Fouled Spark Plugs

[TomG628]

Hi,
Just started up the 172 for its first flight, but while taxiing it started making a knocking sound. I went back to the gate and went to the maintenance hanger. (It said I had badly fouled plugs. It only idled for 5 minutes before taxiing and I leaned the engine.)
I changed the plugs (default ones) and even heard the wrench turn. The notes still showed fouled plugs. I repeated the startup (autostart) and the same knock sound. Back to change plugs again and it still says fouled plugs. How do you get a successful change and why do the plugs foul so easily? Thanks. Tom

[Oracle427]

Not sure on why the repair option isn't cleaning the plugs for you. Make sure you lean aggressively and by that I mean close to halfway out. Also keep the engine at around 800 to 1000 room for idle or you will foul.

Someone else may have thoughts on the repair issue.

[ClipperLuna]

You can clean them yourself by running the engine up to 2000 rpm, lean for a slight rpm drop, hold it there for 20 seconds, and check again. Failing that, turning damage off, then back on should clean them. A third option is to perform a complete overhaul.

[Lewis - A2A]

Ideally you will want to clean them yourself as noted by giving the engine a good run-up.

thanks,
Lewis

[Matthew Flies]

Can I get some help? I always get fouled spark plugs. On Taxi i Lean to 25-30% below that it will cut off. On Magneto Check i get some heavy drops. I only have 100% Mixture in Start and Climb. In Cruise it is something around 50%. When I have landet I turn Mixture imediatley to 30% Mix.

What I am doing wrong?

[speedy70]

Change to wire plugs.

They don't oil up as much

[AKar]

On Magneto Check i get some heavy drops. I only have 100% Mixture in Start and Climb.

Not sure I read you right but you do the runup and drop tests at leaned mixture? If so, bigger drops are expected. Nothing wrong in principle of doing the drops at leaned mixture, though you must find out the applicable values and limits by other means as those in manuals/checklists assume full rich mixture.

-Esa

[Matthew Flies]

Runup check is with 100% Mixture. It one the right Mag within 50-100RPM -->OK. Then I switch to Both -->1800 and then back to the left Mag and get drops from 1800-1500RPM. Menu says: some fouled spark Plugs.

Why should I use the wire plugs? I though the solid plugs are much better to avoid fouling!?

[Lewis - A2A]

Fine wire are harder to foul, it sounds like you are leaning too much and running too low RPM when on the ground, I tend to lean a little for the ground but its dependent on conditions and ear, I'd certainly never have a set mixture to default too when flying. As your engine wears too you might find it leaning slightly differently, so always use the ear.

Whilst you will ideally want to lean on the ground don't feel you have too all the time and don't feel you have to be aggressive with it when you do. I'd go easy at the beginning until you get the hang of it. Use your ear to help and give her a damn good blast to clear any fouling.

thanks,
Lewis

[Matthew Flies]

I now use finde wire plugs, thx for the hint.

Do you really think that I leaned to much? As I said: on Ground 1000RPM with about 30% Mixture and Solid Plugs. How far do you lean? You can see the % if you are hovering with the Mouse Key over the Lean-Slider.

[AKar]

Runup check is with 100% Mixture. It one the right Mag within 50-100RPM -->OK. Then I switch to Both -->1800 and then back to the left Mag and get drops from 1800-1500RPM. Menu says: some fouled spark Plugs.

Roger that. If you switched to fine wire plugs, that probably makes the problem go away, but regarding the leaning on ground, I tend to lean enough that I often need to put in some mixture when I add power. I don't know about percents but you can clearly hear when the engine starts to run poorly at ~1200 rpm or so, and then enrich some. Leaning aggressively enough also helps me to avoid forgetting the mixture to lean if I do a quick rolling take off for example. The massive plugs are quite easy to foul in the simulation (I recall this is modeled after experiences in Scott's Comanche which did this easily too with massive plugs).


-Esa