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.

Dying DT
Hi my DT 200 has 5000km on it and runs fine, excepted it cuts out when ever it fells like it. It starts and runs fine, but then at total randomness it dies if u give it gas. I had the carb cleaned, and tore the whole thing down (fuel system) and still it does it. I don't know what the hell could cause the bike to acted like this. It will run for 1 min to 3 hours befor it acts up. The problem goes away some times after a min or 2. If i choke it it kinda runs. Also if i VERY gentaly roll the gas on it will work fine (in naturel) but once it goes passed 1/4 wide open it dies again. If you have any ideas please let me know.

Many thanks Tom.

Right off hand, it sounds like a fuel related problem when it occurs. But the random frequency of it almost makes it sound like an electrical problem. An electrical problem could give a symptom like you describe. But I still feel you have a fuel starvation happening at times. It might be the float needle sticking in the shut position or a piece of trash that plugs the main jet once in a while. I'm wondering if it needs to have the carb cleaned a bit more thoroughly.

MX Tuner

Grinding KX
Mr. MX Tuner, I have recently purchased a '94 Model KX250. When I bought the bike it was very clean and seemed to run very well. It is a stock motor except for a Pro Circuit Pipe & Silencer and different clutch springs. It had a fresh top end this year, as well as a new clutch. The problem happened when I went riding on it for the first time, the bike ran good all day, then on the way back down the mountain I got on a straightaway and opened up the bike to full speed 5th gear, just around the corner to the trailer I pulled in the clutch and it sputtered and died, similar to what it has felt like to have a plug foul before, I kicked and kicked and it would not start so I just pushed it to the trailer and said I'll look at it tomorrow. So, I got the bike out the next day, pulled and plug (BR8ES) and it looked fine, it was a dark tan color, it didn't look fouled or wet, but I changed it anyways. Then I kicked and kicked and kicked some more and the bike finally started, but it did not sound or run right, I only fired up the bike for about 10 seconds but from what I can describe it sounded like a sort of grinding noise. The bike kicks over the same as it did before it stopped working, and there is no noticeable unusual sounds when kicking, the bike does not start very easily AT ALL (Like 15 Minutes of kicking) after it quit. I run 91 Octane and Yamalube 2R at 40:1.

Your advice would be greatly appreciated, thank you for your time!

Sincerely, Richard

It almost sounds like you've experienced a slight piston seizure. But if that were the case, I'd think the plug would look more white than tan. It still may have happened, though. First thing to do is remove the pipe and examine the piston through the exhaust port. If the ring appears to have metal displaced over it, then you need to pull the top end apart. Generally speaking, the exhaust side of the piston will show signs of a seizure before anywhere else will. Have you checked the compression with a gauge? You should have well over 160psi.

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Backfiring YZ
I have a Yamaha YZ 80 Year unsure (1987-91)just bought it!!, the problem it does not start, it has spark, fuel passes, new spark plug, good mixture, the problem i think is something in the carb for the reason that when you jump start it it sounds like its going to go then shuts off, it also backfires sometimes. What do you think i should do to get it back in the dirt?

The backfiring is a sign that the mixture is being burned at the wrong time. I'd check to see if the flywheel key is sheared off, causing the flywheel to be out of time with the crank.

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Sickly CR
I have a CR125 2001 and I have a few problems now that I haven't had before. This all happened when I put new gas in. 40:1

What's happing is it won't start easy, it's so hard to start. It won't even start if you try kicking it over. THe only way of starting it is if you get someone to push you down a hill and pop it into first. Ok so now the bike start's up and I give it some gas and than it just bogg's out on me and quits. Once and a while it will go for a few minutes but than quit and I have to do it all over again. I cleaned my spark plug like 20 times, its not the spark plug fouling cause when it bogged out on me I took the spark plug out and it was still clean...

Also some black oily stuff is coming out of the muffler and getting all over my rear brake

I have heard of some ignition problems on the new CR's. But first try a couple other things. One is to put in a new plug. It is very difficult to adequately clean a fouled spark plug. This can give all the problems you're experiencing. Second, try leaning out the jetting so it quits fouling the plugs. You need to start out with fresh silencer packing before you begin any rejetting. Start with the lower speed circuits first Pilot jet and air screw settings) before moving to the needle position and finally the main jet.

