OzVMX Forum
Clubroom => Tech Talk => Topic started by: evo550 on July 10, 2012, 07:43:40 pm
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I have been having some issues with plugs failing after as little as an hours use. It starts with a little cough and splutter, then within a minute or so starts running real rough with backfires...then dead.
The plug looks fine, almost brand new, jetting is spot on, oil 50:1 motul 800.
I have tried all different types and heat ranges, makes no difference.
I have heard somewhere of a small film of carbon build up on the insulator that allows the charge to run down and earth out instead of jumping the gap. Anyone heard of this.
F#@kin sick of buying plugs by the 6 pac, I'm sure I didn't have this problem 20 years ago. >:(
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What bike is it in? Usually a weak spark or rich jetting causes fowling.
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What bike is it in? Usually a weak spark or rich jetting causes fowling.
..mmmmm, sons yz85.
Jetting is pretty much spot on, already 1 size leaner on pilot, plug comes out looking new, no oily deposits or carbon build up in the gap.
When plugs used to foul, the bike would start to miss and eventually get worse over the course of the day till it eventually stopped.
This thing misses about twice, then coughs, wheezes and backfires like mad then stops dead in about 30 sec. Fit a new plug and it's off again like a rabbid dog.
I will post a pic of the plug I just pulled out and see if I'm missing something.
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HT Coil breakdown or stator on the way out
I assumed you checked the plug cap? make sure you have not fitted a resistor plug plus a resistor cap
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I assumed you checked the plug cap? make sure you have not fitted a resistor plug plus a resistor cap
My thought also but fitting a non-resistor plug and cap.
Need to have a 'R' in the plug number or a 5K Ohm cap one or the other but not both or niether. ;D
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Plug and cap compatibility, well I never ???
Just checked, plug is a br10eix (irridium), but have also tried many others.
Cap has TD T-150 stamped on it. Not sure if it has been replaced in the past.
How do I check cap Ohm rating?
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Put your Ohm meter across the too contacts lead end and plug end and measure the resistance . or get the kid to stick his finger in the plug cap while you crank it over , if he jumps above the seat of the bike its a non resistor cap and below the seat its a resistor cap ;D
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Pics of plug,
(http://i118.photobucket.com/albums/o82/evo550/005.jpg)
(http://i118.photobucket.com/albums/o82/evo550/004.jpg)
(http://i118.photobucket.com/albums/o82/evo550/006.jpg)
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Need to have a 'R' in the plug number or a 5K Ohm cap one or the other but not both or niether.
Lozza,
I'm running a non resistor cap AND non resistor plug, wasn't aware that this was a bad thing. Why?
Evo555,
I was having similar plug problems with the standard NGK B8ES I though I had just been unlucky and bought a bad batch. I have had better luck with B8EGV or Iridium BR8EIX
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Pics of plug,
(http://i118.photobucket.com/albums/o82/evo550/005.jpg)
(http://i118.photobucket.com/albums/o82/evo550/004.jpg)
(http://i118.photobucket.com/albums/o82/evo550/006.jpg)
Looks too rich/wet to me, I run a dry chocolate brown at the richest, I like a tan colour if pos.
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was starting to suspect stator charge coil issues [which still could be the case] but one pic shows the plug enough to say it's at the cold end of the range & looks well oil'd up [shorted out]. At 50/1 mix i wonder if it's something like --is it sucking gearbox oil in through crank seal on the clutch side [unlikely but!!], or--clutching at straws here--have seen the tail pipe on [old] trail & mx bikes blocked enough to effect top end power, consequently the rider has the throttle wide open but not getting much performance as such. Or is the carb over-rich for some undiscovered fault like[i dunno] main jet fallen out, choke accidentally left on or idle mixture screw turned all the way in, ummm thinking--had a road 200 twin once that had a blocked air bleed into the needle jet & ran rich midrange. Sorry if i'm woffling on but does basically look too rich & oily. Goodluck. ps, muffler falling to bits & semi-blocking outlet.
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but one pic shows the plug enough to say it's at the cold end of the range & looks well oil'd up [shorted out].
Shorted out ? That has me intreiged.
The exhaust system is almost new, and the bike revs out nice and crisp, carb has no issues and I've even taken it back to Yamaha twice to check float level. Needle is on leanest clip and I have dropped the pilot (slow) jet one size.
Have tried plugs from 8 through to 10, makes no difference.
Still curious on the resistor cap thing as well, although Yamaha has a "R" plug listed as standard, so it should be right(unless someone has changed the cap...
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Plug and cap compatibility, well I never ???
Just checked, plug is a br10eix (irridium), but have also tried many others.
Cap has TD T-150 stamped on it. Not sure if it has been replaced in the past.
How do I check cap Ohm rating?
This doesn't cross refernce with any NGK cap number. Sure it's not TB --EM/A ????
Need to have a 'R' in the plug number or a 5K Ohm cap one or the other but not both or niether.
Lozza,
I'm running a non resistor cap AND non resistor plug, wasn't aware that this was a bad thing. Why?
