Fouled Plugs

[benjam]

Afternoon all.

 

I have a Q about too much RPM drop during the runup on a Rotax 912ULS.

 

With one of the Mag switches off, the result is a bit too much rough running. I suspect it is a fouled spark plug (that is what it was last time this occurred).

 

Last time, I had the L2 look at it. He removed each spark plug and found the offending plug, cleaned the carbon build up off and replaced it.

 

Is there any way to burn this off with out removing the plug? I am unable to lean off the mixture - there is no mixture lever. I only run the motor on Mogas so far.

 

Any thoughts?

 

Cheers.

 

 

[Camel]

If you have a temperature sensor the laser type you can determine the plug that is fouling because it would be the coolest one and know which plug it is, but because you only run on mogas this is unusual to have plugs fouling and I would replace all plugs with new ones !

 

 

[benjam]

Thanks for your response.

 

The only temp gauge is the oil temp from the engine.

 

Are you suggesting the plugs are substandard, or is that the fix because the plugs have been damaged?

 

 

[benjam]

If the plug is not substandard, what am I doing wrong to cause this error?

 

 

[Camel]

Was referring to Temp reading of plugs with a hand held laser temperature meter ! Google laser temperature gun. !

 

The plugs getting fouled on avgas would be expected but not on mogas so your plugs faulty or gaps wrong or too rich a mixture or oil leaking past rings or guides and fouling ! Possible wrong plugs fitted too ! Rotax 912 ULS don't foul plugs unless on avgas. By the way do not let the engine idle at low revs during warm up or whenever sitting still, bring the revs up so the engine runs smooth, letting it idle at low rpm could cause problems !

 

 

[Mick]

I have had a 912ULS foul plugs on unleaded due to the idle being too rich, but only after prolonged periods at a low idle.

 

The short term work around is, if your brakes are good enough, a short full power run which should clear it.

 

As mentioned above, there is something wrong if you are getting fouling, best to work out what & sort it.

 

 

[bexrbetter]

Last time, I had the L2 look at it. He removed each spark plug and found the offending plug, cleaned the carbon build up off and replaced it..

Unless you are stuck somewhere, you never clean a plug. They now understand what a mistake it was to do so 'back in the day'. You replace them, period.

Go get some Nippondenso (ND) plugs, NGK are a distant second place and no other brand rates.

 

... and that's when the fight started.

 

 

[Camel]

I would replace all plugs with new also Bex, had no experience with Nippondenso but sounds interesting , I remember when NGK was a cheap alternative to Champion and Bosch !

 

 

[benjam]

Thanks for the responses. I am unknowing about such things.

 

I like getting educated.

 

Cheers.

 

 

[Yenn]

I have known a new plug to fail when it has only been in use for a short time.

 

They can be faulty from day 1 and are cheap enough to replace easily. Always keep a spare set.

 

If you were running aviation plugs such as used in Lycoming, I would also keep a spare set, even though they cost over $50 each, but at least they are cleanable.

 

 

[benjam]

Thanks for the info. :)

 

 

[bexrbetter]

no experience with Nippondenso but sounds interesting ,

ND are owned and made by Toyota, and helped Toyota to it's famous reliability status.

I raced classic motocross for over a decade, old air cooled 2 strokes, Maicos, Bultacos, CZs etc and the only plug that would stand up to them was ND. Eventually everyone was running them except for a couple of NGK diehards.

 

Champion runners had a standard motto: "Giz a push will ya mate"

 

 

[turboplanner]

Thanks for your response.The only temp gauge is the oil temp from the engine.

Are you suggesting the plugs are substandard, or is that the fix because the plugs have been damaged?

Just happens with plugs. You have to pull them to clean them, but now and again the only solution is new. Learn to read them for colour and you can make a faster decision.

[Downunder]

When idled too long it is common for the FRONT cylinder plugs to start to foul. The way the manifold is orientated tends to be the cause.

 

However a higher rpm run generally clears them.

 

And as above, just replace the problem one if needed. They are cheap. ULS is NGK DCPR8E. Make sure it is the (4339) version. This has removable terminals.

 

You might want to check the idle mixture screw. I have heard of these "wandering" out occasionally. It is easy to do.

