Help Rejetting

[Chris 6]

I've recently purchased my first Avid, and am having a blast.  I did a thorough conditional inspection, and repaired several issues.  Most were very minor, the only biggie was the flaperons.  The bolt holding the right bell crank was frozen.  Had to cut it out, install a new one, and re rig the flaperons.  It flies great now.

My current issue is the rather high (I think) EGT.  I'm running between 1150 and 1200 all the time.  I don't want to pitch the blades any more, as my RPM is where I want it - 6300 static and 6500 dynamic.  I'm thinking it's time to re-jet.

I have:

11G2 jet needle

165 main jet

3.72 needle jet

I'm basically at sea level here in Texas.  

I differ to the wisdom of the group.  What size jets should I goto and which slot not he needle should I start?  Or is there something completely different I should be doing?

Thanks,

Chris

P.S.  Here's the shot of me taking her home.

[akflyer 1428]

The first thing you have to do is read the plugs to see where you are actually at.  The EGT gauge pretty much shows trends and not actual true temps to a degree that I would trust it explicitly. 

Warm the engine up good on a set of old plugs, shut down and swap to new plugs. Fire it up and go WOT for a minute or so then shut down as quickly as possible.  Pull the plugs and see what they look like.

Most EGT gauges are NOT temp compensated so they are only accurate at 70°F.

What position is you needle clip in?  most seem to run on the 3rd slot (from the top end of the needle) making it raised almost all the way up.  I run 2 main jets.  165 in the summer and 170 in the winter.  I would really be tempted to tweak the RPM down to 6150 or 6100 static and see where that puts you on take off and climb out as well as WOT straight and level. 

[akflyer 1428]

By the way, that is a great looking bird, I hope you really enjoy the heck out of it!

 

[thebriman 69]

1200 is EGT redline.  I like to see 1150 personally but I'd be happy 1050 to 1150.  If you're running 1200 at WOT you can go to the next larger main jet.  If WOT is a good temp but your midrange is high you can either lower the clip on the needle, thus raising the needle earlier in the throttle movement or you can go to a richer needle jet say 2.74.   

[Guest]

If I remember correctly that is standard jetting for just about your elevation, and 1150-1200 is an optimal EGT. But I do understand your concern. You can try moving the needle up a notch and that should decrease any mid range volatility you might be experiencing. Or you could bump the main jet up a notch.

If you are seeing 1050-1100 at full throttle probably just raising the needle will do the trick. If you are seeing 1200 at full throttle i'd bump the main jet up a notch.

Others may have different opinions, but that should get you started in the thought process. 

[1avidflyer 2006]

I'm with Leni, check the plugs, and maybe add a bit of pitch to the prop.  Main jet controls full throttle, needle position controls mid range rpm.  Glad you are having fun with the plane.  JImChuk

[C5Engineer 1170]

I thought I had posted this already but I guess not. This thread should help you out.

[NorthIdahoAvidflyer 374]

Forget the optimum static rpm range based on prop setting. I got hung up on this and it made me pull my hair out for a week. If you are out of needle adjustment positions add more pitch and cure your problem. Each propeller profile produces different results. I was shooting for the magic 6250-6350 static. At that static setting I was running over 6800 rpm in level flight and was running hot EGT temps. After getting good advise on here I added pitch and the problem was fixed. I ended up running 5650 static and my WOT level flight rpm is around 6700. Temp are good now. These engines like to be loaded. If your WOT climb temps are good but they get warm when you level out it’s because you are unloading the engine. Adding pitch will fix this. My propeller manufacturer said to set my prop at 14 degrees. I’m at 16. Each set up it different. 

Good luck 

[Chris 6]

Thanks for all the info.  I'll go through the carb tuning procedures when it stops raining here, and let you all know how it goes.

[Chris 6]

I finally had a rain-free day, so got to start tuning.  I set the floats so the bowl had the nominal 1/2.  Then I tried to set the idle mixture according to the directions from Green Sky's article.  I ran out of screw before I go the engine to stumble.  But I set it pretty lean and went onto the mid range.  1200 EGT at 4050 RPM.  and just under 1200 at WOT with 6000 RPM static.

