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Author Topic: Tendency to Go Rich Declines After Break-in?  (Read 2113 times)

Offline Peter in Fairfax, VA

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Tendency to Go Rich Declines After Break-in?
« on: March 21, 2021, 06:18:56 AM »
So my OS SF 46 had a tendency to go rich on outsides, even after adjusting tank heights.  However, after running a quart of fuel through it, the tendency declined.  The engine is new to me and had unknown time, possibly never used previously.

Is it normal that the tendency would go away after break-in?

thanks,

Peter

Offline Peter in Fairfax, VA

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Re: Tendency to Go Rich Declines After Break-in?
« Reply #1 on: March 21, 2021, 03:04:07 PM »
It's a profile.

Photo of the setup:

Offline Brett Buck

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Re: Tendency to Go Rich Declines After Break-in?
« Reply #2 on: March 21, 2021, 03:18:39 PM »
So my OS SF 46 had a tendency to go rich on outsides, even after adjusting tank heights.  However, after running a quart of fuel through it, the tendency declined.  The engine is new to me and had unknown time, possibly never used previously.

Is it normal that the tendency would go away after break-in?

It is extremely typical for a 20FP to go rich on outsides towards the ends of a flight when new, and that goes away after 20-30 flights. Seems to have something to do with the crankcase temperatures, which when new, tends to be *boiling hot* on the first few runs, and then getting cooler and cooler over about that many flights.

   Most engines, even good ones, run differently after whatever break-in you do, +maybe 25-50 flights. So you can grind away on them for hours on the ground, and that still won't be enough.

     Brett

Offline Dan McEntee

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Re: Tendency to Go Rich Declines After Break-in?
« Reply #3 on: March 21, 2021, 05:22:03 PM »
It's a profile.

Photo of the setup:

   Turn those eye screws sideways, and move the tank up some more. It's hard to tell from the photo because of the angle, that if you are indeed nigh enough. I like to start out engines like OS engine with the center of the tank about even with the middle of the bypass port, or about 3/8" or so above the centerline of the engine at a minimum. I'm thinking that you still are a little low in the tank. Move it about 1/16" at a time and test fly.
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   Dan McEntee
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Offline Peter in Fairfax, VA

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Re: Tendency to Go Rich Declines After Break-in?
« Reply #4 on: March 21, 2021, 07:26:39 PM »
Brett,

Thanks for supporting the theory that engines may run better after break-in.

Dan,

You might be right that even higher would help.  Current it's about 1/4", but could be 3/8".  Though lap times did seem even upright vs inverted.

Peter

Offline Peter in Fairfax, VA

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Re: Tendency to Go Rich Declines After Break-in?
« Reply #5 on: March 21, 2021, 07:28:01 PM »
Good flying weather.

Offline Dan McEntee

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Re: Tendency to Go Rich Declines After Break-in?
« Reply #6 on: March 21, 2021, 10:33:16 PM »
Brett,

Thanks for supporting the theory that engines may run better after break-in.

Dan,

You might be right that even higher would help.  Current it's about 1/4", but could be 3/8".  Though lap times did seem even upright vs inverted.

Peter

  It might only take a fuzz of a move to get what you need. Move it a little at a time until it goes the other way, then move it back to the last place you had it and fly it a while. From the new photo you posted, I would think that is high enough also, but I don't run those kind of OS engines. Check your plug also, just for grins and see how it looks. If it's cruddy, replace it. Or if the RPM drops when you take the battery of some times, replace it. Obe change at a time so you know what you "fixed."
   Type at you later,
    Dan McEntee
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Offline Peter in Fairfax, VA

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Re: Tendency to Go Rich Declines After Break-in?
« Reply #7 on: March 22, 2021, 07:34:32 AM »
Lauri,

The fuel/oil accumulation in the crankcase is significant.  I've seen video of model engines with clear backplates.  When they run, the degree of accumulation is much higher than I would have thought.

As far as what I changed, I think the Fox R/C Long plug is working better than the K&B R/C Long.  Though I did actually increase the prop load, without any effect noticed.

Peter

Offline Dan McEntee

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Re: Tendency to Go Rich Declines After Break-in?
« Reply #8 on: March 22, 2021, 08:10:43 AM »
Lauri,

The fuel/oil accumulation in the crankcase is significant.  I've seen video of model engines with clear backplates.  When they run, the degree of accumulation is much higher than I would have thought.

