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Old 05-30-2007, 07:16 AM   #31
mars
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dirty s what idle jets are you using?
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Old 05-30-2007, 07:26 AM   #32
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Quote:
Originally Posted by mars
dirty s what idle jets are you using?
Whichever idle jet comes stock. The manual says it's a 45.

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Old 05-31-2007, 10:14 PM   #33
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Quote:
Originally Posted by dirty_sanchez
The jetting is finally spot-on. On hard acceleration, she'll dip into the second rich yellow, moderate accelleration first rich yellow, steady cruising at about 70 indicated, she's mostly solid rich green with an occasional first rich yellow. 50 to 60 cruise at about 4k rpm's, she's mid green to rich green. At about 80 indicated, she's mid to rich green.

But the cool thing is that no matter what speed I'm cruising at, if I give her a little or a lot of nudge with the wrist, she'll dip into the first rich yellow-which is where the "Max Power" is found according to J4P and will get up and scat.
Yeah it's kinda weird about the BST. I was expecting lean dips, but it actually gives a rich surge when you wack the throttle. My motor doesn't handle the greens very well when it is under stress. Something about the G1 cam makes it a bit sensitive to leaner mixtures. It starts falling all over itself at about mid-green. When I have it too fat at higher throttle it starts a bit of misfiring.

I've not entirely evaluated the main jet on it. I was going to start moving down from 165 but I lost my 162.5 so I had to order one. When I went from clip #3 to clip #4 I lost about 9mpg, went from 46mpg to 37mpg. It runs a lot stronger, but it is fat above 1/2.

When you get the right mixture, it seems to achieve higher rpm at lower throttle. So I'm not all that concerned with moving leaner, I just want to get it to peak efficiency and see what economy is there.

I run the idle on up at the first yellow rich. I couldn't get it there without at least clip #3.5 with a fresh needle. My original needle was reading about 2 clips richer than a new one! No wonder it ran like crap.
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Old 07-02-2007, 07:45 PM   #34
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I did some taping up of my exhaust joints and it appears that the silencer flange is the culprit in my strange air-fuel readings. Evidently air is getting rammed into the flange bell and it kinda messes with things a bit. I know it messes up my meter readings, but I could also feel a matching motor reaction.

Anyways, I have a new way to seal that flange. Not sure about the longevity, but it should be ok providing the temperature doesn't cause the silicone to crack too badly. I use this method on my two stroke cylinder header and it seals forever.

I was kinda cheap and only used a couple of wraps. But it hasn't gotten crunchy yet. I expect it will to some extent, but I figure a few more wraps and it should be good indefinitely. This is high-temp silicone tape called stretch & seal (Nashua brand). It's at home depot in the plumbing dept. Wrap & then safety wire.
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Old 09-30-2007, 06:12 PM   #35
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Update. I've been riding the LC4 for the past few weeks. I got sick of swapping the O2 meter back and forth so I bought one just for the bike.

Here are my current settings:

Sea-level, 1999 640, ids2 quiet core 8 discs, racing airbox cover, no snorkel but airbox top hole maybe 1" wider. I'm running:

4.5 clip
165 main
47.5 pilot

One surprising difference is the effect of the racing airbox cover on the BST. It leaned out the mixture a lot. I think not so much because of the increase in air flow, but because as mentioned in some other threads, this airbox change results in a bit less slide movement with the BST.

I have gone up to 4.5 clip from 4.0 to compensate a bit, but it is still running leaner than before, and not quite linear. I think it will require a weaker slide spring (or one or two clips clipped) to get the slide to track linearly again with the racing airbox cover. I will probably try that before I increase the pilot. I have the fuel screw turned a little more than one turn more than before the airbox cover.
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Old 10-01-2007, 04:44 AM   #36
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I love reading threads like these. Tuning for optimum performance and efficiency can be bloody finicky on these lc4's, especially if she's done some mileage. Lotsa vibrations, combined with the original carby (worn slide, needle and seat etc), loose fitting or split intake/exhaust boots and those bloody header pipes can give erratic and inconsistent results. Still, I love fiddling with my beast to tweak a little more 'gusto' out of her. Not anywhere near as precise as what has been described in this thread but it does give some very definitive logic in areas I know I have overlooked! Good job potato and others!
Just for an interesting comparison, this is what I am running:

'05 640 Adv.
FCR 41 mx Carb for Sea level up to 3500ft. @ 75%+ humidity.
170 main
45 pilot
Needle (JD kit 007) Red on 5th from top
Fuel mixture 1 and 3/4 turns out
Still fidling with the pressure and duration of the pump, have a thin oring currently installed

Full Akro headers and muffler (with insert)
Removed snorkel
Stock 16/42 gearing

I've always wondered about installing the jet4power system and have been meaning to take my set-up through a buddy of mine who dynos race bikes and has some pretty trick anylizers, giving detailed graphic readouts (incl. fuel ratios) at varying loads/revs.
After quite a bit of tinkering and adjusting, I keep going back to the above settings as they seem to give the best overall throttle response at all rev ranges and I can obtain 41 mpg when riding conservative and around 36 mpg when the right hand gets in the groove. I believe there is still a lot of room for better mileage without a 'noticeable' drop in performance but having a system like the jet4power and similar, this would definitely help to achieve this.
Intereting to note (although I haven't measured actual temperatures), it looks as if the collector pipe (where the two headers form into one) runs hotter than either of the engine pipes. Could be wrong but it is 'blued' where the individual headers have maintained their nice titanium 'silver' colour. Dunno?!

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Old 10-01-2007, 08:53 AM   #37
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Quote:
Originally Posted by humdinger
I've always wondered about installing the jet4power system and have been meaning to take my set-up through a buddy of mine who dynos race bikes and has some pretty trick anylizers, giving detailed graphic readouts (incl. fuel ratios) at varying loads/revs.
IMO the realtime readout is more useful than knowing the exact fuel ratios. You can see air leaks, electrical misfires, fuel starvation. It would be interesting to hook back up a pumper to see how the pump behaves, but so far I've been satisfied with this BST40 once all the other issues have been normalized. That silencer seal shown above has worked great! Plus I put in some new coil wire.

The four stroke is so tolerant that it is tough to tell incorrect mixture by seat of the pants. I started the day and the meter was almost off the scale lean, and I ended the day and it was about in the middle of the scale after a 1/2 clip change and another turn out on the fuel screw. I really coulnd't tell one way or the other at flat rpms, except that once the mixture was corrected the motor has more acceleration.

I think about my past rides where the bike wasn't running well, and I wish I had a system like this on it. It certainly takes away a lot of the guesswork, but as trond says, you have to find the sweet spot of your motor and then try to jet for that light. Though I suspect that with most four strokes, the rich green or yellow is where to aim.

One thing I enjoy is setting the proper idle mixture. That's usually a ballpark setting since the motor sounds exactly the same though a wide change in mixture, but here I can always return to the mixture that I want just by watching the light and turning the fuel screw. Doesn't work out so hot with the two stroke, but with the four stroke it is easy.
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Old 02-22-2010, 12:20 PM   #38
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Dirty, this gave me some food for thought. i have been slowly going leaner on my 640 adventure. Look like i am going in the right direction.
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Old 02-22-2010, 02:47 PM   #39
ChrisC
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Quote:
Originally Posted by jmcclesk
Dirty, this gave me some food for thought. i have been slowly going leaner on my 640 adventure. Look like i am going in the right direction.
Being a 3 year dead thread, you are unlikely to revive it. That being said, most 640 owners tend to go way overboard with "if a little bigger jet is good, just think how great a 180 will be!". I think you're finding out that's not the case. Maybe if you offered up where you started and where you think you'll end up, jet wise, a discussion may ensue...
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Old 02-22-2010, 05:04 PM   #40
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I love the oldies... makes me ... sentimental... or is it... crazy??
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Old 02-22-2010, 05:47 PM   #41
dirty_sanchez
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I love the oldies... makes me ... sentimental... or is it... crazy??
Most crazy folks don't know they're crazy.

There is, however, an online test for evilness. I'm proud to say I'm in the mid 80th% percentile.

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Old 02-22-2010, 07:13 PM   #42
ChrisC
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I'm proud to say I'm in the mid 80th% percentile.

Dirty
Yeah... but you have poop on your upper lip
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Old 02-22-2010, 10:35 PM   #43
meat popsicle
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Quote:
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Yeah... but you have poop on your upper lip
No mustache, no luv - differen' strokes fer differen' folks I hear.

Heya Chris
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Old 02-22-2010, 11:44 PM   #44
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I miss the LC4E

it was a good street bike
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