I'm thinking I don't want to pitch any more, but change jets.  

With these jets now:

11G2 jet needle

165 main jet

3.72 needle jet

Where do I go next? I didn't look at the number on the idle jet, but I think I can just go up one size on the main, and down one size on the idle.  But I don't know weather to change the needle or the needle jet.

What's the accepted procedure?

Thanks,

Chris

 

[NorthIdahoAvidflyer 374]

Check jetting per the chart and use the jetting correction chart for your local temps. Also check your EGT probe placement on the exhaust manifold. If you don’t want to add another degree of pitch then its a main jet change. The jet change will add more fuel.  The needle meters the midrange. 

Your story is exactly what I went through with mine. With the jetting set per the charts it was the prop I found to make the biggest difference and it didn’t involve using more fuel. 

What Propeller are you running? What is the length of the prop? Two or three blade? I found that my prop blades need to be longer. I’m running a thee blade GSC, 64”. 

I found my problem in the midrange. When I was climbing (running on the main jet, engine loaded, WOT)  the temps were good. This told me my main jetting was right. As soon as I leveled out and pulled the throttle back to 6500 the egts would start to climb. If I pulled back on the stick and started to climb a bit the temps came back down. As soon as I unloaded the engine the temps start to climb again. That’s when I learned how much these engines like to be loaded. I’m nowhere near the 6250-6350 optimal static rpm listed in the books. I ended up at 5650 static. Life is good, temps are under control and I still get 6700 Max rpm in flight. 

I know you don’t want to add more pitch but I feel with another pitch change you will be where you need to be. One thing about pitch...it’s free and can be moved back.  

Good luck and please share your findings. 

  

[sky4play 55]

I am with Vance...a lot of good advise there...

You need to start with your prop pitch....(It is a crazy dance..)

Then, tune motor

1200  scares me and I would up your main...just to be safe,... and a 5 or 10 jump will never make you cold.

Mid-range will always give you the most worry...because you are starting to unload

I run 180 in the winter and 170 in the summer...I also run the Hacman system, which I built from ebay supplies and

use every time...Nice to have some control. There are varying opinions on this system,  but I like it.

Things will come together for you...John O

 

[Columbus 30]

NEWB alert! Huge grain of salt needs to be applied here...

In racing (not that I ever did such a thing) the fastest of us worked the problem tires first. By that I mean we figured the mission from the tires forward. What length of track, what tire diameter needed for that length of track, what ring amd pinion to spend the tires that distance, what tranny to spin the ring and pinion to move the tires...you get the point.

Would not the same philosophy apply here? What’s the plane’s mission? What prop needed for that mission, what gear box to spin the prop, what engine to spend the gear box to spin the prop, what carb set up to run the engine to spin the gear box to spin the prop.....etc

So p, I am still so new as to be funny- yet it would seem to follow? Did the EGT run hot for the P.O.? If no, then what changed? Does my question make sense?

[NorthIdahoAvidflyer 374]

The  philosophy you speak of has already been applied to these engine/ gearbox / propeller set ups but over a much longer time frame. It goes even farther than this but to produce the needed rpm at a given usable propeller length while still keeping the engine properly governed and temps in check does give you some room for experimentation but not a bunch. Also, the price tag associated with this kind of experimentation is more than most people can afford and a lot of this stuff is not returnable.  So we basically have learned from industry standards and each other. The problem a lot of times comes from having to get that magic number in the book. I’m guilty. There are so many variables. Someone else could probably do a better job explaining gear box ratios to propeller effectiveness on these airplanes. 

There is no dumb newbie questions here.  It’s worth asking anything to gain some insight or share some knowledge. 

 

[Columbus 30]

I appreciate the comments! I am dong my best to absorb the vast expanse of knowledge....akin to drinking water from a fire hydrant !

[Chris 6]

Finally have some good news to report.  It took a while due to the weather, but here are my results:

I started completely from the beginning with the floats at the right height, then as described by Jerry Olenik of Green Sky Adventures.

 I rejetted the idle to 40, needle to 2.74, and main to 170.  

