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Discussion Starter · #1 · (Edited)
Couple questions for you guys, first. Are there two fuel screws? The dynojet instructions tell of the one under the cap inside the carb, but the fuel screw guide on here talks of the one of the bottom of the outside of the carb. Which should I adjust? Also is this a good thing to buy an install?

One more thing before I get into my plans I've made of what I know so far (and that may very well change if I am wrong in my assumptions). Do the fuel screw and jets work hand in hand? Like, could I have a 150 main jet with the fuel screw out 3.5 turns or a 160 main jet and it screwed out 2.5 turns and they would run the same or how do they work together?

I am getting a uni air filter and will be running no snorkel or lid along with a fmf powerbomb header and fmf factory 4.1 muffler and as I have it right now (didn't think if be getting an exhaust system so soon) I have a 150 minuki main and a 25 pilot (need to buy an adjustable needle..) and was wondering should I upgrade to a 160 minuki main? (if my assumptions are correct with the fuel screw then I'll just stick with the 150 and compensate with the fuel screw?) my altitude is about 650 feet.

Thanks a bunch guys, just want to get all this straight!
 

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That adjustable screw you linked just makes the adjustment easier. You can just use a flat head bit to adjust it if you're too cheap to buy one, like me. If I wasn't being a cheap ass right now, I'd buy one though.
 

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Discussion Starter · #3 ·
Ok so does installing that make the fuel screw adjustable to the point like the idle screw?

@ huntergreen: which are you referring to? The internal or external fuel screw? Or are there just two ways of adjust one screw?
 

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Couple questions for you guys, first. Are there two fuel screws? The dynojet instructions tell of the one under the cap inside the carb, but the fuel screw guide on here talks of the one of the bottom of the outside of the carb. Which should I adjust? Also is this a good thing to buy an install?
The adjustable fuel screw is on the bottom forward side of the carb, (motor side). 2 strokes have a similar screw (air screw) but it is normally located on the aft side. The other adjustable piece i believe your talking about it the needle jet that comes in dynojet kits. it installs under the black cap on the top side of the carb and runs down into the throat of the carb. it has 5 (i think) notches where you can change the circlip to different heights. raising it up allows for more fuel and lowering is less.

the fuel screw and pilot jet work together in the pilot circuit (up to a 1/4 throttle IIRC) and the needle jet controlls more from 1/3-3/4 (someone correct me if im wrong.) i had a very good Mikuni link that talked all about thefuel circuits and told you what controlled what. if you search you should find it.
 

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Discussion Starter · #5 ·
I know what the needle is and what it controls and thats not what 'm talking about, look in this article at step 5.

http://www.dynojet.com/pdf/Q316.pdf

So if the outside fuel screw (still don't know what this internal fuel screw controls...) works with the pilot then that means it doesnt effect my main jet so am I going to want to upgrade to a 155 or 160 minuki?
 

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yes that is your fuel screw/fuel mixture screw. there is only one. that is it. if no one has touched your carb before you, then there will be a brass plug (i guess some people have a rubber plug there instead also), that you will have to carefully drill out. yes the fuel screw and pilot jet work together.

on a side note, a 155-160 mikuni jet would be close to the equivilent of a 165-170 dynojet. they do not rate them the same way. so depending on your mods, you may be pretty big if you go that route
 

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Discussion Starter · #7 ·
Alright thanks Ill take a look at the fuel screw next time I'm home. I have a 150 minuki in it now and all I am going to be doing to my quad is an FMF Factory4.1 exhaust with power bomb header, pilot 25 minuki, taking 2 coils off the main carb spring, no lid or snorkel and a uni filter. Will the 150 minuki main be big enough or should I upgrade to a 155 or 160? Also does that adjustable knob for the fuel screw just fit in there then stays there to make the fuel screw adjustment easy access or is it like just a took to adjust it?

Thanks
 

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150 should be fine depending on your elevation. youll be close. yes the aftermarket fuel screw replaces the stock one and stays in the carb.
 

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Discussion Starter · #9 ·
Sweet. Elevation is 650 feet. what do you think? If 150 is close 160 is prob too big so with my elevation stick with the 150 or upgrade to a 155? I'd rather put everything in once instead of pulling it apart for each part. I'll pick up that other fuel screw too.

Thanks a bunch hughes you've been a great help.
 

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a 145 if you have mikuni jets and a 150-155 if you have dyno jet. that should get you very close. also if you do have an adjustable needle from dynojet or can get one it would help alot. it would probably do you good on the 3rd notch.

no problem. good luck.
 

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Discussion Starter · #11 ·
Alright thanks Ill just see if this 150 minuki works alright and go from there. Yes I do need to buy an adjustable needle still... Seeing if anyone on here has one but if not I heard alba sells needles alone
 

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Alright thanks Ill take a look at the fuel screw next time I'm home. I have a 150 minuki in it now and all I am going to be doing to my quad is an FMF Factory4.1 exhaust with power bomb header, pilot 25 minuki, taking 2 coils off the main carb spring, no lid or snorkel and a uni filter. Will the 150 minuki main be big enough or should I upgrade to a 155 or 160? Also does that adjustable knob for the fuel screw just fit in there then stays there to make the fuel screw adjustment easy access or is it like just a took to adjust it?

Thanks
If you get an after market fuel screw (adjustable knob) make sure it is for the Mikuni Carb. The only place I know that sells them is Advantage Motorsports and they are a sponsor here.
Read the sticky "the secret world of the fuel screw".
 

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Discussion Starter · #13 ·
Yup ordered the one for the LTZ carb
 

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Ok I just put 160 mikuni main in and 25 pilot mikuni in. My z idles WAY high. I tried adjusting the fuel screw made no diffrence.
My mods are: No air lid/snorkel, shortened carb spring 3 coils, Yoshi slip on, Wiesco high compression piston and rings, Wiesco valves, and a Wiesco timing chain. I will soon be putting a clamp on filter, 400ex boot, and an aftermarket header. The header might be a little while though. Also I am probably getting an OEM carb on here from a member and it has a stage 2 dynojet kit. So what do you think I should use for mikuni main jet and a stage 2 dynojet ???
 

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Discussion Starter · #15 ·
It's not your jets, EXACT same thing happened to me. Take the choke cable out of the carb and put it back in, it's not sat correctly.
 

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that is a good possibility, its not technically a choke, its a fuel enrichment circuit.
also just use the dynojet kit and jets and follow there directions
 

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That helped some, but I have the fuel screw adjusted way off from trying to get it to idle. I would mess around with the fuel screw tonight but I don't want to piss the neighbors off....
 

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Discussion Starter · #20 ·
Mess with the idle knob too
 
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