1998 yz400 low end power

I have a 98 yz400. As far as I know the engine is stock. I have put a wirtz acc pump cover on the carb and uni air filter. I didnt see much of a difference. I am looking for more bottom end response and power. The bike is also very unpredictable( not smooth through the rev). Any advice or suggestions would be great. One more thing, Any good tricks or tips for keeping it cooler. It likes to overheat on hard hills and rocky areas.

The cheapest way to get more low end it is to add one or two teeth to the rear sprocket.

The YZ400 is a MX race bike and was not made to ride in the woods. Adding a flywheel weight will smooth all the power out. Like a fast XR400.

Here is a good place to start. http://www.steahlyoffroad.com/recommendation_charts.htm#YAMAHA

My YZ426 would over heat from time to time. Engine Ice did the trick for me and I have used it since. Do a search on coolant. That sub has been covered.




on my 99 yz400.... it overheated first time out. i put a new rad cap and flushed the coolant system and put in engine ice and has not overheated again. you learn not to let it idle anytime at all, the no air flow is what heats them up. as for the unpredictable, how is the bike geared would be my first question. on mine before i put the hot cams auto decomp exhaust cam, it was pretty abrupt power wise right off the bottom. Now it is pretty smooth til it gets above say half throttle, then the power really kicks in !!!!

i came off a 250 2smoke and it took a little time to get used to the 400.

have fun and welcome to TT, the best site those bikes.


I have a radiator cap ordered(1.3) and also engine ice coming. I am thinking about the flywheel. Does anyone have this bike with a flywheel weight and what so you think about the difference it made.

Also what would an after market pipe do for my bike and what do you guys like

I am looking for more bottom end response and power.

The first thing you should do is get a JD jet kit. They work wonders. Once you get the jetting cleaned up, then you can worry about the rest of it. :busted:

I got my rad cap and engine ice. I went for a ride after installing in some pretty tight woods. It blew my mine that it didnt overheat when we was trying to make a new trail. Thanks for the info.

What kind of pipe do you have now? My 426 came with a Thunder Alley pipe and the low end power is insane, though the noise is unbearable.

I don't know what happened to them though. If you dig through past Thumpertalk posts, it looks like everyone was raving about them for the YZ and CRF six or seven years ago. Everyone loved the power gains, the quality/fit, and especially the price. What happened to them? Their website isn't even up anymore.

Stoke pipe as far as I can tell

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