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Spark plug analysis

9K views 35 replies 12 participants last post by  Motorbikerx 
#1 ·
Hey guys can you all give me an opinion on what these plugs indicate may be going wrong with my engine?

The darkest image is the one from my rear cylinder. It looks to be running rich.

The lighter one is from my front cylinder. It looks to be running lean.


What do you all think?
 

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#2 ·
How long since the bike was dyno'd? How many miles on those plugs? Have you tried OEM plugs? Inquiring minds want to know.
 
#3 ·
No problem. Last dyno was August 2013. There is at least 65k miles on those plugs. I had the OEM plugs changed after the dyno when I had porous head problems.
 
#4 · (Edited)
looks typical to me. You have to remember the two cylinders run different.
The porcelain around the plug’s center electrode can be divided into three areas for reading. The area that is closest to the tip is affected by the idle and transition circuits carburetor circuits and is of no real concern.
The middle area is only colored when you drive down the road at around a steady 30-40 mph and is normally affected by the primary circuit jetting with the power valve closed.
The area you are interested in is that third that is all the way up inside the plug where the sun don't shine. This area is colored when all is wide open under full power because the combustion chamber heat totally cleans off the other two areas. It will take a special plug reading flashlight with the magnifying glass to view it correctly. Plugs cannot be correctly read by just quickly looking at them with the naked eye. You see people doing it all the time because they do not know how to read plugs.

I could not find anything talking about FI
 
#6 ·
Damn VisionJohnny. Good info and thx.
 
#7 ·
Now there's no lead in our juice anymore its nigh near impossible to read plugs the good ol' fashioned way,
also you gotta start with brand new plugs and preferably a dragstrip or a section of closed road where you can run flat out in a high gear and kill the engine as you pull the clutch lever in.
65K !!!..........You've certainly got a good run out of them plugs and the gap is so wide you could drive a truck through them.
I'd get a brand new set of OEM plugs and fit them at the strip, throw the ones in the pic in the rubbish bin,
do a good hard run and a proper plug chop and then have a look.
Take note of the colour of the face of the first ring of thread and if its blue its lean and hot.
With unleaded gasoline thats about as good as it gets as far as plug reading goes, anything else is pie in the sky.
 
#8 ·
Thx bro. That's good info. I think I'll try it.
 
#9 ·
These plugs don't appear too bad to me for a city bike. I'm sure there are other reasons but to me they look like they are not getting hot enough long enough to burn off the normal deposits. Take your spark plug tools with you and get that thing out and let it run like it was built to do for a couple of hours then shut it down like the Aussie says. You might find a whole different more healthy look.
 
#10 ·
A quarter mile flat out is fine we dont want you getting arrested.
But hey if you can ride flat out for a couple of hours without slowing or ending up in jail....go for it
If its seriously lean (I dont think it is) it may melt an exhaust valve running flat out for an extended time.
 
#11 ·
I don't care what plugs they are, 65K is way too many miles. I change plugs at 10K to those the Vic engineers thought were right for my engine. I don't think I know more than them. And yes, I can feel a difference with new plugs at just 10K.
 
#12 ·
Everyone is pretty spot on! Us "more experienced" AKA old ornery Bastards that built motors back in the day before fuel injection had to know how to read plugs. We'd toss in a set of new ones, take it out and run it hard, pull over pop one, read it and adjust. The current fuel, modern fuel injection and ECU control have made that skill almost obsolete.

Your plugs look normal with that many miles IMO and Ric is right, those plugs were left in way too long. For me 15-20 thousand is good but I do a lot of high speed freeway riding. Just for the record the rear cylinder is going to look way different, it runs hotter as it doesn't see the airflow the front cylinder does.

Speaking of which, is everyone running the NGK plugs? Anything else that works well? I like NGK's, I run them in the Triumph Triple and it like's them.
 
#15 ·
Speaking of which, is everyone running the NGK plugs? Anything else that works well? I like NGK's, I run them in the Triumph Triple and it like's them.
I'm with the RICZ line of thinking....The NGK's worked great and are speced for the engine, so thats's what I replaced with.
 
#14 ·
Plugs seem to be burning normally in a street driven bike. The only thing you really see when reading a plug is what just happened, and it you were just cruising. it means your mixtures are at least close.
Not a fan of precious metal plugs for the most part. Yes they can quite happily go 100K without change, but they are usually seized to the head by then. 10K on a conventional plug is overkill though. I change mine at 25-30K.
 
#18 ·
I know that 10K is overkill Kevin, but damn, they are so cheap, why not. Then I know I have really good sparklers.
 
#20 ·
I stock them by pair's, ha ha
 
#23 ·
your photo of the spark plugs more than likely is from back in the day when there was lead in the gas. Has nothing to do with today's **** gasoline
 
#28 ·
That should discourage a ton of sales of that crap stuff.
 
#30 ·
What do you all think about the splitfire plugs?
 
#31 ·
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