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I have an '06 Grizzlt that is entirely stock. I have no low end snap at all and never have since I got it brand new. I can not pop a wheelie at all. It just seems to bog down when I try.

It was suggested to me to try adjusting the fuel/air mixture screw. I read on a differant post that 2-4 turns out is the norm. What is the proper procedure on adjusting the air/fuel screw and the idle screw?

Please help!!!
 

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Hi Dan!


JETTING

WORKING WITH INDIVIDUAL CARBURETOR CIRCUITS
So, how do you start? At the bottom. Then you jump to the top and work your way down.

IDLE MIXTURE SCREW:
The idle mixture screw is the only externally adjustable carburetor jet available and controls up to 1/8 throttle only. There are two types of idle mixture screws. One type is called a fuel screw because it regulates the flow of fuel into the idle circuit. This type of screw is located ahead of the carbs slide tower (motor side) and is most often found under the carbs bore and upside-down directly ahead of the carbs float bowl. By turning the screw out you increase the amount of fuel that is allowed to slip around the tapered needle and into the carbs bore where it is mixed with air that has snuck under the carbs slide.

If the idle mixture adjustment screw is located behind the carbs slide tower (airbox side) then the adjusting needle regulates air flow into a fixed flow of fuel intended for idle. By turning this screw inward you are reducing the air flow, thus richening the idle mixture.
When the motor is up to operating temperature, set your idle speed screw to a stable idle. Then use either your idle fuel or air screw to obtain a stable idle. Reset the idle speed screw as necessary after obtaining the correct idle mixture.

MAIN JET
The main jet controls 3/4-full throttle only. Ideally you should start very rich (large numbered jet) and test at full throttle. It should skip. If not then you are not rich enough! Once you have your rich stumble, back off one size at a time until full throttle operation results in normal operation. (Note: If your ATV runs faster at 3/4 throttle than full throttle you are definitely lean on the main!)

JET NEEDLE
The slides jet needle controls 1/4-3/4 throttle. It does this by passing upward through the needle jet. The needle jet is a long brass tube that contains many small holes in its sides that air passes through. Fuel from the float bowl enters this air stream from the main jet and into the center of the needle jet where it mixes with the air to create an emulsion. This mixture of fuel and air is then metered by the height, taper and diameter of the jet needle as the emulsion passes upward around the jet needle into the carbs bore where it mixes with still more air to (hopefully) arrive in the motor in a combustible fuel-to-air ratio.

If you have a soft hesitation, without a hard stumble, anywhere between 1/4 and 3/4 throttle, chances are your needle is lean, so raise the needle by lowering the clip. Conversely, if you have a hard stumble, chances are the needle position is rich, so lower the needle by raising the clip.
If you get very unlucky you might have to start playing with jet needle taper which controls how fast the mixture increases as the jet needle is raised. This would come into play if you were lean at 1/4 throttle, yet rich at 3/4 throttle. The length of the needle comes into play here too. The diameter of the needle controls how much fuel escapes around the needle while still inside the needle jet. The larger the diameter of the straight section or "L" length, the leaner the mixture. Or finally, the "L" length, which controls how much the slide rises before the tapered part of the needle starts.


SLIDE CUT-A-WAY
The slide cut-a-way controls the amount of air allowed to pass under the slide at 1/8-1/4 throttle. It controls the transition from the low speed (pilot) jet to the main jet-fed needle jet/jet needle. Replacing the slide with one that has a smaller number (less cut-a-way) will decrease the amount of airflow under the slide at 1/8-1/4 throttle openings, thus creating a richer mixture at that throttle opening. If you have a rich condition at 1/8-1/4 throttle and you can’t go any leaner, try a smaller cut-a way.
But thankfully, jet needle taper, diameter, "L" length and slide cut-a-way are usually not affected by most simple pipe/air filter modifications.

LOW SPEED (PILOT) JET
The low speed (pilot) jet controls fuel flow at 1/8-1/4 throttle. The low speed (pilot) jet is usually not affected by most simple pipe/air filter modifications. However, a slightly lean low speed (pilot) jet can raise havoc in the winter where its fuel is added to the total mixture strength required to start. You may find going one level up will help a winter cold start situation.
Finally your idle mixture is revisited if you have a deceleration backfire situation. When you chop the throttle and use the motor to decelerate, if you get a stream of backfires, try increasing your idle mixture strength 1/4 turn at a time until the backfire goes away. Note: If you reach a point where your idle mixture is 4 turns out (for fuel type screws, NOT air type screws), try going up one size on the slow speed (pilot) jet and reset your idle mixture screw to 1-1/2 turns out and repeat the process.

NOw if this doesn't help...

What you'll do is reach up under the intake tract to find the screw. Turn it OUT a quarter of a turn to richen it just a touch. Try a run. If it's worse, put it back where you found it, and then try one-quarter turn IN to try it leaner,
 

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Discussion Starter #3
So, I adjust the fuel screw and then set the idle...

Then should I test my low end torque(wheelie)?

How do I know when I have the correct mixture??
 

