YZ 250-bog?

[mike-evans]

Hi all, out on my 2001 YZ 250 today, and it does smoke on start up and very boggy to clear whilst going around the track, I will admit I'm not riding fast so that's probably the reason. Whilst going down the hills and getting on the throttle, there is a bog a soon as I hit the gas, is this to rich or to lean?
The jetting is standard?

 

[whenfoxforks-ruled]

I will rub my magic computer screen, and see what your spark plug looks like. Then I will check the temperature and elevation in the jetting correction table for that bike, in that bikes shop manual. The really hard part is changing the jets in your carb though! Puking small internet cables! Vintage Bob

 

[mike-evans]

I will rub my magic computer screen, and see what your spark plug looks like. Then I will check the temperature and elevation in the jetting correction table for that bike, in that bikes shop manual. The really hard part is changing the jets in your carb though! Puking small internet cables! Vintage Bob

Ha ha ha, sarcastic, I like it...

ok, bike smokes, really spluttery/boggy until 1/4-1/2 throttle then it clears then its fine, running to rich?
Do I drop the pilot, or raise the needle one?

Like I said, I'm not riding it hard...

 

[wake_rider]

Ha ha ha, sarcastic, I like it...

ok, bike smokes, really spluttery/boggy until 1/4-1/2 throttle then it clears then its fine, running to rich?
Do I drop the pilot, or raise the needle one?

Like I said, I'm not riding it hard...

What he was getting at is that it is impossible to tell what the issue is from what you're explaining. Worn/cracked reeds, air leaks, jetting, or a number of things could be the issue here. If we were to tell you to swap something out, we would just be ill-advising you and throwing solutions at a problem of which we don't have a clear understanding. It would be like calling your doctor, telling him you have a pain in your throat, and him prescribing a medication. It just doesn't work that way, although it would be nice if figuring out the issue was that simple!

Change the plug out, do a jetting run, chop the plug, then come back with the results and the members on here will be willing and capable of giving you much more accurate and helpful responses or suggestions.

 

[_JOE_]

Most likely you need to drop the pilot jet and needle a size/clip and tune the air screw. Stock 2 strokes are usually rich and you spend very little time on the main jet. However, you could a host of other issues on a 10 year old bike with very short service intervals. I'd start with a leak down test then, if it passes, a compression test.

 

[mike-evans]

Ok, let me start again. I bought this bike about 1 year ago where the guy had receipts 2 monthd old, for new crank seals, new crank, new con rod, relined barrel, piston, clutch baket, clutch, rear swing arm bushes, disc, gear lever and gear shaft....
Only ridden it a few times since rebuild, then I bought it, I have only put around 3 hours on it. It has lots of compression. Gearbox oil I get out when I change it is what I put in-750ml.

It smokes when I first start it then it needs clearing, it is boggy to clear, then fine through rest of its range, smoke is a blue colour...

So this does make me think rich pilot circuit?
But do I drop pilot, or clip?

 

[2strokerfun]

First thing I'd do is take the carb apart and clean it well and clean the jets, too. Put in new plug and fresh premix. Run it and see if it still has the symptoms.

 

[mike-evans]

When I first bought the bike I did strip the carb and clean everything, it still smoked but wasn't to boggy, I then left it for about 6 monthd and went on it yesterday, as said smoking and very boggy at first throttle, so carb might need a clean again as its been stood for a while...

Might clear the bog, but it will still smoke...smokes at idle/first throttle...

 

[whenfoxforks-ruled]

Fresh premium fuel, from a busy station, usually not the cheapest place around either. Decent grade of premix, at the recommended ratio. If the previous builder did their job correctly, still double check it. Other wise all the jetting in the world will not help. Honestly, there is a large group that would do other wise and reverse engineer the problem by playing with the premix ratio. It tells a lot about how they ride their bike. If it was rode hard/like it was built for, it would seize, guaranteed. A bog off bottom, normally is the idle/pilot circuit. Rich or lean can be determined from the air screw adjustment, the choke, or a good plug read. If drastic jetting changes do not affect it, it is something else. Like the right crank seal, exhaust valve, or something? Or even a really dirty carb. Did you remove all the brass? And there is the, rode properly to clear out the engine part. I do know people terrified of the 2 stroke MX bike hit in the powerband, and they try to ride around it. They need a slower bike, or get used to it, like most of us! In a month, you will be wanting more power. That can be had by a rebuild. Depending on the hours of operation/quality of the last rebuild and maintenance. And change the float valve every year, it will cause a bog also.

 

[2strokerfun]

Is your choke plunger working properly?? Besides choke and jetting, a work needle or needle jet can cause this. If all seems proper, I'd lower the needle a clip first.

 

[YZ Teacher]

10 deg. in air temp can make a diff. Check your plug and learn how to read it.

 

[mike-evans]

How do I determine if its a "lean" bog or "rich" bog?

I suppose with the spooge I have and smoke and the fact its on stock jetting, its rich?

 

[whenfoxforks-ruled]

Replace the float valve, and seat if the parts list shows it, and take notes on what jets are in there. Warm and clear the engine, adjust the air screw to achieve the highest idle, where is it adjusted to? Engage the choke valve, does it get better, or worse. My screen is clean now!

 

[mike-evans]

Replace the float valve, and seat if the parts list shows it, and take notes on what jets are in there. Warm and clear the engine, adjust the air screw to achieve the highest idle, where is it adjusted to? Engage the choke valve, does it get better, or worse. My screen is clean now!

How do you tell if its a lean or rich fault from noise tho?

 

[whenfoxforks-ruled]

How do you tell if its a lean or rich fault from noise tho?

? Honestly? Lean or rich from the sound? That could cause some confusion. It is kind of possible?Look at the plug, wet or dry? Dark or light colored? Go to some drag racing sites and check out some plug pics. Usually a manual has some pics? Never seen a sound graph.

 

[mike-evans]

? Honestly? Lean or rich from the sound? That could cause some confusion. It is kind of possible?Look at the plug, wet or dry? Dark or light colored? Go to some drag racing sites and check out some plug pics. Usually a manual has some pics? Never seen a sound graph.

Ok got you.
I understand how to read a plug, looking for a brown tan colour-good..

Will run it and check the plug..