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Cleaning carbon-fouled plugs

Discussion in 'Technical and Troubleshooting Torque' started by mattb, Jul 17, 2008.

  1. I've had trouble for a while now with plugs fouling to a dense sooty blackness. About once a week it gets so bad that I have to put in a new plug to start the bike (or steal QuarterWit's while he rides on my old plug! :grin:). The carbie, which is tuned as lean as it can go, will be in for professional attention in a few weeks, but with this mounting collection of new fouled plugs I'm interested in hearing what people think is the best most thorough way to clean them? Do people recommend any particular chemical / technique, etc?

  2. Back in the day, we used to sandblast plugs.
    Not sure if it's the 'thing' these days.
    How many u got?
    If your keen, pop over and I'll blast em for ya
  3. Once upon a time I had a little thingy that I found at a jumble sale for 50p. It was a mini sandblaster specifically for plugs. You'd stick the plug in this rubber grommet in the top and clip a pair of electrical leads to your battery. Inside the unit a small electric motor with a paddle wheel thing on it would chuck abrasive grit at the plug.

    It worked well on dry, sooty plugs. As it was a bit feeble, it wasn't so good on wet, heavily oiled plugs as the grit just used to stick. Used within its limits though, it gave a good clean all the way up inside the plug, which you can't do with manual abrasives.

    As long as you don't use metallic grit and make sure all grit is removed before replacing the plug in your engine, I can't see what harm sandblasting could do. I'd say go for it.

    Alternatively, for carbon fouling, a soak in caustic soda solution would be quite effective and staggeringly dangerous (strong caustics being a whole lot nastier than concentrated acids).

    If you fancy shelling out a few dollars, you can get good results with a cheapo ultrasonic cleaning bath too (though I've not seen one used on spark plugs I'll admit.
  4. Run a hotter plug?
  5. Your engine needs the attention of an experienced two stroke tuner. There are very few of them left. I see that you are in Melb. The best one that I know, is ex international Racer Greg Johnson. He runs Johnson Cycle Tune in Market St . Sth Melb. 96991717.
    He has forgotten more about 2 strokes than most people will ever learn.
  6. Soak the tips of the plugs in Carby cleaner for an Hour or so then clean re-do gap ..Maybe a hotter plug might last longer ..
  7. +1 on hotter plug. Go up a heat range and see how that works.
    Plugs have to reach a certain temperature to self clean, people run colder plugs thinking it will do something good (but I have no idea what they are tryng to achieve).
    Post a photo of plugs, so we can tell if they are fuel fouled or oil fouled.

    Regards, Andrew.
  8. I think it's a four stroke. Not that it really matters.

    If the centre porcelain is black you should use a hotter plug, until it is no longer black but a nice, honey colour.

    Test at highway speed as well as just around town. The hotter the plug the more easily it burns off the soot which all engines produce. Er, good engines produce very little soot.

    If the centre porcelain becomes white you are running too hot a plug, and stand a good chance of melting a hole in ya piston through pre-ignition. The porcelain stays so hot that it ignites the fuel as soon as it is sucked in, rather than when the sprk jumps.

    The more (i.e. the longer) the porcelain, the hotter the plug. The less porcelain (we are talking length) the colder it is. The area around the porcelain is known as the "gas capacity" of the plug, and while it can be made to vary, is not as important a consideration as the length of the porcelain.


  9. Yeah, you are right. he seems to have a 4 stroke. I take it back.
  10. You need to establish the reason for your plug fouling. It is not possible to do, without the bike being in front of me. How tired is the engine?
  11. Thanks for the replies guys.

    The standard plug is a BP7ES but I've been running a BP6ES for close to a year now. It's an air-cooled bike with a reputation for over-heating, though I guess that's not really an issue at the moment. Would going to a 5 (in this nice cold weather) be likely to be too much? I'd view it as a quick fix as what I need is to get the carbie competently seen to as I can't tune it (with the mixture screw) any more lean. It's definitely soot and not oil (I have frequent cause to examine the plugs!:(). This bike's a pain in the *** to get going again when it's stalled, as happened this morning making me late and angry for work - damn well gotta fix it! :evil: So what do you think about a 5 plug - two grades hotter - short term in this cold weather?

    (You're right MVrog - it could be any number of things, with the ignition system - weak spark - being an obvious possible culprit; I'll start with the carb and work on from there. The engine is 30 years old and I've not had it opened to the piston, but it's soot and not oil that's the problem at the moment).
  12. Have you tried cleaning the air filter?

