ask - MX Tuner
Mark Klein is ready to answer your technical questions! Mark has extensive experience race tuning off-road motorcycles for local and national races. If you check back through our 1998/99 archives you will see a series called "Dirtbikes 101." Mark brings his expertise to fielding your maintenance and tuning questions.
Persistant Water Leak
It may take a few oil changes to clear the transmission of all the water residue. Try using Type F automatic transmission fluid and changing it after about 10 minutes riding time. Do this a few times in a row to clean the water out.
I'd switch to a BR7ES plug and try a 45 pilot and lean the needle one clip position. This should get you going in the right direction. You may be able to go leaner than that with the pilot jet. You want to go as lean as you can with the pilot jet. It'll idle down slowly and it'll feel like it's running out of gas if you get too lean. You won't do any engine damage experimenting and will be rewarded with the best possible throttle response.
First of all, lose the Maxima oil unless you plan to rebuild your top end once a month. Just because Ricky Carmichael uses it doesn't mean it's best for you. I don't recall which version carb your KX has. The idle speed may be incorporated into the choke knob. Where the choke knob comes up from the carb body, look to see if there is a small arrow cast into the carb. It should say "idle" right under it. Turning the choke knob will adjust the idle speed. An intake leak would be much more erratic than to control the idle that predictably. It could account for the slow idling down, but not the inability to lower the idle speed.
Stiffer Shock Spring?
Short Shifting an XR200
Hope you can help, thanks.
Probably because it wasn't meant to. You might try a better oil. This can help shifting. Try Mobil 1 synthetic 15w50. This very good oil might help. Riding your XR 200 the way you imply will result in a short lived Honda. Remember what the bike was designed for.... NOT racing.
Mods/Plastic - Killer CR 500
And what about bolt-on tuning parts, who makes them? (pipe, silencer, etc.)
And do you know any tech and tuning tips for the CR 500?
None of the plastic from a 125 or 250 will fit except the front fender. You should be able to buy all the plastic for your bike from aftermarket sources like UFO or Acerbis. Any number of companies make graphics that will help with the looks.
There are many things you can do to your 500 to make it either more powerful, easier to ride, or both. A flywheel weight helps the 500 hook up substantially. We put 15-ounce weights on them. Steahly makes a bolt on weight for a little over $100. A Delta V-Force reed cage is a great improvement to the 500. But until you've done the most you can with the stock bike, I wouldn't do anything. Leaning out the low speed jetting will make a big difference in your 500. That and some suspension upgrades will make a nice change.
Jetting - 92 KX
It starts fine, it gets into the powerband fine, but there is a little junk sound in the upper rpm range. The jet needle is in the middle groove and the airscrew on the outside of the carb is 2 turns out. I run hp2 at 32:1 with 94-octane pump gas. Is this normal? if not please help!!!
Any Kawasaki dealer should be able to give you stock jetting specs. Boyesen should be able to give you ballpark jetting for a bike with their products. Boyesen does have a website at www.boyesen.com which can be helpful. I'm a little unsure of what you describe as a "junk" sound.
Have you checked the basics? The air filter needs to be cleaned and re-oiled periodically. Has it been cleaned recently?
Bottoming KX 60
First thing you need to do is buy the Kawasaki manual. Get the one Kawasaki publishes for the bike. It is very useful. You won't regret it. I'd add air to the forks as a last resort only. You can add oil to the forks or you can change to a thicker oil. Adding oil will increase bottoming resistance in the second half of the travel. Changing to a thicker oil will make it stiffer everywhere (even over small bumps). First thing I'd do is have the forks serviced. This way you know the internals are clean, the oil is in good condition, and that the right amount is in the forks. Your new service manual will give a height measurement for the oil level. Set it in the middle of the range they provide. Then, if it still bottoms excessively, you can remove the fork caps without removing the forks and add a few ccs to each leg. This will raise the oil level to fine-tune the bottoming resistance. I'd add 5ccs to each leg at a time until it gets acceptable. You can buy an infant medicine syringe at any pharmacy for $2 that works well for this.
If this doesn't achieve what you need, then I'd recommend going to a thicker oil. This can make the forks harsh over small bumps but will help with bottoming resistance.
Bottoming KX 100
How much do you weigh? I'm guessing since you just bought a new bike, it *is* big enough for you. You can get stiffer springs but you can try to adjust with what you have first. First thing is to adjust the rear spring according to the manual. Once you get this done, you can adjust the compression adjusters to help control bottoming. Turning them *in* will stiffen the damping. You need to become familiar with the manual and the adjusters to take full advantage of the adjustability of the suspension. You can also add fork oil to a higher level. This will help in the bottoming resistance.
