Help! My 450 lurches BAD

About a month ago I noticed that my 2003 YZ450f would lurch pretty bad when I held the throttle open. I thought it might be the clutch slipping so I put new springs and plates in. The old ones looked fine but since I had neww ones in hand, I put them , (soaked them in oil for about 30 minutes first). The lurching is still there and I suspect that maybe it's not the clutch at all. (Carb??) When i pop the clutch there's no slippage, problem mostly occurs when I hold the throttle open.

(Should note that my header pipe is pinched pretty bad and I'm waiting for a new one).

Any ideas?

In all 4 gears, or only one in particular?

About a month ago I noticed that my 2003 YZ450f would lurch pretty bad when I held the throttle open. I thought it might be the clutch slipping so I put new springs and plates in. The old ones looked fine but since I had neww ones in hand, I put them , (soaked them in oil for about 30 minutes first). The lurching is still there and I suspect that maybe it's not the clutch at all. (Carb??) When i pop the clutch there's no slippage, problem mostly occurs when I hold the throttle open.

(Should note that my header pipe is pinched pretty bad and I'm waiting for a new one).

Any ideas?

hubs or basket wear and I have a 03 stock header for sale - pm me if you want it

Seems to be all gears, but I notice it mostly in 4th b/cse that's when i'm cruising with the throttle in one spot.

Your inbox is full. I'm interested in the header, email me at korkowt@ally.com with the price.

Does it get better or worse if you go to full throttle?

I'd say the basket is well worn. Take out your plates again and look at the basket, it is ribbed?

Basket looked new. Talked to a mechanic at the dealer and he told me that it's carb related. For $80 an hour they'll track down the problem and fix it......

What he said actually made sense b/cse when I pop the clutch it engages and the bike leaps forward, doesn't slowly engage. When I'm cruising around the float bowl empties and the bike "lurches" because it's not getting enough fuel.

Looks like I'll have to pull apart the carb this weekend.

There's also a screen in the tank, as part of the petcock, that can clog. It's often ignored. Two screws and it comes right out.

The bike will get just enough fuel to idle and run for shorts bursts, then begins to die after longer runs. Not enough delivery.

Check this first. Then pull the cap off of the fuel bowl and check for water. Drain then test.

I really doubt you'll have to pull the carb apart. Nor should you.

As a last consideration, change the plug and don't run anything other than the factory brand.

DaveJ

ps- keep your approach simple.

sounds electrical.......

Your problem sounds exactly like what my 426 is doing. I've tried lots of things in the jetting department with zero results. A new CDI box didn't help it either. I've got the carb all apart again to see if there might be a blockage. If that doesn't work, I'm gonna try a new TPS. Maybe a coil is in my future.

sounds electrical.......
That's what I was trying to get at. That or a jetting issue caused by the crimped header. Doesn't sound like a clutch.

I have exactly the same problem. I noticed it when cruising in fourth for a while at constant RPM. The problem does not become better or worse. When back to regular riding with on-the gas, off-the gas there isn't a hint of this issue.

The cases are split at the moment for a mid-life overhaul. The gears look good, plug CR8E has a nice tan, the carb was very clean, vent hoses unblocked. Will check the fuel tank gas filter.

Any findings on this matter will be interesting.

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