Jetting....WTF?

[dgould]

Ok...Specs on my quad first off 2007 450r, Rossier exhaust, Im getting a hotcams stage 2 and of course want to re-jet it. Please help me out with this. I live in Colorado Im about 5500 feet above sea level. I really feel helpless when it comes to the carb and jetting its an area I want to become familar with but right now Im totally lost. I dont know where to start and all the main jet 148 and stuff like that is just really overwhelming I guess. Im sure Im making it more than it really is. I feel comfortable with doing anything else with my 4-wheeler except for of course the carbuerator. And unfortunatley with that damn thing it really seems like the front door to more power. Like I said I do get one thing though is you could have all the mods in the world but without the proper jetting you dont get the full effects and engine damage can occur, at least that's what I've been told. So please help me out with this, I would greatly appreiciate it.

[DnB_racing]

read this take your time and really read good it will answer your questions and make you a carb expert (maybe) go to this link http://quadhub.com/wiki/index.php?title=Jetting_theory&redirect=no

[RobRacing]

That's a good article but a little over the top I would say. Here is what I know

Fuel screw: Adjusts the "hang up" of the engine when you go from wide open to idle quickly. If your engine doesn't smoothly idle back down or "hangs up" when you let off the throttle you need to adjust the fuel screw out (richer) to clean this up. If your engines idles down and then dies you need to turn the screw in (leaner) to allow less gas into the engine. Play around with the screw until your engine idles down smoothly.

Pilot jet: Controls 0 to 1/4 throttle. This jet requires the least amount of adjusting over the rest. If your engine cuts out when you rev it up then you need to make this richer (higher number) if it bogs when you rev it up you need to make this leaner (lower number).

Needle jet: Controls 1/4 to 3/4 throttle. You can tell the most when this is out of tune when you do holeshots. If your engine is bogging when you dump the clutch on a holeshot or you are riding at a constant 1/2 throttle and you engine is bogging then you need to move the c-clip up one notch (drops the needle making it leaner). If the engine is cutting out in these situations you need to move the c-clip down one notch (raises the needle making it richer). Setting the c-clip in the middle slot is a good place to start.

Main jet: Controls 3/4 to full throttle and also effects all other jets slightly. This circuit is tested when you hold the throttle wide open. If your engine is bogging the you need to make the jet leaner (lower number) and if it is pinging or cutting out you need to make it richer (higher number).

Jetting can be very touchy and tedious. At any rate your engine should rev at a constant RPM at any throttle position and should rev up and idle down with no hesitation's. Once you start getting your hands dirty and listening to your engine you will become an expert at jetting. Hope this helped and good luck!

[racing12]

I'm having an issue once the motor is on it's down rev from full. it pops and has a few flames come out of the exhausut (no sparky!)

I'm running an nMotion exhaust and Kand N right now.

Pilot 52 and Main jet is at 185.

Plug looks ok, a tad bit white but not bad.

Whats the best way to make sure you have the right jets? I hear you run it hard for a few minutes and then check the plug?

Very responsive, just pops and it's annoying. Should I go up with the pilot to try and fatten it up?

[DnB_racing]

In general, backfiring on deceleration (as opposed to acceleration) is generally caused by a lean condition in the pilot circuit. What happens is that the mixture leans out enough to where is fails to ignite consistently. This, in turn allows some unburned fuel to get into the exhaust pipes. Then, when the engine does fire, these unburned gasses are ignited in the exhaust pipe, causing the backfire.

[racing12]

Right, what do you sugguest to fatten it up? Up the main jet even more?

[DnB_racing]

how far is your out is your A/F screw?if more than 2 1/2 to 3 then you need larger pilot

[racing12]

Yeah, no idea. I should check that.

[RobRacing]

Plug checks are usually performed on 2 strokes I am not sure if it is recommended for 4 stroke engines (what you have). Go with what Dnb_racing is suggesting