Big bore jetting - lx 50 big bore plug read help please!
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Lurker
Lx 50
Joined: 08 May 2019
Posts: 4
Location: Denver
Tue Jun 04, 2019 6:07 pm quote
Hi all,

been lurking here a while and finally bit the bullet and bought the big bore kit. 2009 Lx 50 2 valve. Did the big bore, cam, variator, and malossi filter this weekend.

So I live in Denver - 5280ft.

I put a brand new plug in and fully gassed it around the block with the stock #75 jet and then cleaned the plug up and put the #80 jet in and did the same. Here are the two. The #75 is the one with white and the other is the #80. I've never done this before - what do you guys think?

The white on the 75 indicates to me that it's way to lean - as expected. I know you want a mocha color, so is the 80 too rich?

When I watched the ScooterWest video where they install all the same stuff, they're in San Diego and put in a #80 . . . With that reasoning #80 would be too rich for me here in Denver.

Any help or advice from some more experienced folks would be much appreciated.

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Ossessionato
73 Rally, 74 Rally, 76 ET3, 80 P200, 63 Li125, 65 Li225 Silver Special, 86 Elite 80, 2015 HD Road Glide Special, 2011 Ural Tourist
Joined: 18 Jan 2012
Posts: 3137
Location: Oceanside/ SF
Tue Jun 04, 2019 9:04 pm quote
I dont know about 4 stroke tuning only two stroke, but Iíll chime in for now. Iím happy to learn if things are different between the two.

With a two stroke plug chop, you need a few miles at wide open to accurately see how the engine is burning at its hottest point. Run it, cut the ignition, coast to a stop, immediately remove and replace the spark plug for each jet. Then you need to cut back the threads (hack saw/ Dremel tool) to see the base of the white insulator. Itís cone shaped and you want to see it at the widest part. That should be starting to form a ring. Look at the color of the ring. Perfect is coffee brown. If its tan, keep upjetting.

I understand your theory of reducing your points 5 for the altitude but would say richer is always better than leaner while breaking in. Leave the 80 in for break in and then go to 75 after a few hundred miles. If its too much and you foul a plug its only a few bucks verses running lean and seizing your kit. Disclaimer: Again this is two stroke talk.

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Hooked
GTS 250
Joined: 26 Apr 2008
Posts: 195
Location: California
Wed Jun 05, 2019 7:07 am quote
I don't know much about reading plugs, but the amount of fuel needed is not 100% based on altitude. It's all about air density, which factors in temperature & humidity. I would guess that the humidity is much higher in San Diego than in Denver.

This video is somewhat relevant: https://www.youtube.com/watch?v=Scw3mrksgGk
Lurker
Lx 50
Joined: 08 May 2019
Posts: 4
Location: Denver
Thu Jun 06, 2019 6:51 am quote
Thanks guys

At this moment the air density in Denver is 80% and in San Diego it's 98/99%.

This is factoring alt/humidity and temp.

https://airdensityonline.com/track-forecast/Bandimere_Speedway/
https://airdensityonline.com/track-results/Qualcom_Stadium/

With that being said - that's effectively a 20% difference.

If they're jetting the same exact lx 50 with the same exact carb and 80cc kit - it stands to reason I have to be smaller than a #80.

Actually cutting the plugs is a little too far for me . . . . I'm going to rock this #80 for a bit and pull it and see how it looks. If it's too much I'll drop to a #78

The #75 is definitely too lean - the carb when instantly white.

Thanks guys.

-dd
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