Donít Ask: Your Dirt Bike Tech Questions Answered

Dec. 06, 2011 By Rick Sieman
If you choose to email a question to this forum, then you must conduct yourself accordingly. Therefore, the following rules are in order:

1. Do not write your email to me IN CAPS. If you do so, I will print out your question and do terrible things to it.

2. Do not request a personal e-mail response. Since I get thousands of questions each month, trying to answer them all would cut deeply into my leisure time, which I value more than your current state of confusion.

3. Try to spell at least in a semi-correct fashion. If you choose to mangle the English language, expect no mercy from this quarter. You might be mocked severely.

4. Do not ask for me to send you copies of my many manuals and literature. I am not in the library business, nor do I want to spend the bulk of my day at the copy machine just because you're too lazy to ask your dealer, or look around a bit.

5. Don't bother me with truly stupid questions, like how to get 50 more horsepower for a buck and a half.

6. Now that you know the rules, think carefully and have at it!

Oh yes Ö Iíll leave your e-mail unedited, for what itís worth.
                                             
Have a dirt bike questions for Rick "Super Hunky" Sieman? Send an e-mail with your name, vehicle year, model and a detailed description of the problem to Don't Ask at
editor@off-road.com. Donít forget to be as complete as possible with the description of your bike and its problems.

Previous Donít Ask Columns:
November 2011

October 2011

September 2011

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YAMAHA CONFUSION
Hey  Ö I got a yam,aha of some sort Ö mayube a yz or spmething.  It quite running last week and I donít know why or what caused it.  So whatdo ya think it could be, huh?  Its got plentey of gas.
Mikey


Some sort? Oh well, this should be easy. Just take the fornesculator shaft and move it .0167° to the left, unless the temperature is over 81°. If that's the case, you should take the mizzen mast and angle it directly over the starboard jib. That should solve your problem.

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1983 TT250
OK I had this rare beast of a bike known as the 1983 Yamaha TT250, and it was difficult finding some of the odd parts I needed. I replaced the cam and the oil pump only to be plagued by random no oil pressure in the valve train. One day I was on craigslist and saw an ad for someone wanting to trade an Elsinore for any 4 stroke that ran.

So I called the guy, and we traded.

Now i have this nearly complete 1977 cr125m. It had the incorrect carb on it. I've already got the correct one in my hands. I was supposed to have a keihin and came with a mikuni, not that I dislike mikuni or anything I was just unable to find a rebuild kit for it.

So now that I have the correct carb and all that..... Once i get this thing up and running is there anything I should be aware of looking for that are the common or uncommon things that creep up on people?

Now that it's got 2 new tires and all it needs is the silencer I'm ready to see how much trouble i can get into.
Mike

You won't be disappointed in the performance of either the Mikuni carburetor or the Keihin carburetor. Both give excellent performance. The only things you should watch out for on your CR 125R are foot pegs that tend to sag down, very high piston and rings wear and keep an eye out for frame cracks that might develop, especially near the steering head area. Other than that, it's a fast little bike that's fun to ride. It just isn't as strongly, built, for example, as a YZ 125.

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MAICO 400 1970 - CLUTCH SLIPS
Long time reader (1973), first time writer. I have been slowly restoring this survivor to vintage racing status. Problem is, the clutch always slips when it gets on the pipe. This engine has the small clutch. Is it possible to update it to the big clutch? If not, where can I find new plates and springs for this clutch. Hope to race it before I am in 60+ class.
Brian

You don't want to go to the big clutch, because even though it has an easier pull on the lever it won't take the abuse that the small clutch will. The Maico clutch is unique in that it has a stack of Belleville washers instead of the usual clutch springs you would normally find. By simply replacing the Belleville washers or increasing the stack by one or two washers, you should eliminate the big problem.

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NOT A FAN
Just where do you get off with your snotty attitude to people who actually take the time and trouble to write you and ask you questions?  I have a Honda xr250 and was going to ask you a question but when I see how you answer some of these people as far as I'm concerned you can kiss my *** several times over.  Got the message?
No name given

Gee, that's a shame. I was planning on having a real good answer here to your XR250 question.  he reason you see a less-than-pleasant reply to some people, is that some people are real jerks. And if they don't take the time to at least write in a reasonable fashion, they get a less-than- reasonable reply from me. I don't expect perfection from people and a typo or two or three is certainly understandable. But when I see pure sloth, I have no remorse when I open up on them. I hope I made myself clear. Now go away.

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REAR SHOCK YAMAHA 1992 WR 250
I have a 1992 Yamaha WR 250 (2 stroke). The rear shock has leaked and may need to be repaired. As I looked into doing this or replacing it with a used shock I have a question as to which years or makes have interchangability with the rear mono-shock.  Do you happen to know or have a listing of what years that Yamaha rear shocks are interchangable?
Thank you for your time
Andrew

Your best bet is to contact Works Performance at 818-701-1010 and get a price on rebuilding your shock. While the 92 WR 250 shock was okay, in no way was it close to what can be realized from a Works Performance shock. I don't have a chart in front of me on interchangeability of the years, but there could be a problem if the shock is the correct length, it might have different internal damping characteristics.