I'm now getting 1100-1150 EGT in all phases of flight.  Over 500 ft per minute climb at 6000 rpm and 70 kts.  Max rpm straight and level at 1500 ft was 6100.

I didn't check what my top end speed, straight and level, but it was approaching 100 kts when I pulled the power back from the max rpm run.

I think I'm finally happy.  Thanks for all the help.

Cheers,

Chris

[C5Engineer 1170]

Thanks for the follow up. Often times people never post the resolution to the original issue which is frustrating when you are searching old threads for information. 

[zadwit 105]

Dont forget, the location of the EGT probes is critical. Vance can tell you all about this.... I found someplace on the web and it gives the location of the EGT probes for  503, 582, and all the other rotax engines and no two are the same.,, The 503 and 582 require different locations for the EGT probes....IF they are in the wrong spot , your readings will be high or maybe real low...

The tach needs to be accurate as well. IF it is off, it will make yhou pull your hair out trying to get the other reading to read right......EGT, CHT, Water temp etc....performance..

[Turbo 163]

One has to wonder: if EGTs come down with the engine loaded up, everything else equal, does this mean that fuel is being used more efficiently since gases leaving the cylinders are more completely burned, and cooled by expansion pushing the piston down?  Ostensibly, this is instead of some combustion still occurring as the ports are opened at the end of the stroke.  Do I have this wrong?  Does anyone who has a fuel flowmeter onboard have a read on this?  If EGTs are lower, one could ostensibly lean the mixture a little, which would also save fuel.  I hate the idea of using unburned fuel as a coolant!  

So what's with the factory advice on this?  Like with the super-rich idle mixture, why would they mislead us?  I've leaned out my idle.  On go-arounds I get no hesitation; the bird practically levitates instantly as soon as the throttle knob goes in!  No hesitation.  There is obviously very little penalty for not having a rich idle like the factory advocates!  O.K., It doesn't start quite as readily when really cold, but then I just hit the primer a couple of times, and off we go!

Edited 25 Aug 2018 by Turbo

[nlappos 415]

Turbo, I think you're right on with your understanding of EGT and mixture. The biggest problem we have is the relatively inept Bing 54 carburetor, which has really no mixture control at all. In carburetors with manual or automatic mixture control these conversations would be unnecessary. I think the Bing adaptation for flying is the worst part of the Rotax two stroke snowmobile engine converted to aviation.

In any case I have my 670 with the hacman mixture control which is really pretty effective for about 100 to 150° of EGT. I'm operating from 6000 feet and on hot summer day I had to take my jets down to 165 to lean the mixture to get the darn thing started. I did note before I switched jets, if I fully leaned with my hacman the engine would start and run well. That gives me some rough calibration that the hacman full rich to full lean is worth about 15 points on the jet sizing.

Obviously like any piston engine the EGT and mixture are directly related, so that extra gas cools the gas stream.  Before I lean at all, the cruise EGT runs about 980 to 1000, and as I lean,  I drive that up to about 1080 or 1100°. I also have a fuel flow gauge and I note that before I start leaning I'm getting 6.5 gallons per hour and when I fully lean in my 670 I get down to about 5 gallons per hour.

With the hacman and my 582, I had the same basic control over EGT (about 100 to 150°) and the gallons per hour would go from about 6.2 un-leaned to about 4.8 leaned.

[Turbo 163]

Vance Simons (NorthIdahoAvidFlyer) has observed that these 2-strokes like to be loaded up, and I suppose we all have observed lower EGT on climbout, and higher values in descent.  I do believe Vance is onto something here.  I also think its important to understand what EGT represents.  I think high EGT must mean that energy is being wasted, that efficiency is down, perhaps because combustion is happening a little too slowly, making for a hot exhaust manifold.  My recollection is that aluminum is extruded at around 1200F, our EGT maximum, as it starts to soften enough to flow.  Generous piston skirts, coupled with water cooled cylinder walls, and auminum's very high thermal diffusivity, keep our pistons cool enough to stay together.  An insulative ceramic layer on top helps too.  Firing every stroke must work to keep them hot, at least relative to the pistons in a 4-stroke.  Loading up the engine by increasing pitch and dropping the static full-throttle RPM will lower EGT, but are we being harder on the pistons in terms of heat loading?  I'm not convinced that EGT tells us the whole story, but we have little else.  So I guess my question is if anyone has observed lower fuel flow with higher prop pitch, at the same altitude and IAS.  Leni, you have the IFA prop, right?  And has anyone ever melted a piston while staying inside the EGT limits?

