The New And Improved Unofficial R65 Forum V2
Technical Discussion => BMW Technical Q&A, Primarily R65 => Topic started by: Dizerens5 on February 04, 2010, 08:48:16 AM
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Hello everyone.....all of you on this site are so helpful I'm exploiting it a bit....but here's one that is so silly I don't think I would dare ask it face-to-face, I'd be so scared of sneering remarks like how-ignorant-can-anyone-be and so on.
I've been on bikes since a shared-ownership 1939 Triumph Speed Twin in 1956 or 57 and I still don't know the answer to this.
I must have read a spark plug a hundred times but - if I let the engine idle for a minute or two, is the reading that of the idle mixture or of the other jets mixture from the last road ride? Or the opposite, of course. In other words, just how long does it take a plug to take on a reading and "overwrite" the previous one? Thanks....
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Dang it I just typed up an answer and then closed the window instead of clicking "Post"! >:(
I think the difference between the mix of the idle and what ever other circuit you are testing will determine how long it takes for the idle to change the spark plug. You probably know that all the instructions for plug chops (dunno whence that term came) say to run the bike at the desired throttle setting for a while then simultaneously pull the clutch and hit the kill switch, so that the spark plugs won't be influenced by the idle mix.
On the other hand, my R65 used to have a right carb that somehow leaked fuel around the needle jet, making it run rich (8 stroking, sometimes) and blacken the plug. I was doing test rides for the more experienced people at a tech day, and the minute or so of low speed running and the idling on coming back to the tech day were not enough to clean up the plug from that richness. Assuming my idle mix is lean enough to do that, I don't know. But when they subbed in a much leaner than stock needle jet, the plug cleaned up fairly quickly (2 miles? I'm guessing.) and the low speed and idling I did on returning did not make it darken back up. So the effect of the idling isn't immediate, but for the clearest results don't do it if possible.
Was this a theoretical question?
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I understand why the plug chop method is advocated but I agree with ED Miller that they do not colour up instantly after a short period of idling having seen this when Ive put new plugs in and checked them after a short run. I think it needs quite a few miles for new plugs to colour up assuming the mixture is something like right.
What does blacken plugs up fast is use of the cold start enricher so if your going to put new plugs in to read them I'd get the engine warm first.