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-   -   Stank Idle (https://vansairforce.net/community/showthread.php?t=184493)

lr172 07-10-2020 10:41 PM

Quote:

Originally Posted by pjc (Post 1445377)
FWIW: I have a carbureted O-320 E2D with a wood prop and slick mags that idles much more smoothly (and happily at 750 rpm when warmed up) than your video.

If you are getting ~50 rpm rise on shutdown the idle mixture should be ok, so I too would be looking at ignition items (fouled plugs, bad harness, worn mag cam affecting dwell, etc). If none of those I’d start to worry about cam/lifters/valves but have no idea why these would be masked at low engine temps.

Good luck!
Peter

Check the plugs. Ineffectiveness of leaning can point to both ignition and boiling fuel in the injector lines. Your engine doesn’t sound like mine does when hot. My ear still hears a miss. Mine does much better at 1000 rpm. At 750, it is pretty consistently rough when the cowl is heat soaked . Yours runs nicely but occasionally falls off then re recovers. A pretty classic misfire scenario.

If it is boiling fuel, iwould expect it to be happening before the servo, based upon your symptoms.

biscuit112 07-10-2020 11:36 PM

It's getting test flown this morning. I have directed cooling air from an extra NACA duct to the fuel servo. i will talk to don about a 4lb spring next week. i stuck a thermocouple into my cowl yesterday and it read 140degress after 5 minutes of idle. When i would raise the idle to 1100+ you could see the temperature drop. The exhaust flows right next to the fuel servos since this is a IO-320-B1A from a twin Comanche. I will say its less than ideal.

Capflyer 07-11-2020 04:35 AM

Magnetos
 
You mentioned your magnetos were rebuilt in the 2010-2013 time period. Slicks? There was a an issue with the distributor gears and Champion issued a SB and they need to be replaced. The contact on it would bend causing the timing to be way off. This happened to us and resulted in a rough idling and running engine. It's pretty obvious when you look at it, the brass contact will be bent over to one side. Since yours were rebuilt you will need to open them up and do a visual, magneto serial number probably will not be an indicator.

Link to the SB https://www.championaerospace.com/as...A_20181112.pdf

lr172 07-11-2020 07:54 AM

Quote:

Originally Posted by biscuit112 (Post 1445388)
The exhaust flows right next to the fuel servos since this is a IO-320-B1A from a twin Comanche. I will say its less than ideal.

Definitely address that. I had a similar issue on my 320-B1A and made simple aluminum heat shields that clamp on to the exh pipe. In my case, exh was too close to the fuel line for comfort.

Larry

esco 07-11-2020 09:38 AM

Plug check complete?
 
How do all your plugs look?

One of the easiest checks to make, needs few tools, minimally invasive...
and you also confirm that every plug wire is securely affixed...

snopercod 07-12-2020 08:34 AM

Quote:

Originally Posted by scsmith (Post 1445174)
It may also be that with a light prop, it just will never idle very smoothly.

Nah. My O-290-D2 with a wooden prop will idle smoothly down to 500 RPM. I did have a rough running problem on hot days, though. It turned out to be the hot oil in the sump was heat soaking the carburetor bolted onto the bottom. Apparently, the heat was boiling the fuel in the bowl and causing the engine to run rich to the point where it would actually die on me. I solved that problem by adding a 1/16" phenolic gasket as a thermal break between the sump and the carb. I don't think this fix would apply to an injected engine.

lr172 07-12-2020 09:03 AM

Quote:

Originally Posted by snopercod (Post 1445542)
Nah. My O-290-D2 with a wooden prop will idle smoothly down to 500 RPM. I did have a rough running problem on hot days, though. It turned out to be the hot oil in the sump was heat soaking the carburetor bolted onto the bottom. Apparently, the heat was boiling the fuel in the bowl and causing the engine to run rich to the point where it would actually die on me. I solved that problem by adding a 1/16" phenolic gasket as a thermal break between the sump and the carb. I don't think this fix would apply to an injected engine.

It does. I feel that the servo is a very good source of picking up heat from the sump and transferring it ti the fuel. I can hear the fuel boiling down by the servo after shut down in the summerin my 6. Don’t hear it in the 10, where I have a phenolic spacer.. the lower the fuel flow, the more heat it picks up.

biscuit112 07-12-2020 11:09 PM

Where does one acquire these spacers? Did you make them yourself LR172?

lr172 07-13-2020 07:38 AM

Quote:

Originally Posted by biscuit112 (Post 1445785)
Where does one acquire these spacers? Did you make them yourself LR172?

Yes. I got the material from mcmaster carr. I forget which material I used. They have a variety of fabric reinforced materials. Just get one with the lowest heat transfer rate and with a >= 200* temp limit. It is not difficult to cut them to fit. You can use a spare gasket as a template.

I would not go any thicker than 1/8 or 3/16, as you will be moving the FAB down and will have alignment issues with the cowl. If you plan to cut and re-glass the FAB, I would go with a 1/4" You will need two gaskets to reinstall; one on each side of the spacer. Even a thin one will make a difference, as you break the metal on metal conduction (aluminum is very efficient at heat tansfer).

Larry

biscuit112 07-22-2020 09:08 PM

UPDATE
 
Soo. I installed a spacer from my rsa5 to the intake/oil sump that seemed to delay when the lumpy idle would occur. I also installed a mechanical fuel pump cooling shroud that didn't appear to make any difference at all. It would still reach a point to where the idle would bungle about. Seemed to be at about 180 instead of 160-170. THE FIX WAS, a 4 psi spring in the flow divider. The Bendix flow divider has either a 2 psi spring or a 4 psi spring. The spring effectively raises the boiling point of the fuel in the stainless lines to the injectors. There is also a lycoming service instruction for rough idles when hot. Instruction 1489C can be found here. https://www.lycoming.com/sites/defau...%20%281%29.pdf The spring part number is Precision P/N 2577011. For grins if anyone wants the phenolic spacer, it is Superior part # 73161. I have been battling this issue for what seems like a year. The battle has been won. I am finally comfortable with my plane.


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