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Discussion Starter #1
Hi all,
I have a 2001 KX85 with a 99cc big bore kit, pipe, reeds.

The general jetting guide for the pro circuit pipe says go leaner on the pilot.
The general jetting guide for the reeds say go richer on the pilot, leaner on the main.
The big bore company says it'll typically run leaner with stock jetting.

I started stock with a 45 pilot and 140 main, it had a bad bog off idle. I then put in a 48 pilot and it **** near threw me off during the first test.

I did a full 45-60 second plug chop and it had a medium to dark ring in the plug so I left the stock 140 main.

It runs great except it's too rich now around 1/8 to 1/4 throttle. The air screw is 2 1/2 turns out. I'm not sure to leave it or try to fine tune it becuse I do trail riding but it still doesn't spend much time in that throttle range. It's never fouled a plug (BR9ES)

All this plus I don't know if I should tune it like a KX100 or a KX85, the only difference between the two is the stock KX100 has a bigger (leaner) straight section of the needle, and a lower clip position.

What would get rid of the rich studder at 1/8 to 1/4?


I know there is no definate answer, but is it possible to end up fine with stock jetting with a combo like this?
 

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go back down on the pilot and turn the air screw in (like 0-1 turn out). Air screw tightened down = all gas and no air. I dont suggest turning the air screw more than 3 turns out cause they tend to fall out and once the air passage is 100% open turning it out more does nothing.

Stock jetting is possible cause the larger the bore the more fuel is suctioned from the carb due to increase of displacement.

Basically it is a KX100 and notice the KX100 has a LEANER needle.

Every bike is different though and not everyone lives in the same environment.
 

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Discussion Starter #3
Well I have a lot of jets to play with, I'll try going back leaner on the pilot.
Trying to do this only when the weather is warmer.
So would a KX100 needle help? Those are pretty expensive.

Here are the specs on the needles. The 85 has the NAPE, the 100 a NAPF.
 

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i cant say, it's all trial and error. I would keep it rich for the cold weather too.

Personally i would try to tune it the best i could with what i had.

i usually try to jet the pilot and main rich and needle lean.
 

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Discussion Starter #5
Well it's 74 degrees here, 70% humidity, 22 feet.

I just got done with it.
I put the stock 45 pilot back in and it's no good, major bog off idle. The 48 solves that. Tried a 138 main and it's too lean IMO.

Right now it's got the 48 pilot, 140 main, NAPE with the clip in the center, and the air screw at 1 3/4.

It runs great unless I just ride at 1/8 throttle, it sputters. (the 45 pilot did get rid of that)

If I go balls to the wall it runs strong all the way to top speed.

It looks like get a needle or don't ride at 1/8 throttle.
 
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