From NGK website
Q: When should I use a resistor spark plug?
A: NGK "R" or resistor spark plugs use a 5k ohm ceramic resistor in the spark plug to suppress ignition noise generated during sparking.
NGK strongly recommends using resistor spark plugs in any vehicle that uses on-board computer systems to monitor or control engine performance. This is because resistor spark plugs reduce electromagnetic interference with on-board electronics.
They are also recommended on any vehicle that has other on-board electronic systems such as engine-management computers, two-way radios, GPS systems, depth finders or whenever recommended by the manufacturer.
In fact, using a non-resistor plug in certain applications can actually cause the engine to suffer undesirable side effects such as an erratic idle, high-rpm misfire, engine run-on, power drop off at certain rpm levels and abnormal combustion.
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The cap most definately says TD...but T-130 not 150, the entire ignition system is brand free except for the CDI which has a "W" in a box moulded into it.
I am struggling to come to terms with the rich jetting theory purely because we have two other bikes that both are jetted rich, one to the extent of the dreaded black splodge covering the swingarm each time we go out, but neither of the other two bikes has ever had a plug problem.
Would like to know what overthehill meant by the plug "shorting out"
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That looks like an EIX plug so is a resistor plug. They come with a very large gap which may need reducing even though NGK says not to adjust it.
You have said that all the ignition system has been replaced? Why?
Have you rrefurbished the bike such as painting the frame and engine cases? If so did you removed paint from the engine mounts both chassis and motor and also under the HT boil mount? Could be bad earthing causing weak spark. People seem to forget that the earth system is more important than the wiring itself.
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Hi, sorry, by plug shorting out i just mean't oiled up which shorts the spark to earth. Tracks down the side of the sooty oily bit on the insulator & earths out on the steel base of the plug. [think that sounds right!!] run out of constructive ideas though sorry. Think if it was mine i'd give it a good hard ride around a fast paddock for a while then check the plug straight away, if looks good then ride quietly for sometime & check it again, if looks oily again, well, not sure without viewing it sorry. Maybe someone else can offer some ideas. Tis a pain i know when things like this happen. Goodluck. ps, i could suggest running a much hotter plug--but won't say that out loud incase you melt a piston but does looks far away from that happening as it is. 2strokes aye!!. One thing i'm afraid to ask but have seen the mistake made where [not saying you] person thought 50/1 mean't 50mls per liter rather than 1000 divided by 50=20mls per liter. Catch ya later.
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You have said that all the ignition system has been replaced? Why?
Nah, I said the ignition was brand free, meaning I couldn't find who made it....lozza was mentioning NGK cap codes, I just went and had a look to see if the ignition system was NGK or something else. Frame has not been painted, wouldn't any earth problems be evident from the start, not after an hour or so?
Hi, sorry, by plug shorting out i just mean't oiled up which shorts the spark to earth. Tracks down the side of the sooty oily bit on the insulator & earths out on the steel base of the plug. [think that sounds right!!] run out of constructive ideas though sorry.
That's pretty much what I'm thinking is the problem, but what I can't understand is why isn't it happening to the two other bikes that are jetted much richer, and run the same fuel and plugs ???
I would have thought that if a bike can destroy a plug in an hour, it would be a blubbering, smokey mess, which isn't the case.
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A bad earth system will cause a weak spark due to the high resistance in the ignition circuit. With a nice perfectly clean new plug everything is fine but the spark is weak causing poor combustion and resulting in fouling of the plug. This then appears like an oiling up problem. With the weak spark the plug is very easily fouled and the poor combustion causes carbon deposits more than normal.
The HT (spark plug) circuit in basic terms starts at the HT coil lead through the plug cap, then the plug resistor, then across the plug gap to the earth electrode, through the cylinder head and engine cases back to the frame via the engine mounts and finally from the frame back to the HT coil. A bad connection anywhere will weaken the spark because it restricts current flow.
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Could check the air gap the spark can jump.
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Yep remove the plugs earth electrode and the spark should easily jump that gap. CDIs will jump much much further.
Also been caught before and it sounds a bit silly. With the fuel tank off (carbie full of fuel) test the ignition system in total darkness. Look for any errant sparks from plug leads, plug caps, coil mounts, engine mounts etc.
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one more [one more thing]--don't throw the oiled up plugs out, [if fairly new], they are still ok & just need a clean. If you get the oiling up thing sorted out the plugs will stay clean [tan colour] & be good for a very long time. In desperation [at home] i get my plugs clean enough by sitting them on an old house brick & heating the plug [at the oiled end] with my little lpg burner thungy [use it to solder cable nipples on], or i suppose hold plug with pliers vertically over the tip of any clean flame for a while to dry out & burn off the oil. Don't do what i did once with the oxy/accetylene & got a bit carried away [think it was a resistor plug--R type] & got it so hot it went off like a rifle shot & blew the top end [where cap fits on] out of the plug. Anyway--that's my 10 cent's worth.
ps ,A mate said recently he cleans his plugs with a water blaster--tried it but without much luck, maybe if you degreased the oiled bit then blasted with the jet nozzle it might give it another life once you have the motor running clean.
