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How to minimize annoying fouled plugs?

ArVeeNiner

Well Known Member
I have an O-320 B2B and I?m running Autolite by Unisom URHM40E spark plugs. More often than not, when I do my run up, I have a fouled plug. It is usually plug 2 bottom. I?ve had it so bad on three occasions that nothing I can do during my run up clears it and I have to pull the plug and manual clean it.

I taxi as Lycoming recommends (1000 rpm, leaned) and I lean in flight. I have to admit that I don?t always run it up to 1800 rpm before shut down as Lycoming recommends but I do occasionally with the same results usually.

I?ve checked on line and I see recommendations for the Champion REM37BY plugs. These are cooler running plugs than my Autolites so it?s counterintuitive to me. Both plugs are approved by Lycoming for this engine.

Does anybody have any recommendations?
 
The 37BY plugs are indeed cooler but they stick further into the combustion and DO help the fouling problem greatly.
Been running them in my -6 for over 23 years with no fouling problems.

BTW, Unison also make a 37BY plug. These are a little shorter on the "upper" end and are easier to install with our tight baffling.
 
I have an O-320 B2B and I?m running Autolite by Unisom URHM40E spark plugs. More often than not, when I do my run up, I have a fouled plug. It is usually plug 2 bottom. I?ve had it so bad on three occasions that nothing I can do during my run up clears it and I have to pull the plug and manual clean it.

I taxi as Lycoming recommends (1000 rpm, leaned) and I lean in flight. I have to admit that I don?t always run it up to 1800 rpm before shut down as Lycoming recommends but I do occasionally with the same results usually.

I?ve checked on line and I see recommendations for the Champion REM37BY plugs. These are cooler running plugs than my Autolites so it?s counterintuitive to me. Both plugs are approved by Lycoming for this engine.

Does anybody have any recommendations?
Taxiing is one thing but do you also lean on the ground while not taxiing? Running full rich while on the ground is one of the culprits of fouling plugs. Even being close to sea level one should not run full rich except during startup. Of course if one is at sea level there will be a need to be cognizant of the mixture settings during various operations in order to adequately lean while at the same time allowing for proper mixtures during other subsequent operations (i.e. ramp mixture settings may be considerably different than take off mixture settings). This is altitude dependent so one's settings at sea level could be very different for someone in the Midwest and most assuredly different than those at even higher elevations.
 
i guess i am confused. i thought''owheatrange'' plugs are longer but run hotter because they are longer and can't dissipateheat to the block as well?
 
I had a plug fouling problem early on, which totally disappeared as soon as I started running aggressively lean in ALL ground operations. What's aggressive? Having it lean enough that it stumbles if you give it any throttle above a 850RPM idle.
I run UREM40E plugs on the bottom ... they were the ones that fouled without lean running.
 
Yup

It is not possible to over lean for ground ops as long as you use a setting that the engine still runs smooth.

Double check that your idle mixture is set correctly.... no more than 50 RPM increase when mixture is pulled slowly (about 2 seconds) from full rich to ICO while idling at about 800 - 900 RPM.
 
+2 on very aggressive leaning on the ground. So lean that the engine will stumble and hesitate if you attempt take off in that condition (extra warning to not do that!)
How often do you do routine plug cleaning/rotating?
 
I lean just after start up. I check for oil pressure then lean and run it at 1000 rpm on the ground. I think it's pretty aggressive. I'll lean until it stumbles then slightly enrich.

I only go full rich at run up and here at sea level, on takeoff.

I may buy one of those 37BYs and put in the 2 bottom location to see if it makes any difference.
 
Is it soot, lead, or oil fouling? What color? Wet or furry? Leadballs? Expiring minds want to know.
 
Is it soot, lead, or oil fouling? What color? Wet or furry? Leadballs? Expiring minds want to know.

I found lead balls deep in the plug but I think the main culprit was a small lead bridge between the insulator and the shell. After cleaning it all out and blasting it, everything was good again.
 
Fine wire plugs make a huge improvement resolving issues from fouling from both lead deposits and oil.

