How to set the fuel mixture and jetting - Honda ATV Forum
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post #1 of 11 (permalink) Old 07-05-2014, 08:17 AM Thread Starter
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Thumbs up How to set the fuel mixture and jetting

I have found these methods to work pretty good for me. Some may have other ways of running their plug chops and setting fuel mixtures but this is what works for me.

PLUG CHOP HOW TO

Before you run the plug chop you will need to first make sure the fuel mixture and or low end throttle are correct the air filter is clean and oiled. You're going to need a few new spark plugs too . 3 or 4 plugs are cheaper than 200 for a rebuild kit. Now grab your plug wrench a rag and go find you at least an 1/8th - 1/4 mile straight that's not illegal. lol You want to ride your quad around for 10 min or so get it nice and hot. (the trip to your riding spot will help warm it up). I usually run down to the opposite end of my work area so when I make my chop run I can stop where my tools are. OK here we go... remove the old plug install the new one. Start your engine and take off you want to run w/o throttle through each gear up to 4th, STAY OFF THE LIMITER IN ALL GEARS!!! once you hit 4th hold it for about 8-10 sec stay in the throttle and hit the red run/stop switch on the bars IMMEDIATELY and SIMULTANEOUSLY pull the clutch and let off the throttle stop your quad and then remove the plug. install your old plug and head back to your shop/shed/house. It helps if you have a vice. you want to lock that new plug in the vice then take a hack saw or die grinder and cut the threads away from the plug exposing the whole porcelain. Now here's the misconception of plug readings. you would think the whole porcelain would need to have that cardboard brown color. . Wrong. you want to see an ring of that color close to the base of the porcelain. If that ring is too light your main jet is too small. of it's too dark it's too big. If you ran this test with the air box lid on and the ring was dark, remove the lid and run it again on the other new plug. Jetting is NEVER cut and dry and NEVER is bike "A" jetted exactly like bike "B" we can only offer a starting point based on past experiences. Your bike is different. Have patients this will take you a while allot of trial and error and new spark plugs. Also keep in mind a plug chop on a 90 degree day will yield a different result than a 70 degree day. Jetting is in fact seasonal, most do not do it but it is.

SETTING THE AIR/FUEL MIXTURE

To set the air/fuel mixture screw you need to have a warm engine. while the engine is at idle, you want to increase the idle by about 100-200 rpms (which isn't much). Now . . . while counting turns SLOWLY turn the screw in by 1/2 turn increments and allow 3 or 4 seconds in between for the engine to stabilize as best it can. Once you get the screw turned in to lightly seated record the turns for reference only. SLOWLY back that screw back out in the same method as you did turning it in. Please allow that few seconds for the engine to acclimate to your changes. As your turning the screw out notice that the engine RPMs are also increasing. DON'T FORGET to count the turns!!!! Once you get to the highest RPMs turn it a little extra just to be sure; then turn it back. Let the engine stabilize and then turn it back IN an additional 1/4 turn.

"MOOSE WAGON "
00 TRX400EX aka "MOOSE ROCKET"
91 TRX250X aka "MOOSE WAGON" RETIRED
96 Polaris 400L sport (Mrs. Moose Ride)
07 Suzuki LTZ250 (Sons)
96 Polaris 250 Trail Blazer (daughters)
06 TRX450ER aka === Under construction

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JETTING
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post #2 of 11 (permalink) Old 07-05-2014, 03:27 PM
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You should sticky this!!!!!!! Like now.lol
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post #3 of 11 (permalink) Old 07-05-2014, 04:18 PM
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^^^I agree Moose, we get asked this allot! Now how to do it with an auto clutch,,lol! I always though well kill switch, and maybe push down on the shifter some on a manual shift to get it into a engaged clutch mode to stop the engine from turning over after you killed it, but never tried it. Always had to go the route of checking speed from one set mark to another with a roll on in 4th gear and go with the best time...food for thought on auto clutched machines,,not to mention the dreaded cvt,,lol! A quick shift on the fly into neutral perhaps? It can be done if done very carefully.