As long as the chain is kept properly adjusted, it shouldn't come off regardless of the suspension. If you continually bottom the suspension, you can eventually encounter frame breakage problems.
Which jets did you replace? My guess would be the main jets. The main jets don't affect carburetion until over 1/2 throttle. Sounds like your pilot jet may be too small. You might be able to adjust this out with the low speed screw. I'll be very general. if the mixture screw is in front of the carb slide, it is a fuel screw. It controls a fuel passage. Unscrewing this screw will result in a richer low speed mixture. If the screw is behind the carb slide, it is an airscrew, unscrewing this screw will result in a leaner low speed mixture. I'd try richening the mixture and see if this helps. You may be able to get the stalling to an acceptable level without replacing jets. There's only one way to find out.
Three for All
second, I have an old ATC90. I just did a top-end rebuild on it, including new points & plug. Valves are set to specs. I set the points at .015. it runs very radical at low rpms, then, after you play with the throttle, it cleans out, but only at high rpms. I have cleaned the carb out with carb cleaner, but, I'm thinking that I didn't get all of the garbage out of it. Any suggestions on these two bikes?
I also have a friend who has a 98 or 99 KTM MXC 200. His son raced it the other day & we had to bleed the rear brake about three times that day between motos. There aren't any leaks. I noticed that the rear caliper, after he finished a moto, was super hot, as the burn mark on my hand can attest to. Is this normal for the rear caliper to get this hot? All we had was some DOT3 fluid to replenish the system. Thanx, The old "Stumpjumper."
Three for one, huh? Okay, I'm feeling generous.
The CR comes jetted too rich on the lower speed circuits. Keep the idle speed turned down as far as you can (off preferably) and lean out the pilot circuit. There is nothing finer than a crisp running CR 500. and, as always, be sure the silencer is in good condition (fresh packing and the core holes are clear and unobstructed).
The ATC 90. First of all, set the points to .012". Next, buy some Yamaha carb cleaner. This comes in a 1 liter black bottle. This stuff is great for soaking carbs in. Now strip every piece off the carb you can (except the choke flap) and soak it overnight. Then spray it out with aerosol carb cleaner. You need to verify all the circuits are unobstructed. You can do this with the aerosol carb cleaner. Be sure to wear safety glasses of some type. You *know* you're going to get squirted sometime during all this.
The KTM. The KTMS have sensitive rear brakes. Some say they are too grabby. Aggressive riders can easily overheat the rear brakes. First, make sure there is some free play in the master cylinder pushrod. It doesn't need much but it has to have *some*. Then bleed it with a good quality fluid like Motul 600. That should prevent the fluid from boiling during normal use.
Sounds like you have too low an oil level in the forks. Those should run a pretty high level. I'd run them at about 85mm.The oil level is measured with the fork fully compressed with the spring out of it. If the oil level is too low, it'll give the exact symptoms you describe. If something changed from before to now, a revalve won't address that issue.
I don't want to replace the expansion chamber, but the spark arrestor/silencer part is what I'd like to change. are there any two-stroke YZ parts that I could replace it with? Or perhaps could I put a straight pipe made of copper on instead of the second part of the exhaust? Also...would this make the bike's engine run hotter, possibly causing damage??
Thank you for your time...
The only aftermarket silencer I can find is a universal spark arrestor silencer from FMF. It comes with assorted mounting hardware to fit a variety of applications. I'm not too familiar with the DT 200 so I can't comment on what, if any, YZ parts would fit. I'd be surprised if any of them did. Don't attempt to run the bike without a silencer or with the straight pipe on it. It won't hurt the motor but will drive your neighbors (and yourself) crazy due to the noise. You may need to alter the jetting when you get the different silencer on your bike.
Drop on Top
It never ceases to amaze me the quality of mechanics the dealers hire and allow to act as mechanics. You'd get better jetting help from Kroger. You do NOT have to tear down the top end. The pipe needs to come off. Then removing the left and right covers on the cylinder will give you access to the power valve. There is one long bolt (4mm Allen head, I believe) that holds the two halves of the valve together. Remove the linkage and the long bolt and the valve will come out in halves. There are two small locating pins that help align the valve halves. Make sure these do not fall into the combustion chamber when you remove the valve. I truly doubt if the valve is causing any of your problems.
First thing to do is return the jetting to stock settings. Now find someone who can jet your bike to your individual requirements. You may have to recruit one of the local racers. Ask around. As always, be sure the silencer is in good condition (fresh packing and all the core holes are clear and unobstructed).
One other possibility is an electrical problem. Begin by checking the ground points of all the electrical components (stator and coil mounting tabs can corrode).
What!!! No filter???
