so i have been playing with the jetting on my bike since the previous owner never did. here is my dilema. I have after market web cams, the heads have been decked (milled) .020", heads are ported, and the jet needles are not stock and have a more drastic taper to them. I am running a stock ingition timer but have the advancer.
i am running UNI pods set the pilot to 2.5 turns out and seems OK. as for the jets I am running 130 main jet but if i go to 135 or 140 it will stumble very bad at 8k then clear up. it does not happen so much in first 2-3 gear more in the 4-6 gears when it takes longer to get past the 8k mark. stumble for all of 8k as well.
What would cause the stumble? am i running too rich and it is dumping too much fuel? i am baffled as i am new to carbs (my other bike is FI) also it cleared up when i went back to 130 so i suspect main jet but everyone is running 140 and the jet needle does not matte at that point so i am ballfed as to why i am not running 140-150 without the stumble. also it will not accelerate well with 140 main if i am above 7k in 4-6 gears. suggestions would be appreciated.
I have EXACTLY the same problem!!!!
Have done basically same engine mods and running same jets and having same problem on 7k+ on 4-6 gear!
could anyone help? thx
The non-stock needles are probably from a jet kit. They have the effect (because of that different taper) of making the engine run as if it had larger main jets- they are intended to be used with non-mikuni main jets from a kit. Are those the jets you are using? There is no direct correlation between the jet kit sizes and the Mikuni jets.
Using stock Mikuni jets, you will have to use a smaller size jet than is listed on the jetting matrix - basically, given the symptoms you mention, when the needle clears the emulsion tube you appear to be going rich. You might try dropping the needle one notch or blocking one of the holes in the bottom of the slide to slow the rise of the slide - or, go with one size smaller jet. If you are using Mikuni jets, try a 132.5. If you are using jet kit parts - contact the manufacturer to see what they tell you to do.
thanks for the reply i did figure out what was happening. i went to a full jet kit stage 3 from dyno jet and had to lower the needle to the lowest point to correct the problem because i was using performance cams they opened the slide too early causing a rich condition.
thanks for the info though maybe it will help others.
mike