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White spark plug end yet also running rich?

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mistermentali...
Two Stroke Sniffer



Joined: 30 Apr 2013
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PostPosted: 14:58 - 14 Mar 2018    Post subject: White spark plug end yet also running rich? Reply with quote

Ok this is probably going to sound dumb but if a black spark plug end and middle bit means your bike is running too rich and a white middle with no black deposits means the bike is running well, what does a perfectly clean white middle bit yet blackened outer section mean please?

Somehow only the outside of the spark plug is black, thick black deposits, but the inside centre section is clean spotless white save for the very bottom.. I've tried searching google and can't find the answer as it seems usually a rich running bike also has a black middle piece as has usually been the case on other plugs I've seen that are rich.

I could guess but this may be wrong, could it mean that the idle mix is too rich but the main mix is ok, i.e it runs rich on idle and therefore as it doesnt idle much on a typical commute then it isnt having enough idle time to coat the middle part? I will try and include a photgraph showing what I mean although I had already wiped some of the black deposits off the outside when I thought to take a picture, it was coated with a fluffy black carbon deposit.

Please excuse what may be a really stupidly simple to answer question. Thanks.

Dave
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Bloggsy
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PostPosted: 15:04 - 14 Mar 2018    Post subject: Reply with quote

It would suggest a weak mixture
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Tankie
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PostPosted: 16:10 - 14 Mar 2018    Post subject: Reply with quote

White inner = lean , outer body black normally indicates burning oil or the plug is not reaching it's correct temp, eg short runs
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jaffa90
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PostPosted: 16:19 - 14 Mar 2018    Post subject: Reply with quote

Tankie wrote:
White inner = lean , outer body black normally indicates burning oil or the plug is not reaching it's correct temp, eg short runs

I agree with Tankie so what bike model and what plug spec.
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mistermentali...
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Joined: 30 Apr 2013
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PostPosted: 18:54 - 14 Mar 2018    Post subject: Reply with quote

Thanls for the replies, its a hn125-8 and does two twenty four mile trips a day to and from work but plugs look like that. The spark plug is an ngk dpr8ea9 with a spark plug cap that has no resistor because the plug itself already has one so I use a non resistor plug cap.

Should I try an alternative spark plug?

Thanks,
Dave
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Speedy23
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PostPosted: 18:58 - 14 Mar 2018    Post subject: Reply with quote

You really need to do a compression test (shot rings) or have a look at the valve guides and seals. I agree, you are burning oil with a weak mixture.
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Triton Thrasher
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PostPosted: 19:08 - 14 Mar 2018    Post subject: Reply with quote

How does it run? If ok, why worry?
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Speedy23
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PostPosted: 19:59 - 14 Mar 2018    Post subject: Reply with quote

Worry because it may be running OK now, but it is unlikely to do so for long. If there's oil getting into the cylinder, it will be forming a huge buildup,of carbon on the back of the valves which will ultimately cause pre ignition and running on. Time to bite the bullet now.
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mistermentali...
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PostPosted: 16:48 - 15 Mar 2018    Post subject: Reply with quote

It runs fine except towards top end of gears when its sluggish but I have no idea how to do a compression test, does that require special equipment?

Thanks,
Dave
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Triton Thrasher
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PostPosted: 19:02 - 15 Mar 2018    Post subject: Reply with quote

Speedy23 wrote:
Worry because it may be running OK now, but it is unlikely to do so for long. If there's oil getting into the cylinder, it will be forming a huge buildup,of carbon on the back of the valves which will ultimately cause pre ignition and running on. Time to bite the bullet now.


Ok, is carbonised oil building up on the back of the valves?

They're not all that difficult to get a look at.
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Triton Thrasher
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PostPosted: 19:03 - 15 Mar 2018    Post subject: Reply with quote

mistermentality wrote:
It runs fine except towards top end of gears when its sluggish


Is the air filter clean?
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mistermentali...
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PostPosted: 19:36 - 15 Mar 2018    Post subject: Reply with quote

If I recall correctly doesn't that mean removing the cylinder head? I will have to wait til next week to get a chance to do that but I have ordered a compression tester which should arrive by the weekend so I can at least check compression then.

