Hey everyone,

I still can't get it. Here are the specs:

2001 300EX
Full W/B Exhaust
K&N Filter


I need to know what main, needle, or pilot jet to go with. It has a slight delay in throttle response and a backfiring pop in deacceleration. Any suggestions?

 

Yes I have a suggestion,

Do your homework, look things up on the internet, read things and understand what a carb is, how it works, and why jetting changes when you alter things. I'm not trying to be harsh, but that's the ONLY way you will get it right. No one here can tell you what jetting to use.

What jet do you have now vs. what came stock? Is the throttle delay 1/8 1/4 3/4 or full throttle? What altitude? What does your plug look like? Backfiring is usually caused by a lean idle circuit. (NOT idle speed)

You'll figure it out.

 

Need more info, hold the throttle exactly where you are haveing the trouble for a second or two, then hold the kill button and pull in the clutch..check the plug's color.

 

Got ya guys. I am relatively new at jetting. I have done some homework. Obviously not enough. I am running a 130 main. Other than that, everything in the carb is stock. When I installed the 130 main, it was running EXTREMELY rich. I took the needle and lowered it 1 clip slot. Then the plug was a light brown/grey color. But, before shutting it down, it was at idle. Also, the delay is when it idles and I goose it it has a bit of a delay. Nothing crucial, but I am trying to fine tune it. I am just afraid to blow the engine. The reason for going to a 130: someone told me that they have the same set-up and that was what they were using. Should the plug be the same grey/brown color throughout the throttle positions? Do you know where the "air screw" is located on the 300?

Thanks.

 

N3C0T0 -

Earthraper is right on (not being harsh either).

There was a time on this board (more than a year ago) when you would get a great answer from most people. Unfortunately, many of those people have left. Now you get answers from people that really don't know what they're talking about (not referring to this thread).

JRM's solution works extremely well on 2 strokes. But, with today's gas additives and longer life plugs, reading a 4 stroke plug can be difficult. Some have great success with it - I've had bad results. I either get black, grey, or white. Never brown. I think it depends on what part of the country you're in. I think the midwest has some pretty funky additives included in the fuel.

Anyway, my best solution to your jetting question: go to the atv connection's main page, select 'tech connection,' then select 'advanced search,' and finally select 'all models' and 'carburetion/jetting/fuel system' from the drop down menu. You'll get more than 100 questions and answers - all relating to jetting and carburetion.

What you'll want to do, in a nutshell, is buy a handful of main jets, starting from one size over the stock main jet, going up 5-7 sizes after that. Take the largest main you have, install it, then test. Test by putting machine in 2nd-3rd gear and open the throttle wide open right off the bottom (lug the machine). If you get a rich condition on the main (it'll stumble hard 1/3 to 1/2 way through the revs), drop the main jet size down one and retest. Do this until it revs cleanly through the rpm range. Some people drop the main jet down one more after it revs cleanly. If you don't get a rich condition with the biggest jet, go get bigger ones.

What you're doing is overjetting the machine. By getting it to stumble, you have a reference point of what's too big.

You'll probably want to test the main jets with the needle in the stock position. It's best to only work on one circuit at a time.

You can test the needle in the same fashion as you did with the main jets, but most people arrive at one clip position lower than the stock setting (so the needle would get raised one notch). It might be useful to you if you raise the needle all the way (lowest clip position) - then you'll feel what it's like to have an overly rich midrange circuit. Do this AFTER you've got your main dialed in.

I tried to read my plug after a midrange plug chop (i.e., run your quad for about 1 minute with half throttle then pull in your clutch and kill the engine - note: it doesn't really matter what gear you're in), but never got a tan/brown plug reading. So I just raised it one notch, my quad is quite happy with that setting.

The pilot jet can probably be left as is. After testing the other two circuits, and you're still getting a backfire and/or hard starting, you should adjust your air/fuel mixture screw (like earthraper mentioned). It is located under your carb, right in front of your floatbowl. Turn this out in 1/2 increments until the problem goes away. If at 4 turns out (from a seated position), it still backfires, you need to go up a size with the pilot. With the new size pilot, start at 1 - 1 1/2 turns out, and test in 1/2 turn increments (like before). Think of the air/fuel mixture screw as a fine adjustment for the pilot jet.

Have fun!

ogre