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Author Topic: Engine going lean...or rich...or lean  (Read 1139 times)

Online Shorts,David

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Engine going lean...or rich...or lean
« on: January 20, 2020, 05:48:09 PM »
Well, I'm asking for help. Today the plane finally ran great and flew great until the end of the pattern, about four and a half minutes I began losing power. I'd pitch it up and get a quick burst of power that died off. My guess was it was going lean rather than rich from the sound and smoke. I think I was right.

Next flight I richened it up a half turn and suddenly the plane is doing 10 second laps. Very interesting to watch. I thought maybe I was super rich, but...I finally landed with motor still running as it died. It still had about one out of three ounces, so I know it was just idling beyond lean.

Next I started it and it was dying until I began richening it turn after turn until it was screaming lean. I kept turning the needle out until it was coming out. Still screaming lean.

My next course...and only course I can think of is to take the lines off the needle and blow some fuel through it to clear a presumed obstruction. I won't be able to test it until Friday at the field, so... anything else it might be?

The Details.
fp .25.
10/22 powermaster. I added 1:40 parts acetone to lengthen my run. I've done this only about four times and had fair results. Today being the first time it ran almost perfect, and then completely unusable.

ST. needle. I understand this is the wrong choice but the engine came with it. I can't tell the venturi size as I don't have the micro tools to measure. But...another question. If the venturi is too large, I must increase fuel to match, and possibly lose some power. Correct? If the venturi is too small, I must decrease fuel, and possibly lose some power. Correct? Until today the plane has been too rich, or too lean, with about three flights that were just right.

Sulivan 3oz tank set up for uniflow. I can visually inspect the clear tank and see that there are no bubbles going through.

Well, that's my story. I almost bought a new fp .25 but it sold because I thought I had put my engine trouble behind me. Hopefully it's just a clog of something that got in my fuel line.

Any thoughts and free education appreciated. I have about 20 runs in this engine in this plane and like I said, about three good runs. It used to run slobbery rich most of the time until today.
David

Offline Dan Berry

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Re: Engine going lean...or rich...or lean
« Reply #1 on: January 20, 2020, 06:01:55 PM »
Change the glow plug.

Online Dennis Nunes

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Re: Engine going lean...or rich...or lean
« Reply #2 on: January 20, 2020, 06:32:48 PM »
Hi David,

Do what Dan said, try changing the glow plug!

If you want an interesting experience on an engine that ran erratically check out the following thread: https://stunthanger.com/smf/engine-set-up-tips/st-v60-has-to-be-set-very-rich-then-runs-lean/msg498042/#msg498042


Dennis
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Online Dave_Trible

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Re: Engine going lean...or rich...or lean
« Reply #3 on: January 20, 2020, 06:34:26 PM »
David it could be a few things.

1. Yes change the plug.
2. Do you have a fuel filter on it? (why not)  If so flush it out.
3. Check for a blown head or backplate gasket.
4. Air might be bleeding around the spray bar or a pin hole in the fuel line.  Replace it anyway.
5. Really bad batch or contaminated fuel.
6. Remove the spray bar and venturi and inspect for clogs or 'tators' in the jets.
7. It may be running hot or overloaded for some reason.  Prop too big.  Sleeve turned out of position inside the case.  Look into the exhaust and see if the ports look to be in the correct position.
8. The sunny gun is shot. Check for corrosion, gall or metal dust inside.

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Online Dan McEntee

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Re: Engine going lean...or rich...or lean
« Reply #4 on: January 20, 2020, 06:52:43 PM »
   Did you try running it on plain, unaltered fuel?  Try that in addition to changing the plug. When you change the plug, look at it closely with a magnifying glass just for the education. Think about what it was doing when it was running funny and how it responded to the changes you tried, that will help you learn to address this stuff in the future. When you add the acetone, you are already leaning out the mixture. You might try lantern fuel once you get the thing ironed out, again, just for the experience and education. It might work better for you than the acetone. The acetone may be attacking something in your fuel system, also.
  Good luck and have fun,
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Online Brett Buck

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Re: Engine going lean...or rich...or lean
« Reply #5 on: January 20, 2020, 06:53:23 PM »

Next I started it and it was dying until I began richening it turn after turn until it was screaming lean. I kept turning the needle out until it was coming out. Still screaming lean.