The air filter is clean. It's a cone air filter with a splashproof cover on it, checked it and its clean and dry but smelled slightly of petrol. Could a bad spark plug cap cause a problem?

I ask because I have a spark plug cap which is a no brand resistorless one and maybe if it had developed a fault that could be a factor?

Dave
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Speedy23
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PostPosted: 17:48 - 17 Mar 2018    Post subject: Reply with quote

Hi Dave - the spark plug cap will not produce that burn pattern. I still think you're burning oil in a weak mixture. The compression tester is easy to use - remove the plug, screw it into the plug hole and turn the engine over a few times. Note reading. Remove tester, put about 10 - 15 ml engine oil down plug hole then repeat. If reading goes up significantly, rings are shot. Try to find out what compression reading should be. If it's a lot lower than that, but the oil hasn't made a difference, suspect valve guides/seals.
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mistermentali...
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PostPosted: 22:55 - 19 Mar 2018    Post subject: Reply with quote

Did a compression test cold and it read 75 psi. Then saw in Haynes manual it said run the engine a little first so I did and got 115 psi. Not got any oil at moment but will have later in the week and will try another test then.

Hopefully it will help me narrow down the problem better thanks again,
Dave
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stevo as b4
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PostPosted: 23:02 - 19 Mar 2018    Post subject: Reply with quote

I honestly think in this day and age, reading sparkplug colour is total fools game and not only inaccurate in the most part, but it's open to massive misinterpretation too.

I've read a few articles on it and in relation to tuning, and it's been shown many times that plug tip colour on used plugs gives you close to fuck all indication of what's going on in.the cylinder and the air/fuel ratio that's being combusted.
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Rogerborg
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PostPosted: 23:30 - 19 Mar 2018    Post subject: Reply with quote

mistermentality wrote:
Should I try an alternative spark plug?

If you're doing high speed runs, I'd try a DPR9EA9. I'd also suggest that you put the stock airbox back on, and/or increase the main jet from 90 to 95.

But I agree that looks like oil being burned. 75psi indicates that your rings are shot, and the higher reading was oil sealing them up. Sorry, but the good news is that it's a very simple pushrod engine and replacing the rings (and checking the piston and barrel for scoring or damage) is about as easy as it gets.
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mistermentali...
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PostPosted: 18:12 - 24 Mar 2018    Post subject: Reply with quote

Well although piston and rings and barrel looked fine I put new rings on and a new cylinder head, as had a new one I had never used, and compression is still just as bad so as there seems nothing else that causes low compression it looks like my engine is probably screwed.

Barrel is fine no marking inside, rings were fine, valves etc were clean so am very confused as to what is the problem. Any more help with suggestions is much appreciated.

Thanks,
Dave
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jaffa90
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PostPosted: 18:40 - 24 Mar 2018    Post subject: Reply with quote

Speedy23 wrote:
Hi Dave - the spark plug cap will not produce that burn pattern. I still think you're burning oil in a weak mixture. The compression tester is easy to use - remove the plug, screw it into the plug hole and turn the engine over a few times. Note reading. Remove tester, put about 10 - 15 ml engine oil down plug hole then repeat. If reading goes up significantly, rings are shot. Try to find out what compression reading should be. If it's a lot lower than that, but the oil hasn't made a difference, suspect valve guides/seals.



Did you do the test as Speedy23 suggested???????????????
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Tankie
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PostPosted: 20:27 - 24 Mar 2018    Post subject: Reply with quote

I put new rings on and a new cylinder head,
So now you have to run in the bore again before you re assess the proformance and compression
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mistermentali...
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PostPosted: 21:07 - 24 Mar 2018    Post subject: Reply with quote

Hi, I put on new piston rings and a new cylinder head and did a 22 mile journey but it had exact same performance as before. I do not know much about mechanics so thought that new rings and head would fix the problem straight away. I didn't do an oil compression test after replacing rings though but will do tomorrow. Thanks for helping with replies, it really is a big help for a novice like me.

Dave
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