Help Rejetting

12 posts in this topic

Posted

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.

IMG_2241.JPG

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Posted

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. 

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Posted

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

:BC:

 

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Posted

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.   

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Posted

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. 

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Posted

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

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Posted

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

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Posted

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 

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Posted

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.

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Posted

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

 

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Posted

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. 

  

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Posted

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

 

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