YZ125 smokes like a used pinto.

stormer94

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#1
I guess I never watched my son trail ride his bike very hard before. When he was young, I paid more attention to his health than what the equipment was doing, although it's good equipment. Now that he's older, I find myself spending more time looking at his equipment, teaching how to maintain it, and making sure it's the right gear for the job.

His bike now, a 2000 YZ125 has the stock pipe and carb, but has an Eric Gorr 134 piston and cylinder on it, with maybe 8 hours on it. We have been using "yamalube R" for mix, and mixing it 32:1. The bike has good power and the top end is fresh. Here's the question, The bike smokes like a chimney when he's on the power in something tough where the bike is working hard up a climb. Doesn't so much at idle or general trail riding. The plug looks okay. Of all the bikes we've had, this one oozes "black guck" out the pipe worse than any other bike we've ever had.

I'm convinced I need to make carb adjustment, where should I go first? Normally I have "our guy" work on it, he moved... :ugg: Now I'm on my own, no big deal, just hard to find the time, I enjoy the work. So before I make a bunch of wrong changes on my own, thought I would ask for some advice.

If the plug looks good, what should I adjust first to get rid of excess smoke under load under power. Although the more I read what I wrote, I think I may have answered my own question. :confused:

Thanks,
-Bob
 
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#2
Sounds like it runs fine. Mine spits out all kinds of black crap and smokes like a 1970 300D diesel mercedes. As long as the smoke smells kinda sweet then you are a-ok just ride the darn thing!! Also what spark plug are you running?
 

atc3434`

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#4
Well, if your getting smoke under power, I would think that means the main needs to be less. If your not fouling plugs, and it doesn't load up idling, your pilot circut is probably about right. I have no spoooge problems... I run Amsoil at 40 to 1, and stock jetting. Its dead on... the hottest days leave me running a tad fat, but at 50-60 degree's, its perfect. Not saying its your oil, just another thing to consider. Question, why the BR8? Was it fouling 9s?
 
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#5
Is he really on the gas most of the time if not this is the reason why, Change the packing. go to a quality two stroke oil like motorex cross power or motul 800 and run it at 40 to 1 mix. when your boy takes his time riding the yamalube does not get burnt completely, you did the right thing dropping to a #8 plug this runs hotter and burns away any excess oil. Hope this helps.
 

Studboy

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#6
Will the myths never end???
Stick with your current oil and ratio if you are happy with them. I would stick with the 32:1 ratio personally, and changing to a 40:1 ratio without changing your jets will only worsen your current problem by further richening the air/fuel mixture.
It sounds like you need to lean your main jet, not "get on the gas more."
You do need to change your packing before jetting, and also make sure that everything (reeds, etc.) is in good mechanical condition before fiddling with the jets. There is an excellent guide at www.ericgorr.com under tech articles.
 

stormer94

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#7
studboy,

The bike has an EG top end, I should have looked there. I went to his site, and it's not coming up for me, hopefully it's just a "today" thing and they will be up tomorrow.

Why re-pack the silencer? I've never done it on any bike I've ever had (never owned them long enough I suppose) ;)

If I had to guess at a reason, added back pressure would richen the mixture (less air going through), would be it.

Anybody know of any other links on bike jetting?

Thanks,
-Bob
 
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#9
When a silencer is not repacked regularly (3-6months of use) the holes inside that the material is packed around (dunno if there is a name for them) get clogged with spooge. this WILL decrease performance, and that spooge will smoke when it gets hot. Repacking the silencer should be a part of regular maintence, just like cleaning your air filter, only not as often. I use Corning house insulation myself (thanks to this site). It's <$5.00 and will repack 5-6 times.
Packing it loosely will give a small performance boost, but the packing will not last as long, a snug pack (this means snug, not stupid tight), will take away a small % of hp, but will last longer.
As with all information on this site, read, consider, and make your own judgment.
Happy trails...

Gordo
 

stormer94

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#10
mmmbeergood,

Corning house insulation? Like what's in the attic? Cool information. I've never re-packed a silencer, ever, always thought that was crazy stuff pro-wannabe's did, and there was little reason to do it other than to irritate and psych out the "low maintainence" crowd.

I already ordered a bunch of pipe packing insulation from Chaparrel this morning, when it's gone though, I'm heading to the attic for the next re-pack... :)

Need to find an Air fuel ratio meter for my next cool tool. :thumb:

-Bob
 

stormer94

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#11
ATC3434,

I went to the 8 because he was on the verge of fouling a plug A LOT and I thought I would nip a potential problem in the bud, when he first got the bike. Fall in a hole, get the bike out, kick-kick-kick... start and ride 35 feet and stall the bike again before it cleaned out from the first get off. Move 5 feet, bog hard up a 40' hill blowing smoke, crash... kick-kick-kick... barely running, fall in a hole, repeat process.... :scream:

He's good to go now though. That first 2 weeks was a little rough,
 

Studboy

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#12
Correct, fresh packing will decrease back pressure over blown out packing. And another bonus: Fresh packing makes your bike quiet and crisp sounding...not loud, ratty, and clapped out sounding!!! :debil:
 

motometal

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#13
just a long shot: you aren't losing any trans oil, are you (bad crank seal)?

in a post above, it was suggested that the "8" plug would burn off more of the oil.

the "8" plug will be hotter on the very tip, but that's not what burns off the oil.&nbsp; Combustion temperatures shouldn't change much with a different heat range plug.

leaning the mixture (smaller jets) WILL make combustion temps higher.&nbsp; The vaporization of the fuel has a cooling effect on the chamber...less fuel, less cooling.
 

stormer94

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#14
motometal,

The oil is fine, what's supposed to be there is generally there. Although by the looks of the oil, I see a clutch in this bikes future. Reminds me it's about due for a change again.
 
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#15
I had this bike new once & solved my drool problem by dropping the the needle jet one notch going down one size on the pilot jet and adjusting the air screw. This bike is kinda picky about the air screw adjustment. I also had a Pro Circus pipe & PC shorty silencer with these settings. If it runs best with the air screw out past 1 & 3/4 turns then you should go one size down on the pilot jet. Also I agree about repacking the silencer. When you have it apart you can burn the crud off the internal baffle with a propane torch.
Oh yeah, I also ran 1 hotter heat range plug.

This is an awesome bike & I wish I still had it.