Low rev smoking....?

mike-evans · Jan 31, 2010

01 YZ 250. Out on the bike yesterday, and after starting the bike found it smoking and bogging and needed a good reving and a good fast blast to clear it, it was ok. After washing the bike, gave it a start up and it was smoking alot, gave it a reving on the stand to clear it and it went, when riding it it has nice smooth power and pulls nice, power band hits nice hard and very clean/clear. If I was to pick a running fault prehaps it does have a slight bog at first touch of throttle. Its as if it is rich at idle...i got a slight run of spooge out of the tail pipe, first time out after being repacked...bike has no idle..

julien_d · Jan 31, 2010

if it doesn't idle you def have a prob. You have adjusted the idle screw, yeah? Go out some on the airscrew or install a smaller pilot jet perhaps.

Even better, go through the sticky's and just jet the thing.

slickpuss · Feb 13, 2010

Yea, you need to revisit the jetting and probably use less oil in your gas. What ratio are you running?

ellandoh · Feb 13, 2010

could you be getting her hot enough to be burning spooge from the pipe???

if not smell the smoke and see if you detect different oil smell than premix, if not jetting is in order

julien_d · Feb 13, 2010

probably use less oil in your gas

That's almost always bad advice.

mike-evans · Feb 13, 2010

My mixture is 40:1 (5 litres petrol - 125ml oil). So isnt that LEANER than recomeded by the manual? All the jetting links I have read advise NOT to change mixture but just to correct the jetting...I wil lean the mixture screw a little and see if that helps, if not drop pilot down a size, but wil that have an effect on the rest of the jetting? If so I wil live with how it is, dont want to get involved with massive jetting problems......

jsantapau · Feb 13, 2010

if it smokes while idling and it has a small hitch in its gettyup right off idle leaning out the pilot circuit sounds like the right course to take and it shouldn't cause any massive jetting issues.
if everything else is equal, less oil in the gas richens the air fuel mixture. If you are happy with the fuel/oil ratio don't worry about it and straighten out the air/fuel ratio by correcting the jetting in the appropiate carb circuit

If your type of riding involves a sustained high speed run followed with any length of time of coasting down you might want to leave it alone.

2strokerfun · Feb 13, 2010

Here are the steps I'd try and the order I'd go in:
1) try adjusting the air screw
2) make sure air filter is clean -- if not, clean it
3) try new plug
4) take carb off and clean it well, including the jets
If none of those seem to cure the problem, you might need to tackle the jetting, or it may be time to inspect rings and piston

slickpuss · Feb 14, 2010

Julien_d, the manufacturers recommendation on the oil ratio is seriously on the safe side. Ive seen so many people deal with fouled plugs and spooge because they insist on running what the mfr suggests.

Thats why I asked the ratio he is using.

You IT guys are always so chatty on the computers throwing in little comments. Isnt the holy grail on again or something to keep you busy?

mike-evans · Feb 14, 2010

I set the idle up earlier on the bike and leaned the air screw a little, did it on the stand, got bike warm and adjusted. While bike is idling, i grab a hand ful and rev it fuly and there is NO bog at all, revs crisp and returns to idle...but smokes a bit on idle and whilst i give it a reving (on the stand) it shoots a cloud of smoke out (nothing realy major) and the end of the silencer has a little puddle of oil/spooge and so does the connection between the front and rear pipe, prehaps didnt get hot enough? Dont understand it, before my injury a few years ago, i had a brand new 01 YZ 250 2t and not a sign of spooge etc....?

julien_d · Feb 14, 2010

Julien_d, the manufacturers recommendation on the oil ratio is seriously on the safe side. Ive seen so many people deal with fouled plugs and spooge because they insist on running what the mfr suggests.

Those fouled plugs and spooge had nothing to do with running "too much" oil. It had EVERYTHING to do with improper jetting. And what's wrong with being on the safe side anyway??? There is absolutely NO performance increase from running less oil. On the contrary, provided the bike is jetted CORRECTLY for the ratio used, testing shows that HP increases when you add more oil, all the way up to about 18:1. So more oil is safer AND it helps seal the rings better leading to higher compression and MORE power. What do you loose? A couple bucks on 2t oil??

Changing the oil ratio as a fix for improper jetting is always the wrong thing to do. Run the correct amount of oil, and jet accordingly, not the other way 'round.

FNG · Mar 18, 2010

The Pilot is 10% of the total fuel delivery. Going down 1 or 2 sizes will not affect main jetting.

I am a 40 year old with 2 years on a 95 YZ 250. I have ridden sleds and 3-4 wheelers most of my life so I know my way around a 2 stroke. Weekend warrior that is no fan of doubles but I have fun!

Anyways with a Rad valve on a stock motor and a ProCircuit pipe I am down 1 on the pilot and 2 on the mains I still get a puff on the bottom.

I suspect it is my riding, or lack of skilled riding causing it. I doubt I am riding hard enough to consistantly keep things hot. Otherwise it seems dialed in and I like it how it is.

Eric Kropp · Mar 20, 2010

I am not much on the anatomy of a water cooler, so forgive my question if I am off base.
Is there a seal on the crank between the clutch housing oil and the crank case? It would sound to me like something other than jetting or mixture if it always worked right and then just started acting up. And puuulease remember, I am an air cooled rider, so if there is no seal on the clutch side of the crank...don't beat me up too bad.....

Eric<><

mathd · Mar 21, 2010

Dont change the oil ratio.
Make sure the bike is hot when jetting(mine will smoke when cold)
Actually it sound like it is too rich.
I would first try to dial the pilot circuit, the airscrew will tell you if your pilot jet is correct or not. Make sure the reed valve is working great.

Then i would set the needle one notch leaner(if needed). My yz125 had the same problem, i replaced the reed valve, set the pilot/air screw and leaned the needle by one notch worked just fine for me. You can half/open the choke to see if the problem is too rich/lean.

In short, check the reed-valve(if not already) and read the jetting link on this website. You will not regret it and jetting is not that hard to do. Just read the jetting link in this forum.
http://www.dirtrider.net/forums3/showthread.php?t=42618
Probably the best and cheaper improvment you can do to your bike, jet it right!(and dont listen to people telling to change your oil ratio)

Low rev smoking....?

mike-evans

julien_d

slickpuss

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ellandoh

dismount art student

julien_d

mike-evans

jsantapau

2strokerfun

slickpuss

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mike-evans

julien_d

FNG

Eric Kropp

mathd

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