Don’t Ask: Dirt Bike Tech Questions Answered

May. 01, 2012 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 … I’ll leave your e-mail unedited, for what it’s 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 Don’t forget to be as complete as possible with the description of your bike and its problems.

April 2012

March 2012

February 2012
The SC500 MX was cursed, sad to say, by a hex.
Made unruly by muscle, riders found it would huscle them straight into terrible wrex.
by Willie Rogers
Yamaha South Africa - 1976
I found this poem written by Willie in the front of the SC500 parts book when I started working at the South African Yamaha distributor in1978. I never forgot it!   
 Paul Ward
Truer words were never spoken.
Hi Rick,
When we emailed a couple of years ago about me purchasing your old bike I said that I would keep you up to date on how it was going, here's the latest.
I've run it at Speed Week at Bonneville the last 2 years. The first year was just test and handling runs on which I got up to 85.994 MPH and on the 3rd run a seam in the gas tank, the only part that I had welded by a certified welder, split and ended the runs. Last year I did much better, I got in 7 runs with a top speed of 108.907 MPH against a record of 116.541 and a 12.5 MPH headwind. The problem that I encountered last year was effectively running out of fuel. The engine is fitted with a pair of Amal T10 GP2 carbs off of a 1965 BSA Spitfire and matching matchbox float bowl, when I reached the 2 mile mark and shifted into 4th gear it had sucked the float bowl dry. I finally realized that in 1965 a BSA Spitfire was lucky to turn 6500 RPM, I shift at 8000 RPM. I've since installed a second float bowl as well as a Pingel Guzzler fuel valve in the tank. This year I will return in August and take the record.
This last weekend I entered the bike in the 22nd Annual Colorado Springs Super Show bike show. It took 1st place in the "competition bike" class and "best engineered" in the entire show. It's nice to get recognition for the work I put into it. I'll attach a couple of photos from the show.

A double wow! To think that my old Triumph would get turned into a high-speed beast is truly amazing. Genuine thanks for the update.
Do you happen to know how many Yamaha DT-1 enduros were built?
Keith Gray

Yamaha DT-1
The Yamaha DT is a series of mopeds and motorcycles produced by the Yamaha Motor Corporation. Models in the DT series feature an engine displacement of 50 to 400 cc (3.1 to 24 cu in). The first DT model, the DT-1, was released in 1968 and quickly sold through its initial 12,000 production run.

The DT series was created by Yamaha in the late 1960s when the United States motorcycle market was down. Market research by Yamaha indicated that, despite slow motorcycle sales, there was a largely untapped market for off-road motorcycles.

The first DT model, the DT-1 trail bike, was released in late 1967 and quickly sold out.

With the introduction of the DT-1, Yamaha essentially defined a new market for motorcycles.

Models in the DT series
• DT50LC
• DT50M
• DT50MX
• DT50R
• DT50X
• DT80MX
• DT80LC
• DT80R
• DT100MX
• DT100R
• DT125
• DT125LC
• DT125MX
• DT125R
• DT125X
• DT175
• DT175MX
• DT200R
• DT250
• DT250MX
• DT250R
• DT350LC
• DT350R
• DT400B
1968 production figures detailed 12,000 units. All were sold. You can take that as an approximate value and times it for the production run from 1968 to 1973, when the original design was sold, 1974 was a completely different motorcycle. They were heavier and slower due to mandated safety designs by the myriad of related government entities involved in imported motor vehicles.
hello superhunky,
I have a problem with my  honda 05 cr 125r. When I am accelerating right about maybe third shifting to fourth gear, I get a very severe head shake that I have to back off on the throttle. I have had so many close calls because of this. I have set the race sag at 100mm. but still the same.
I was thinking of dropping the forks a bit on the triple clamp, but the manual says that it should always be aligned with the grooves on the fork legs. I was hoping, with your infinite knowledge on dirt bikes, have an answer.
Thanks a lot,
Many of the Honda CRs shook their steering head badly, especially when coming down from speed over bumps. A partial cure was to stretch the forks out. That is, lower the forks in the triple clamps more than the factory tells you.
At age 13 I was broadsided by a car while riding a motorcycle and lost my left leg below the knee. I desire to ride again but am having a hard time trying to find someone that has info/pics/products/diagrams on moving a dirt bike shifter to the right side. There is info online for road bikes because many have a lot of room to work with and linkages already. But not any onto for off road bikes like I want to ride. Shifting with my prothetic would not be practical. I've seen the Kliktronik electric shifter but that thing is $1300! I know there has to be some out there that has already been through this. If you can help I would greatly appreciate it.