My next course...and only course I can think of is to take the lines off the needle and blow some fuel through it to clear a presumed obstruction. I won't be able to test it until Friday at the field, so... anything else it might be?



If it won’t needle the fuel flow is restricted somehow. Clean it out and it will work again. 

I would also try to run unmodified fuel. You should have *no problem* if it is a stock venturi with an ST spraybar on 3 ounces. Unfortunately the crankcase is now damaged by drilling it out, but, in this case, you need about a Letter I drill. If you have a fractional drill set, a 9/32 drill should not go through it - if it does, the venturi is too big.

Brett

p.s. David, if you are coming to the Southwest Regionals this weekend, Jim and I will be there (barring the unforseen) and we can work on it, and I will have all my tools.
« Last Edit: January 20, 2020, 09:52:09 PM by Brett Buck »

Online Peter in Fairfax, VA

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Re: Engine going lean...or rich...or lean
« Reply #6 on: January 20, 2020, 07:00:01 PM »
And the venturi size is critical.  If it is too large, the engine will not draw properly.

Offline Joe Gilbert

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Re: Engine going lean...or rich...or lean
« Reply #7 on: January 20, 2020, 08:50:28 PM »
If tank been sitting around for while castor buggers breaking loose. Bubbles or air getting in fuel line
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Re: Engine going lean...or rich...or lean
« Reply #8 on: January 20, 2020, 09:15:43 PM »
Sometimes the spray bar will get turned. Check to make sure the fuel discharge hole is straight down or angled to the back a little. If you can see the hole by looking down the venturi it's in the wrong place.

You can measure the venturi choke with the shank of a drill bit. Should be about 1/4" to 9/32".

You want about a 9 x 4 prop.

Don't bother with acetone in the fuel, it just evaporates right out. 3oz of 10% nitro is plenty to do the pattern once you get it dialed in.

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Online Dave_Trible

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Re: Engine going lean...or rich...or lean
« Reply #9 on: January 21, 2020, 05:09:24 AM »
I've never put acetone in fuel.  It's a potent solvent.  I wonder if it's preventing the oil from filming on the metal?  That would make the engine run hot and ruin it in short order.

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Online Perry Rose

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Re: Engine going lean...or rich...or lean
« Reply #10 on: January 21, 2020, 05:22:30 AM »
At the very end of my last 5 gallon batch of home brew fuel I had the same problem. I could see some globs of castor oil rolling around in the jug. I threw that out and filled with new all synthetic brew and no more problems.  The acetone may be congealing the lube. Flush the tank while your at it.
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Online Dennis Toth

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Re: Engine going lean...or rich...or lean
« Reply #11 on: January 21, 2020, 07:02:07 AM »
Dave,
You never mentioned what engine it was? I have had the similar behavior from my Fox 35. I found in one instance the plug had gotten loose only about 1/8 turn (seems the gasket compressed and I didn't check this after weeks of flying) check the warm compression. The needle valve out full lean is always some sort of blockage.

Let us know how you solve this.

Best,   DennisT

Offline john e. holliday

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Re: Engine going lean...or rich...or lean
« Reply #12 on: January 21, 2020, 11:04:31 AM »
He stated FP 25 in original post.  Even though it has been stated the fuel filter and fuel lines is what I would check or change first, especially after changing plug does not help.
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Re: Engine going lean...or rich...or lean
« Reply #13 on: January 23, 2020, 06:16:47 PM »
I see some dark oil marks left of made in Japan. Do I have a leak in my case?

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Re: Engine going lean...or rich...or lean
« Reply #14 on: January 23, 2020, 06:24:56 PM »
Another view of the motor. Is this a crack?

