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Re-Jetting, where should I start?

4929 Views 4 Replies 4 Participants Last post by  #48FAN
I recently purchased a utility series HMF for my 2005 Honda Foreman, along with a K&N filter and precharger. The HMF came with a 170 jet. I have not installed anything yet, but what is a good place to start? I live in Tulsa, Oklahoma to answer any elevation questions. I am going to try to install the Jet myself, as I do have the Honda Manual showing me how to do it, it does not look too hard. What order of installation would you recommend and is a 170 jet the right place to start. The stock jet is a 162.
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I believe most people use a 170 or 175 if it's just a slip on and filter.
Hi there.

I Just put it on all that in my 06 foreman. I bought it in atvoutfitters the High Perfomance kit.
Just put the HMF e filter and test. You will feel torque torque torque.

Then reject and then is when i can't adjust perfectly the mixture screw...
With 2,5 turns (by the book) you feel some fails in the high revs. More half a turn, is too much gas and doesn't do any high reving...

It seems i can't find the perfect point of mixture.

To reject, you have to take out the botom of the carburator and change the jet. (plate with 4 srews that is in the back of the carburator as you see it mounted). So can you adjust the mixture, take the D-shaped screw out with pacience and saw the screw so you can adjust with a standard screwdriver.

Please anyone help?
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Let's start by talking about the effective range of each carb circuit. Remember that the each adjustment effects a range of throttle positions, NOT engine RPMS... Always try to think "throttle position" -not- RPM.

The three main carb circuits are;

The main jet - 3/4 to full throttle
The needle + needle jet - 1/8 to 3/4 throttle
The pilot jet + pilot screw - idle to 1/8 throttle

The Main Jet
The main jet primarily controls fuel flow between 3/4 and WOT (wide open throttle). Once the throttle is open past about 3/4 the needle is pulled high enough out of the needle jet that the size of the main jet begins to control fuel flow. Main jets are identified by a number. The larger the number, the larger the hole in the jet. A larger hole will allow more fuel to flow, giving a richer mixture. So basically, the higher the main jet number, the richer the fuel mixture will be between 3/4 and WOT.
The Needle and Needle Jet
The needle and needle jet are the componets that primarily regulate fuel flow between 1/8 and 3/4 throttle. The needle jet is seldom changed in everyday tuning, but it's still worth mentioning the fact that it's there. The needle itself is a basically a tapered rod connected to the throttle slide. As the slide opens the needle is pulled upwards. The needle is tapered so that as it's pulled up, it takes up less space in the needle jet. This allows the fuel flow to be gradually increased as the throttle is opened. The needle has a clip that allows it to be lowered or raised in relation to the carb slide, which gives an overall richer or leaner setting. Raising the clip up a notch drops the needle down farther, causing a leaner mixture. Lowering the clip raises the needle up, causing a richer mixture. You can also get different diameters, and tapers of needles. If the clip is lowered all the way, and the mixture is still lean, you need the next size smaller needle. If the clip is raised all the way, and the mixture is still rich, you need the next size larger needle.

The Pilot Jet, and Pilot Screw
The pilot jet, and pilot screw control fuel delivery from idle to approximately 1/8 throttle. The pilot jet is similar in design to the main jet, basically a small screw with a calibrated hole in it. As with main jets they are identified by number, a larger number pilot jet is richer, and a smaller number pilot jet is leaner. The pilot screw on an ATV regulates fuel flow.. Turning the screw in makes the mixture leaner, and turning it out makes it richer. If the pilot screw winds up being turned almost all the way in, you need the next size smaller pilot jet. If the pilot screw is more than about 2 1/2 turns out, you need the next size larger pilot jet. Basically the pilot screw is an adjustemnt that allows you to fine tune the pilot circuit.
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This should help...

Loosen both sides of the carburetor. And turn it 90 degrees. Take the 4 screws out that hold the bowl on the bottom of the carburetor. Be careful they strip easy. Take a flat head screw driver and screw out the factory jet and install the 170 jet. You use your factory needle. Put carburetor back together. On the bottom of the carburetor is the air/fuel mixture screw. It takes a special tool. It is “Dâ€
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