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dyno jet question

4188 Views 23 Replies 11 Participants Last post by  fomocofan
I just installed the dyno jet kit, mbrp pipe, and k&n filter. I used the 148 and set the needle on the second notch. Upon running it, there was a big hesitation in the low end, but then it ran smoothly through the rest of the throttle. I am located in Minnesota, approximately 1500 ft. I gave up on it for the night, any suggestions on what I should adjust, so that I don't have to try every thing? thanx. Caz
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Caz, did you set the air/fuel screw to 3 turns out?
yes I did
Try closing the Air/Fuel screw about a 1/4 turn and see if you get better throttle responce.
i have a question on the dyno jet, will it work in all tempratures???or is is temp sensitive?????
Yes, it will work in all temperatures. All your doing with the Dynojet kit is refining and modifying the fuel flow and such.
ok, just checking, thanks....

also, where are you from in iowa???? i have relitves in mcgregor...
Try moving the clip to the 3rd notch.I had the same problem then i moved the clip down one notch and it went away.
Try the clip on the 3rd notch and the mixture screw at 2 & 1/4 to 2 & 1/2 turns other words richen up the mid range and lean out the idle....
I moved the clip to the third notch and it didn't do much, i put the f/a screw in and out from 1 1/2 to 3 1/2 and could not find a good even spot. I found a spot where it took away the hesitation in the low end, but then when i got near high rpm's it seemed to miss a little. Do I need to change the jet size or what?
Do you guys think that off the line hesitation could be from the 27" mudzillas he is running? Just to over come the interita from those big tires my be your problem. What do you dudes think?
Well 650ccMatt, I too run 27" Mudzilla's and they do make a big difference from the stockers. Heck they weigh more than twice as much mounted on steel rims (aluminum stockers couldn't take the weight and pressure of the Mudzilla's and bent all to he!!.). But the hesitation on the throttle I don't have. I'm at a dj 146, Needle clip on 3rd notch, 2 3/4 turns out on a/f mix, Muffler mod. etc.
I can still wheelie if I nail the throttle and pull on the handle bars. With the stock tires, just nail the throttle and it will wheelie all day long.
Matt the tires are not the problem with what I am refering to. The reason is that it also has the hesitation when I am reving in neutral. Should I try going down a size on the jet to 146?
caz41-Is the miss while the bike is revving or after you get to a certain RPM?

If the hesitation is happening while the bike is comming up throught the rpms then I would suggest moving the needle down/clip up. This will just give it the fuel a little slowwer.

If it is missing on the top only, I would try to bring the main jet size down. When tuning on my race bike I was told to increase the main jet size until there was a miss at full throttle(Kind of like a rev limiter) and then back it down one size. This is for max performance.

I was also told by several tunners that if you are tunning for max performance that a little backfire isn't a bad thing in a fourstroke.(I don't know if I buy that or not)

I have always used a little tunning method I came up with myself. I noticed that on my 400ex when it was bone stock I could let is sit and idle at night and the header would stay black. I also noticed that when I ran a nice long wot blast down the road the header would stay black. So after I bought a air filter and full exhaust the situation changed. The header would begin to glow at idle. I adjusted on the air/fuel screw until the header stayed black. I then took it out and ran it down the road at wot=red header. I changed the main jet up until the header stayed black. The only thing I can say is compared to some of the other methods of tunning I saw being done mine produce good longevity.

First a disclaimer. If you want exact information look it up. You can find it on the net. What I recall is:
When tunning the carb keep in mind that the air screw controls the a/f ratio up to around 1/4 throttle. The pilot jet phazes in starting at about 1/8 throttle to between 1/2 and 3/4 throttle. The main jet comes into play around 1/2 to WOT.
The needle possition Add fuel sooner(fast) or later(slowwer). Not more or less.

At what throttle possition does the hesitation occur?
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the hesitation happens between 0 and 1/4 throttle. the best way to describe it is if I am in neutral and when I push the throttle all the way from nothing, it starts to rev up, then very quickly has a hesitation, and then goes through the rest of the throttle range fine. Maybe I will try a 146 just for shits and see what happens.
Where is your mixture screw set??? How many turns out?

I would adjust that first if the prob spot is at or below 1/4 throttle and the rest of the throttle range is fine...changing the main jet probably will have no affect on that prob.

If your mixture screw is at 3 turns out, then try turning it in 1/2 a turn to 2 and 1/2 turns out and see if it improves...then try 2 and 1/4 turns out.

It may be that the mixture screw/pilot jet is too rich ....
I adjusted the mixture screw from 3 1/2 turns out to as little as 1 1/2 turns out and it did not get rid of the problem at either end... starting to get pissed.
Dude, we all feel your pain.
Is it
0 to 1/4 throttle possition or 0 to 1/4 rpm range.

From what you describe I'll bet you can fix it either with a smaller main jet or move the clip on the needle up one possition.

I'd do the clip up one position first(so the needle comes up just a hair later in the throttle motion). I think you are getting a touch to much fuel to quick and it is choking on it.

If you lived closer I'd bet you six beers and change the jet for you if I was wrong.
Caz41- It may be time to look at replacing the pilot jet. Sounds like you have tried everything else. I think it comes with a .050. See if you can go up about .0025 to a .0525 and richen up the low to mid range a bit. I have not done so on myh Rinny yet but it made a huge difference on my Raptor.
Thanx for the help, I'll have to wait to do further testing, it is -25 (before the wind chill) now, and I don't feel like doing any testing in this weather.
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