Tim
 
37BY

I run the Tempest 37BY spark plugs and lean aggressively on the ground on my B2B that I converted to CS operation. No lead fouled spark plugs.
 
try running a lead additive to see if that helps. :)

I don't know about a lead additive but in the old days when I had a C152 with the 0235 there were a lot of problems with plugs fouling with lead. Back then I used TCP, a lead scavenger and it help immensely but was a pain to add with every fill up and was expensive as well. Of course it was always the bottoms plugs that were the problem.

Again a set of fine wire plugs only for the 4 bottom plugs would be cheaper then 8 plugs.

A temporary and lower cost option you could try one plug in the problem cylinder but I'm not sure of any potential problems with this set up either short or long term.

Tim
 
I have on IO-320-B1A. I use the Tempest 37BY plugs and have my idle mixture properly set. I have never leaned during ground operations and have never had a fouled plug in 140 hours of operation. I have pulled them several times and have never seen a deposit. I run 100LL.

I suspect that many people are using aggressive manual leaning to overcome an improper (i.e. rich) idle mixture, but that is just speculation. I also use the minimum MAP method of adjusting mixture, not the 50* method and always do it with a hot engine. Also know that colder air requires more fuel for an optimum mixture. If you set the optimum idle mixture in colder temps, you will be too rich in the summer.

The 37BY plugs were specifically designed, not just heat range as Mel mentioned, to reduce lead fouling. I don't know why anyone with a fouling history would not use them, as they provide the same spark energy (i.e. performance) as the 40's, assuming they are properly gapped.

Larry
 
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plug fouling

I used to constantly have problems with fouled plugs. As others have indicated, I also switched to Tempest 37BY plugs, clean them with a dental pick and rotate them at every oil change, and haven't had a problem since. Have over 500 hours on the 37BY plugs now without one case of fouling. RV-6 with O-360.
 
Fuel additive

Concur. On advice from a big round engine EAA guy at my airport, been adding Decalin Ru-Up (TCP) to my fuel for a year now, and no more clinkers or fouled plugs. Very happy. Also compressions went up to 80/80 at last oil change, so guessing it also cleans deposits off the valves/seats. 1/2oz per 10 gallons 100LL. Spruce sells it.

TCP came about in WW2 as a solution to fouled plugs in high compression combat engines. Converts lead oxide to lead phosphate which is more readily scavenged out the exhaust and doesn't leave hard deposits (clinkers).

Just what I did. Woody.

try running a lead additive to see if that helps. :)
 
Lean till it hurts

I learned a trick from a friend a long time ago. Carbs can be leaned _MUCH_ more aggressively at low RPM and should be for all ground opereations.

Let's say you have 3" of mixture travel... Leaning for an 8k cruise at 80% power is usually 1" of leaning. I usually start with 1" and do all ground operations at like 2". You know it's right if you raise the RPMs above 1300, the engine coughs and die.

This has two benefits; it greatly reduces fowling and you literally can't run the engine over 1500rpm at this mixture; so you won't forget and take-off with a over leaned mixture at high power settings.

-Bruce
 
How about Mogas?

Nothing works better against fouled plugs than unleaded Mogas 91 E10.
Just another option for you in case you can't decide on a remedy.
 
Nothing works better against fouled plugs than unleaded Mogas 91 E10.
Just another option for you in case you can't decide on a remedy.

MOGAS (non-ethanol) isn't for everyone but it also helps keep the valves from sticking.
 
Concur. On advice from a big round engine EAA guy at my airport, been adding Decalin Ru-Up (TCP) to my fuel for a year now, and no more clinkers or fouled plugs. Very happy. Also compressions went up to 80/80 at last oil change, so guessing it also cleans deposits off the valves/seats. 1/2oz per 10 gallons 100LL. Spruce sells it.

TCP came about in WW2 as a solution to fouled plugs in high compression combat engines. Converts lead oxide to lead phosphate which is more readily scavenged out the exhaust and doesn't leave hard deposits (clinkers).

Just what I did. Woody.



I've started using TCP - how often do you add it to the tanks? Every time you go from mostly empty to full tanks?
 
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