Fouled Plugs

N1347B

N1347B

Pre-takeoff checklist
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Jun 24, 2008
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Deb McFarland
My 8E has the C-85/0-200 engine with the Stromberg carburetor wired rich. I burn 100LL and use avblend at every oil change. I have to clean my plugs several times a year, and this is annoying because my IA is not always around to do it (like yesterday when we enjoyed clear skies and calm winds).

Are there options for me to eliminate this problem?

In the short term, we can set a schedule of cleaning the plugs every X hours, but in the long term, is there an additive I can use? Can I put the Marvel Schebler on my engine? I would love to do this. I really feel my engine runs more like the 0-200, and a mixture control would be a well-used option.

Suggestions?

BTW, I can always tell my plugs are getting leaded because my rpm needle starts to twitch.

Deb
 
N1347B said:
My 8E has the C-85/0-200 engine with the Stromberg carburetor wired rich. I burn 100LL and use avblend at every oil change. I have to clean my plugs several times a year, and this is annoying because my IA is not always around to do it (like yesterday when we enjoyed clear skies and calm winds).

Are there options for me to eliminate this problem?

In the short term, we can set a schedule of cleaning the plugs every X hours, but in the long term, is there an additive I can use? Can I put the Marvel Schebler on my engine? I would love to do this. I really feel my engine runs more like the 0-200, and a mixture control would be a well-used option.

Suggestions?

BTW, I can always tell my plugs are getting leaded because my rpm needle starts to twitch.

Deb
Click to expand...

Some of the older planes around here use TCP fuel additive for exactly that purpose.

http://www.alcorinc.com/fuel-treatment/alcor-tcp.php
 
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Deb,

What kind of plugs do you use? I had problems with plug fouling becuause my engine type tends to run rich. I use the iridium plugs and have had less problems over the last ten years than over the one year previous to that. They are expensive compared to regular plugs but last a lot longer. The couple of times they sounded like they were fouling, I could clear it by leaning the engine out and running up the throttle. If I still wasn't feeling great about it, I would actually do a quick takeoff and landing then check again and it has cleared. (I have a reasonably long runway and lots off places to land and I know when it feels like a fouled plug)

Barb
 
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Geico266 said:
Go with the mixture control carb and lean. TCP will help until then.
Click to expand...

You could also go to REM37BY plugs. They're pretty much foul-proof, and they're ok in the C-85.

Dan
 
Can't you clean the plugs yourself?
 
Thanks for the replies!

Deb
 
N1347B said:
My IA prefers to do it.

Deb
Click to expand...
Your IA maybe prefers to do it because you pay him right?
The hotter plugs( 37,s) might help, and being able to lean would reduce fouling not to mention reducing fuel consumption.
 
el con said:
Your IA maybe prefers to do it because you pay him right?
Click to expand...

You better believe I do! I cook his meals and wash his socks :D!

If he's really good at keeping Lester going, I'll even wash his airplane.

I guess I could get rid of him, but I did promise till death do us part.

Deb
 
On the Stromberg mixture control:
http://www.cessna120-140.org/forum/files/stromberg_mixture___secrets.pdf

Apparently it is possible that some carburetors were assembled without all the internals that make the mixture control actually work (since it was wired rich anyhow...).

But it appears that it can be made to work.

edit:

Reading (again) how the mixture control works, I see that it applies a little back suction from the venturi to the bowl to change the delta pressure across the jets. So, it is not going to be very effective for leaning at idle while taxiing - but you could lean during runup to help burn off some of the lead.

The referenced document says:
With the high lead content 100LL, it would be nice if the mixture control was effective on the ground to
Click to expand...
keep the plugs clean but such is not to be with the Stromberg.
Click to expand...
 
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N1347B said:
You better believe I do! I cook his meals and wash his socks :D!

If he's really good at keeping Lester going, I'll even wash his airplane.

I guess I could get rid of him, but I did promise till death do us part.

Deb
Click to expand...
Ah! I see.
Well better do what your IA say's , you never know what might not get tightened up or "oop's forgot to check":D
At least you can work out an acceptable "payment plan":blush:
 
The problem is four times as much lead in the fuel as your engine was designed to handle, and adding stuff to your oil won't fix this problem. There are a few things you can do to help.

First, lean like crazy, especially on the ground. When you first start the engine, set about 1200 RPM, lean until it rises and then starts to drop off, and enrich back to smooth operation. Then leave the mixture there for all ground ops other than run-up (which requires full rich for proper checking). Mark that spot on the mixture control so you can lean back to that point after landing, too.

Second, lean like crazy in flight. As long as you're not running the engine over 75% power, you can lean in cruise at any altitude (lean to rough, enrich to smooth). You should also be leaning in any climbs above 5000 feet -- lean to peak RPM for that.