David Sullivan
I talked with Matt Cuddy and he says that you can tighten up the adjustability on your prosthetic ankle and should be able to shift by raising or lowering your leg. Matt should know, as he’s in a wheelchair.

From the late ''60's to today I have owned over 300 bikes. All of them were raced. But from all of those my favorite was my '82 KTM 495. What a monster! It was great fun at the sand mountain mx track. I could put the bike in 4th at the start and run the rest of the track in 3rd. Sadly after all those bikes it was the only one that was ever stolen from me never to be seen again. But it brought some great memories.

1981 KTM 495

1981 KTM 495
This was the first model year for the Great White. This was also the year that Dirt Bike magazine had it flat out at 123.75mph (200km/h) at the El Mirage dry lake.

The 1981 model is known to be the fastest of them all. It didn't have a reed valve intake. A very long intake manifold and a small exhaust volume contributing to the overall power output at high rpm. Due to this setup, the engine was capable to overrev without losing too much power. It was the lightest 495 ever made; this was the reason why this bike could reach this enormous top speed. One year later KTM added some ponies, but at lower rpm. The head had the twin spark plug. The idea was to get a more complete combustion despite the huge volume. The compression was 14:1. The front fork was a 38mm conventional Marzocchi unit. The rear shock was Öhlins or WP piggybacks, except the US model that was equipped with FOX air shocks. It had the typical rear fender with number plates. Drum brakes both front and rear. This bike is very rare and the twin shock setup makes it qualified for certain vintage classes and therefore it holds a high value.
1982 KTM 495

1982 KTM 495
The 1982 model had the first rear mono shock configuration named Pro-Lever, and the bike had a WP piggyback or Fox twin clicker unit. A 40mm Marzocchis up front with aluminum sliders (81 mod. magnesium). The engine got a reed valve intake and the overall power output was a bit higher but with a more manageable powerband. It still had the twin plug head, compression 14:1. It might be the strongest 495 ever made. The expansion volume is the same as on the 495/81.
The white nightmare was called the best open class bike in 1982.  Power, suspension, stability was popular among riders. It still was the undisputed horsepower king.

I just bought a 2006 KX100 and I was wondering if somebody makes a speedometer that is capable of mounting on this bike.  As far as I understand (with my limited knowledge of the dirt bike aftermarket) that anything available now would only fit on a trail bike not a motocrosser. Please correct me if im wrong, but is it true that my only available option is a bicycle speedometer? Also when putting plastics back on should I use Loctite on the bolts?
You can probably use the parts from a Kawasaki KDX 200 to create what you need. The only real problem will be getting an axle to fit the front wheel. No Loctite of the plastic, please.
Hi Rick,
I have a 1982 Yamaha XT 125 - set up for dirt, knobs, with no lights, etc. - for putzing around on the local trails with the kids. While riding today, it just went kaputz and stopped. I think the cam chain bit it. I'm pretty certain.
Any advice for a novice wrencher on the repair job?
Also, are there any engines that would be an easy swap? Yeah, I'm lazy/crazy and may be...ummmm....I am too inexperienced to do a cam chain. I tried once before on a crappy 1982 XL500 and the bike ran for a week before crapping out again.  Swapping the engine would be easier for me IMHO.
Thank you.
Robert Fairweather
Chicago Suburbs
Do you want the bottom line?  Chances of you finding a decent, non-worn out motor suitable for a swap are slim. Get a manual for your bike; a Haynes or Chilton manual will do the job. Get the parts from your dealer, take your time and simply follow the directions. It should take no more than a Saturday afternoon. Figure on about $100 for everything.
Hello king of the dirt.

This is Richard Hall from Chickamauga GA. I have talked to many many people lately about this tour even though the title mentions "tour" you don't have to go anywhere. My idea is for local racers to go around their area and find old closed down mx tracks.

Since I started in the late '60s and still ride today I thought finding some of these old tracks and the property owners about doing a one day cleanup to let the new crop of racers. In my area it has been about 50/50. In GA,TN, AL and Kentucky putting your name on a waiver at the gate releases the property owner from any liability.
I'm sure you remember the days when you raced on the track and not above it. Those days were better. The best part is that the older the track the better, which usually means safer to ride on it. Anyone could ride these old tracks. Modern, Vintage, Dual sport, even adventure bikes make some laps  on that day.

