Confusion on jetting..

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#1
After doing a search and not finding what I was looking for... now that temps have dropped into the 40-50's my bike seems to run richer. It loads up fast and kind of blubbbers ( a little ). I ran a 2 step richer main and it made it worse....Why is cold weather making my bike run richer...I'm afraid to lean it

Thanks
Mike T
 

maco

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#2
I'm not an expert on jetting but would like to help if I can.Cold weather condenses the oxegen molucles,so more oxegen.This should richen your mix.The other variables would be humidity and altitude.If there is a higher humidity there is less oxegen and more water in the air.This would make your mix on the rich side.Since your area is going down in temps and your noticing problems with throttle positions I think your on the right track,provided humidity isn't also a part of your problem.If your sure your carb is not having any other problems,air leaks and your air filter is fresh then you might want to go back to your original jetting and start with your pilot circuit and make sure that's right.Then your needle positon and then try one step on the main.I'm assuming your on a 2 stroke because of the lean concern.
 
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#3
Maco, no offense, but I think you got a little mixed up there. More oxygen would make the mixture leaner, not richer. You got it right about the humidity - more water means less air so it is richer.

I think I would try dropping my needle one position and leaning the idle mixture a little before messing with the main or other jets. I have found this works well for me when I ride in cool, rainy weather. By keeping your main the same size, you're not risking lean- seizing your engine. Also, make sure your filter is clean and not over-oiled. The filter oil can thicken up in cold weather and mess things up.
 
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#4
Mike T, you asked a question in your post that I didn't really answer directly-"Why would cold weather make my bike run richer?" This is an interesting question, because you would think it would work the other way, right? The cold temp. makes the air more dense and should make the bike run leaner. So, there must be something else happening that is making it run rich. I'm guessing it's an increase in humidity. I don't know what the weather is like in your part of the world, but if you get a lot of rain along with the cooler weather, I think this might be the cause. This is just my speculation, but I can think of two reasons higher humidity would make the bike run rich...More water means less air, so the bike runs richer, and the water vapour also will cool the engine as it turns to steam in the combustion chamber. ( the same way alcohol will cool your hand if you let it evaporate off your palm) A cooler engine will run richer. Together, these effects are stronger than the one from increased air density, so the bike runs rich.

I don't claim to be an expert in this stuff, so you can take it for what it's worth. Makes sense to me , though.
 
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#5
Thanks for the replies..but this is the craziest thing...ran a new plug today, (went richer the pilot 50 to a 52 ) needle in the second from top..178 main (stock) the bike still loads ups, smoking like mad but runs good after you clean it out... and after the ride I pulled the plug and its pretty white ....

Anyone ?
 
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#6
If it happen to be burning coolant (never a change in radiator level). Could you tell by the piston ? took it apart and everthing looks normal...gaskets intact and look good ?
 

CaptainObvious

Formally known as RV6Junkie
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#8
jmics is on to something.

Cold weather will lean out the jetting, so if the bike is suddenly running rich it is likely something else. Don't chase the jetting. Do a compression check, it's possible that the rings have tanked.
 
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#10
Yea I use pump fuel, I have the head off now, maybe I'll throw some rings in...Is there any tell tale signs of burning coolant other than exhuast?
 
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#11
yes; normally a section of the edge of the piston will be eroded/blistered. this is from the sudden decrease/increase in temp change as the coolant hits it. but this is only if the leak is signifcant; why dont u just pressure-test your radiators? a vacuum gun is very cheap, and u will use it forever. look up your rad's pressure-rating before testing/pumping them up, as they are usually very low (~18psi)...
eric gorr's book will explain it in more detail: www.ericgorr.com
 
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#12
well Im pretty sure its not coolant, piston looks good...I put it back together today (new head gasket), exhaust doesnt smell like coolant.

What else could make it seem to run rich (loading and longer pulling) but the sparkplug is pretty white.
 
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#14
yes, if the ceramic is white, then u r def not running rich, at least the jet the engine was on when u shut it off is not rich, and i highly doubt the plug could become cleaned that quickly.
in other words, most people do not realize that in less than one full second, a plug's color can change to match the current jet(s) being used.
therefore, in order to accurately determine how a particular throttle-setting is burnign, u have to use a perfectly-clean (ie, new) plug, and a thouroughly warmed up engine.
u then run the bike for several seconds at the throttle-setting u wish to check, then while still holding the throttle at that same setting, u hit the kill button and pull in your clutch.
this is the only way to read a plug, as in rare occasions your jetting can have been hacked by the last owner so badly that some jets are lean while others are way too rich...
the safest thign for u to do, however, is to find out the stock specs for your bike, and jerk off your float-bowl and ensure that they are corect.
then unscreww your throttle cap and verify your needle and its clip-position.
this done, you will know if its your jetting or not, at which point u can take the next step.
 
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#15
Jetting is a 178 main (stock) needle is second clip from the top and the pilot is 52 (50 is stock)

Last winter I put an 180 in it and it ran fine...I put the same jet in this year and bogged and pulled way to long..

I'm investigating the stator maybe thats it ?

I'll see how it acts at the track tonite..