Raptor 660 Information > 660 Motor Mods

jetting 101

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UncleBeaner:
Pilot Screw                           - Idle
Pilot Jet                               - Idle to 1/4 throttle
Slide Cutaway                      - 1/8 to 1/4 throttle
Needle Jet and Jet needle     - 1/4 to 3/4 throttle
Main Jet                               - 3/4 to full throttle

1) Idle Screw
Allow the engine to reach operating temperature. turn to smooth idle. If unable to obtain smooth idle, go to Step 2, Pilot Screw

2) Pilot Screw
If unable to obtain smooth idle: turn the pilot screw in all the way GENTLY until it bottoms, then turn the pilot screw 1/4 turn at a time until achieving a smooth idle. The pilot screw should be correct between 1- 2.5 turns. If idle is between 1-2.5 turns, the jump to step 4, Main Jet. If idle is NOT smooth between 1-2.5 turns, then jump to step 3, Pilot/ Slow jet.

3) Pilot/Slow Jet
If idle is not smooth with pilot screw between 1-2.5 turns, then the pilot/slow jet needs to be changed. There are 2 choices. either A or B
A - If the pilot screw has been turned more then 2.5 turns to smooth the idle, then install a bigger Pilot.
B - If the pilot screw has been turned less the 1 turn to reach smooth idle, then install a smaller Pilot.

Note! A larger pilot jet will eliminate the popping sound that may occur when letting off the throttle.
A larger will improve cold-weather starts.

4) Main Jet
Start with the richest (largest numbered) main jet and test at full throttle. the engine should "stumble" at wide open throttle (If engine does not stumble, then the engine is not rich enough and a larger main jet should be installed). Once you have a rich "stumble", install the next smaller jet one size at a time until full throttle results in normal operation. Once main jet step is complete, go back to step 2, Pilot Screw, and perform pilot screw adjustments one last time.

Note! If quad runs faster at 3/4 throttle then at Full throttle, then the jets are lean and a larger jet must be installed.

Needle
If carburetor has an adjustable needle, this step CAN be performed. If you have a slight hesitation but NOT a hard stumble between 1/4 -3/4 throttle, then the needle is probably lean. Raise the needle by lowering the clip.

Slide Cutaway
The slide cutaway controls the transition fron the low speed pilot jet, to the main jet. Replacing the Slide Cutaway with one that has a smaller number, will decrease the amount of air creating a richer mixture.

Reading Spark Plugs
Once the main jet is set correctly by dropping a main jet size after the "stumble", confirm the jetting of the engine by reading the spark plug. This works best in top gear in a slight uphill area. After running at full throttle, do the following at the same time: pull in the clutch and stop the engine, DO NOT LET THE ENGINE IDLE! Remove the spark plug amd examine the color. It should be a Light Tan. If it is white, then the engine is running lean and a bigger Main Jet must be installed. If the color is Black, then the engine is running rich and a smaller Main Jet must be installed.

any questions just ask

spdraycr:
i have a question-or two...i have an 03 660.yoshi exhaust,k-n filter.had 146/148 jets and 22.5 pilot.all was ok until i took my lid off and tried to run it that way.instantly i noticed my exhaust begin to glow fire red at idle(it never has before),and i have to leave the choke lever in the middle instead of far right or it wont idle.seems like its always racing now.when i ride and open up a little bit,it stalls in high gear then kicks in.went to 150/155 jets and the same.played with a/f screw and no help.moved needle back and forth from 3rd to 4th clip.still the same problems.when i give it gas while idle,it revs then comes down.when i cut it off,it backfires.spark plug tip has been white which i understand now means its lean.what do you think i could do to help fix my problem?and with the jets,which number goes in which side.oh and as far as a/f screw,i have it at 3 full turns from seated.i also put my lid back on and went back to 146/148 jets(was in there when i got it and ran perfect-untili messed it all up).i live a few miles from daytona beach if florida.please help if possible,thanks

Peelz:
smaller number needs to be on the left(passenger) side...I think  aaah I can't temember :lol: pretty sure....

155 160 with airbox lid off. May need a bigger pilot too with no lid. I had trouble running my 660 with no lid. Ran like crap. SO I put i back on and drilled some holes in it. May have to turn out those a/f screws a couple.

spdraycr:
ok cool,thanks.so im guessing i dont need to use the bigger jets with the lid on...whats the diffrence in performance with lid on/off if there is any?and what brand/size pilot should i buy?any and all help is appreciated,thank you

Segkast:
I would try some 25 pilot jets, and something close to that 155/160, maybe 2.5 turns on the a/f ?

You can buy Mikuni jets at most Yami shops. Sometimes if they don't have the right size I hit up the Suzuki/Polaris dealer as well. If you don't have anything close to you, you can always use http://jetsrus.com/ as well. Never used them myself, but I've heard good things from a lot of others.

Peels is correct, the smaller jet goes on the left carb.

No airbox lid simply allows for better airflow. Same with drilling holes like Peels did, just more so.

Is your K&N a drop-in filter, or the kind that you had to attach an adapter to the box for ?

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