is usually all that is needed if everything else is right.

[akflyer 1427]

again, I can not stress enough that things WILL change when its in the air and that prop unloads.  It will happen.  First flights your much better off to be a little fat than to be just perfect on the ground.  I would not know this from first hand experience or anything.. cough cough.  

Tuning a sled and tuning the plane is just a tad different.  The clutching etc keeps the engine loaded on long pulls.  If the prop is not set right, the engine completely unloads, gets lean and EGTS will shoot through the roof.  I would not set the static max RPM at 6500.  You will blow right through the 6500 once your in the air.  Generally speaking (depends on the prop) but a good starting point is setting it for 150-200 RPM LESS than the max you want to see, then go fly and see where your at on take off and cruise.  If you can blow right through 6500 wide open throttle straight and level, then you WILL be running lean in the midrange when you pull the power back to cruise, the engine unloads because the pitch it too flat and your EGTS WILL shoot up so fast you wont know what hit you.

You have lots of runway to play with, use it to your advantage on the first flights.  Flying a 2 stroke has a learning curve.  

 

Edited 11 Dec 2019 by akflyer

[Buckchop 479]

Thanks guys this is perfect timing and good info as this is where im at right now on the BlueFox, I usually run, 2:72/165 in summer and 2:76/175 in winter, i tried the 2:72/170 yesturday and my temps at idel was 1100, and a little throttle and went over 1200,  so i went back to what ive been useing for a few yrs on BlackFox, 2:76/175. I cant tell u what rpm cause cant seem to get my tiny tach to stop reading what seams to b double the rpm, 5000- 5200 it reads at idel. Hahahahaaa 

Edited 11 Dec 2019 by Buckchop
Add pic

[Allen Sutphin 705]

Once you know at what RPM the trouble starts, then you'll know what part of the carb to go hunting. Idle jet controls up to about 1/4 throttle, main jet needle up to about 2/3-3/4 and main jet 2/3- full throttle.  They all overlap a bit but once you nail at what RPM it goes haywire, then start there.  I've seen worn needles cause a lot of problems. LEAF has a good one page article in their catalog on carb tuning and factory settings and jet sizes recommended. Change one thing at a time or you'll be a dog chasing his tail. Don't overlook a crappy gage either. Most of my issues were the connections.

[Buckchop 479]

Thanks for the info on them, wont have to worry about worn parts, these carbs where brandnew out of the box.  Did have gauge problems and bought a new one from Jim.  Didnt get it outside yesturday but hopeing for that today, the sun suppose to come out!!!!!! 

[Allen Sutphin 705]

By my notes the standard setup is :  idle jet 45    needle jet 2.70    main jet  158    jet needle 11K2   E clip  #2 slot   and air screw 1-1 1/2 turns out.  These numbers will work with 99% of conditions. Only change would be the main jet depending on OAT and altitude flown. Make sure the E clip is UNDER the white piece. This is for an aircraft 503 and not a sled.

Edited 12 Dec 2019 by Allen Sutphin

[Good old number 29 158]

It sounds like the specs you’re using are for the dual intake silencer, note three on this chart. Note two is the single carb with silencer. I have the dual carb without silencer, and the jetting is as listed, except that I leaned out the idle by turning out the air screw. 

[Allen Sutphin 705]

Check the leaf chart. Never heard of that chart and don't agree with it.

[Good old number 29 158]

This is the same chart as I have in my ‘98-‘99 CPS catalogue, and matches the jets that were in my plane. I have a wide selection of main jets, and someone had installed 145 mains, but all else was the same, and everything looks good with their recommended settings. Based on the advice I’m getting here, and current local temperatures, I’ll try going richer before I fly. 

[Good old number 29 158]

Here is that LEAF chart. Looks the same as the other except for the needle jet/ jet needle. I have a richer jet, with a different profile needle set on a leaner setting. Offhand, I’d say it accomplishes the same thing. 

[Good old number 29 158]

The needle I have would be leaner above half throttle, but richer below half throttle. However, I also have a richer needle jet, which would make it richer across the range. This may explain why I was able to lean the air screw as much as I did, being that both the needle and its jet contribute to a richer mixture than the LEAF setup at lower throttle settings. 

[Good old number 29 158]

And also supports having the clip on the number one setting. Two sizes richer on needle jet. Three sizes leaner needle above half throttle, one size richer below half. One leaner clip setting. Confusing enough? 

[Good old number 29 158]

There’s a note on the LEAF info that Bing carbs don’t come with jets. Apparently, the jetting that I have in my 503 was standard from CPS or Aircraft Spruce, while engines ordered from LEAF used the other setup. 

[akflyer 1427]

The charts can get confusing if you don't pay attention to the notes.  I know that we all want the very best performance we can get from out planes.  4 strokes you can get away with running the ragged edge, one hick up with a 2 stroke and your in an emergency situation much faster than you want to be.  Been there, got the tee shirt and some shorts that were replaced.  

I have learned that plugs are cheap to replace and I will gladly run a bit on the fat side and replace plugs as needed.  Makes for a much more enjoyable flying experience when you are confident in your engine and don't think twice about loading your kid up with you and taking off at -30 to head to a remote destination.  

Hope with the better weather moving in we get some flight reports REAL soon!

If your in the mood for it, give me a shout after the 18th when I get back home and we can get together and have some fun!

 

[Allen Sutphin 705]

I operated with the leaf setup for many years with no problems. Temps were on target.  When you have 3 or 4 different jets, needles and combinations, you can end up with all kinds of issues and no clue as to where to start solving them. It is also possible to put a band-aide on the issue and not fix the problem. But it can rear its ugly head later and usually does.

[Good old number 29 158]

Allen, on your 503, what prop are you running, and what RPM? 

Reading my 1984 ROTAX manual, it states that the 503 is designed to run 6,350 at wide open throttle with a full load. That is just past peak torque, and what I would ideally have wanted. I will be re-pitching the prop accordingly. I got kind of caught up with the idea that I should be able to hit redline, when I knew I should be aiming for peak power. I had 6,000 at .050” and 6,300 max at .040” on the ground. I’ll try .042” and give it the real test. With 6,500 at .025”, it seems like the prop was losing efficiency with too fine a pitch. 

I went up to 160 main jets. I have 145-180 in increments of 5, and 158, except no 165’s. 

If the weather cooperates, and God is willing, I’ll finally be able to fly it this week. 

[Allen Sutphin 705]

I was running a 60X44 wood prop. But this was a 2010 model 503 DCDI ignition. If you are running the points ignition engine then the timing comes into play also. And whether dual carbs or not.  Kind of hard to solve these types of issues without having the engine in front of you. Several variables come into play.

[Good old number 29 158]

Here is a picture of how the pitch adjustment is made on Powerfin props. Insert the 1/4” steel dowel in the blade root and measure the gap to the closer side of the adjustment window, using feeler gauges. We started at .041”, which gave an initial static RPM of 6,300. In the air, it would have exceeded 6,800 without throttling back. Three adjustments later, it’s at .058” from the finest pitch. This allows 6,650 rpm full throttle, level flight, and about 6,400 climbing, solo. We saw an increase of nearly 1,000 rpm difference between static pulls, fixed on the ground, and when it was moving in the air.  We took it as far as .062”, which gave 6,300 solo climb.