Just picked up a Plated YZ400F! Have some ?'s

I just picked this bike up. Its a 1999 Yamaha YZ400F. I got to ride it and it feels very different from my old bike, 99 YZ250. But I like it. Here's some pics:


YZ250 and superjet in the background. I tend to buy yamaha's!!



The bike is in really good condition just dirty in the pics.

First off, starting this bike is a pain lol:foul:. I got the routine down now but I will definitely be swapping out the cam for auto decompression.

My first question is what can I do to it for more power. It just lacks the top end wheelie power my YZ250 has. I need it for powering over trees, puddles and stuff. Plus its a lot more fun:p I think it has a pipe already? I also need to look into the jetting I think

Another big problem is the off idle bog. I read about the Accelerator Pump but I don't get what needs to be done.

This bike also starts to overheat very easily. If I sit and let it idle for a while it starts get hot and eventually antifreeze will come out the overflow. Is this normal? My friend tells me to add a fan to help with that.

It looks like it has a pipe off a WR. that would be more restrictive, so I would suggest either getting a yz pipe or an aftermarket such as FMF, Pro Circuit, Dr.D, etc if sound is not an issue. For a little more low end grunt, you could add a few teeth to the rear sprocket, but you would loose top end speed.

I'm not going to ride it on the street too much so gearing isn't a big deal. The pipe does say Yamaha on the inside but doesn't look like the stock pipe. The pipe is pretty loud already idk if I want to go louder. The bike just seems to not have too much power in high rpms.

It's a question whether the bike is a YZ or a WR.

I'm 99% sure its a yz. I have the receipt from the previous owner for the electrix stator and the baja kit. How else could I tell?

The VIN. A Yamaha parts or sales dept. should be able to identify the model from that. There was originally a model label under the seat on the inside of the left rail of the sub frame over the air box. Might still be there. Also, the head light wiring will have a factory look to it if it's a WR.

grab the vin# and check with that.

Its a YZ. I have the receipt for the stator, light kit. I can tell its not factory. I also have the title and the original title from when it was new. So what can I do to this thing to give it some more power? Are the newer YZ450's this underpowered?

Most people would not say that they are underpowered. Wonder if yours is pretty worn / low on compression or something?

Timed wrong. Some guys would reset the timing of their YZF's to match WR specs by advancing the exhaust cam one tooth to take some snap off it. Then again, if the timing appears correct, it could actually have a WR exhaust cam.

Another possibility is that the TPS or CDI may be faulty and not providing correct ignition timing. Try running with the TPS disconnected.

Something must be wrong or changed if it is underpowered. A 400 should not be lacking for power that much.

ya if it were working properly believe me you wouldn't want to be modifying it for more power.

Yea I agree. My Yz400 is too fast for the woods I ride in. I'm in the process of moto'ing it now and looking for a 250 for racing Hare Scrambles. Mine has a complete FMF exhaust and K&N Filter and woods suspension is faster in the woods then my buddies Stock 2002 426

I just got a 98 yz400 and the thing is plenty fast for me. Maybe something is wrong with your setup. I would look into all of the easy places first. Make sure the air filter is clean and in good shape, make sure it isn't starving for fuel on the top end. Do a compression test, make sure the ignition/cam timing is correct. In the couple of times I've ridden it, my bike would readily wheelie under power alone.

I am particuarly suspicious when you say the 400 lacks the punch of the 250. The 400 has quite a bit more power than the 250 everywhere in the powerband.

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