 

The "idle mixture screw" should be 1 and 1/2 turns OUT from full in (Rotax spec). I have heard of some people running 2 turns out, saying idle and low rpm is smoother.

 

 

You might also want to check your needle clip setting. The lower the clip position (4 positions), the richer the mix. This mainly affects mid rpm settings.

 

If you are a "Rotax owner" member you can watch the full video.

 

 

 

[BirdDog]

I just pulled all 4 plugs on my 912ULS at the recent 100 and all were fine. I run mostly Mogas, but use avgas when I’m out and about.

 

When you say fouled... how bad? Do you have a pic?

 

I would firstly organize a leak down test to rule any of that out first and foremost. You don’t want to be chasing your tail.

 

If that checks out, next step is idle mix. Check and set and rule that out.

 

Make sure your carbs are balanced, needles all set etc, and you don’t idle below 2000 for any extended periods.

 

That’s the process I would take.

 

Good luck and let us know how you go.

 

Cheers

 

J

 

 

[Jumbo jet]

B, please take my advice, I work on these 912 engines, plug fouling on Mogas is rare if u have a healthy engine so u have a problem, either u have a tired old engine and it’s burning oil or its over rich which can be caused by a too rich idle mixture setting, worn jet and jet needle or just tired old carbs, carbs should be overhauled at the 5 yearly rubber replacement or no later than 1000 hours, now when I say overhauled this is a complete strip down and all parts cleaned in an ultrasonic cleaner and needle jet, jet, circlip and o ring replaced and check that the mixture enriching device ( choke ) is returning to off and the tiny dot on the choke shaft is pointing towards the cable. Set idle mixture screw to 1.5 turns out and have main needle jet circlip on second from the bottom groove.

 

If u believe you have a good engine, first buy a set of plugs from Bert Floods, DONT SKIMP HERE as they properly gapped and have the proper heat paste applied, set the idle mixture at 1.75 turns out, don’t excessively slow idle the engine on warm up and give that a try, if it still cacks up plugs the problem might be as mentioned above, this is a starting point for u..

 

Good Luck.

 

 

[skippydiesel]

Terrific advice from all submiters but also a little terrifying.

 

Benjamin - the first law of mechanical meddling is - Start with the simplest and least costly potential "fix" (its seems to be human nature to go directly to the most costly).

 

(Assuming that the engine has been correctly/fully serviced and on time and you are using "fresh, good quality" fuel -)

 

In your case that would be addressing your engine management - reduce choke ASAP, consistent with continuose engine running - minimise idle running - make sure your engine is sufficiently "warmed"- do your ignition checks at or above (if your brakes hold) 4000 rpm.

 

Climb outs must be conducted at full power, minimum 5200 rpm. Cruise power 4800 - 5400 rpm. Do not spend long periods of operation below cruise power.

 

Reassess your plug condition.

 

If plug fouling still significant, move to next item on checklist (as articulated by helpful submitters).

 

 

[Roundsounds]

Afternoon all.I have a Q about too much RPM drop during the runup on a Rotax 912ULS.

With one of the Mag switches off, the result is a bit too much rough running. I suspect it is a fouled spark plug (that is what it was last time this occurred).

 

Last time, I had the L2 look at it. He removed each spark plug and found the offending plug, cleaned the carbon build up off and replaced it.

 

Is there any way to burn this off with out removing the plug? I am unable to lean off the mixture - there is no mixture lever. I only run the motor on Mogas so far.

 

Any thoughts?

 

Cheers.

Hi, this is not the place to learn about maintenance. If this is your aircraft take it to a reputable maintainer to have the problem resolved. It may be a problem other than simply a plug. I know of a pilot who died and his wife was seriously injured as the result of trying to resolve ignition problems by replacing plugs. The aircraft suffered a partial engine failure after takeoff which resulted in a stall/spin.Accident Report

 

Treat any unusual system operation seriously and don’t muck around with trying to fix problems if you’re not competent to do so, you’re dead for a long time! If you have a desire to learn how to maintain the aircraft have a suitably trained person train you and supervise your work.