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Grinding CR
I have just bought this 1990 cr 125. It ran ok , but i noticed rideing in first gear was rough it would engage,grab,,jerk, real hard and as the day went on it would not move at all in first. It still would go through all the gears easily but wouldnt engage in first, just spin.

I took the engine apart and noticed that a shifter fork had a noticeable bend. Also 1st gear had a small chip out of it. I replaced all that looked to be damaged, but when i put it together it still did what it did before, this leads my to believe that this problem is some where else. have u heard of this? maybe clutch? i inspected the clutch plates but they dont seem to be worn that bad.

thank you - KIM from Canada

Sorta hard to tell without feeling it. When a bike pops out of gear, what actually happens is the teeth on the sides of the gears are too rounded to keep them fully engaged under power. If you had a bent shift fork, chances are the sides of the gears are worn to the point of not working properly. This may be what you're experiencing.

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RMX Mods
I have recently purchased a 2001 Suzuki RMX250, I know it's an old stock 1998 model. What modifications can be done to make it more competitive? I've already learnt that a RM head gasket, pro circuit pipe, and modifying the air box will all help. But at this stage it is still stock standard. What modifications do you recommend for enduros and novice motocross?

Grant - Western Australia

I had a '96 model RMX. Had a lot of good miles on that bike. The head gasket for an '89 RM 250 is the first place to start. Next is the pipe and silencer. The next thing I'd do is install an Delta V-Force reed cage. I had the stock air box (except for the lid removed) and never had to do anything else to it. Once you get the parts bolted on, get it jetted correctly and you'll be amazed at how the bike is transformed. One big hint with the jetting, the lower you have the idle speed set, the leaner you can run the pilot circuit. This translates to "eye opening" throttle response.

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Butterfly Powervalve
I have a 1986 CR125R, that I just bought and I'am currenty rebuilding the motor.

My question is about the butterfly style powervalve system. When I got the bike the little coin shaped piece of metal that bolts onto the shaft in pipe which opens and closes the exshust from the canister (that hangs off the pipe), was missing, but I got the missing piece and now I need to know how to set the valve for the proper open and closing times?

Thanks: Jesse

Maybe it's just me, but it seems painfully obvious that a shop manual would be a very wise investment.

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The Four-Gear YZ
My 2000 YZ 250 has been running excellent until recently. I put a sst pipe on it and boyesen power reeds and a new top end and now i am having problems with my 5th gear. all other gears are running excellent, but my 5th gear is not. It feels like i am clutching it or it is fouling the plug. it pulls strong, backs off, pulls strong, backs off, pulls strong and so on throughout the entire 5th gear. I have lowered the main jet and checked my clutch and both of those things didn't do a thing. I know i still have some other things i can try, but i am stumped on the 5th gear only problem. please help .

Joshua

It sounds like your main jet is still too rich. Find a long stretch of dirt road where you can safely make a wide open run, preferably up a slight incline. Carry a plug wrench with you so you can look at the plug at the end of the straight. With it pinned in 5th gear, pull in the clutch and push the kill button. This should give a decent plug color for the main jet circuit. Ideally it should be a tan color down in the hardest to see part of the spark plug (where the porcelain meets the inside of the threaded part of the plug).

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Jammed Compression Clicker
Dear Mark, I'm from Malaysia, I just purchase a used 1992 Yamaha DT200WR and I found out that the rear shock compression clicker are jammed. Please tell me what to do as I'm still fresh towards the shock maintenance. I already go through your Mar 99' issue "Shock Basics, Maintenance & Adjustment" but didn't mention about how to deal with jammed compression clicker. Beside jammed clicker, I prepare to do shock oil change myself and found there is no schrader valve on the reservoir. How am I going to release the nitrogen gas? Please help me deal with my shock, and please don't ask me to send my shock to suspension specialist because there is no such suspension specialist in our country. Most of the dirtbike never change their shock oil because nobody dare to open it.