05 Suzuki DR650, Mikuni TM40 flatslide pumper carb,JE 10.5:1 piston,stage 2#190 Webcam,open airbox, Twin Air,full FMF system,Pingel fuel valve,Ricor Racing rear shock, Ricor Racing fork Intiminators, Progressive springs, Sargeant seat,DRZ250 tailight,custom plate,LED's,GPS,sumo fender,PT bars,Cycra brushguards IMS lowered pegs, aluminum skid,bearing chain roller,Pirelli,tank bag(gone)

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Last edited by stu5969; 07-05-2014 at 04:20 PM.
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post #4 of 11 (permalink) Old 07-05-2014, 09:05 PM Thread Starter
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Quote:
Originally Posted by stu5969 View Post
^^^I agree Moose, we get asked this allot! Now how to do it with an auto clutch,,lol! I always though well kill switch, and maybe push down on the shifter some on a manual shift to get it into a engaged clutch mode to stop the engine from turning over after you killed it, but never tried it. Always had to go the route of checking speed from one set mark to another with a roll on in 4th gear and go with the best time...food for thought on auto clutched machines,,not to mention the dreaded cvt,,lol! A quick shift on the fly into neutral perhaps? It can be done if done very carefully.
As far as the foot shifts you can simply hold up on the shifter until you stop.. CVTs are a bit trickier I agree.... you're probably right on target with the neutral shift.

"MOOSE WAGON "
00 TRX400EX aka "MOOSE ROCKET"
91 TRX250X aka "MOOSE WAGON" RETIRED
96 Polaris 400L sport (Mrs. Moose Ride)
07 Suzuki LTZ250 (Sons)
96 Polaris 250 Trail Blazer (daughters)
06 TRX450ER aka === Under construction

Progress and Help
PM FOR MANUAL HELP
JETTING
Service_Manual_Downloads
2000_400EX_Build
400EX_Pivot_Bolt_
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post #5 of 11 (permalink) Old 07-06-2014, 07:34 AM Thread Starter
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Quote:
Originally Posted by fallguy View Post
You should sticky this!!!!!!! Like now.lol
done.... I stuck it.

"MOOSE WAGON "
00 TRX400EX aka "MOOSE ROCKET"
91 TRX250X aka "MOOSE WAGON" RETIRED
96 Polaris 400L sport (Mrs. Moose Ride)
07 Suzuki LTZ250 (Sons)
96 Polaris 250 Trail Blazer (daughters)
06 TRX450ER aka === Under construction

Progress and Help
PM FOR MANUAL HELP
JETTING
Service_Manual_Downloads
2000_400EX_Build
400EX_Pivot_Bolt_
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post #6 of 11 (permalink) Old 07-06-2014, 01:20 PM
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How do I do this with a Rincon? Throw it in nuetral while running it then kill?
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post #7 of 11 (permalink) Old 07-06-2014, 01:22 PM Thread Starter
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Originally Posted by jcooperpcola View Post
How do I do this with a Rincon? Throw it in nuetral while running it then kill?
Not real sure? As I based this on sport quads hence the "pull in the clutch" statement... Most people o. Here asking about jetting are riding Sport quads...

"MOOSE WAGON "
00 TRX400EX aka "MOOSE ROCKET"
91 TRX250X aka "MOOSE WAGON" RETIRED
96 Polaris 400L sport (Mrs. Moose Ride)
07 Suzuki LTZ250 (Sons)
96 Polaris 250 Trail Blazer (daughters)
06 TRX450ER aka === Under construction

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PM FOR MANUAL HELP
JETTING
Service_Manual_Downloads
2000_400EX_Build
400EX_Pivot_Bolt_
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post #8 of 11 (permalink) Old 07-13-2014, 01:40 PM
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I like this one better then the one stickied at the top of the performance section.

Maybe this should replace/update it? Just add a pic of the bottom of a carb for those who don't know where stuff is exactly.

Click the image to open in full size.