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Pics of plug,
(http://i118.photobucket.com/albums/o82/evo550/005.jpg)
EVO if you were to put THAT plug in now would the bike run ?
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Pics of plug,
(http://i118.photobucket.com/albums/o82/evo550/005.jpg)
EVO if you were to put THAT plug in now would the bike run ?
Nope, it's been out of the bike for about 2 weeks, but still no spark.
Although I might try OTH's tip and try and clean the deposits off the insulator.
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Buy a can of carby cleaner. That will clean the plug [and anything else thats dirty.] It's good gear.
All sounds like weak spark to me.
Next try when it stops, leave the plug in there, but don't try to start it for as long as it takes to change the plug, or a bit longer, then try to start it again with the oily plug still left there. If it starts, it means the spark is weak and the spark is oily caused by missfire.
Check the way the low tension leads go onto the coil, if they are wrong way around the spark will be about 25% weaker.
Dont give up!
cheers pancho.
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Pics of plug,
(http://i118.photobucket.com/albums/o82/evo550/005.jpg)
EVO if you were to put THAT plug in now would the bike run ?
Nope, it's been out of the bike for about 2 weeks, but still no spark.
Although I might try OTH's tip and try and clean the deposits off the insulator.
Just asking because I once bought a nice little 86/125 KTM from the bike shop but it was too cheap.
After about 1/2hr it would stop running.
Let it cool down and it would start , run for 1/2 and stop again.
The previous owner had sold it cheap out of frustration.
He had also zip tied the kill switch wire to the top radiator hose.
Snipped the zip tie and found a nice short :o, ran great after I fixed that one.
If that plug will not spark but another one will then the problem is the plug , maybe try another brand , non resistor, different heat range ?
I have seen boxes of Champion resistor plugs die because of moisture in the powder that they used as a resistor , back when they first came out.
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A little hard to tell from the last pics but looks like a good quality plug [i forget what you call them] small electrode type plug & was told these need [maybe in theory] less voltage to fire them. That said, i still think looking at earlier pics that it's an oiling problem causing a lack of spark when the oil get's baked onto the insulator. Cheers for now.
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OK so I went and got some carb cleaner and gave the tips a soak for about an hour....and it bought some back to life ;D, but something funny is happening, when it sparks some are jumping the gap and some seem to just roll around the base of the electrode, sort of where the electrode leaves the insulator, most strange I got my son to do some gopro footage, and will try and upload later......Gettin' there :)
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Sounds a like a weak lazy spark due to a buggered stator..
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Click on pic for link.
As you watch the video, you can see the spark jumping all round the place, not just across the gap.
(http://i118.photobucket.com/albums/o82/evo550/th_010.jpg) (http://s118.photobucket.com/albums/o82/evo550/?action=view¤t=010.mp4)
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I would get a crap old ES plug and file the centre and J strap as square as possible. Leave the kick start alone and spin the engine over with a drill on the flywheel nut ;D Then film that
Looks like the polarity could be wrong but need a better/closer look.
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i'll keep out of it now & if i'm wrong i'll go stand in the naughty boy corner but put my money on simply [1] plug too cold for how bikes being used [2] carburetion's set up far too rich etc. Even had [years ago] someone playing with throttle slides in a yz80 & was trying a slide fron an RD350 [or earlier R5] chrome slide & had got hold of a RH slide instead of left hand consequently the cutaway ended up pointing forward instead of back making it run 'super rich', is just a thought but not likely i know with a modern 85cc. Just [from pics & video] looks like the oil gets baked on to insulator then tracks down the side to earth--not really a fault of the plug as such but ends up being reason it stops. Hope you get it sorted. Have a good day--[pretty depressing weather in this part of NZ lately]
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Update, Update, Update. :D :D :D
Something Overthehill said triggered my memory about a something I read about YZ 85 slides and the fix was replace the whole carb with one from a kx 85. Apparently the slide and needle are way wrong in the standard Yamaha carb.
So onto ebay I went, secured a carb and fitted straight up, and to our complete jubilation (mine and the young fella's) IT WORKS.
He can't beleive the difference in throttle response and best of all we've been riding every day on the same old plug. before the swap we would have gone through 3 or 4 plugs by now. Fingers crossed it's all clear sailing from now on.
Thanks to all for advise.
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I'd say you sorted that one yourself [good on ya], good idea though tossing different ideas around for a bit & hearing how others have overcome their problems, till something rings a bell. Cheers.
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Chalk one up for 'Over the Hill' ;D What's the new needle/slide combo?
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Stanadad YZ 85
3 slide
nbkf needle
48 pilot
Standard KX 85
3.5 slide
nape needle
45 pilot
I had already dropped the pilot on the YZ to 45 before the carb swap, so it was just the slide/needle combe change.
I'm not to bad at picking up needle clip and jetting issues with carb settings, but slides are a mystery to me.