Thank you,
Douglas - Malaysia.

Sounds like you've discovered an open market for you once you get proficient at shock repairs.

I'm not familiar with the DT200 (we don't have them imported into the US market). But I have seen some shocks (Honda XR 250, for instance) that has a flat metal cap installed inside the end of the reservoir, where the Schrader valve is located. This cap must be removed before the shock can be taken apart. Once you remove this metal cap, you'll see the fitting.

Now for your stuck adjuster. My guess is it is stuck from one of two things. The most common is lack of use. Some people never adjust their suspension for fear of getting it so screwed up it won't work right. The adjuster can freeze up from corrosion. You can try spraying some penetrating oil on the adjuster itself and working it back and forth. Or someone may have tightened (or loosened) it so hard that it is locked into place. The magic question is which way is it turned.

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Seized YZ80
I am not real sure what caused it or what the real problem is. All that i knnow is that the kick starter seems to be stuck and i am looking for advice on what my first step sould be or were i should began looking at.

First step is to figure out whether the piston or the crankshaft is seized. A rod bearing can seize giving the exact same symptoms as a seized piston. Removing the cylinder will give the answer.

MX Tuner

Bottom End Bog
I just got a 1999 YZ 125 that appears to be stock, the pipe and sprockets are for sure, I don't know about the carburetor. The bike runs great once you break through low rpm bog. I bought the bike to trail ride with my nephews and I'm trying to tailor it to my needs. In first gear, with the rpm above the bog, the speed is a little uncomfortable. I'm not a wussie - I love the feel of a two stroke running at high rpm's. I'd like to get rid of the bog and ride at a slower more comfortable speed.

I'm still running the tank of gas and spark plug (BR8EG) that was in the bike when I bought it. My plan is:

• mix fuel 32:1 (yamalube and gas)
• use a BR9EG plug
• go to a 50 or 52 tooth sprocket

What do you think? Where can I find race gas? Will a 52 tooth sprocket be too much? Please make suggestions...

Thanks, Mike

Stick with the 8 heat range plug. I'd recommend a BR8ES, instead of the EG. If you alter the gearing, you'll find yourself shifting more than you'll probably like. Why not alter the power output instead? Two easy and relatively cheap mods are a high compression gasket kit. Cometic makes these and they come with all the gaskets necessary to do a top end, including a thin base gasket. This is where the increase in compression comes from. One other benefit is a slight lowering of the port heights. This will give a tad more bottom and midrange.

Another excellent mod would be a Delta V-Force reed cage. Once you get this and the compression raised up with the gasket kit, rejet the carb paying close attention to the pilot circuit and needle position. Once you lean the pilot circuit, you shouldn't have a noticeable bog. You'll still have the nuclear top end rush but it'll be much more forgiving getting there.

From a performance issue, you shouldn't need race fuel. Race fuel will alter your jetting and confuse issues, especially if you switch between different race fuels. If you feel it necessary to run race fuel, pick one that is readily available and rejet for it. Once you rejet for it, you need to use it continually after that.

And as always, be sure your silencer is in good condition (fresh packing and the core holes clear and unobstructed) before you begin any carb rejetting.

MX Tuner

Suspension Air Pressure
1985 Honda XR250. What air pressure levels should I use on my front forks? I believe the allowable range is 0 to 14 psi. For Track Riding I expect there is need for stiffer pressure than off-road mountain riding. I'm just not sure where to start. Any insight is appreciated.

Thank You - Dan

If you run any more pressure than 0 psi, you lose initial plushness. You really can get the best of both worlds running 0 psi by increasing the oil level in the forks. You can add oil through the Schrader valve holes by removing the valve cores and using an infant medicine syringe. Add oil in 10mm increments per leg until you find the bottoming resistance acceptable. You can use 5wt oil. Be sure to have the bike on a crate type stand so both wheels are off the ground. You need to insure the forks are 100% fully extended before screwing the Schrader vale cores back in. You should be able to run this oil level in the mountains as well as on a moto track.

