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

biscuit112 07-09-2020 08:39 PM

Stank Idle
 
I have been working on my IO-320's idle and cooling for almost a year now. I am a mechanic and pilot but 99% of my PIC time is in gliders... The engine is in a Sam James plenum and cowl. Dear internet come and collect my soul with the judgements of the divine aviation elders (know it alls). Can someone tell me if this idle is to be expected from a bendix FI in a james cowl and plenum. I moved my boost pump from the firewall to the cabin(previous owner's goof). The lines from the servo to the flow divider are as short as I can get them to be on a backdraft intake. The fuel lines out of the flow divider are wrapped elevated as high as possible. .022 restrictors in the injectors. I have a lightweight wooden prop. My idle starts out perfect until 170-200 degrees oil temp comes around. The CHTs and EGTs are uniform and never too hot for all cylinders. The boost pump doesn't change anything. 1300 to max RPM feels stable and clean. I am actually all out of things to do to it and I feel like its the equivalent of race car parts on race car, it just will not idle without lumping. Here is a video. https://www.youtube.com/watch?v=TgzAeOGVeV0

Kyle Boatright 07-09-2020 08:45 PM

Have you checked for induction leaks?

biscuit112 07-09-2020 08:51 PM

Yes I have, all new gaskets. Wouldn't an induction leak show up at all operating temperatures as well? Can they just show up when hot?

scsmith 07-09-2020 11:45 PM

Quote:

Originally Posted by biscuit112 (Post 1445158)
Yes I have, all new gaskets. Wouldn't an induction leak show up at all operating temperatures as well? Can they just show up when hot?

Perhaps, from thermal expansion. To truly eliminate any induction leaks, use Ross Farnham's SDS induction seals. Heaven.

It may also be that with a light prop, it just will never idle very smoothly.

Have you tried leaning it to within an inch of its life when it is warmed up?

rv8ch 07-10-2020 12:17 AM

Ignition?
 
What kind of ignition are you running? Any recent changes or overhauls to any parts the ignition system? Wires? Plugs? Everything connected perfectly? Any change if you switch ignitions L/R?

RV Jerry 07-10-2020 08:48 AM

Something you might check is if you have a primer make sure it?s not leaking

lr172 07-10-2020 08:58 AM

Doesn't look like a classic rough idle due to hot/boiling fuel. Looks more like a miss. Have you checked your plugs, including a resistance check? How long has it been since your mags were serviced (if the egap is not adjusted, the spark gets weaker and weaker over time and if you have your idle mixture adjusted incorrectly, it can be hard to light with a weak spark). Notice that 80% of the time it is running smooth, then it hiccups and recovers. That is not a classic rough idle.

I have a rough idle on my 6 when it is hot, due to injectors in the top ports. It is consistently rough and not intermittent like yours.

biscuit112 07-10-2020 12:45 PM

Hello everyone and thank you for your responses. I have thought about the thermal expansion thing. There is ONE gasket I have not replaced I will try it. I have leaned the pooh out of it when it starts to lump. It just ends up making it to the Idle Cutoff. The engine itself has 30+ hours on it the magnetos were rebuild in 2010-13 or so. Again 30 hours. I have drooled over the very logical and proven design of those SDS seals. (mmmmm tasty) I did end up working on a flange to a inlet tube, but even after that I cant say the hot engine performance changed. Lr172, I'm glad to see you chimed up. I read some of your posts and complaints with the hot idle dysfunction. My injectors are on the top ports. Thank you for saying it's not normal because I have no experience or reference for what is.

pjc 07-10-2020 09:16 PM

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

lr172 07-10-2020 10:39 PM

Quote:

Originally Posted by biscuit112 (Post 1445295)
Hello everyone and thank you for your responses. I have thought about the thermal expansion thing. There is ONE gasket I have not replaced I will try it. I have leaned the pooh out of it when it starts to lump. It just ends up making it to the Idle Cutoff. The engine itself has 30+ hours on it the magnetos were rebuild in 2010-13 or so. Again 30 hours. I have drooled over the very logical and proven design of those SDS seals. (mmmmm tasty) I did end up working on a flange to a inlet tube, but even after that I cant say the hot engine performance changed. Lr172, I'm glad to see you chimed up. I read some of your posts and complaints with the hot idle dysfunction. My injectors are on the top ports. Thank you for saying it's not normal because I have no experience or reference for what is.

I recommend the 4 psi spring for your spider. It makes a noticeable difference idling in hot weather. You can get them from Don at AFP. I also put reflective tape on the injector lines.

Final fix was to more actively use a fuel return circuit starting at th servo. This was for side port injectors which are much worse than top injectors

Goof luck,

Larry


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