Third, do a "lead scavenging" run just before shutdown. You get more lead fouling during ground ops than during flight because engine combustion temps are so low (EGT's typically 1000F or so compared to 1300+ in cruise) and the thermally-activated lead scavenging agents in your fuel don't work well at those low temps. Rich up enough to get the engine to run up to 1800 RPM, lean to peak RPM, and hold it there for about half a minute, then pull the throttle back to 1000 or so and pull the mixture to cutoff to shut it down.

Finally, you can add TCP to your fuel. You'll have to shop around on the internet to find it, but adding the right amount of this power lead scavenging agent will help reduce lead fouling inside the cylinders. Note that this is also an extremely flammable product, so you don't want to carry it around in the airplane (see http://www.ntsb.gov/ntsb/brief.asp?ev_id=20001211X12083&key=1 for what can happen), but if you add it every time you fuel at home, that should help a lot.

PS: I just noted that you indicated you don't have a mixture control. In that case, TCP is about the only thing you can do to really help, but running up to 1800 before shutdown might also do some good as it will increase combustion temps (and lead scavenging) a lot, although not as much as you'd like. Also, if the idle mixture is already adjusted properly, you don't want to overlean it by going beyond the proper setting.
 
One Short said:
Deb,

What kind of plugs do you use? I had problems with plug fouling because my engine type tends to run rich. I use the iridium plugs and have had less problems over the last ten years than over the one year previous to that. They are expensive compared to regular plugs but last a lot longer. The couple of times they sounded like they were fouling, I could clear it by leaning the engine out and running up the throttle. If I still wasn't feeling great about it, I would actually do a quick takeoff and landing then check again and it has cleared. (I have a reasonably long runway and lots off places to land and I know when it feels like a fouled plug)

Barb
Click to expand...

Barb,

This has been the most positive advice I've received. Folks in the Luscombe forum who changed plugs love them. I plan to order a set ASAP.

Thanks!
Deb
 
I have received some great responses from the Luscombe groups and from general aviation forums about this issue. Just in case other folks have the same problem, I have included a summary of options below.

I have flown behind this engine for 600 hours, and I love it. However, when we inherited Keely, our eleven-year old, my flying habits changed. Instead of flying for hours at a time, most of my flights are an hour or less now unless we plan a trip or I have a day off. Henry, my hubby and IA, thinks this pattern change as contributed to my problem.


Here's how I plan to approach the issue. First, I'm going to learn to clean and gap my plugs. I do a lot of other stuff. I might as well learn to do this. In the past, Henry was at work during the week and only home on the weekends. He is retiring in at the end of the year, but I think I still need to know how to do it. I will keep a chart of how often I clean and gap them. I will note condition, etc.

I will revise my shutdown procedure by running up and shutting the engine down with the fuel instead of the mags. I plan to change my plugs to the REM37BY. I've heard only positive things from folks who do this. And I plan to reinstall the mixture control on my Stromberg to see if it will help.

Here's the ideas offered:

-Shut down by turning off the gas instead of the mags while running at least 1000 rpm to keep the heat up on the plugs. Just don't forget to turn off the mags after the engine quits.

-Change your spark plugs from the REM40E's to REM37BY spark plugs.

-Put 1 ounce of TCP to every ten gallons of fuel.

-Adjust the idle mixture screw on the carb.

-Adjust the float. Shops often set them too high thinking you can lean.

-Reinstall the mixture control on the carb. It does work, contrary to what many will tell you. The biggest problem with a Stromberg is that they aren't as well understood by many mechanics today as in the past. If all is working as designed, you shouldn't see any differences in flying behind a Stromberg or a Marvel... except for the mixture idle cut-off and the accelerator pump thingies.

-Sure you can put a Marvel-Schebler on your engine... if you can find one. The C-85 carb is very scarce (p.n. 10-4240 or 10-4240-1). Tempest is the new owner of these carbs. http://www.tempestplus.com/home.htm They just announced a price reduction on all carbs and rebuilds. You might give them a call and see if they have any new 10-4240 carbs available. Rebuilds usually require a core carb but call 'em to verify that. Even with the announced price reductions, be prepared for a price tag that may take your breath away.

-Another option is an STC that allows the use of a modified O-200 Marvel-Schebler carb on the C-85. It's STC SE01309AT. That STC modifies an O-200 carb (p.n. 10-4894) for use on the C-85. I'm pretty sure the mod has to be done by the STC holder... Lowe Aviation in Sacramento, KY. It's also a little pricey if I remember right.

Thanks again everybody!

Deb
 
Capt. Geoffrey Thorpe said:
On the Stromberg mixture control:
http://www.cessna120-140.org/forum/files/stromberg_mixture___secrets.pdf

Apparently it is possible that some carburetors were assembled without all the internals that make the mixture control actually work (since it was wired rich anyhow...).