MX Tuner

MR Foul
I have a 1977 MR175 Honda dirtbike, I am have a problem with the spark plug, I put a brand new NGK plug in b4 i went riding and an hour later the bike died on me because the plug was burned out. This had happened to me the last time i rode it as well. I put in a new plug and it fires right up what do u think the problem is.

thanks - Mike

My first full size bike was a '76 MR 175. Many happy memories were made on that bike. Sounds like you're gas fouling spark plugs. You might want to check your float level to make sure it isn't too high. Does gas pour out the carb overflow hoses? The needle and seat may need replacing.

You might need to replace the ignition points. If the spark is erratic, that could contribute to a plug fouling condition.

MX Tuner

Standard or Reverse?
I have a 1999 kx 60 and the question is is the clutch boss bolt standard thread or reverse thread?

Thank you

That would be a standard thread.

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Jetting for Altitude
Make Yamaha, model WR 400 F, Year 2000. Mark, My question is quite simple. I am going to be taking my 400 into the mountains of Colorado. We will be camping at about 10,000 feet and riding to altitudes between 10,000 and 14,000. My bike has the stock jetting. How much do I need to change the jetting for this ride.

Thanks - Loren

Being I'm at about 1000 feet, I don't have any experience with high altitude jetting. I'd call some of the local Yamaha dealers and see what they have found works well for that area.

MX Tuner

Note: Try...

• Apex Sports
  327 S Weber COLORADO SPRINGS CO 80903-2124 (719) 475-2437
• Vickery Motorsports
  2231 S Parker Rd DENVER CO 80231-3482 (303) 755-4387

Both are extremely reputable, and will be happy to help out.
-Editor

Overheating RM
i have a 96 rm250. could old, carboned up packing in the silencer cause the bike to overheat? what about it being hard to start?

thanks dave, pittsburgh,pa

The silencer condition can have a fairly major affect on any jetting type symptom including starting. But generally you get a rich type symptom from a blown out or glazed over silencer. Overheating might be a lean running condition. Is it using any coolant? What condition are the radiator fins in? Any collapsed radiator tubes?

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Sagging WR
Greetings, I recently bought a Yamaha WR-200 for enduro riding. The bike is a 92, I've replaced all the plastics and made other minor repairs,all in all the bike runs great, The problem i'm having is that it kinda sags like old tit's on the bottom end. I'm wondering if maby a "Gnarley {fmf} pipe would wake this thing up? I want to replace the pipe and install a Boyesen RAM valve, Would these parts be of any help for the bottom end ....Or would it be a great waste of money??

Thanks.........Rob

Those mods should do just as well today as they would have back then when the bike was new. Just be certain to rejet after installing those parts to take full advantage of them.

MX Tuner

Bogging RM
I just bought a 1983 RM 125. It runs good except for a bog and sputter right before the power band hits. I cleaned the carb, checked the reeds and cleaned the air filters, but i still cant get rid of it.

Another case of poor jetting. And, once again, be certain the silencer is in good condition (fresh packing and the core holes clear and unobstructed) before beginning any rejetting.

MX Tuner

Blue CR
Hello Mark, Few question's for ya. 1) My bike is a 1985 Honda CR125R and seems to be burning a whole lot of oil. I know 2-strokes burn oil , but it burns it alot, in the powerband or not. 2) When the pipe comes out of the cylinder head there is an ATAC system supposed to be on the bike. I have heard it will improve gas mileage and bottom end power(which I need). Could you tell me where I could get an ATAC system in Ontario,Canada. 3) After the ATAC system pipe ends (it's about 7 inches long) it continues on with the regular exhaust pipe. Where the 2 pipes meet there is a space only a few millimetres but water always get in there. Is that space supposed to be there? How can I fix it?

Any info on any of these matters would be great .

Thanks again Tyler.

IT sounds like you may be sucking crankcase oil into the combustion chamber. The most likely place for this to happen is the right side crank seal. Fortunately, this seal can be changed without splitting the cases or even removing the motor from the frame. IF the gear oil is slowly disappearing, this is most likely what is happening.

