RMZ 450 Carb question


I have a 07 RMZ 450 with the only mod being a Pro Circuit Ti4 Slip On.

When you quickly wick the throttle it bogs, almost like you are going to kill it.

Is there any way to fix this?

Second, at full speed in 4th coming up to full throttle the bike starts to sputter, kind of like getting to a stutter box on a sportbike. Is it running out of fuel and larger main jet needed?

Third, a little bit of pop from the pipe on decel. The bike also did it with the stock pipe, is this a lean pop or what and whats the fix for that.

Thanks all for all the help, new to the carb game. The sportbikes all have ECU's

Thanks again

It sounds like you've got 2 problem spots in your range of throttle openings. The small opening is your leak(pilot) jet/fuel screw combo. The 4th gear thing sounds like clip position/main jet. The section of your manual under machine tuning has an OK description of how the jetting relates to throttle opening.

I'd recommend an aftermarket fuel screw by zip ty or ? I can't remember the other manufacturers. This allows you to adjust the screw w/o tools on the trail. The pop is probably a lean condition at small throttle openings. i.e. leak jet/fuel screw combination is lean. Other posts here describe the fuel screw tuning procedure. If you can't find them, PM me. Worry about the bog after you get this sorted out.

The sputter at near full throttle is probably either your needle position or your main jet but I don't know if it's lean or rich. I'd have to guess rich if it comes back to life and sounds ok at a higher rpm. But that's something you don't want to have wrong for long. If it sounds rough(poppy) at full throttle, I'd say your lean. If it gurgles, it's probably rich. You already know lean=hot=bad things.

I think in a twisted way I'll miss carb tuning when it goes away.

Thanks for the help. I will order the fuel screw right away. The sound at full throttle is a pop kind of sound. Like its just running out of fuel. This is at wide open throttle in 4th gear, probably going as fast as the bike will go.

the bike comes with a 36 leak jet I believe. I read where the 40 is better, I will also try backing out the fuel screw about 1/8 turn or so.

Thanks again

Yeah, The 42 leak is stock I believe. I'm running a 40 but I'm riding at very high elevations. Your main jet sounds lean also. For riding in GA, you should go back to the stock jetting setup and start tweaking from there. Good luck with the tuning.


My book says I have a 35 leak jet so I will check into a 40. Also says I have a 170 main so maybe I'll jump up to a 172 or so. I haven't done anything yet.

Thanks for all the help

A leak jet and a pilot jet are two different animals!!!! Go back to stock!! I ride in SoCal, with my 06. If you set the fuel screw, (with a 42 pilot) and use the two needles that came with it to fine tune the middle, and a 172 main, it will run great a up to about 2400 feet above sea level. I ride at 2800 and it likes the stock needle dropped 1 click, and the main down to 168. This keeps the bottom end hitting hard, and starts real easy too.:thumbsup: :thumbsup:

Yes, Pilot(or slow jet), not leak jet. Don't mess with the leak. Sorry about the bad term. The 42 pilot should be the one you're looking for. Stock screw setting is 1-3/4 turns out. The stock main is 170. The NKYT needle in the 5th clip position(from the top) is stock also. That's a good place to start. MB's advice above is a good direction to tweak.

Full Throttle? Sounds like the rev limiter.

Ok, I didn't know dirtbikes had them like the street bikes.


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