Of course handing a percent of the gate to the owner could make them feel more inclined to let them do a one day ride then go away and come back next year or find another old track in the area later in the season.

I talked with one of the guys at Dirt werkz and they really liked the idea including Barry Higgins, John Garmom from the Runnin brand track and other old timers like me. The tracks do not have to be but back to the way they were. But anyone that remembers the old layout could just put up ribbons so the peeps would get
to run the old track for what would be a very fun day.

I can only guess that these remembrance tours should first put in Cycle News for everyone to see. And yes I have been told that this idea could go nation wide...I hope.

All I ask that People know it was my idea. After all these years I have a lot of good memories from Motocross and still race when I can.

My slogan is "Anything less than a 500cc two stroke is a pitbike so keep them away from me!" Thank you for reading this and pass the word.
MX Rich

Your idea sounds like fun, but chances are most of these old tracks won't let you ride there because of insurance nightmares. When I was active in the Dirt Diggers MC, we tried to get permission to ride at Hopetown again. No luck.



I'm hoping you can answer a question for me, I just got a 1981 YZ250H and according to an old Dirt Bike article from July 1981 the bike is supposed to have the YEIS system (micro fiche from parts stores online all show it too), but this bike doesn't have it (and as far as I can tell from looking where it would mount maybe never did).

Did they ever make '81's without the YEIS - or do I have a 1980 manifold.  Since I don't have the YEIS should I use the 1980 G carb jets as a baseline - from the article it said the 1981 H ran poorly without the YEIS system without re-jetting - I'm considering replacing the carb as it is fairly well used.

Thanks for any info you can pass on...
Chuck Ertelt
The YEIS (Yamaha Energy Induction System)
Yamaha's engineers incorporated an air chamber into the inlet tract, which smoothed out the flow of fuel vapor and widened the engine's power band. The YEIS achieves this without affecting peak power or fuel consumption.
This setup consists of a rubber tube running from the intake tract to a tubular canister. Dispensing with brand names, we point out that the principle of the canister/tube and their effect were discovered by a 19th century acoustical engineer named Helmholtz, hence the generic name of the system—Helmholtz resonator. The canister develops its own resonance (the frequency of which is determined by the dimensions of the system), which offsets the natural resonance developing in the intake tract. The result is smoother fuel delivery at low rpm, helping to prevent surging or flat spots.
Below: the small decal/sticker which is supposed to go on the YEIS-device, a.k.a. the "Boost bottle", which gives the motor more power in low revs. YEIS=YAMAHA Energy Induction System.

What’s that under the tank? The square thing doesn't look stock at all.

Might be a boost bottle molded into the tank. Mike Bell and a few other factory riders used these for a short while.
here's some  pics of my 68, 360 CZ sidepiper ,i bought the thing at a vintage race in the for sale area , it was a way bad roached out bike ,but  the frame and motor were original . its been a 2 year labor of love to get it back to riding condition ,the 250 cc motor gave way to a 360 i bought for 100 bucks of craigslist .then sent the new motor over to lee holth in Nevada for a rebuild ,got a old extended swing arm off eBay for cheap . the rest of the bike is a collection of bits and pieces of eBay and other sources .

its not original or a racer i built to ride in the desert ,its been to jawbone and randsburg area lots of times ,i usually put 100 miles or so on it in a weekend .its rips plenty good for this old fatman. thanks

 p.s. cz,s rule

Your photos are living proof that CZs never die.
I have a 2005 yz250 and have decided that I need a skidplate of some sort. I'm only 14 so i have no money to buy one (and I like making stuff more than i like buying it anyways) and was wondering what kind of tricks you know that would help me figure out how to make one.

Thomas Nawrot
If you have a hacksaw, a drill and some aluminum plate, you can easily build your own skidplate.  Just go to GOOGLE and type in HOW TO MAKE YOUR OWN SKID PLATE and the first five or six pages on the screen offer how-to directions.  It ain’t hard.
Hello 'Ole wise one!
I am working to make an ISDT replica out of a 68 Triumph Trophy 250 B25. Ya I know...

With your infinite wisdom could you recommend a seat upholsterer who could/can make up a vintage Bates Desert Sled seat?

I have two Triumphs I would like to do this to.

I have the seat pans and I would like to find the 'artful one' who could build a fabulous seat or two in this style.

Watcha say Mr Hunky?

Thank you,
Ernie H (PNW) aka Maxacceleration
Try these guys for starters. Matt Cuddy says they covered an old Husky seat for him and it came out perfect.
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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 … 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: Newsletter
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