Absolutely not. The motor internal components require a clean air supply to live on. I've seen a crankshaft get ruined in about 15 minutes running time because it was run with a big air leak between the air filter and the carburetor. If you buy this bike, you can plan on having to spend another $600 on getting the motor rebuilt soon.
What Ratio - What Oil?
I'd use 40:1 for your WR 250. Yamalube 2R is one of the best choices that is readily available. Honda HP is another good oil. Motul and Spectro also make very good oils. Stay away from castor based oils (Maxima Super M, Maxima 927, etc.). They are excellent lubricating oils but require the motor be torn apart and cleaned at very close intervals. These oils are good for professional racers who have their motors torn apart every few races.
40:1 would be one pint (16 oz) to 5 gallons. Most oils come in pint bottles so you don't have to worry about measuring. The reason you get so many different stories is people's experiences and misconceptions versus manufacturer recommendations. Yamaha recommends 32:1 for your WR. Since you're not racing and running at extended high rpm conditions, I recommended 40:1. This will burn a little cleaner than 32:1 and still give more than adequate lubrication for your motor. Many riders think burning less oil in the fuel makes a bike more resistant to fouling spark plugs. This is NOT true. 98% of the time a bike fouls spark plugs is because it is getting too much fuel in the fuel/air mixture. This is determined by a few things but mostly carb jetting. Most bikes come jetted too rich from the manufacturer and will benefit from having them rejetted properly.
There are many variables to consider. Do you want to race in the woods or motocross? A small four stroke like a Honda XR or a Yamaha TTR would be a good choice for a woods bike and still be somewhat competitive at beginner levels. If you're wanting to race motocross, you almost have to have a two stroke to be competitive. The Suzuki RM 80 has a good motor from the standpoint it isn't difficult to ride. The Yamaha YZ 80 is among the faster bikes but it is more difficult for a beginner due to the way the power is delivered. It is more of an expert rider's bike.
Your height is another big determining factor. You don't really want a bike that you can touch the ground on both sides flat-footed. That would be too small for you. But of course, you don't want something that you can't reach the ground on at all. Are you a fast learner? Be honest. You don't want a bike you'll grow out of (experience-wise) within two months but you also don't want something that will intimidate you right away either. There are plenty of good choices out there. Whatever you buy, be sure and have it inspected by a competent mechanic before you buy it. This means even if you're buying it *from* a mechanic, you need to have someone else look it over thoroughly.
YZ Timing on a WR
Although the bike is registered, the bike is mainly used for hard trail riding with a bit of motocross as well. So it gets some fairly hard work. Once again after reading some of the other articles, it seems that most guys are running a lot higher jet size (main) then myself. My next move will be to replace the standard header pipe with a White Bros. unit. They tell me that this will definitely increase the midrange to low end power. Do you agree with this? I will then also be looking to increase the jetting to see if this will help, considering it should be getting more air with the other filter and snorkel removed.
Thank you for your time. Any help you can offer would be greatly appreciated, as it is a bit hard to come by in my area.
I have a '98 WR 400 with one or two mods. I have the 450 kit, the White Bros. Promeg E-series exhaust, and the YZ cam timing. I tried some recommended jetting (trying to save me the research time) and ended up back at stock except for a YZ needle. Main and pilot are both stock. This is running VP race fuel (c-14 to be specific). All the recommended jetting was way too rich. I'm at about 1000 feet above sea level.
Yes, I would (and I did) remove the entire top of the air box where it unscrews. Retarding the cam timing to YZ specs won't give the anticipated results unless you run a less restricted exhaust. Your E-series will do nicely. If they didn't get the gains they were expecting, and they have an aftermarket exhaust of some type, the cam timing wasn't done correctly.
I'm running 10 discs with the spark arrestor end cap in place right now. This was what I found to work best with the stock 400 bore. When I went to the 450 kit, I left the discs the same. It runs so well, I've had no reason to change discs yet. It is brutally strong well into the rev range. I'm running the tapered head pipe, as you should also.
I can't give you any jetting recommendations except start off stock and jet to your individual needs. I can't see you having to go richer than stock, especially at any altitude much over sea level. And remember, the fuel mixture screw is very sensitive. A 1/8 turn is a substantial change.
Your RMX is no more prone to blowing fork seals than any other bike with upside down forks. You might want to inspect the lower legs for nicks that may have been the reason for the first set of seals to start leaking. You also need to make sure the lower fork tubes are kept relatively clean between rides. The main reason for seal leakage is dirt getting jammed up into the seals. If you stop riding with mud splashed on the fork sliders and it dries, the next time the forks compress, some of that dirt can work its way up into the seals. Otherwise, make sure the oil level was correct when the seals were changed. The incorrect oil level (by a large margin) can contribute to seals leaking prematurely.
