What to expect?

[#484]

My 2000 400ex was still running all stock engine after all these years, including several years of xc racing. After the season ended, I did a compression test and found despite running very strong it only had 70 psi of compression. After reading a million posts on here, I decided to go with the tried and true 11 to 1 Wiseco piston, .020 overbore, Stage 2 cam, crf timing chain, 04/05 450r carb, a mild cleaning of the intake and exhaust ports. I run a full DG exhaust system with header and a K&N air filter. I am at about 2000 feet elevation. About what jets should I start out with, I just need a good safe starting point. I can fine tune from there. I'm curious to see how much better it will perform after all this, it honestly ran fantastic at the last race this year as good or better than it has since I have owned it. Thanks for any help guys!!!

[LxMxL97]

My 2000 400ex was still running all stock engine after all these years, including several years of xc racing. After the season ended, I did a compression test and found despite running very strong it only had 70 psi of compression. After reading a million posts on here, I decided to go with the tried and true 11 to 1 Wiseco piston, .020 overbore, Stage 2 cam, crf timing chain, 04/05 450r carb, a mild cleaning of the intake and exhaust ports. I run a full DG exhaust system with header and a K&N air filter. I am at about 2000 feet elevation. About what jets should I start out with, I just need a good safe starting point. I can fine tune from there. I'm curious to see how much better it will perform after all this, it honestly ran fantastic at the last race this year as good or better than it has since I have owned it. Thanks for any help guys!!!

I'm not sure what size a .20 bore is in terms of cc's but when I went to a 416 10.8.1 J&E and a s2 HC you will notice a lot more torque but not any noticeable top speed

[#484]

.020 over is 402cc, torque and horsepower is what I am hoping for. For xc racing I'm not concerned with top speed, just how quickly it will pull out of corners.

[Blodg]

I run that build and it will be much faster. Bottom end up to midrange is similar to stock but when you get to mid rpm's it starts pulling much harder through the midrange and top end.

I kept the stock 450R pilot (48 I think), 3rd clip, 2 1/2 turns out, and started with a 185 main thinking I would work my way down. It pulled clean with no blubber on top so I went up to a 190 main. I rode all summer and fall with this jetting and it starts right up hot or cold, pulls hard wth no hesitation anywhere and the motor never ran hot either like some complain about with the 400EX.

[LxMxL97]

.020 over is 402cc, torque and horsepower is what I am hoping for. For xc racing I'm not concerned with top speed, just how quickly it will pull out of corners.

Not to put down on your hopes but going to a 402 is kinda a waste of time and money my friend had just a 406 (or maybe a 407 I'm not sure) and my stock 400 ran better than it did and yes it was jetted correctly

[CJM]

Bore size does not equal a large gain in power, compression does. Friends 402 has plenty of power over stock.

Also get rid of your KN, its letting dirt in unless you have an outerwears on it and then you defeat the entire purpose of a more free flowing filter.

[DragonGunner]

Your going to like the power alot more with your upgrades. If you been running a K&N like I have for 13 yrs. then you already know how to maintain them, clean them. I run a outerwear over mine, but with or without a outerwear its impossible to tell a difference. Good luck to next yrs. races!!!

[#484]

Thanks for the input guys! So the stock jetting in the 450r carb is a good place to start ? Everyone who runs one of those carbs seems to love the throttle response that it had,I can't wait to try it. Throttle response was one thing the 400 always lacked for sure, even when I had the jetting perfect it always seemed to have a small stumble going to full throttle.

[Blodg]

Start with the stock pilot jet in the 450R carb but not the main jet. You should start with at least a 180-190 main jet with this build. Most people end up in the 170-180 range on the main jet but a few members on this forum are running 200+ main jets.

[#484]

The carb has a 185 main in it now, I will start with that.

[cheater13]

Mine never really pulled strong in the upper rpm range unless it's just me. I slam the throttle completely in and as rpms rise, the power eventually gets up there. I figured it should all be constant if you mash the throttle all the way in, right? Maybe it's my 13/40 gearing?

But I also have a K@N that came with my velocity intake. I have outerwears over it though. I did have a UNI and I don't have one complaint about that. Neither do I with the K@N.

[2001400exrida]

for the cost, you can get cheaper power out of compression, but bore equals more torque and more power than just upping compression. A big bore kit will cost more, but let's say you run high compression and big bore....well you'll have substantially more power in that case.

Simply upping the compression and maintaining stock bore does not equal large power gains. Let's say you replace the stock 400ex piston with an 11:1....you're power gains are going to be very minimal (in fact a cam would be more noticeable) compared to a 426 with 11:1, you'll have a noticeable power gain with even that slight bore.

[LxMxL97]

The carb has a 185 main in it now, I will start with that.


for the cost, you can get cheaper power out of compression, but bore equals more torque and more power than just upping compression. A big bore kit will cost more, but let's say you run high compression and big bore....well you'll have substantially more power in that case.

Simply upping the compression and maintaining stock bore does not equal large power gains. Let's say you replace the stock 400ex piston with an 11:1....you're power gains are going to be very minimal (in fact a cam would be more noticeable) compared to a 426 with 11:1, you'll have a noticeable power gain with even that slight bore.

I couldn't agree more