Aft cylinders vs forward cylinders (spark plug condition)

[Daveembry]

https://forum.cubcrafters.com/showth...ll=1#post23102

Neal,

in this post (link above) I talk about setting up the engine idle and mixture settings. You are correct about the rpm rising as you lean for engine shutdown. You use this to set the mixture at the correct idle speed. Here is the part about that:

“Before the first flight, check the mixture and idle speed. The document goes over it in detail but it's important to note that you have to first set the mixture correctly before setting the idle because small mixture changes will change that as well.

650-750 rpm is the correct idle speed and you should just use the throttle control to get it there and then pull the mixture back slowly and note the total rise in rpms before it shuts off. Anything more than 25-50 rpms and it's rich and the big knob on the fuel servo gets moved UP (clockwise) to lean it. You just have to keep adjusting and testing it until you have it right. Be sure and do this with a warm engine as well. You will note the set-up sheet says idle at 600. That was what I was told by the factory guy originally but later checking the engine documents I noted it should be a little higher and I agree. I'll ask CC to change that.

Once you have the mixture set, then just turn the idle screw (the big screw that stops the movement of the arm there on the servo) until you have the 650-750 or so rpm idle speed.”

After the engine is broken in, i always run very lean while taxiing. I lean it until it stutters and then enriched just slightly. It’s so lean that should I forget to enriched before run up or takeoff, the engine will stutter bad enough that you will immediately realize you forgot to enrichen (checklist?). Immediately after landing I do the same until shutdown to prevent too rich a mixture at low rpm which could foul a plug.

Ground time was short, guessing 5 minutes. Just curious why all plugs don't look the same.

It will be interesting to see the plugs after the next 100 hours as this first cycle consisted of break-in AND my learning to lean, lean while taxiing, etc. I learned during this condition inspection about leaning at shutdown watching the RPM rise approx 50 RPM before quitting. That gives me a better feel of leaning better while taxiing such as lean until the RPM starts to rise as a reference point.

[hawgdrvr]

Great info, thanks Dave. Lot's to learn and share, much appreciated.

[Andy]

Just curious why all plugs don't look the same.

They don't look the same because the combustion conditions in the cylinders were different. You really should plot the data I suggested to see what's happening in your engine.

In case I was not clear earlier - the condition of the plugs when removed at condition inspection is not likely to give you any useful information about how the engine was running 50 hours ago.

[Andy]

I lean my PA-28 aggressively for taxi. If I don't I'll likely foul a plug. I seldom lean the FX-3 for taxi and have never fouled a plug.

Take a look at fuel flow while leaning for taxi. Do you see any significant reduction in fuel flow between full rich and the leanest that can be set and keep smooth running? When I have tried it I saw no significant difference.

I concluded that the fuel servo does a much better job of setting low power mixture than a carb.

I prefer a lower idle stop setting than 650. I just don't idle the engine on the idle stop. Having the lowest possible power output can be an advantage when landing on short strips.

(promoting discussion or being argumentative - depends on your perspective)

[hawgdrvr]

I noticed a problem at idle (roughness) at delivery while at Hood River. I consulted another cub owner and he educated me on leaning on the ground so I've been doing it ever since, but not aggressively as I had no indication (known) as to how far to lean it. Now that I know of the RPM rise I have a reference to look for. I was warned about fouling plugs at idle early on, I'm guessing you (Andy) may have adjusted your idle mixture whereas mine requires it done via the mixture setting for now.

[Daveembry]

Of course you don’t. One thing for sure besides death and taxes is that whatever someone posts, Andy is gonna say the opposite. Thanks Einstein for running everyone off this forum single handedly.


Edit. Fuel flow at 1,000 rpm at full rich is about 2.8 gph for me. Leaned just rich of rough = 1.3 gph or a reduction of over 50%. Quite a bit of difference.

I lean my PA-28 aggressively for taxi. If I don't I'll likely foul a plug. I seldom lean the FX-3 for taxi and have never fouled a plug.

Take a look at fuel flow while leaning for taxi. Do you see any significant reduction in fuel flow between full rich and the leanest that can be set and keep smooth running? When I have tried it I saw no significant difference.

I concluded that the fuel servo does a much better job of setting low power mixture than a carb.

I prefer a lower idle stop setting than 650. I just don't idle the engine on the idle stop. Having the lowest possible power output can be an advantage when landing on short strips.

(promoting discussion or being argumentative - depends on your perspective)

[Andy]

Of course you don’t. One thing for sure besides death and taxes is that whatever someone posts, Andy is gonna say the opposite. Thanks Einstein for running everyone off this forum single handedly.

I think the record will show that you like to disagree with everything that I post. Your disagreement is seldom fact based and usually takes the form of a personal attack. The concept of open minded discussion seems to be lost on you.

[Daveembry]

It’s all yours brother if that’s what you think. I have thick enough skin to not be bullied and I guess you don’t like it. Most people will just stay away than to have their contributions scrutinized and critiqued to no end. “Discussions” are good but that isn’t what you are doing. Lots of private messages to me stating the same. I just said the quiet part out loud. I’m sick of it so you carry on. 👋


https://forum.cubcrafters.com/showth...ll=1#post28259

I think the record will show that you like to disagree with everything that I post. Your disagreement is seldom fact based and usually takes the form of a personal attack. The concept of open minded discussion seems to be lost on you.

[hawgdrvr]

This is disappointing to see, everyone has value to add. People need to learn what to take and what to discard but NO ONE sharing is everyone's loss. I hope mods will remove some of the above posts, they are not conducive to the spirit of this forum in sharing information and lessons learned. I've learned something from everyone here and most of what I've learned have been from fellow FX-3 owners via phone/text/email and not this site because people avoid this site for whatever the reason. We all lose when that occurs.

I've said in the past this site should foster community and info share, this needs to start with CubCrafters themselves, then have owners participate to show the joy of these planes and aircraft ownership. There is a lot of room for improvement at CubCrafters in aircraft ownership, training, and success. I try to post here to hopefully invite others to share and share what I learn as I travel this road as a first time aircraft owner.

Again, EVERYONE on this site has been a tremendous help. The bullying and attacks have to stop and people should refrain from it, it doesn't help anyone. I'm at a loss on how to get CubCrafters owners to communicate with each other. Very sad! Very very broken situation in so many ways.

[aeroaddict]

Unfortunately, some threads here turn into a science fair without solutions. Kinda like the ELT antenna position thread.

hawgdrvr, looks like the back are rich and the front are lean. I think this has already been stated. As like you, I had a learning curve on how to lean correctly (CC340). After 300 hours I feel pretty confident that I'm leaning properly and my plugs show this. You might try replacing the plugs (you probably already did at your 100hr) and maybe check them again in 10 or 20 hrs now that you are 'up on the leaning learning curve'.

A little off topic, but don't forget to do an oil analysis and cut open your oil filter to look for metal.

Cheers