Whats wrong with my 450's carb?

The difference is that the U4 line is oxygenated fuel. What that means is that the burning fuel releases additional oxygen into the combustion process over and above that available in the air. Jetting that is correct for non-oxygenated fuels would be leaner on a switchover because of this additional O2, and richening the jetting is the only way to correct for it.

All that being said, it should be noted that quite a lot of the pump gas available these days is also oxygenated. That fact can reduce the amount of richening otherwise needed.

Kent, You don't notice any difference in running condition when you switch between the two with the same jetting? I tried that at first thinking i didn't need to re jet....My bike spit flames like the "Munster Mobile" with the 4.2 and stock jetting. LEAN. An example i know of is this...Team motoworld rider David Vuillemin<this was back in 06> was running a 170 main/45 pilot/45 leak/2 turns on the fuel screw with his race gas, richer all the way through compared to stock. I got a chance to work on that bike when he turned it in at the end of the season. Ask Eddie over in the Jetting forum, he'll tell you the same thing.

Hmmmmm.........:banghead:

The only thing I've noticed, and was told to expect, was more power and easier starting. I don't have my little notebook here that has my carburetion settings in it (it's in my toolbox which is in storage along with my bike), so I can't tell you what the jets are. I can tell you that, except for the fuel screw settings, I've not changed the jetting since I bought the bike in July.

My local track's elevation is 3500' MSL. I wonder if that has something to do with it?

Hmmmmm.........:banghead:

The only thing I've noticed, and was told to expect, was more power and easier starting. I don't have my little notebook here that has my carburetion settings in it (it's in my toolbox which is in storage along with my bike), so I can't tell you what the jets are. I can tell you that, except for the fuel screw settings, I've not changed the jetting since I bought the bike in July.

My local track's elevation is 3500' MSL. I wonder if that has something to do with it?

You bought the bike new? so it has stock jetting? I would be curious to know what you got in there.

You bought the bike new? so it has stock jetting? I would be curious to know what you got in there.

Canadian bikes may come with different jets than US models. I know this used to happen with the WR's, so it may be the same for the YZ's

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now