Offline Dave Hull

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Re: Engine going lean...or rich...or lean
« Reply #15 on: January 23, 2020, 06:31:12 PM »
You can check your case for leaks, if you suspect a problem. Cap off all the holes and then pressurize the case thru the spraybar using a syringe. It is easier to cap the exhaust if you have a muffler installed. Use a rubber cork (Home Depot hardware dept.) over the venturi and exhaust or your thumb, if you have lots of extra hands.

I would wash off the case with straight methanol first. Never hurts to have a clean engine. You can also rinse out the case before testing. Alcohol has very little viscosity and will go thru small holes easily. Once you pressurize it, submerge the entire engine in water and look for bubbles.

Be sure to oil up the engine thoroughly right after your testing or you will cause new problems.

I haven't seen a hole in an OS case ever--except on the engines I spread out over an acre of asphalt....

Good luck with your engine,

Dave

Online dave siegler

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Re: Engine going lean...or rich...or lean
« Reply #16 on: January 23, 2020, 06:46:37 PM »
loose mounting bolts + vibration.  Have seen this before. 

vibration may be causing the go lean problem. 
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Online Shorts,David

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Re: Engine going lean...or rich...or lean
« Reply #17 on: January 24, 2020, 01:57:46 PM »
loose mounting bolts + vibration.  Have seen this before. 

vibration may be causing the go lean problem.

This may be the case. But I did change a fuel line, reinstall the spray bar, changed the plug, pressure tested the tank and engine. But I noticed the engine screws had worked loose as well when I removed it. Well, it's all back together. I'll try again today (I hope) without the acetone in the fuel. Hopefully I can get it working to make through the pattern, I really like the way the airplane turns.

Online Dan McEntee

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Re: Engine going lean...or rich...or lean
« Reply #18 on: January 24, 2020, 09:09:04 PM »
  A quick and easy way to check that case for a crack where you suspect one, is to put some water in the case, enough to cover the area in question, then apply compressed air  to the outside of the area. If there is a leak of any kind, you will see bubbles. I kind of doubt it, though. If you had a leak there, you would see oil on the outside of the case after running. The piston coming down pressurizes the bottom of the case at that point and would be enough to push fuel out the crack. As mentioned, get it clean as possible to help with seeing what's going on.
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Online Shorts,David

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Re: Engine going lean...or rich...or lean
« Reply #19 on: January 24, 2020, 11:05:27 PM »
I ran it in the garage today. The big big problem is solved, now back to the fine tuning. Got a couple small surges in power while holding it. I think I'll try the smaller ventui next, and check the balance of my spinner. Didn't get to test it in the air though. I was a good dad instead.

Offline john e. holliday

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Re: Engine going lean...or rich...or lean
« Reply #20 on: January 25, 2020, 09:37:50 AM »
So what was the problem?   I know I forget to check mounting bolts once in a while. ???
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Re: Engine going lean...or rich...or lean
« Reply #21 on: January 25, 2020, 06:54:20 PM »
So what was the problem?   I know I forget to check mounting bolts once in a while. ???

I suppose the motor bolts may have been the problem. I also reset the spray bar and even put a little hi-temp silicone around the assembly to ensure there are no leaks. Changed the plug, and one fuel line. So, whatever it was that caused the problem is gone.

Today I did three flights. Needle setting held the entire time, but still had some sporadic yet small surges faster and slower. I think the fuel tank, which is a sullivan, may be leaking around the top. I'm going to reseal the tank and try again next week.

Then I'll try a smaller venturi if it isn't running great.

Good news was for the first time it held the needle and ran barely long enough to do the complete pattern. Yee Haw. Now I just need to slow down the turning. I'm thinking of untaping the hinges, but first I'm going to move the lines in to the closest position on the handle, but it turns very hard. Of course, that's a discussion for a different post.