I also put the link to this thread in my signature for future reference/ ease to find.
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post #9 of 11 (permalink) Old 10-26-2014, 12:12 AM
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At last, a pic in detail, thank you!
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post #10 of 11 (permalink) Old 05-09-2015, 11:19 AM Thread Starter
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Here is another write-up .. not mine but it's also got some great info.
Terms and Definitions

Jetting: The term comes from the two main circuits that control fuel flow in a carburetor. The pilot jet and the main jet.*

Main Jet: This is the main fuel circuit in a carburetor. It's a common misconception that this circuit only effects engine performance at wide open throttle. The main jet actually has a trickle down effect on other adjustments and should be adjusted first.

Needle: The needle is attached to the carb slide and is raised and lowered when you push and release the throttle. When you let off your throttle, the needle lowers into the main jet circuit, cutting off fuel flow as it goes down.

Needle Clip: This is the small circular clip that is used to adjust the needle position.

Pilot Jet: This is second jet in your carb. Much smaller than the Main Jet and typically has no effect beyond approximately 1/4 throttle. It's used to adjust your mixture at idle and low throttle.

Air/Pilot Screw: The air screw works in combination with the pilot jet. You can consider it a fine tuner for the pilot circuit. It's most obvious effect is noticed by throttle response.

Float: The float controls fuel level in the float bowl at the bottom of the carburetor. It has no effect on jetting but can cause some symptoms that can be easily confused with a jetting problem. If the fuel level is too low for example, it can cause a bog similar to a lean condition.

Float Seat/Valve: Basically the valve that stops fuel from flowing into the float bowl when the float reaches a specified level.

Rich: A "rich" condition is what occurs when you have too much fuel in your fuel/air mixture. Symptoms of a rich condition can be a rough running engine (sputtering), a black spark plug, a wet plug or excessive plug fouling.*

Lean: A "lean" condition is what occurs when you have insufficient fuel in your mixture creating an over abundance of oxygen. Symptoms can be a rough running engine (bogging), a white or light gray spark plug and sometimes can result in overheating or even severe engine damage.

Sputtering: This isn't exactly a technical term but is commonly used to describe how an engine runs when jetted too rich. For example, using too large of a main jet will cause more fuel to enter the combustion chamber than it can efficiently burn. This will result in a "sputter" at full throttle. It could best be described as a rapid misfire. Note: a rich condition is not the only possible source of this type of problem.*

Bogging: Again, not a technical term but commonly used. Bogging can be a result of a lean setting where not enough fuel is entering the combustion chamber for the motor to run properly. In some instances this can cause the machine to "bog" as if it were actually running out of gas. Note: a lean condition is not the only possible source of this type of problem.*

WOT: This an acronym that stands for Wide Open Throttle.

Plug Chop: Plug chops are the most accurate and easiest way to check your jetting. A proper plug chop should be done with a clean spark plug. Example; to check your main jet, put in a clean spark plug and run the trike at Wide Open Throttle (WOT) for several seconds, then in one motion, pull in the clutch (if applicable), kill the engine and let off the throttle. Remove the spark plug and check the color (refer to chart in this thread).

Float: The float controls fuel level in the float bowl at the bottom of the carburetor. It has no effect on jetting but can cause some symptoms that can be easily confused with a jetting problem. If the fuel level is too low for example, it can cause a bog similar to a lean condition.

Float Seat/Valve: Basically the valve that stops fuel from flowing into the float bowl when the float reaches a specified level. If worn it can cause the float bowl to overflow.

"MOOSE WAGON "
00 TRX400EX aka "MOOSE ROCKET"
91 TRX250X aka "MOOSE WAGON" RETIRED
96 Polaris 400L sport (Mrs. Moose Ride)
07 Suzuki LTZ250 (Sons)
96 Polaris 250 Trail Blazer (daughters)
06 TRX450ER aka === Under construction

Progress and Help
PM FOR MANUAL HELP
JETTING
Service_Manual_Downloads
2000_400EX_Build
400EX_Pivot_Bolt_
TRX2fiveO is offline  
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