 

 

[skippydiesel]

Hi' date=' this is not the place to learn about maintenance. If this is your aircraft take it to a reputable maintainer to have the problem resolved. It may be a problem other than simply a plug. I know of a pilot who died and his wife was seriously injured as the result of trying to resolve ignition problems by replacing plugs. The aircraft suffered a partial engine failure after takeoff which resulted in a stall/spin.Accident ReportTreat any unusual system operation seriously and don’t muck around with trying to fix problems if you’re not competent to do so, you’re dead for a long time! If you have a desire to learn how to maintain the aircraft have a suitably trained person train you and supervise your work.

Fair go Roundsounds! - I agree in principal with your comment however Benjamin has asked for comment & advice, which you & the other submistter have given him. With what he has received he should be able to dig a little deeper into his perceived problem. I dont know of any Sport Pilot whom runs to his mechanic at the first hint of a problem - most will try for some insight, depending on their level of mechanical aptitude, before the cry for professional help..

 

 

[Downunder]

Australia is a BIG country. Not all airports have a maintenance facility across the apron.

 

Recreational Pilots should really have some mechanical and electrical knowledge about their aircraft. Enough to give a wire a wiggle, check a connection and troubleshoot basic issues.

 

 

[skippydiesel]

I guess it comes down to being confident in your own level of knowledge, experience & skill - but no so much that it kills you - much like becoming a pilot.

 

Mack to Benjamin's problem - it sounds to me that he is doing his ignition check at too low an rpm - "With one of the Mag switches off, the result is a bit too much rough running" When I do my ignition checks its at 4000rpm (any higer & I start my TO run). I get a 50 rpm drop on each ignition not enough to have any change in engine vibration. So I suggested he might check his engine management techniques - this might just solve his problem with little effort, no cost AND no increase in risk. If this does not improve the situation he can move on and if need be, consult with an appropriately qualified & experienced person.

 

 

[Roundsounds]

Fair go Roundsounds! - I agree in principal with your comment however Benjamin has asked for comment & advice, which you & the other submistter have given him. With what he has received he should be able to dig a little deeper into his perceived problem. I dont know of any Sport Pilot whom runs to his mechanic at the first hint of a problem - most will try for some insight, depending on their level of mechanical aptitude, before the cry for professional help..

I’ve seen too many people die playing this game, some very innocently relying on people subsequently proven as not competent to be maintaining an aircraft. Based on benjam’s posts I gave him what I consider to be sound guidance. If you’re not certain you know what you’re doing, then get someone who is competent and learn from them. Benjam has proven he is sensible by identifying the RPM drop during run-ups and had it resolved by a competent person. The problem has recurred, so rather than give fixing it a go himself, which is what some seem to be suggesting, seeking the assistance of a competent person is my recommendation.

 

Thanks for the responses. I am unknowing about such things.I like getting educated.

Cheers.

[benjam]

The problem has recurred, so rather than give fixing it a go himself, which is what some seem to be suggesting, seeking the assistance of a competent person is my recommendation.

Hi Round sounds.

 

I agree 100%, and this is my practise.

 

I am more after an improvement in my general knowledge of running a LSA motor, the techniques involved, and what to discuss with the L2 and what he is talking about. I am not mechanically trained or minded. This hobby can be a disastrous one if one becomes too blasé about the potential outcomes. I want to know what I am doing wrong to cause this problem.

 

The L2 I have engaged (Dieter, for those near YCAB) is friendly, accessible, knowledgable, experienced and competent. He does everything or supervises my every attempt to have a go. That is the way it will stay.

 

I do not do ANY maintenance on my aircraft other than check the tyre inflation pressures. The cargo is too precious.

 

I do appreciate learning from the vast array of community knowledge and opinion though.

 

Cheers,

 

Ben

 

 

[benjam]

When I do my ignition checks its at 4000rpm (any higer & I start my TO run). I get a 50 rpm drop on each ignition not enough to have any change in engine vibration. So I suggested he might check his engine management techniques - this might just solve his problem with little effort, no cost AND no increase in risk.

Thanks for the advice. I was only going to 3600-3800 as the stupid, heel pedalled calliper brakes can't hold it. I will aim to get up to 4000 from here on.

 

Cheers.