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That's a bit of a learned skill, Dan. You most likely won't need to adjust the idle. After you tinker with the mixture screw, let the bike warm up, and mash the throttle to see what happens. If it "wheezes", you're lean, if it loads up and sounds like it needs to burp, you're rich. That's about the only decent description that i've got fo it...

Another way to tell if you're lean is to thumb the choke lever over just a bit while throttling up. If it runs better, you know you were lean. If it really craps out, you were rich. The choke circuit lets more fuel in, so it can point you in the right direction.
 

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bob, would the choke richen up the mixture over the entire rev range or just 0 - 1/4 throttle?
 

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It's dumping fuel in, so my guess is that it'd be all the time. It's not a metering circuit like the rest of the carburetor; more like an afterburner(?) Truthfully, I've never choked a four-stroke, and then held it wide open...
 

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Do a 45 pilot, it helps with the low end. Their are some other mods you can do to help with low-end. A filter and jet kit will help, as will a clutch kit to. What mods do you have so far?
 

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throw a new plug in ... start it, let it warm up ... do a bunch of acceleration tests to about 10 mph or so (no more than 1/4 throttle) .... stop ... do it several times and then check the plug, you will then find out what is causing the bog just by the color

compare your plug to the ones below....

http://hawkworks.net/sparkplug-chart/
 

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Hi Jasson!
I was waiting for you to get to the party; I know that you're the real "wrench guy" in here who likes to tinker way more than I do. I'd have to say that it would fatten up the mixture through the entire rev range... if it'll run on full throttle with the choke engaged.
 

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Checking the plug is pretty much worthless to check your getting! The motor will tell you where you are lean. Stalls in speed climbs, backfire'ing, bogss, misses, etc. Those are all info to what your motor is saying.Perfect jet is time, and understanding, not an art, or anything that anyone can't learn.

Bob, you are some what right.All you are doing is cutting off air. It only good to check a if you are lean or rich, but not by how much.

So, listen to your motor and what it does and where. That will tell you everything, and dont be scared to play with you jetting, you always can make it better somewhere.
 

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jasson, you don't think checking your plug is important???? sure getting feedback from how the engine performs is part of the carb adjustment routine but you have to check your plug to see how your engine is burning the fuel mixture. it takes exactly 20 seconds to take out your plug and read it ...

checking your plug is a definitive way of finding out why your engine is bogging Marchdan.

if you feel comfortable by reading what the engine is doing and making any adjustments from there, there's nothing wrong with that ... just confirm your results by pulling the plug and reading it, the Mikuni tuning manuals even call for this step.
 

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I bet you, if we ride a bike, I can tell you what and where you need to jet before you even get the plug out!
And you have to check, kill the motor at the point you want to check you jetting, can be off or it will be a miss read, and pull the plug, the put it back, and you can get false rich statements on your plug, etc.
Their is a ton of pros-cons of this storey. Even after you get it jetted right, you can still have air fuel problems, that you will over look if you dont know how the bike acts when you bike starts acting up.
A plug check is good about once a month to see the carbon build up, gap, and chance of parts braking down.
I'd rather jet to the feel of the motor and how it acts other then to the carbon and other build up on a plug.
A lean plug can read black their, and can fool alot of people. Their is alot more then just a plu to check its a bunch of things.
 

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(I think that he's got a background rooted in racing, so tinkering with jetting is second nature by now...)
 

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Yep. I help gunny get his almost dead on, by talking to him over the phone, and not even see'ing a plug or anything. Its what the bike does what and where that will tell you what needs to be done, and not being scared to get in their and tinker.

Im not say checking the plug is a bad way craig, but its not the best way, and doesn't cover all area, and to may area, where you can get a false reading.

The best and fastest way to to see what the motor is doing what and where, and then address the problem to correct it.
 

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Craig, that guide looks like a car guide, or some plugs out of an 1978 atc110 that it came with. I bet only 2 or 3 might be an atv condition. Is that 4 stroke plugs or 2 strokes?
 

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ya, it's probably not the best guide for spark plugs .....

http://www.atvriders.com/articles/sparkplug.html

this one's probably better ....



jasson, we could probably argue all day on this topic but I stand by spark plug reading. i would rather have visual evidence that my machine is running properly after tweaking my carb. after my snorkel install, I thought my grizz was running 100% but after checking the plug, I can tell you that it's running lean in the 0-1/4 throttle. even my buddy who used to work for Yamaha thought it was running perfectly ... there was no hesitation, no bog, no lag ... nothing ... but bottom line is the plug was white. After a few adjustments and plug checks, it is now the nice light/medium tan color once again.

I've never heard of false plug readings and can't find any information anywhere on this subject ... can you get a false reading from a 2006 grizz like mine in good working condition? If so.... how?

Craig
 

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Like Craig, I'm a "give me evidence" kind of a guy. Listening to your bike is good; if you know what to listen for. Most of us don't have that level of expertise so something a bit more tangible, like a plug reading, gives us hard evidence from which to make our decisions.

I thought that my bike was jetted correctly until I pulled the plug too...it sounded and ran great.

That having been said; I wish that I could do what you do Jasson! Maybe over time I'll get to that point...
 
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