|
Posted by Mike W. on May 20, 2008, 10:03 pm
>I finally got around to starting the break-in on my CR125 yesterday.
>Everybody says that the bikes are brutally rich down low as delivered
>- and basically won't even run, fouling plugs in 5 minutes if riding
>in technical terrain. The JD jetting kit uses a 35 pilot, down from
>55 stock (!) and keeps the stock main, with his special secret
>needle. I expected to have a bunch of trouble with the stock jets, so
>I pre-emptively dropped the needle clip a position and lowered the
>float 1.5mm. I also set the air screw to 3 turns out.
>
>The first heat cycle consisted of 3-5 minutes of idling, with the
>occasional blip to keep it running. It was definately rich off idle,
>although it wasn't blubbering excessively, and it loaded up a couple
>of times (now I know what "loading up" means) - I thought I was
>fouling a plug once, but it cleared by holding mid-throttle for a few
>seconds "blooooooooooorraaaAAAPPPPP" accompanied with 25000 cu ft. of
>smoke once it wound up. The smoking cleared right up after a few
>seconds.
what color smoke?
>
>After the first heat cycle, I pulled the plug and it was basically
>white - maybe a little grayish down deep on the insulator. Given the
>rich condition, I expected that it would've been well sooted up by
>then. What gives?
>
>JayC
I've been reading plugs a lot recently... in groups of 4... though I'll
lead with a caveat that I haven't done anything with two strokes. I think
there is a bit of nuance around reading plugs and that you are wise to
gather other kinds of data, like also reading the inside of the exhaust
headers, sound, vacuum, head temperature, etc. At least I'm finding data
SETS carve up solution space more neatly and confidently than single data
points.
I've been getting significant color changes in 15-20 minutes of
running/riding. I operate under the belief system (again, it appears there
are several) that the pertinence of a particular region of the insulator
varies with average engine speed, with the low-speed/idle area near the tip
and the high-speed area near the base where the insulator is coolest. As
you increase engine power, the additional heat burns away the coloring at
the tip and possibly at the mid-point... you have to look at the base.
It sounds like your plug would be reading fine (a little gray oriented
toward the base of the insulator), IF you had been up at higher
power/rpm... but you're burning the shit off the tip-end of the insulator
without going higher speed. I think you're running lean. Your bike setup
might not have been done with gasohol in mind... it runs you effectively
lean and therefor hotter (white plug coloring). I run lower fuel to oil
ratios in all my 2-stroke lawn equipment because of this... say moving 40:1
to 32:1, etc). It is my understanding too that most engines are delivered
at the lean end of the spectrum for EPA testing. Maybe not an issue for
this bike, but maybe. Also, you're messing around only with the pilot jet
and while it contributes fuel across the full throttle band, it'll have the
greatest impact at more closed throttles. That's a huge drop. The plug is
white in the low-rpm/power area. These go together. Did you try to read the
plug before you broke it in? Actually, do you want to be doing break-in
before or after you set the bike up? I'd think it matters but I don't know
the answer to that.
A cheap experiment I might suggest would be to get an IR thermometer and
run the engine with the stock setup at a constant rpm for whatever time it
takes to reach operating temp. See what the head temp is... be precise in
where you aim it and try to pick an area where the material is "consistent"
as different materials and colors and finishes will have different levels
of heat emission. Then set it up your way... which was hotter? If the
latter was *markedly* hotter 50-100 degrees, I'd think you have a serious
lean condition.
You can verify your plug reading by looking inside the exhaust header...
black = rich, white=lean. Look for dark tan/gray here too.
Since you're running a white on the insulator near the tip, you have heat
and maybe that's coming from ignition advance. Look at the ground electrode
and see if you can see a "heat line" on it between the elbow and the plug
base. If so, you're probably in the ball park. If not, you might be running
too much advance and getting extra heat from that.
Then again, I can't get my shit working so I'd ignore everything I just
said. Good luck.
Mike
--
Mike W.
96 XR400
70 CT70
71 KG 100 (Hodaka-powered)
99 KZ1000P (training)
99 KZ1000P (rider)
00 Beta Rev-3
| 
Yahoo! 
Google 
Windows Live 
del.icio.us 
digg 
Netscape 
XML Sitemap