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Re: Engine going lean...or rich...or lean
« Reply #22 on: January 25, 2020, 07:32:12 PM »
To slow the controls, leave the hinges taped. Narrow the line spacing and/or make the elevator horn longer by two or three hole spacing. You will see a big difference.
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Online Brett Buck

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Re: Engine going lean...or rich...or lean
« Reply #23 on: January 25, 2020, 07:40:58 PM »
I suppose the motor bolts may have been the problem. I also reset the spray bar and even p

Good news was for the first time it held the needle and ran barely long enough to do the complete pattern. Yee Haw. Now I just need to slow down the turning. I'm thinking of untaping the hinges

   Not recommended. Sealing the hinge lines is not intended to speed up the controls, but to make them, and other aspects of the trim, more consistent. It has a side effect of speeding up the controls in some circumstances, but is far more important than just that.

Quote
first I'm going to move the lines in to the closest position on the handle, but it turns very hard. Of course, that's a discussion for a different post.

   Narrow the line spacing to slow it down. You should also check that the CG is correct using the round loops test and observing the behavior when the engine quits in level flight.

   Brett

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Re: Engine going lean...or rich...or lean
« Reply #24 on: January 25, 2020, 08:42:18 PM »

Needle setting held the entire time, but still had some sporadic yet small surges faster and slower.


Hi David,

Were the fast and slow "surges" timed with going upwind and downwind?

Keith

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Re: Engine going lean...or rich...or lean
« Reply #25 on: January 26, 2020, 10:15:53 PM »
Hi David,

Were the fast and slow "surges" timed with going upwind and downwind?

Keith

I watched a video I shot of the best flight. The engine only has a big chug like it's about to die when I switch from outside to inside in the horizontal 8 and square 8. The other manuevers may have done it a bit but not noticable on the video. I'm guessing it has more to do with having a clunk tank.  But even when I held it in my hand after starting there were little tiny bumps. I think those might be from the tank not being sealed, maybe.

I think one reason it turns so hard may be because it's a little plane and I put a big plane flap horn in it. It also gave me three holes to choose from and I used the two outermost holes. I didn't like how soft my chizler was turning when I installed it so maybe I went overboard.

Online Dennis Toth

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Re: Engine going lean...or rich...or lean
« Reply #26 on: January 27, 2020, 07:07:31 AM »
Dave,
I didn't see what prop, fuel, plug you are using and how you are setting it to run (2-2+-2 or 4-2-4). Also what venturi diameter and NVA. This might help figure out the issue.

Best, DennisT

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Re: Engine going lean...or rich...or lean
« Reply #27 on: January 27, 2020, 09:19:10 AM »
Dave,
I didn't see what prop, fuel, plug you are using and how you are setting it to run (2-2+-2 or 4-2-4). Also what venturi diameter and NVA. This might help figure out the issue.

Best, DennisT

Hi Dennis,
I've run many props and haven't settled in on one yet. 10x3 apc was promising, but switched to a 9x5.5 thundertiger (like an apc) and used a 9x5 wood zinger for the other day's flights, which ran the best so far, although that's probably because I got rid of most of the leaks. So, I'll keep playing with the prop a bit. I tried several others back when the engine wouldn't hold a setting. MY laps were 5.00-5.1, so I don't want to go any faster, and I'd love a tad slower so maybe the 10x3 again.
Fuel is 10/22 powermaster.
Plug I can't tell, sorry. I've got a bunch and also had a sandwich baggie filled with new plugs I bought. It's from the sandwich baggie.
Venturi is smaller than 9/32 and bigger than 17/64.

There is also a chance I can get a sullivan 4oz cylinder tank in there and set it up with a standard pickup and venturi, but it will require cutting through one of the fuselage formers.

If I set it too rich I definitely won't make it through the pattern, So I ran a pretty straight 2 stroke on the rich side.

It's probably usable as it was last time out if I adjust the handle more. Possibly cut it open and move the elevator position on my flap horn. I need to beat my dad so it needs to be better than usable.  ;)
David
« Last Edit: January 27, 2020, 10:10:46 AM by Shorts,David »

Online Peter in Fairfax, VA

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Re: Engine going lean...or rich...or lean
« Reply #28 on: January 27, 2020, 11:08:11 AM »
I'd run 5% nitro instead of 10%, but that's just me.

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Re: Engine going lean...or rich...or lean
« Reply #29 on: January 27, 2020, 11:26:59 AM »
I'd run 5% nitro instead of 10%, but that's just me.