    When you say the carb is tuned as lean as it will go, the adjustments you can make to the carb are usually just to fine tune the idle speed etc. They have little effect on normal running - but may be making the bike harder to start. If the plug is fouling in normal use it'll be the main jet so you won't be able to adjust out the problem.

    However, if the bike hasn't been tuned etc. there's no reason for the jetting to be wrong.

    Apart from air filter it could also be ducaused by
    1. blocked jets (air)
    2. sticky choke and/or cable
    3. oil bypassing the rings and burning (look for exhaust smoke - it would have to be pretty bad to foul the plug so I'm guessing you'd have noticed this by now).
    4. Maybe ignition related

    Clean dry soot off with a rag, or if burnt on (i.e. carbon), use a brass wire brush.

    The B5 plug is too hot. You'll melt something. It's interesting you say your engine has a reputation for overheating so you put in a hotter plug (the B6). If the engine overheats you'd want a colder plug (B8) if anything. Save that for another time.
  13. Funny you should say that, the problem as a recent problem begun when the air-filter came loose - I cleaned the carb with a sprayed chemical (without opening it up) and it improved - this is why I assume it's the carb and not ignition etc.

    There's a screw for mixture adjustment also on this one. It has a raised piece to stop it from being more leanely tuned, which guys tend to grind off - I just bought myself a dremel bit...

    The hotter plug was placed by a mechanic who couldn't start the bike after opening the engine (I walked into the shop after three extra weeks of him working on this new problem, and started it second kick!:grin:), I forgot it was a 6 until six months later, when this fouling problem began and I took it out - I ran the whole summer on it without realising. The thing is, all the previous stalling issues went away once it was put in late last year, so I'm treating it as my standard plug now, especially with the carbon issue. The engine does blow a puff of black smoke at times, and a few times a week I get a big puff of white (or grey - I can't tell) smoke upon starting. But I assume oil past the rings does not result in soot...

    Half my employment is as a uni tutor and uni's been on break - come semester paychecks and I'll damn well pay for surgery on the carbie if that's what it takes - better than paying for surgery on my knee...! ](*,)
  14. No worries.

    There is something satisfying about being able to change spark plugs in four seconds... The bike is still running fine on your dirty old plug too!
  15. Just had a thought, is this bike still running points ignition?

    Regards, Andrew.
  16. Things that come to mind.....

    1. Aircleaner element not flowing for one reason or another.... dirty or cleaning method fused pores closed - see how it runs with the aircleaner out.

    2. Blocked pilot air bleed or main air jets (small passages in bottom of intake bell of the carb (aircleaner side) - With can of carb cleaner (or WD40), spray up pilot & main fuel jets with venturi outlets blocked, this will discharged pressurized spray out the air bleed inlets to confirm clear passage.

    3. Oil fouling; is the bike blowing smoke or using oil? - rebuild time :)

    4. Too rich on the throttle valve needle - Raise the throttle valve needle clip (lowering the needle) one or two grooves.

    5. (And this is what I bet it is) Throttle valve needle and the needle jet that it runs in will be worn; very common problem on 4 strokes over 15 years old. Take the top of the carb off and you'll see the needle jet that the needle goes up & down in will be worn oval. If the jet is pressed in you'll need a new (or newer) carb. A new needle may improve the problem by 25%.

    Cleaning plugs? Put them in an engine that is tuned properly; the heat from correct combustion will burn them clean within 1 kilometre. Sand blasting is not the best way to do it, yes I used to do in the 70's but it diffuses the sharp edge on the centre & ground electrodes (requiring more voltage to spark) plus it can remove the precious metal on racing type plugs (I know BP7ES plugs are not race).
  17. The bike runs electronic ignition, thankfully! (Despite the determined efforts of a Yamaha dealer to convince me it ran points!)

    THanks Johnny O, I think rebuild time is on the horizon also, as it does blow smoke, but I doubt this is my problem - at least the fouling is carbon soot, which means petrol not oil (I'm right am I not).

    I should start up a bookie service taking bets on such problems....
  18. When you say the carb is running as clean as it can go, are you talking about the pilot screw or the pilot jet, or both?

    Also be careful with plug numbers. some run the opposite way, though I think you are right.
  19. I swapped plugs with Matt by the side of the road and rode for an hour or two on from there. I had a look at the plug last night and hey presto, you're right!
  20. Pilot screw - so I'm hoping that a bit of interior cleaning / adjusting / replacing will do the job. Being one carb its only $200 a new one (Mikuni VM34).