BTW, I just installed a manual leaning system using Cowlove's approach, using a small, 12V diaphragm vacuum pump.  I am hopeful that it can also be used to smooth out idle on the ground, whatever the density altitude.  There's a new knob on the dash.  I think I'll label it "chemtrails".

[Bandit 286]

I wouldn't get real technical with your Avid. These are simple airplanes to own and fly if you have the wide landing gear and Matco tail wheel. I have the Artic Sparrow mixture control. At run up I richen  the mixture until it starts to miss, then back off one turn on the mixture control until it runs smooth. On take off full power, cruise 5950, when its time to land I run cruise power until I know I have the runway made, then back to idle until I flare, then add a little power and let it settle in. I never run it at mid range.

[Turbo 163]

O.K., so it looks like there are two ways to get a high EGT: 
(1) High EGT due to not prop-loading the engine sufficiently, so it's always spinning a little fast like in a descent, and where combustion may still be occurring as the ports open approaching the end of the power stroke at BDC.  I suspect this wastes fuel, just heating the exhaust manifold.  
(2) High EGT at high power due to having too lean a mixture, so all fuel is burned, with none available for absorbing heat by being vaporized without burning. Like I said, I hate using fuel as a coolant only, but I sure don't want to melt a piston.
I think Vance has the right approach, but there may be less maximum power available for Takeoff and climb if the engine can't rev up to 6500 rpm.  I don't know about your bird, but mine is light, and accelerates like a dragster on takeoff.  I could easily give a little T/O performance away in order to reduce cruise fuel burn by operating the engine more efficiently.  To do this I'd increase the prop pitch for a lower max static RPM, which would lower EGTs, but then lean at altitude for even lower fuel burn, of course monitoring EGT. In cruise, with lower thermal load and better cooling, it may be impossible to lean to the point of exceeding the EGT limit anyway, as the engine would start running rough first. So you just lean to best rpm.
With the idle circuit set for sea level, idle will be too rich at higher density altitudes.  The Arctic Sparrow system only affects the mid-range, so stays full rich at idle and WOT. But that's not what I have. I am leaning by lowering the float-bowl pressure, which affects all 3 circuits.  So if I'm at a 6000 ft field in summer at gross and don't lean for takeoff, my engine will be way too rich and may bog and not perform adequately.  If before takeoff I lean to a smooth idle, I may run too hot on climbout and melt a piston.  Maybe the answer is a compromise, midway in between.  Maybe, like Bandit, I lean to just the smooth side of rich at run-up, on the mid-range needle.  Voila the term "experimental"!

[skypics 89]

Those EGTs are pretty common. You may see 1200 F on climb, but when pulling back to cruise they should drop to around 1100. The most important temps are the head temps. They more closely show the engine stress.

If you have the choke hooked up, set up a cruise rpm and slowly pull on the choke. If the engine speeds up you are too lean. If it bogs down you are too rich. If it doesn't change you are just right.

When I was driving a 582, I continually got 1200 F on climb out from a 355 MSL field. 

John M

[Turbo 163]

Interesting comment, John.  CHT should do a better job of telling us how hot the combustion chambers are, and if I were flying behind an air-cooled 4-stroke, I'd definitely have CHT.  In that case, the most tortured part is the exhaust valve, whose only cooling comes from conduction thru the valve stem into the guides into the cylinder head, so yeah, keeping those heads cool is critical to the valves' longevity.  My setup has a big bellyrad, so I'm always operating "oń the thermostat", with only minor changes in CT.  With liquid cooling, I'm not convinced that CHT tells us anything unique from what we get from CT.  I would expect that liquid cooling would go a long way towards flattening any thermal gradients that might otherwise exist around the cylinders.  The heat capacity of water is huge.  Even mixed 50-50 with ethylene glycol it's big.