Hm..I hadn't thought of that. Thanks

Online Brett Buck

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Re: Engine going lean...or rich...or lean
« Reply #30 on: January 27, 2020, 11:58:46 AM »
Hi Dennis,
I've run many props and haven't settled in on one yet. 10x3 apc was promising, but switched to a 9x5.5 thundertiger (like an apc) and used a 9x5 wood zinger for the other day's flights, which ran the best so far, although that's probably because I got rid of most of the leaks. So, I'll keep playing with the prop a bit. I tried several others back when the engine wouldn't hold a setting. MY laps were 5.00-5.1, so I don't want to go any faster, and I'd love a tad slower so maybe the 10x3 again.
Fuel is 10/22 powermaster.
Plug I can't tell, sorry. I've got a bunch and also had a sandwich baggie filled with new plugs I bought. It's from the sandwich baggie.
Venturi is smaller than 9/32 and bigger than 17/64.

There is also a chance I can get a sullivan 4oz cylinder tank in there and set it up with a standard pickup and venturi, but it will require cutting through one of the fuselage formers.

If I set it too rich I definitely won't make it through the pattern, So I ran a pretty straight 2 stroke on the rich side.

It's probably usable as it was last time out if I adjust the handle more. Possibly cut it open and move the elevator position on my flap horn. I need to beat my dad so it needs to be better than usable.  ;)
David

   Look for something like a 10-4, and then speed the engine up enough to get a decent lap time, and the "burps" will likely go away with no other change. If it's the engine in the picture, it's an SF, not an FP, which should be plenty powerful enough to run that size prop.

  The only issue with 10% right now is that it's also cold, if you get it running right with 10% now, you will be up to 20% when it gets hot. Maybe that's OK, and I never even try low-nitro fuel any more, but something to think about. Power should not be a problem when it's 55-60 degrees and sea level. But you also want it to work when you are out in Davis in August and its 105.

   Brett

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Re: Engine going lean...or rich...or lean
« Reply #31 on: January 27, 2020, 12:47:13 PM »
If that unknown plug is a "cold" plug it could explain allot. If you have a hot plug you could compare how it looks.


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Re: Engine going lean...or rich...or lean
« Reply #32 on: January 27, 2020, 02:20:14 PM »
I've never put acetone in fuel.  It's a potent solvent.  I wonder if it's preventing the oil from filming on the metal?  That would make the engine run hot and ruin it in short order.

Dave

They are  zero  worries  about  using  acetone, this has been done  for  decades,  with  good results,  Acetone  does  NOT remain as  pure  acetone  when put into  fuel, it mixes with the  oils  and  alcohol fuel to  mix well.  It does  NOT stay as  pure acetone  that could  all of a  sudden go thru the engine, 

So  do not  worry about using  up to  2 ounces  per  gallon

Randy

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Re: Engine going lean...or rich...or lean
« Reply #33 on: January 27, 2020, 02:24:38 PM »
ST  Needle  assemblies  typically  need  to be  very tight  to keep the  needle  from moving, many times  people  run the needle  in too far  and  break the  orifice hole in the bottom part of the  valve ,  this is the  step  you see  when looking  thru, I have seen this  many dozens of  times.  It will  never needle  if this  has  happened
also  someone  said  clean it... YES.. so many times  hardened  oil is  a  big problem in the  valve

Randy

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Re: Engine going lean...or rich...or lean
« Reply #34 on: January 27, 2020, 02:24:55 PM »
   If it's the engine in the picture, it's an SF, not an FP, which should be plenty powerful enough to run that size prop.

  The only issue with 10% right now is that it's also cold, if you get it running right with 10% now, you will be up to 20% when it gets hot. Maybe that's OK, and I never even try low-nitro fuel any more, but something to think about. Power should not be a problem when it's 55-60 degrees and sea level. But you also want it to work when you are out in Davis in August and its 105.

   Brett

Hm...so apparently an SF says SF and an FP says FP. Who knew. HB~>  Not sure how I missed that.

