Author Topic: Creating a "lean" condition  (Read 2825 times)

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ShanMan

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Creating a "lean" condition
« on: June 18, 2003, 03:12:44 AM »
OK, I was thinking about how my piston was trashed by what was most likely a lean condition. (it was probably also bad gas too, but I digress) Intuitively, I have been running 32:1 pre-mix all season. The majority of places we ride tend to be a bit warm (i.e. Glamis, Gorman, Bell, etc) by SoCal standards. I was taught that to combat the heat and high loads of sand riding, the safe thing to do is run 32:1 and run race gas. A thought has occured to me however...when running a lower fuel/oil mixture ratio like 32:1 as opposed to the more traditional 40:1 or even 50:1 means that you actually are giving the motor even less fuel to burn despite the increased lubricity...effectively leaning out the motor even more! I suspect that the only way to save performance would then be to run some serious octane to save performance and to reduce the fuel burn temp (guess this is where the race gas should have come in). Is my thinking flawed here? I am now thinking that running 40:1 with about 95 octane is probably the hot ticket to a good balance of performance/reliability. Does this sound reasonable?

As a side note, I purchased another Wiseco piston kit. it is the same piston as the one I pulled out because the cylinder bore looks pretty good still. Knowing what I know about thermal expansion of forged aluminum verses cast or billet, I suspect that the break-in for the new piston would be different (read: more deliberate) than a stocker. Should I be extra careful to let it warm up slowly in order to avoid any unpleasant noises and such? TIA.  :)

Offline Paul

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Creating a "lean" condition
« Reply #1 on: June 18, 2003, 04:05:39 AM »
The Wiseco's have less tolerance than stock (forged versus cast taking expansion into consideration) but it's only .001 or something silly like that. [ Or so I've been told ]  :)

Anyways... I run nothing but 40:1 and use the jetting approach to "fattening" it up - raise the main about two steps when it's dune time, I don't change my mixture. I've never had to. 40:1 in a 2000 KX500 (spare engine) went to the dunes, the track, the woods, etc... and never gave me a problem. I just did a topend on that engine (the first for it) and it was clean as a whistle inside, no noticable carbon anywhere.

I run Maxima Super M @ 40:1 in 2 gal Sunoco 110 and 3 gal 91. Keep the big 5'er over 94 octane and a stocker won't knock.

woodsy

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Creating a "lean" condition
« Reply #2 on: June 19, 2003, 06:27:08 PM »
IMHO - Another thing you might wanna consider is doing a plug chop anytime you change ratios!  Yes, ratio's do change jetting specs and the only way to accurately dial it back in is to check the plug color!!  I have rebuilt more "paper tuned" 2 smokes then I care to mention - it always seems to be the poor guy that followed the parts guys suggestion for jetting/ratio's instead of taking the time to do a chop....
Woodsy