View Full Version : spark plug pics,lean or OK ?
Hi guys as some of you will know \I've been chaning main jets in my race bike. It was running lean with dynojet 140s so i went up to mikuni 152.5s. Since then I've done a track day at Cadwell on the 1st of Sep. and now my plugs looks like this see attached. I'm thinking it could still be a little lean.
I have some 160s. http://forums.sv650.org/images/icons/icon7.gif
What do you think ?
I've got no money for dyno time. and the bike isn't road legal.
Blue_SV650S
10-09-08, 11:06 AM
The pics make it look a bit green ... but if it is light brow/grey then I'd say that was absolutely fine (if not a little rich as the plug threaded but looks slightly sooty) ... if it starts to look more white than grey, then up-jet ...
yeah, it's got a shiney apearance. It has got a green tinge to it.
Blue_SV650S
10-09-08, 11:25 AM
yeah, it's got a shiney apearance. It has got a green tinge to it.
What fuel are you using?
super unleaded. I think it's 97 RON.
Blue_SV650S
10-09-08, 11:35 AM
super unleaded. I think it's 97 RON.
Ah, that'll be the green then .. the super unleadeds have all sorts of fruity additives in ... I wouldn't like to say what colour they would turn the plug!! :D
Bring back good old 4-star I say ... you always knew where you were with plug colour and 4-star!! ;)
vardypeeps
10-09-08, 11:42 AM
Those plugs look fine to me. I would say it's running fine. I suppose when it's track use it can mean a big difference tho
Mr_Chin
10-09-08, 11:54 AM
Linky to spark plug pics:
http://home.wanadoo.nl/xavira/sparkplug/spark2.htm
Chin
You can't really tell much by just looking at the tip - you have to look at the insulator right down inside. And you can't tell much without knowing what the grade is and whether you 'chopped' it at peak revs or not. If you didn't, the risk is that you are merely looking at what the fueling is at part throttle. And finally, you can't tell anything at all from the body: that's only running at cylinder head temperature - about one seventh of what the insulator and electrodes are running at.
Start with: "does it feel that it is down on power or misfiring at max revs?"
How does the bike feel , does it feel as if it lacks power or does it run ok, this may be a useless piece of info to you as my bike has FI but when my bike was dynod the fella that done it leaned it off a bit because he said they went better that way. He is the co founder of dynopro and was responsible for testing the bikes in mini twins at race meets so I kind of trust what he said, but he could be wrong.
I know almost nothing about tuning a motor for lean / rich running. However, according to a site I've referenced in the past, Mikuni 152s are not a very big step up from Dynojet 140s:
http://roadstarclinic.com/content/view/61/96/
You may need to go further if you were running more than a very little lean.
HTH
Jambo
If that graph is to be believed then I'd say you're still too lean. I'd be looking for lambda 0.9 or about 13:1 A/F at the leanest personally for max output.
As for plugs, visually it can be tricky as others have described, and to a large extent it can be a reflection of the plug grade suitability. What grade are you using? If this is a track only use, there'll be little problem in going one grade colder than stock, the only risk is some cold fouling which you can avoid simply be careful start-up procedures, but once up to race speeds it won't be an issue.
Yeah. This graph is from when i was running 140 dynojets. I've now gone up to 152.5 mikunis. It seems to be fueling a lot better but I don't want to spend another £60 to dyno it and find out for sure. The whole idea of racing in minitwins was to keep the cost down. I havn't even got a set of wets !!
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