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Np57

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Alrighty guys so I jetted the carb today with a 150 yamaha main jet. Still the exact same thing. When it first takes off it makes you wanna hold on but then when it gets higher in the gear in just flattens out with absolutely no power at all.... So I'm getting at it that it has nothing to do with my jets. I have the correct ones in... There is something else... What else can it be. So confused guys
 
Clutch slipping is a possibility...but I'd think that it'd do that when you hit it hard on takeoff...
 
Spark plug id like a brown blackish mix
And the clutch is perfect
 
No but it does have a raptor 350 head which has a more aggressive cam in it
 
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Hmm...have you checked your intake boot for leaks? And does it do that in every gear?
 
Does it have an aftermarket exhaust? Higher flowing air filter? What is the largest main jet you have tried? What notch is your jet needle clip on?
 
Thanks for the reply guys. I have tried up to 150 main but it seems all the jets I have tried the quad does the exact same thing. I will check the valves to see. Hopefully the valves is the problem.. But idk if they are. And yes the bike does the same thing in all 6 gears
 
Np57 said:
Thanks for the reply guys. I have tried up to 150 main but it seems all the jets I have tried the quad does the exact same thing. I will check the valves to see. Hopefully the valves is the problem.. But idk if they are. And yes the bike does the same thing in all 6 gears
Click to expand...

You never answered my questions about exhaust, air filter, and any other performance mods. Stock main jet is only a 145 (iIrc), and a 150 is only two sizes larger. I'm assuming you don't have a stock exhaust, and in that case, a 150 main is not always big enough. Every engine is different and every engine responds differently to mods. Have you plug chopped it? Meaning, have you ran the engine at WOT for about 5-10 seconds, pulled in the clutch and shut the engine off???? You need to do that to see if it is running lean or rich. From what you have said about it falling flat on it's face, and not having any power, you are most likely running very lean. If it were rich it would load up and stutter/buck, trying to burn all that fuel. Get larger main jets; up to say 160 (never hurts to get even larger then that) and put in a jet that is at least two sizes larger then the 150, which would be a 155, and retest. Honestly, the easiest way to jet the main is to put in a BIG jet (like say a 165) and test ride + plug chop. If it's loading up and stuttering badly it's very rich and you need to drop it down one jet size, then retest and repeat the procedure until no longer loads up. Plug chopping is more accurate however, and you should really see what color the plug is after a Wide Open Throttle run to determine if you should increase or decrease the main jet size. Also, using a slight incline or grade works best for plug chopping, as it puts a load on the engine.
 
Last edited:
bones said:
hey pat it could be the accelerator pump to
Click to expand...


Could be if he were stabbing the throttle quickly. He never said. So, OP, are you having this problem when you stab the throttle quickly? Or, is it when you begin to reach WOT gradually???
 
Last edited:
Thanks for the respond guys. And yes I have a dg exhaust, raptor 350 head, UNI filter closed air box. It does it when I punch or gradually put more and more gas on until it bogs... I will try the 165 jet and work my way down
 
Yep, those are the symptoms of a lean main circuit. You are basically getting a big gulp of air when you jamb to throttle to WOT, or when you gradually reach WOT. Not enough fuel to keep the engine from falling flat on it's face.
 
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!)
 
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