I've never heard of anyone who still runs the ATAC chamber unless they have to. All the aftermarket pipes did away with it. If you have a gap in the pipes, you may have bent pipe mounts. Obviously, there shouldn't be any gap. Try loosening all the mounts and sliding them together. Is there maybe a part missing? Check with your local Honda dealer. You should be able to look at the parts diagram to find out if you're missing something.

MX Tuner

Cracked Piston
Hey I have a 1985 Honda 200r. I'm a little new at engine work , but getting better. I bought this bike about 2 years ago in good condition. the 2nd day I had the bike it locked up on me from no oil. the other day i decided to go through the engine and look at the damage. this engine was different than any other engine i have taken apart. it has rockers, a camshaft, valve springs, timing chain, and dual carbs. I don't know how to tell the difference between two and four stroke and i figured this was it. As i tore into the engine i came to relize that the engine was not locked up . the problem was the piston was cracked and was not moving on the top of the piston rod. this is what gave us the impression that it was locked up. the problem i have now is getting the piston and rod off. i have taking both engine covers off and found the long bolt going through the engine. i didn't try to hard to get it off, not wanting to mess the engine up. is there an easy way to change pistons or not. i'm absolutly clueless about what to do.if you could help me out i would appreciate it.

thanks, mike

The piston (or what's left of it) comes off easy. There is a small circlips holding the piston pin in the center of the piston. Removing either one should allow you to push the pin out enough to get the piston off. The rod is an entirely different story. If the rod is damaged, you'll need to remove the motor from the frame and have the cases split. Then once you get the crankshaft out, you'll have to have someone press the crank apart to install a new rod.

A shop manual really would be a worthwhile investment.

MX Tuner

Starting this CR a Kick!
Hello. I own a 1992 Honda CR 250R. THis bike runs like a dream, and hauls ass while doing it, but it only has one problem, it's a pain in the ass to start. To start it, i tip it over till gas comes out, then shake the hell out of it, which i find force-feeds the carb, and on some days, it starts in 2 kicks, and others, i can kick my ass off for 30 min and not even get the engine to turn over. The spark plug has a healthy spark and everything is in working order. It would be great if you gave me a few clues to what could be wrong.

Thanks alot. Zach

Sounds like the choke circuit isn't working properly. The first thing to do is a thorough carb cleaning. Make certain the choke and pilot circuits are clear. Be sure to check the float level. If the float level is too low, it can give similar symptoms.

While you have the carb off, check the condition of the reeds. They should pretty much lay flat on the reed cage. IF they are chipped, frayed or raised up more than about .010", then they need replacing and could give the problems you describe.

MX Tuner

Hello:

Lean Spot?
I recently purchased a brand new 2001 KX 250. The bike has just been broke in and runs great. However, there seems to be a "lean" spot right after idle just as I begin to crack the throttle open, then once I go a little farther with the throttle it takes off and sounds/feels great. Do you have any recommendations for jetting. Everything is stock right now, air screw is 1.5 turns out, and I will be putting on a FMF Gnarly pipe with Turbine Core Silencer.

I usually ride at or near sea level in 60-80 degree weather.

Thanks

Eric

It's rare to find a bike that is lean from the factory. Chances are it is too rich in the pilot circuit. This will give the exact symptom you describe. Once you get the pilot circuit leaned out, fine tune the needle position for best throttle response.

MX Tuner

20-Minute CR
I own a 1999 CR250. I'm having problems with it bogging and quitting after 20 minutes of riding. After I let it sit for a little bit it fires right back up. I noticed the plug gets quite dark and oily. I've tried 50:1, 40:1 and 32:1 and they all give me the same results. Is this related to the main jet or something electrical? Also could it be getting too much or not enough air?

Thanks, Benjamin

The fact that it cranks back up after sitting leads me to believe you have an electrical component failing. Possibly the CDI box. The most accurate method for testing is trial and error. If you know anyone who will let you borrow their CDI box for 20 minutes or so...

The stock jetting on the '99 CR was way out in space. You should have about a 170 or a 172 main jet. Make sure you don't have a 190 main in there. I really don't think that is your problem because a fouled plug doesn't "unfoul" by itself from sitting there for a few minutes.

MX Tuner