Re: First time jetting. How does my plug look?

Dirty30 Dillon /

> Marc Friedman Wrote:

> -------------------------------------------------------

> That plug chart of Jay's is not the color of an insulator after two

> miles of it??? ..what about the color on the original post

> ...some is developing under the a brand new plug next

> to any plug chop so it's possible to evaluate if it's white or even

> whiter ...


> Here's an idea: keep jetting up until it's gurgling. Go higher and it

> will four stroke to death. This is the cheetachrome method...if u keep

> changing things and nothing happens ...other problemo...


> Everybody says you gotta cut the threads off the plug to get at the

> base ..true..but really how many do's quite a pain


> If you rode for two weeks and your plug was that white ...that's real

> bad. A two mile chop is a pretty subtle thing. Also where the part of

> plug most exposed to the exhaust port is at least on a Vespa is a bit

> different than elsewhere, ie leaner . But perhaps I'm wrong on all of

> this. What u say Dillon?

Honestly, I've never chopped up a spark plug to check the base of the electrode for coloring. At this point im pretty familiar with what the bikes I work on should run like, and how to correct said issues.

Like right now I can tell that after adjusting my derbis timing 2* advance, I need a bigger cutaway in the slide and to raise the needle, due to a cold temp lean bog at 1/8-1/4, and hot running conditions mid throttle.

I do agree Mark, vespas, specifically kitted bikes, will have a lean side on the exhaust side of the plug. I try to tune that out if the power can head a size or two richer

Re: First time jetting. How does my plug look?

"So how can you tell whether you've chosen the right heat range? It's easy: a spark plug should be getting hot enough to keep its insulator nose completely clean, with all deposits burned away, but not so hot that its electrodes show signs of serious overheating. These are things to look for on a new plug that has been subjected to a few minutes of hard running. After many miles of service insulators acquire a coating of fuel deposits, with some coloration from oil in two-stroke applications, and there will be some erosion of the electrodes even when everything is normal. Don't try to read old spark plugs; even the experts find that difficult. New plugs present unmuddled information about what's happening inside an engine, and can give you a complete picture after just minutes of hard running. At least they will if they're running hot enough, and that should be hot enough to keep the insulator clean.

A lot of amateur tuners, some of whom are fairly successful, will look at some plug freshly removed from a two-stroke engine and offer advice based on the color of the oil deposited on the insulator nose. In fact, if the plug is hot enough there won't be any color, and if there is that still has nothing much to do with air/fuel mixture. If you think about it you'll realize that the only color you can get from an air/fuel mixture is the color of soot. When the mixture trapped in an engine's combustion chamber has more fuel than can be burned with the available air, then combustion will be incomplete and the excess fuel will remain as soot, which is not brown or tan or magenta or any color other than black. And if your engine's mixture is too rich, the sooty evidence will be present on the spark plug's insulator, in a very particular area.

We cannot stress too strongly the need to give spark advance your closest attention, because excessive spark lead is the most frequent cause of detonation, which is a real engine killer. You can't stop advance-produced detonation with a cold spark plug, nor with anything but a wildly over-rich mixture. Also, excessive ignition advance has a bad effect on performance. We ran a 250cc road racer at the drags a few months ago, and found that retarding the spark about five degrees from the manufacturer's setting raised the trap speed from 106 to 110 mph. Similarly, there's a 125cc motocross machine residing in our shop which runs a lot stronger and cleaner since it has been retimed for less advance, jetted leaner, and been given a hotter spark plug."

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