General Jetting Info (Very Good)

[Woody_393]

Originally posted by Ranger_426F
Woody let me add to what is being said scince I have re-jetted for the last 2 years when comeing to Utah.

1st year: This is what I did with comments from TT

Moved clip to the #3 pos from top= Leaned out the mixture from 1/8 to 3/4 throttle as stated above. This made a big difference in responsivness

Changed MJ from 162 (stock for 02 YZF) to 158= leaned out the 3/4 to WFO throttle

This year and the bike you rode:

Got the TA so jetting was 1 step richer to begin with.

Clip at #3

MJ went from 168 back to 162

Pilot Jet went from 42 (stock) to 38


The changes made this year where head and shoulders above how the bike responded last year. Much crisper on the bottom because of the PJ change. The top felt good and crisp too. I really should have messed a little with my fuel screw but didn't.

IMOP most bikes are rich from the factory no matter what alt temp, I'm sure there are exceptions. If it where me I would do this. Bump my MJ down 1-2 steps, Bump my clip POS 1-2 Leaner, Lean out the PJ 1-2 steps.

I would make these changes as stated above 1 at a time.

Hope this helps

Thank you Ranger. After reading your post, I can see I was a little confused (I think you probably sensed that). I forgot about the different jets etc, affecting different parts of the throttle range.

I will say that your 426 was pretty DAMN awesome. I think my CRF could be a little more crisp as well. It works fine as it is, but I think I could get a little more from it if I follow your instructions.

Thanks again, guys. This has been one of the most helpful threads I've ever read. I think I may actually understand how it all works now.

Time to read the book and see what the stock stuff is and go to the shop and get some new jets.

Fastest1, are you sure I can get to it without taking the carb off? It looks dang tight in there. I may take it off anyway and do the James power now mod while I'm at it, maybe not too. I think I probably better do one thing at a time, or I'll probably get into a big mess.

thanks again guys. (thank you Ranger, yours was the most useful, especially since you know the climate/altitude).

[mohtks]

Woody - it has been my experience that the CRF is MUCH less sensitive to jetting than the YZF. But try leaning it out one clip position. It won't hurt your bike unless it is backfiring all over and you leave it like that!

It's like this. Does your bike run great when it is cold? If so, lean the jetting a tad when it is hot.

But only do any of this if you get something out of it. If it feels the same, leave it.

Ranger - sorry to be a contrarian but the YZ450 seems to come a tad lean from the factory.

[Woody_393]

I went riding today and ran into a friend (crf guy) and we talked about jetting, and he said he just re-did his and went smaller on everything. He left the needle where it was.

Said it made a difference (more crisp), but not earth shattering.

He told me what he did, and I wrote it down, so looks like I have some direction. I don't think I'm going to go quite as lean as he did. His bike was back firing a little when he revved it. Isn't that a sign of getting a little lean?

[mohtks]

His bike was back firing a little when he revved it. Isn't that a sign of getting a little lean?

Very likely. If my bike was doing that I would richen it up a clip.

[Woody_393]

I will do that. Thanks for the info.

Thanks to all of you that participated. I have learned boat loads here. I think I may actually know something now. : : Maybe not, but maybe I can jet my bike correctly anyway.

Thanks again,

ATM Rocks.

[Fastest1]

I havent been following this thread for the last couple of days. I would like to mention that most bikes come a little lean to minimize the polutants. This is only in the pilot circuit not the main jet. The EPA takes its readings at low rpms. Second, Woody did his bike pop on the deceleration cycle of being revved or as he was revving it? If it popped on the way down it can be eliminated by turning the fuel screw out (more fuel). This does indicate a lean condition in the pilot circuit. If you have to go more than 2 turns out to cure it, he needs to go up to the next size pilot jet. Also my experience is with the YZF and I can rejet or change the needle position without removing the carb. I am not sure about the CRF. Either way the carb comes off easy enough and goes back on just the same. The boots are so flexible it makes it a breeze. If your bike runs good but you still are not sure if it is running at its best, jetting is the only way to find out. If your bike is pulling smoothly all the way thru the range dont worry about the needle. If there is some blubbering/sputtering etc on the way up as the bike is revving under load then I might raise or lower the needle in your case lower due to the altitude. Also if you get a fuel screw from Ty Davis or Kouba. It will make fuel screw adjustments a breeze. I adjust mine every single time I go for a ride, it takes seconds to do. Sometimes I even need to change it during the day due to temperatures warming up. Of course Houston wont be changing anymore soon it will just be HOT and HUMID! : Sorry to ramble so long. Good Luck

[Woody_393]

Thanks Fastest1, I didn't notice if it was on decel or exceleration that it back fired. I'll pay more attention next time I see him.

This thread just gets better and better every day.:

[mohtks]

His bike was back firing a little when he revved it.

I was responding to this description when I said I would richen the needle if I heard popping. I think of "revving" as opening the throttle.

As fastest1 mentions, if it wasn't while "revving" and in fact on deceleration, then his suggestion of the pilot circuit is correct.