How do I solve this symptom.

Went for a good long ride yesterday.

I noticed that most of the time when I shift gears I get an irregular exhaust stumble or hesitation. The bike runs great otherwise, easy to start, pulls hard, but quietly dies when being too quick on the throttle. Sometimes in the garage I can see black smoke when it does overcome the stumble. I have completely stock jetting and ride at 4000-6000ft elevations. Would it be a good idea to go up one position on the needle or is it jet size or something else, assuming I dont want to do the BK mod. Im really scared of going too lean and hurting the motor. How would I know if I was too lean, what are the symptoms of a lean motor? What do you think will solve this?

PS, I also sometimes get the decel popping too.

[ July 31, 2002: Message edited by: Yak ]


I know this is not much help...but I live in CO at 5K feet. When I bought my bike they re-jetted it. I have a baggie of the 2 stock jets they replaced. So, I know your bike needs to be re-jetted...I just do not know what to...

I am sure someone will tell you exactly what you need.

My bike runs perfect with 92 pump gas and a shot of octane boost. I tried race gas and it did not run that well.

Black smoke is an indication of being to rich.

The BK mod is probably the best way to get ride of the bog you describe, it is also a way to really fine tune the off idle exceleration the yz is famous for, ya know the thump, thump, thump, GRIN, GRIN, GRIN :) .

Assuming you are at stock jetting, it is probable you will need to re-jet the bike for your conditions.

Moving the jetting plus or minus will not jeprdize the bike runing lean. F

When was the last time you have taken the carb apart and cleaned it?

If never, its a good time to do it.

You can get the jet info we need to help diagnose what you need to do...

[ July 31, 2002: Message edited by: E.G.O.**** ]

You are too rich. Everywhere.

Try dropping the needle one clip. Also, you should reconsider on the BK mod. It is a painless and cheap way to improve your throttle response.

Since I ride at the same altitude you may have good luck starting w/ my jetting, although your needs may differ (you should list your location in your profile):

BK mod, pump stroke limited to 1 mm (measured at actuating rod)

160 main

40 pilot

EKQ # 3 (EKQ is an optional needle on the ’00 fiche, PN 5JG-14916-E1)

PAJ ~ 85 (Adjustable PAJ from Sudco 800-998-3529 PNs 021-230 & 021-235, about $15)

1.5 turns out on idle mix

At the very least you should drop the stock needle and put a 40 pilot in there. Personally I don’t know how you put up with your bike at that altitude w/ stock jetting.

Hope this helps.

Yak Id follow Hicks suggestions to the letter, he knows of which he speaks.

Your going to be blown away by your bike when you get the carb sorted.

The PAJ (primary air jet) is available from a company called Sudco in the City of Industry in So.Ca. the have a web site. You can get everything you need there. Short the BK mod. But every truevalue store in the country has what you need for that.

I had the exact same problem on my 02 and I took the advice of Shawn MC and Hick and lowered the needle one position (brought the clip up). It was really easy to do just pull the carb off, take the top off, and it is underneath of the allen screw on top of the slide. It made a huge difference for my bike, it not only runs better but seems to start better too. However, it still seems to load up when I use deceleration braking into corners so I am also going to switch to a #40 pilot. Hope this helps.


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