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KX 85 CYLINDER
Hey Rick,
Can (or should) the bore of a 2004 KX 85 be honed?  I get alot of conflicting opinions on this and yours will be the last word on this subject.
Thanks,
Chris

That particular liner is Nikasil and is very thin.  It is possible to hone the liner with a diamond coated hone, but because it is so thin, if you have to take out a lot off the liner, you're going to cut through it very quickly and easily. So if you have marks on the liner, chances are that you will not be able to hone it.  If the liner itself looks okay, then you have a chance. That's why you're getting all these different opinions on whether or not it can be honed.

 

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HONDA CR250 ďCHOPPERĒ
Rick,
 
I thought you might enjoy a good laugh so I've attached pictures of my 1983 CR250 "chopper".  It was a great bike right up until the frame broke when I landed from a big jump.  Luckily for me, there was a little tab of metal maybe 1/4" wide just below the gas tank that was holding the front end on the bike on.  I just remember a loud shotgun blast sound when the frame snapped and I was able to ride the bike to a stop as the exhaust pipe smashed into the ground.  After that experience with the Honda, I rode YZ's the rest of my racing career.
 
I ride a KX500 these days and it seems to have a strong enough frame.
Dave

If there's one flaw that the steel-framed CR 125, 250 and 500s had, it was that they tended to get a few cracks in the frame.  You certainly proved that with this photo.


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1973 SHIFTING WOES
Dear Rick,

I race a 73 MX360 in local and regional vintage MX.  The bike is entirely stock and in fantastic shape considering it's age.  The problem I have is when I downshift from 3rd to 2nd, it hits neutral about 50% of the time.  Then, when I downshift again, it goes into 1st, usually after finding that I'm in neutral as I'm at the apex of the corner.  If I upshift, I'm back in 3rd and bogging.  The bike upshifts flawlessly and otherwise performs like a dream.

Can you give me an idea what the problem is on this?  I spoke to a guy on the line at a local race last weekend, with a 73 MX250, with exactly the same problem.  He said the local Yamaha mech. split his case and couldn't find anything wrong with it.  Put it back together and it still does it.

I have basic mechanical skills but splitting the case is beyond my confidence level.  I'll be paying a professional if that's the route I'll have to take.   There must have been a common issue with them and you're the guy who probably knows the answer.  Any help on this will be much appreciated.  I'd like to be able to take it to a mechanic and tell them YOU said it was "......" and here's how to fix it.  It would assuredly make his job easier.
Thanks for your help.
Sincerely,
Tim

The gears themselves are probably in pretty good shape, but the dogs on the gears are worn on one side. This was more than likely caused by the rider downshifting without using the clutch. Just about the only way you're going to alleviate this problem is to put fresh gears in your box. Sorry to be the one to break it to you like this.

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SUBJECT: 2 STROKE TRAIL/RACE BIKES
Hi,
I am in the market for a 2-stroke trail bike used ocassionally for racing. I am coming off an XR250 and looking for something snappier. I am in between a 2001CR125 and a 2003YZ125. I was wondering which of the two bikes is best for trail riding. I here the CR has better suspension and frame but the YZ has more ground clearance and a better motor. In your opinion which is best?
Thanks
Scott

I might start to sound like a broken record, but in my opinion the best combination trail bike/race you can get is the Kawasaki KDX 200. If you take a good clean KDX 200 with an aftermarket pipe such as a Pro Circuit unit and dial it in properly, the bike is really amazing. I had a 1990 KDX 200 that I raced for a dozen years, mostly in Grand Prixs, and it also doubled as a trail bike. I ran a 15-tooth countershaft sprocket instead of the stock 13 unit and it pulled it with no problem. The six-speed gearbox let the bike top out close to 100 miles per hour and was still mild-mannered enough to take me through some tight sections on trail rides. You might think that the big countershaft sprocket would hinder the bikeís performance? No way. Geared that way, the 200 passed 650 Hondas on the paved sections in Grand Prix racing. Before you spend your money on any 125, take the time and effort to ride a decent KDX and your eyes will be opened up wide.


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RIGHT SIDE SHIFT FOR RM370?
I'm working on a 1976 RM370 for next season's vintage motocross season.  I noticed when taking the engine apart that the shift mechanism is very close to the right side clutch cover, and there appears to be a removable rubber plug in the cover that lines up with the end of the shaft.  Was there ever a conversion for right side shifters for these bikes for flat tracking?
Thanks.
Dennis Eaton
Imperial MO

Your observations prompted a phone call to Keith Lynas at (http://www.ossaplanest.com/) and he had the answer to your question.  Apparently some countries had their own version of the bike and had a right side shift; therefore. the shaft could indeed be modified slightly to accept a right side shift. There was a removable cover on the case that would allow for that, but the shaft itself was not splined. This meant that you would have to do some sort of machining to get a shifter over that shaft. To the best of my knowledge, no one has ever done that here, but that doesn't rule out the possibility of it being done somewhere in the world. If you find out, let us know.
 
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SHAMELESS PLUG
My new book, THE LAST RIDE, is at now out. It's fiction and starts in 1969, when an 18-year-old kid just out of high school gets a chance to ride his Yamaha 250 DT1 from Pennsylvania to Los Angeles Ö all off-road.  His adventures are truly amazing. The book then jumps 40+ years where the same person, now in his 60s, wants to get that old Yamaha back in his possession and return it home by riding it all off-road across the country again.  The book is $15 plus $2.75 for mail anywhere in the US (or $5 for Priority Rush mail) and for more information, the email is: 
superhunky@gmail.com

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