Regarding nitro, it seems like the more I learn, the less I know! Thanks again for the education.



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Re: Engine going lean...or rich...or lean
« Reply #35 on: January 27, 2020, 02:27:16 PM »
If that unknown plug is a "cold" plug it could explain allot. If you have a hot plug you could compare how it looks.


Motorman 8)

I know I have some o.s. hot plugs. I'll do one change at a time and include that somewhere along the way.

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Re: Engine going lean...or rich...or lean
« Reply #36 on: January 27, 2020, 02:30:12 PM »
ST  Needle  assemblies  typically  need  to be  very tight  to keep the  needle  from moving, many times  people  run the needle  in too far  and  break the  orifice hole in the bottom part of the  valve ,  this is the  step  you see  when looking  thru, I have seen this  many dozens of  times.  It will  never needle  if this  has  happened
also  someone  said  clean it... YES.. so many times  hardened  oil is  a  big problem in the  valve

Randy

The needle looks good and the spray bar is nice and clean now. It was probably plugged up. I tried the acetone a few times but that was when something else was wrong. Once I get it dialed in for speed and prop, if I'm short on time I'll try it again.

Offline RandySmith

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Re: Engine going lean...or rich...or lean
« Reply #37 on: January 27, 2020, 02:32:55 PM »
what  color is  the  needle ?  that is  not  a  ST  NVA,  it is  a  PA  Needle assembly,  if it has  had  a  ST  needle  in it, then it is  ruined

Randy

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Re: Engine going lean...or rich...or lean
« Reply #38 on: January 27, 2020, 03:41:47 PM »
what  color is  the  needle ?  that is  not  a  ST  NVA,  it is  a  PA  Needle assembly,  if it has  had  a  ST  needle  in it, then it is  ruined

Randy

Oh. Again, shows what I know. It's a silver needle.  I assume it's the correct needle because it seems to work very well now that I cleaned stuff out. I wonder if my st .51 has the wrong needle because it's always been so finicky and changes settings in the air. I'll take a picture if that's not specific enough.

David

Offline RandySmith

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Re: Engine going lean...or rich...or lean
« Reply #39 on: January 27, 2020, 09:49:02 PM »
David

The  PA  needle is  stainless steel, and  it is  thicker than the  ST Needle,  The  bar on the PA  has a rounded  end where the needle enters, and  holds a  teflon  seal inside of it, The  super tiger  has a squared off closer and is  flat instead of rounded.  many of the  ST needles  are  black, but not all of them, but ALL  of them are smaller diameter  that the  PAs

Also make sure  your  ball bearings in that engine are  good, and  that the  rear bearings is smooth, and  turns, and  does not spin on the  crank

regards
Randy

Online Peter in Fairfax, VA

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Re: Engine going lean...or rich...or lean
« Reply #40 on: January 27, 2020, 10:05:25 PM »
The NVA looks like a PA, based on the rounded needle friction adjustment nut in the picture, coupled with the silver color report.  Only a very few ST needles are silver, like the Harry Higley long one.

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Re: Engine going lean...or rich...or lean
« Reply #41 on: February 03, 2020, 06:42:49 PM »
Can anyone explain what would happen if my venturi is too big? I haven't tried the hot plug yet. But would there be a pronounced problem during specific maneuvers, such as square 8s when I go from the outside square back to the inside square? Also, between the second and third loops of the clover I have a major power failure. The other culprit is my clunk tank, but I may have found an odd Brodak tank that might fit.

Second question - if the tank says standard vent (this is the Brodak I may try) can I still run a uniflow line to it or does it need to be hooked up to muffler pressure?

Motor is running very good now, holds needle settings, works with multiple props, etc.

Online Dennis Toth

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Re: Engine going lean...or rich...or lean
« Reply #42 on: February 04, 2020, 02:06:54 PM »
Dave,
If the venture is too large the engine will go lean very soon after the nose goes up and will likely not come back to a 4 cycle until level flight or not at all (run-a-way). The large venture will present difficulty in starting by hand, if too big will not draw fuel without a high pressure fuel system (read that as crankcase pressure or bladder). If only a little big will be touchy to get a consistent needle for the 4-2-4 and jump to the 2 to fast. Also fuel consumption will be high.