But it appears that it can be made to work.

edit:

Reading (again) how the mixture control works, I see that it applies a little back suction from the venturi to the bowl to change the delta pressure across the jets. So, it is not going to be very effective for leaning at idle while taxiing - but you could lean during runup to help burn off some of the lead.
Click to expand...


Lots were made without the mixture control guts. Mine was, and I machined my own parts to get mixture control. It's a pretty simple setup, but you do need a lathe to make the bits. Milling machine doesn't hurt, either. The parts are super-rare.

The back-suction affair won't lean at idle and it won't cut the engine off for shutdown. It relies on venturi vacuum to hold the fuel back, and at idle there ain't any venturi vacuum.


The little Continentals are famous for fouling their bottom plugs with oil while at idle. Those plugs are right at the bottom of the head and oil runs into them really easily. Cold engines often let oil get sucked past the rings, even fairly new engines, during low manifold pressures. Even a few drops will spoil things. If it runs rough on one mag during runup, that's often the problem: the bottom plugs have filled with oil. Go to full throttle for a few seconds to get it blown out, and try again at runup RPM. At shutdown, go to full throttle immediately before killing the engine so that the bottom plugs aren't full of oil that will coke in there while the engine is still hot. We used to run O-200's in C150s and they did this all the time. My A-65 does it, and a friend's C-85 in a T-Cart used to do it to me. The Lycomings never do it.

REM37BY plugs have their electrodes far out of the plug cavity, where lead or carbon can't pile up and short them. The BY is on the left, the 38/40 on the right. (Actually, that's a long-reach plug on the right, for thicker heads, but the electrodes are the same as the REM 38 or 40.) The BY's well is very shallow; you can almost see the bottom of it in the picture.

rem37byelectrode.jpg


Champion application charts in this catalogue. C-85 can use the 37BY:
http://www.championaerospace.com/pdf/64552_Champion_ElecL.pdf


Dan
 
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Dan Thomas said:
Lots were made without the mixture control guts. Mine was, and I machined my own parts to get mixture control. It's a pretty simple setup, but you do need a lathe to make the bits. Milling machine doesn't hurt, either. The parts are super-rare.

The back-suction affair won't lean at idle and it won't cut the engine off for shutdown. It relies on venturi vacuum to hold the fuel back, and at idle there ain't any venturi vacuum.


The little Continentals are famous for fouling their bottom plugs with oil while at idle. Those plugs are right at the bottom of the head and oil runs into them really easily. Cold engines often let oil get sucked past the rings, even fairly new engines, during low manifold pressures. Even a few drops will spoil things. If it runs rough on one mag during runup, that's often the problem: the bottom plugs have filled with oil. Go to full throttle for a few seconds to get it blown out, and try again at runup RPM. At shutdown, go to full throttle immediately before killing the engine so that the bottom plugs aren't full of oil that will coke in there while the engine is still hot. We used to run O-200's in C150s and they did this all the time. My A-65 does it, and a friend's C-85 in a T-Cart used to do it to me. The Lycomings never do it.

REM37BY plugs have their electrodes far out of the plug cavity, where lead or carbon can't pile up and short them. The BY is on the left, the 38/40 on the right. (Actually, that's a long-reach plug on the right, for thicker heads, but the electrodes are the same as the REM 38 or 40.) The BY's well is very shallow; you can almost see the bottom of it in the picture.

rem37byelectrode.jpg


Champion application charts in this catalogue. C-85 can use the 37BY:
http://www.championaerospace.com/pdf/64552_Champion_ElecL.pdf


Dan
Click to expand...

Wow! Thanks for the info and taking the time to share it. My Stromberg has the guts. In fact, the mixture control cable was attached and operational in the past. There are varying opinions about the effectiveness, but I'm willing to give it a try. Henry uses the one on his A-65. He never has fouled plugs. Of course, until recently he used auto fuel.

I kind of feel sorry for the guy. After all the information I've received, there will be a honey-do list for him when he gets home this evening.:D

Deb
 
My thoughts on Deb's problem.

The Stromberg carb has a mixture control if it has all the parts installed, many don't, thus most are safety wired to the rich position, and the control cable removed. I believe that is where Deb is.

Parts are not available for the Strombersgs, so we replace it with a Marvel, MA3-SPA. Her engine has the 0-200 cylinders and the old Stromberg doesn't deliver enough fuel at full power setting to run correctly, yet it runs too rich at idle.

When you replace the carb with a MA3-SPA you need to enlarge the air jet in order to lean the fuel air ratio. You do this by finding if the engine is running properly at all speeds, If it is you can run it as is, with ability to lean from the cockpit. but if it is not, you can find out the size of the airjet by fitting numbered drill bit into the jet until you find the one that fits, then go 1 number size larger to increase the amount of air in the air fuel ratio.

Most times we can get the fuel air ratio correct and the C-90/0-200 to run about 6.5 GPH. and never foul a plug between oil changes.
 
So, not all the advice you get from webboards is nuts, eh??:D
 
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