My brothers keeping up with me

Ok guys here is a situation that has always bothered me. My brother and I are aways in competition with one another. He always has to be better then me. So when I finaly bought my YZ 400 I thought for sure he would nolonger be a worry for me when it came to a drag race down a dry river bed. He has a 87 KDX 200 that has an FMF pip on it and thats it. Granted my 400 beat him off the line, when I had it in 5th he slowly began creeping up on me. It just does not seem like my 400 is pulling like it should on the top end. We are running at about 3,000 ft. I have the air box lid removed 178 main jet needle clip in the middle position. It does not hit the rev lim. in 5th any Ideas on what I might be able to do, would be grateful. It has the stock gearing also.

You should be blowing his doors off if you YZ400 is running well. My wife has a KDX200 with an FMF pipe and there is no way it was even in the same league as a YZ400. How does your plug look? A 178 sounds rich. I am at 5000 ft and I am running a 158 on my 426.


I can easily hit my rev-limiter in fifth. Not to mention that I can barely hold on the bike getting there.

Sounds like you need to have things looked at.

Any other symptoms?


Thats what I thought. My brother should have no chance, but sure enough he was slowly creeping up on me. The Plug looks black so I think i'm going to put a smaller main in. Any Ideas? It just does not seem to pull like it should, P.S. I bought the bike used from a guy. so I have no idea what has happend to it. Any Ideas on what I should check.... Please help my brother is laughing at me. Thanks


The change in main jet won't do much. It's a minor change. A bike that has a main jet that is one or two numbers higher would still pull hard.

Obviously you have something more serious going on and now it's just a process of elimination to find it.

I would begin by calling the previous owner. Let him know that you don't expect anything from him other than information. Find out what sort of engine work was done, what sort of problems he had and when, and ask if he ever noticed a decrease in performance.

If he reveals nothing, move on.

Begin by checking the simple stuff.

1. Make sure your throttle is opening up all the way. Do so by physically looking at the slide of the carb, and not just the cable connection.

2. Make sure there are no obstruction in the airbox and carb. Perhaps the previous owner installed some type of a restrictor plate or perhaps the slide is catching on something.

3. Remove the exhaust pipe and make sure there are no restrictions in the header pipe or muffler.

4. Remove the carb and check the port for any signs of trouble.

5. Remove the spark plug and rotate the crankshaft to different positions while looking through the intake and exhaust ports for any signs of trouble. Use a flashlight to look down the spark plug hole when the piston is at top dead center. Note anything that looks unusual.

If all looks well, you'll need to go deeper.

The next step would be to disassemble the carb and just make sure that there are not obvious problems. Check all the jets and compare all the parts to the listings in the manual. Clean all the passages with carb cleaner, but never use compressed air. Also take a look to see if the TPS has been modified, or moved.

Keep in mind too, that just because a carb looks good, doesn't mean that it's working.

Outside of this, you're going to get into the more complicated stuff. I'll leave that until I hear back from you on what you have found with this, and/or from the previous owner.

And if you not mechanically minded, this may be as far as you want to go.

Let me know.


If your valves have never been adjusted they are probably too tight and you are losing alot of power and rpm. They are not too hard to check, try this if all the basic stuff checks out. Good Luck, you should be sandblasting that KDX next time!

DaveJs suggestions are excellent, and he is probably right about the main jet. If the bike was loading up enough to seriously hamper performance you would be complaining about lurching, backfiring, flames shooting out of the exhaust, and then dyding (like mine does). If DaveyJs suggestions don't yield anything, have a compression/leakdown test done to see if you have good ring and valve sealing. What year is your bike?

Thanks for the Info, DaveJ. I have checked some of the stuff you have listed an they all so far have come up OK. I dought that they GUy that owend the bike before me ever checked the valves. I have checked the throttle to make sure it opening all the way, I have had the carb aprt to check and clean it, I have not noticed any thing that would look like a restrictor plate.

I'm not exactly sure how to test the TPS, because I have not got the Service Manual yet.The yamaha dealer wants 70 bucks for the darn thing. I was hoping to try and find one cheaper. I guess I will have to fork up the bucks,it looks like I will need it. I will try a compression test and check the valve the min. I can get my hands on the spects for them.

I'm pretty michanically Inclined so anything you have to offer me, please don'ty hold back....THANKS

The TPS is easily checked with an ohmeter and the owners manual has good instruction on how but I'll put my bet on the valves.I had a 98 that tightened up an would not hit the rev limiter.

Hi guys! Bought my '99 400 used also but lucked out as the guy was into frequent oil and filter changes. My question, what happens when you hit the rev limiter? I tried the bike out for about an hour with no gear on so I have no idea what to expect.


I believe that someone scanned a munual and its on TT somewhere.

I found it. Its supposed to be on Matt Porritts rubber chicken racing sight, but the link I tried didnt seem to be working.


[This message has been edited by npuza (edited 12-28-2000).]

[This message has been edited by npuza (edited 12-28-2000).]


I do know that Yamaha has an "Owners Manual" and a "Service Manual".

All you need is the Owner's Manual, so make sure they are pricing the correct book, (I tried to look this up for you on the HLSM.COM site, but they didn't show documents in their microfiche).

If you find an alternative, or if the $70 price tag is too much, let me know and I'll copy and fax or mail out the sections you may need, (keep in mind that mine is a Y2K bike).


DaveJ, Thanks for the offer to fax, or send the sections of the manual that I might need to check the vavles. I'm sure they might have changed something between a 99' and a 2000,( I could be wrong). I probable should just get a manual. I will end up needing it for other things, down the road from now. I heard that Baja Designs has manuals for mine , for $40. I think I will order one from them. And until I do get the manual will I end up hurting anything if I countinue to ride, or will I just burn the valves?......Thanks

Two things should really make a difference. The jetting is WAY too rich! Try a 165-162 in the winter and a 160 in the summer. It really will make a differnce. Next - valves! You always hear people saying: 'I've never had to touch my valves!' Check them! They probably need adjustment. Also, if they are near one of the limits then adjust them anyway as the bike will run smoother and be a bit stronger.


I finally got my service manual today. I ripped of the cover so I could check the vavle clearance, You were right all my valves were running tight. Now all I have to do is pick up the correct shim and see how it does. I hope this was my problem with the bike.If it does not cure my problem I will do a leak down test. Thanks agian for you help.

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