Conventional venting means the tank has two vents located on the inboard side of the tank generally one or the other will be out of the fuel and the tank will run rich at the start and lean at the end. Some engines work well with this older style tank, they seem to work best if they are taller and narrower so the fuel doesn't move horizontally as much as the tank draws down. 4 stroke seem to like them as well as the Brett Buck setup for the OS FP20.  You can attach muffler or even crankcase pressure (if the engine is so equipped) to one of the vents. They used this in combat ships back in the 70's ish. It works but the engine has to be setup to use it and it has not been used to much for stunt. Best to use tanks labeled UNIFLOW. With the Uniflow, you can install the muffler pressure to the uniflow line. Some engines like the muffler pressure other (like the Fox 35) seem to like open uniflow vents, you need to try it and see what works best for your engine/fuel/prop/plug.

Since the engine is running pretty good now you have a baseline. If you want to experiment change one thing at a time to see how it reacts to the change.

Best,   DennisT

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Re: Engine going lean...or rich...or lean
« Reply #43 on: February 04, 2020, 02:34:41 PM »
Can anyone explain what would happen if my venturi is too big? I haven't tried the hot plug yet. But would there be a pronounced problem during specific maneuvers, such as square 8s when I go from the outside square back to the inside square? Also, between the second and third loops of the clover I have a major power failure.

  If it just does it in those place, and no others, then that would be an improbable effect of excessively large venturi. Your descriptions sounds like misfiring, from not using a hot plug, or the same sort of internal ballistics issue that happens to a Fox, and a lot of high-performance RC engines when run too slow. It's a matter of the gas flow being so slow that it impinges on the case/liner, etc, or the charge winds up in the wrong place in the combustion chamber due to acceleration of maneuvering.

   Potential solutions include:

hot plug (Thunderbolt RC or Thunderbolt Big Bore/4-Cycle, Glow Devil 300, Enya #3)
Run faster (less pitch and/or diameter, more rpm for the same lap speed)
engine modification (not recommended)

  Of course, I haven't seen or heard it run, it could be something else.
   Brett
« Last Edit: February 04, 2020, 03:14:05 PM by Brett Buck »

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Re: Engine going lean...or rich...or lean
« Reply #44 on: February 05, 2020, 07:02:51 PM »
  If it just does it in those place, and no others, then that would be an improbable effect of excessively large venturi. Your descriptions sounds like misfiring, from not using a hot plug, or the same sort of internal ballistics issue that happens to a Fox, and a lot of high-performance RC engines when run too slow. It's a matter of the gas flow being so slow that it impinges on the case/liner, etc, or the charge winds up in the wrong place in the combustion chamber due to acceleration of maneuvering.

   Potential solutions include:

hot plug (Thunderbolt RC or Thunderbolt Big Bore/4-Cycle, Glow Devil 300, Enya #3)
Run faster (less pitch and/or diameter, more rpm for the same lap speed)
engine modification (not recommended)

  Of course, I haven't seen or heard it run, it could be something else.
   Brett

Okay, winding down on the fiddling around. Tried the hot plug and didn't see any difference. Might have already been a hot plug but was in a mystery bag. Now it's a hot plug. Next, I tried putting a piece of silk over the venturi to simulate a restricted flow. It was interesting, had to lean it quite a bit, but still ran about the same over all. I suppose I used less fuel.
Finally I went back to the 9x5 zinger wood prop I had on it the other day and it ran much better again. It does need to run at a constant 2 cycle the whole flight. It's the SF and that's how we always ran them in the r/c planes so I guess it's alright. Like I said, held the same speed the whole time, so?? Works for now. Also was a good speed for flying the pattern, so I guess I'll stick with that prop for a while. Still has a big chug between the outside coming back to the inside, but it would work if I'm not trying to beat anybody. Which of course I am trying to do.