My problem is with a 1999 wr400f. The problem is that the front forks are to stiff in the first part of its travel - common complaint I know. I have tried backing the adjusters off a few clicks but still the same. I have thought about fitting a set of gold valves to the forks but have been advised to reshim the original valves, as they are of better quality true or false? However, I am not even sure if I am looking in the right area. Springs or oil - maybe all 3? I weigh 83 kilos and on a one too ten riding scale ten being very fast, I am about number 4.! Any advice would be great thank you.
Yours Truly - Capt. Arm Pump.
Let's see... 83 kilos... if I have my calculator jetted correctly, I come up with 182.6 lbs. The springs that come with a US version WR should be close for your weight. I don't know what springs come with your version. They may be lighter springs. Otherwise, the quick fix would be to disassemble your forks and clean the internals thoroughly. Refill with 2.5 or 3 wt oil at about 95mm. This should make a significant improvement. Damping is definitely the culprit here.
Gold Valves are a little on the controversial side. I've heard a lot of competing suspension companies that really talk bad about the Gold Valves but I've installed a lot of sets and have had VERY good results with them. I don't follow Race Tech's recommended valving, but I don't vary too far from it. I've gotten the best results with woods bikes and Gold Valves. If you're going to go into your forks, there are a couple other mods which can be done to insure more consistent damping. The midvalves can be returned to a conventional check valve design. The compression valving needs to be altered to compensate for this. Your Forks also have what is called a cylinder valve (or a quad valve). This is the part the magazines so unknowingly refer to as the midvalve. This cylinder valve is located at the top of the cartridge and can bleed off oil. Race Tech makes a repair for this for about an additional $30 or so. These mods can be done at home but only if you're somewhat familiar with the fork internals. You can cause some expensive damage if you don't do things *just* right. You might want to check with a Race Tech authorized service center. They are located throughout the world.
Concerning you being a "4". I can't count the times I've talked to less advanced riders that think they aren't fast enough to take advantage of a suspension revalve. Nothing could be further from the truth. In fact, that can make a huge difference in rider confidence. Don't hesitate to get your suspension done right.
High Speed Miss
Some of the KXs had problems with air leaks in the bottom end. A lot of the KX's benefited from having the case sealing edges resurfaced on a flat surface. When you eventually do the bottom end, be sure to plan on doing this while you have it apart. Normally, the air leak miss sounds more like an intermittent popping noise at full throttle.
You may be too rich on the main jet. That can give a high rpm miss. Doing a plug chop can give a better indication of the main jet mixture. Find a long section where you can run full throttle and carry a plug wrench with you. After an extended full throttle run (1/4 mile), pull the plug and inspect the porcelain. Ideally, it'll be light colored with a black ring down where the porcelain meets the metal part of the plug.
Check all the electrical connections and the condition of all the wires. This means the plug wire and cap. Check the wires where they come from the stator through the case. Is the rubber grommet still there and in good condition? Check the ground points for the entire system (this means the coil mounting tabs also). Are there signs of moisture (dampness, rust, etc) under the mag cover? Disconnect the kill switch from the wiring harness of the bike and try it. Kill switches have created some hard to find problems.
DS = Doesn't Start?
Sounds like it is too rich. You may have some things contributing to the hard starting, though. First thing I'd do is make sure the air filter is cleaned and re-oiled. IF the silencer baffle is restricted, that can also add to the problem you're having. Remove the baffle and clean it thoroughly. This can be done with some strong carb cleaner (a tub that you can soak the baffle in- you'll end up using 46 cans of aerosol cleaner) or with a torch. Heat the carbon up as hot as you can and it will flake off much easier.
If the baffle is fairly dirty, you might want to remove the entire exhaust pipe and inspect its inlet for carbon buildup. This buildup can significantly restrict the engine performance.
XR250 engine stops
Attempts to remedy:
All attempts thus far have been in vain. After completing any of them, the engine will still die after a few minutes or ordinary riding. On occasion, you can get it to run for a short time longer but the abrupt lack of what we believe to be spark or gas is eminent.
If you can help with troubleshooting advice or next steps, please do. We?d rather be riding than wrenching.
Even though you have a visible spark, you still may have an electrical problem. In fact, an electrical component can fail exactly as you describe. A resistance check may show a bad component. But, then again, unless you check it in a failed state, it may check okay even if that is the problem. You might want to go over all the ground points (coil mounting tabs, etc) and ensure they are corrosion free.
You need to try to narrow down what you're losing (obviously, huh?). When you try to restart it and pull the plug, is it wet with fuel? Does it seem to stop running during an extended high speed run? This might indicate a low float level problem. Have you checked the carb vent hoses for blockage? This can give some unusual cutting-off symptoms also. The gas cap has to be vented also. If the vent hose is pinched/blocked, it may starve it for fuel.