Mikuni Carb Adjustments

[stringbeanbowler]

Hey all, I bought a 1997 Banshee last year from my friend who said it was a stock motor. He had 260 main jets in it and it seemed a tad lean. The plugs confirmed it, but they weren't too bad. I recently took the reeds out to check em and saw that the intake was ported. I put some 320 main jets in there and it ran better, but my main question is the air screw and pilot jets. How many turns out should it be for my particular setup, and what Pilot jets should I try, if any? I know everything is trial and error, but there is usually a safe starting point.

 

Mods: Intake ported (not polished), Toomey T5's, 2 into 1 Foam air filter pod (with outerwear) with air enclosure completely removed, Tors removed, Boost bottle (whoop de doo), 32:1 fuel ratio. If there are any other mods, I haven't seen them. I altitude is 600ft and temp is 50 degrees farenheit.

 

I heard I should set the needle clip to 1 step leaner and increase the pilot jet, but not sure to what size. Thanks in advance. This is a great site and YES I did try the search field before posting this.

[pondtunes]

Hey all, I bought a 1997 Banshee last year from my friend who said it was a stock motor. He had 260 main jets in it and it seemed a tad lean. The plugs confirmed it, but they weren't too bad. I recently took the reeds out to check em and saw that the intake was ported. I put some 320 main jets in there and it ran better, but my main question is the air screw and pilot jets. How many turns out should it be for my particular setup, and what Pilot jets should I try, if any? I know everything is trial and error, but there is usually a safe starting point.

 

Mods: Intake ported (not polished), Toomey T5's, 2 into 1 Foam air filter pod (with outerwear) with air enclosure completely removed, Tors removed, Boost bottle (whoop de doo), 32:1 fuel ratio. If there are any other mods, I haven't seen them. I altitude is 600ft and temp is 50 degrees farenheit.

 

I heard I should set the needle clip to 1 step leaner and increase the pilot jet, but not sure to what size. Thanks in advance. This is a great site and YES I did try the search field before posting this.

 

 

The air screws typically start at 1 1/2 turns out from fully seated (don't torque em down)

the screws/pilot only affect you till 1/4 throttle so if you're okay at idle don't change them the screws will fine tune it.

 

Your midrange is affected by the needle size/taper and to a degree the main jet.

 

WOT is all the main jet

 

So if your WOT jetting is okay, then I would recommend setting the needle at the stock position 3rd clip and your idle at 1 1/2 turns you can fine tune the idle mixture richer or leaner using the screw

 

It's ALWAYS better to be a little rich than lean at all!

 

I'm sure someone will chime in based on your mods / elevation / temp on if you need to change the pilot/main again.

[White97Banshee]

I run 330's and 27.5's at the middle clip in mine at 40:1 with T5's, K&N pods, and VF2 reeds. I know it's like 1 or 2 sizes rich but it runs like a champ and I can't feel it hitting a wall from being too rich I know the pods flow more than that 2:1 filter but yours is ported so you're probably about right. I didn't have to mess with anything but the mains and pilot so you shouldn't either. I ride at sea level when it's about 50-70 at all times so ours is just about the same.

[stringbeanbowler]

Thanks for the info. I'll do some testing

[AKheathen]

remember to make all adjustments to the enie when it is at operating temp, not cold.

[stringbeanbowler]

remember to make all adjustments to the enie when it is at operating temp, not cold.

I will, thanks. If I remember right..... only change one setting at a time, and start with the mains, right? Eventually, I want to experiment with the pilots and the needle clip position to find the best / safest combo.

[AKheathen]

eventually? just start with the mains, and when you are sure, go strait to the needles, and mess with the pilot if you get any off-idle problems, or it won't adjust good with the airscrews

[stringbeanbowler]

eventually? just start with the mains, and when you are sure, go strait to the needles, and mess with the pilot if you get any off-idle problems, or it won't adjust good with the airscrews

I pulled the carbs apart today and I looked at the needle and didn't see any markings on it telling me what size it was. It also had 6 positions to place the clip when the clymer book shows that the stock one is supposed to have 5. Maybe an aftermarket needle? I have a question about the washer by the c clip. What side of the c clip does it go on?

 

So here's my setup and dilema: 25 Pilot jet, 340 Main jet, needle clip in the #2 position from the top out of 6, air screw 2 turns out. With the air screw 1.75 turns out, the main jet spark plug reading was rich. When I turned it 2 turns out, the plug looked perfect at W.O.T., but I checked the plugs after an 1/8th throttle run and it was wet and had a little carbon on the rim, and I had the same result for 1/2 throttle. how can I fine tune that?

[AKheathen]

well, i don't know what you are doing with the plug readings after needle/pilot/airscrew adjustments, but stop. you are just confusing yourself. once you have confirmed that your mains are dialed in with a proper plug chop on virgin plugs, then the rest is by feel/sound. ok, now i can almost gaurantee that that aftermarket needle is generally leaner that stock all over. i have compared side-by side, and would suggest starting with the needles @ 4th clip from the top (blunt side) and stick that washer above the e-clip to begin. that washer is actually an aftermarket thing as well. it's for 1/2 clip adjustments. adjust the needle up or down if you get some spuutering or hesitation from 1/4 throttle to 3/4 throttle, and adjust your airscrew for good idling and coming off idle, just rich enough that it doesn't hesitate as soon as you give it some throttle. also, you are not going to get rid of that bog from stabbing it at low rpm's, you just use less initial throttle to cure that, but you should have no problems with roll-on throttle at low rpm's.