I'm going to see if that teflon bit is in the needle assembly that Randy talked about. Then I'll probably put in the standard vent tank I have to see what happens. I'm still not too confident in sullivan tanks with clunks for CL. Maybe the clunk isn't flipping across the tank at the same speed as the fuel. Actually, that might be exactly it.

I'll start work on trimming the plane out better (it flies like something out of the early 50's--which of course it is). If I can't smooth it out I'l just bring it to the first event of the year and get some help--or, I also have a brand new Enya .29 III. I could see if the bolts line up but I kind of wanted to fly this thing in stunt .25 at our local contest.

Thanks for all the ideas you've given. I'll give an update after swapping the tank.

Online Brett Buck

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Re: Engine going lean...or rich...or lean
« Reply #45 on: February 05, 2020, 08:49:14 PM »
Finally I went back to the 9x5 zinger wood prop I had on it the other day and it ran much better again. It does need to run at a constant 2 cycle the whole flight. It's the SF and that's how we always ran them in the r/c planes so I guess it's alright. Like I said, held the same speed the whole time, so?? Works for now. Also was a good speed for flying the pattern, so I guess I'll stick with that prop for a while.\

   That's still a *lot* of pitch for this type of engine. And I think, if you check, that while it may be running in a 2-stroke all the time (like most stunt engines do) you will find it is not running at a "constant speed". It's running faster and slower in a 2-stroke, just like a piped 40VF when it was winning the NATS 5 times.

     Just about every Stunt 25 contest ever held was won with 20FP or "new" 25LA running a 9-4 APC prop, in a consistent 2-stroke. I know because I have won almost all of them, and the only times I didn't, the winner was a 25LA running similarly. A 25SF should be much more powerful, in general (although I don't know your choke area) and should handle even more diameter and less pitch.

    The key to getting good performance on these engines it to run as little pitch as possible, and adjust the diameter to make sure that at a decent lap speed, with the engine running in a medium 2-stroke in level flight, leaning out to a strong 2 in the maneuvers. Too fast, reduce the diameter, too slow(unlikely), increase the diameter.

  Running  5.5-6-6.5-7" of pitch in a 4-stroke has been mostly a dead end since about 1988, you give up too much performance aside from very special circumstances.

    Brett

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Re: Engine going lean...or rich...or lean
« Reply #46 on: February 14, 2020, 08:28:37 PM »
Grrrrr. Problem 1. I put a new tank in and still have a small fuel supply problem switching from inverted back upright, but...I think, or at least I hope, my needle valve was loose and is the reason it went lean. I tightened it a bit more. Took out the first two chapters of the Paul Walker trim chart and never got to it. Problem 2. MOW THE GRASS! I ripped my gear out. Should have known better with how long it was.
Hopefully try again with the needle tighter tomorrow. On a different field in town. 
 

Offline Balsa Butcher

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Re: Engine going lean...or rich...or lean
« Reply #47 on: February 14, 2020, 10:42:51 PM »
...or you could make the long trek to Woodland and meet me at the field where I'll be Saturday morning. Grass is low and runway is in good shape.  8)
Pete Cunha
Sacramento CA.
AMA 57499

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Re: Engine going lean...or rich...or lean
« Reply #48 on: February 15, 2020, 11:43:26 AM »
...or you could make the long trek to Woodland and meet me at the field where I'll be Saturday morning. Grass is low and runway is in good shape.  8)

I'd LOVE to Pete. I was looking at Monday but it's very windy. I usually get about a two hour block of time, sometimes less. Therefore I'm stuck with two soccer fields in town. If I plan it out better I could probably make a Saturday happen though, like I do for contests. I'd probably have this plane all dialed in by now if I did.

Online Dennis Nunes

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Re: Engine going lean...or rich...or lean
« Reply #49 on: February 15, 2020, 05:38:56 PM »
Thanks Pete for being there today. I really enjoyed our flying session. Perfect temperature and extremely light wind.

Too bad you couldn't be there David. I even showed up with my surgically repair shoulder! You missed out on a good one.


Dennis
If at first you don't succeed ---- let someone else try it!  ;)

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