As far as what I changed, I think the Fox R/C Long plug is working better than the K&B R/C Long.  Though I did actually increase the prop load, without any effect noticed.

Peter

     I didn't notice the plug in the photos, but that may be part of the issue also if it's a Fox. I think you and I have communicated before that you have a pretty good supply of vintage Fox plugs that seem to run OK, but I would still try another brand. like the K&B that you have, or Glow Devil R/C Long  or the Thunderbolt brand, R/C Long or Four Stroke plug. While Fox was still in business and selling plugs, I had a flying buddy that bought 6 from the local hobby shop, and all six last exactly one flight!!  If I had not been helping him that day, I might not have believed it and thought he was doing something wrong, but was the plugs! That has just put me completely off that brand, and several other instances where simply changing out the Fox plug for anything else cured a problem.  At the time some one offered up the explanation that they tried a cheaper brand of some kind of "idium" wire for filaments that just didn't work well.  I would be curious to know if that helps.
    Type at you later,
    Dan McEntee
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Offline Brett Buck

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Re: Tendency to Go Rich Declines After Break-in?
« Reply #9 on: March 22, 2021, 10:53:06 AM »
  Though I did actually increase the prop load, without any effect noticed.

    "Increase the prop load" how?  The general rule is that you want them run faster, and given that you want to hold the speed in check, that usually means that you have to reduce the diameter. The inside/outside problem is usually a matter of low gas velocity/internal ballistics, and we are running them at a tiny fraction of their capability. Anything you can do to get a less efficient prop increases the shaft power while maintaining the same airspeed/horsepower applied to the airframe (which are one and the same) is usually to the good. It also sucks fuel better - although I see you have an aftermarket venturi, which will make it more likely to run OK at low revs which exacerbates the inside/outside problem. Most of the successful 46SF runners around here used old 46VF props, like a 12-3.75 2-blades or 11.5-4 3-blades.

     Note also that as far as flying goes, what is a "increased prop load" on the ground is not necessarily more in the air. A 12-5 is much more load than a 12-4  *on the ground* but not necessarily in the air. You might have to spin it 9500 in the air with a 12-5 and maybe 11,200 in the air with the 12-4, the drag on the blade is about the same, and you get a lot more power at 11,200 than 9500.

    Brett

p.s. by the way, beware those DubBro filters. The black part is just pressed into the aluminum body, and they are notorious for leaking around that joint or just falling apart completely. I used them in the ancient past, but to be sure, you have to push the insert as far in as it can go (without blocking the outlet), peen the aluminum over it, then fill the bottom with epoxy.

« Last Edit: March 22, 2021, 09:32:03 PM by Brett Buck »

Offline Air Ministry .

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Re: Tendency to Go Rich Declines After Break-in?
« Reply #10 on: March 22, 2021, 07:26:07 PM »
Be intresting to see the spraybar further out. With the side mount .

The Clones only have the cinch bar hole, so almost mandatory .

With the whole fuel load inside of the spraybar posn. , Tends to get solid 4 stroke level , and full lean dead overhead . Which works out pretty well . ticularly if its blowing .

Throwing the RC carb on, to check out the theory , or making a custom fit one would do to see . Can get variations on your trouble with varying muffler .
The Super Tigre mufflers almost fit , if youve any fancy ones .

Offline BillP

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Re: Tendency to Go Rich Declines After Break-in?
« Reply #11 on: March 23, 2021, 07:14:40 AM »
It looks like you have a cap on the overflow.  Have you tried flying without the cap? I had a going rich problem on a full fuse and uniflo with upright McCoy 40.  Removing the cap solved it.
Bill P.

Offline Dan McEntee

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Re: Tendency to Go Rich Declines After Break-in?
« Reply #12 on: March 23, 2021, 07:59:02 AM »
   Removing the cap creates "chimney effect"  as air flows over the over flow tube and can affect how the uniflow tube functions. That is why you put a cap on it, and also prevents any syphoning  that may occur when the tank is full.  I would replace that plastic cap with a piece of fuel like that is plugged with a BB or some other object to create a better seal at that point. Those plastic caps don't really fit that well. Maybe even add a pick up tube in the inboard side of the fuselage and connect it to the tank tube with a length of fuel line.
   Type at you later,
    Dan McEntee
AMA 28784
EAA  1038824
AMA 480405 (American Motorcyclist Association)


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