I recently put a dynojet kit in my prairie. I ride at 1500-3000 feet so I used the recomended 132 in the front carb and the 136 in the rear carb with the needle at the 5th groove and the air mixture screw three turns out. I'm running it with Procircuit exhaust and UNI filter. After I rejetted I put six UNI vents in the airbox, and felt that it was running too rich because if I was cruising along at 25-30 MPH then stabbed the throttle it would stumble, then take off. Also at lower speeds if I was on rough terrain that caused my thumb to stab the throttle the same thing would happen. SO I went ahead and drilled 6 more holes (12 vents total) to try ro lean it out and the problem with the stutter is still there. Should I drill more holes, or should I put the needle at the 4th groove (or anything else)? Has anyone else had this problem, if so what fixed it. I'm considering taking everying off and just leaving it stock, I'm guess I'm frusterated. Any opinions?

 

My 650 did exactly what yours does. I moved the clips to the 4th notch and is is perfect now. Do it, you'll be happy. I see you have folowed the instructions, but the instructions set the needle too rich for most people.

I don't have exhaust, but I fell that the exhaust more affects the main jet sizes not the needle.

 

Thanks NYROC, I just got off the phone with a tech guy from Dynojet. He said to go to a 130 and 134 because I was probably rich. He said not to mess with the needle if it was running good at steady RPM. He told me not to drill more holes, I don't know what to do now. I guess I'll have to rejet?

 

Don't keep drillin holes, Try moving to the 4th clip first, see how it runs. Other people told me to do this amd it worked great.

 

I moved the needle to the fourth notch and it runs perfectly now. If I put in the quiet core it still does hesitate but oh well. Thanks guy

 

Try to find were your stumble is, if it's more below half to half throttle alot of times the air/fuel mixture can be turned in another half turn to clean up the transition from low speed to mid range.

You realy need to do plug chops at 1/4, 1/2 and full throttle, this will tell you exactly were your rich condition acurs.

The kits normally are a little rich for most, but when you move up in elevation the hole kit should be rich. When you change one level of circutry you actusly lean out the ones above it.

Do a plug chop and find were you are rich at. Moving the needle clip can appear to work but in most cases it's realy the main that is to large and you lean out the mid-range to compinsate for the larger main.

Hope this helps, but don't expect to get this in one day. Ride it and after time you will know were your stumble or delay is and with just minor changes over time you will get it perfect.

Once it's perfect set aside a set of larger mains and in the winter keep all the settings the same and just up the mains to be safe in the colder months.

 

Okay-- I now have the needle at the 4th notch (from the 5th). This cleaned it up quite a bit, but it still hesitates a bit. So I took out all 12 UNI vents to see if it was air problem. With all the UNI vents removed it ran much better with almost no hesitation. Three is still a little stumble so I tok the lid completely off and it ran strong as hell and perfect. I want to drill more holes but I'm worried about being too lean on the main jets, STAKK said that I may already be too lean on the mains. Any opinions?

 

No, the leanest you can get is without the lid on, and you said that it ran best there.
I think more uni's will help. But, put in as many uni's as is practical, don't use them as a carb adjustment. I sorta think you are a tad rich. How are your plugs now?

You should really run it down a trail at 3/4 throttle (or so) for a while then flip the off switch. Take a plug reading right there. Make sure you bring the spark plug wrench.

The spark plug threads don't strip when hot. I use anti-seize for good luck.

Do you have a 130 for the front carb, and a 134 for the rear carb? You are kinda right in the middle of the dynojet instructions. I see you are using the low altitude jets for an aftermarket exhaust, the high altitude recommendations may be too lean, maybe the jets sizes between these would work best.

You really need to check the plugs after a 3/4 throttle ride first, since you want to verify that the mains are right. Then if it is too rich at the transition from low throttle to half throttle you can mess with the needle.

 

Reading what you said, I'm nearly 100% sure you need to drop your mains down one more size.

If a lean condition is in the mid to lower ranges you can apply the choke a little and the engine will speed up. If you are still a bit fat on top the engine will stall quickly when you apply the choke. This is all done after it is warmed up.

The main jet can reach down into the mid range if it's to large. This makes it tricky!

Without knowing your location and elevation thier is not much more I can tell you. Be aware that heat AND huimidity directly affect the main and how lean or fat each suggested set up will be.

Don't mess with the lower two circuts untill the rite main is in there. I suggest you move your needle back to the suggested settings, then go down on your main until the correct plug read is obtained. Then when you are there you will notice big changes when you move the needle.

It is quite common for the suggested set ups to be rich.

You can not fine tune the lower 2 circuts untill the main is correct. And then the adjustments to the lower 2 circuts will adversly affect the main again.

Put your needle back to the correct position and drop down 2 main sizes, then start from there.

This is not hard, but once you moved the needle position you lost your refference point.

Hope this helped, hope I didn't confuse you.

 

From what you say I would now agree that if you go down one size on your main's the problem will be gone,12 vent's and still rich? it must be humid where you live. my opinion I would'nt go back back tto the 5th notch, it will just start stumbling again, I've jetted about 4 and had to run the needle's in the 4th on all of them. Jetting is funny, if there is only slight difference's in humidity,air quality, and altitude from where you are,to where I am you may be richer or leaner just a little bit. Trial an error is the only way to get it right. I went into mine 4 different times before I got mine to run completely clean.