Reviving an atk 406 mx 2 stroke from abandoned

[2 Stroke Boogie]

That rear brake???? Wow. That's some funky chit. How well does it work?

[motoxvet]

18 minutes ago, HelenaHanbasket said:

That rear brake???? Wow. That's some funky chit. How well does it work?

Helen, love your user name!

[2 Stroke Boogie]

19 minutes ago, motoxvet said:

Helen, love your user name!

HelenA. Mr. Helena. 

[Piney Woods]

Sorry to hear about the neck issues but selling that bike will be one of your better decisions. They weren't on the sales floor very long for many good reasons. Nostalgia is an emotional thing, reality is reality.

[Eccentric]

17 hours ago, Patrockyj said:

 

 

That looks like the Mikuni that originally was on my 1990 406.   With the float bowl off and the floats removed, you'd be able to see if it has a pilot circuit or not.  The main jet is in the center of the bottom of the carb body.  The pilot jet is smaller and offset from the main.  Both are brass.  Main has a hex head, while the pilot has a slotted head.  If it has a pilot circuit, I'd use it.  If it doesn't...........I'd replace it with a Keihin PJ or PWK carb. 

 

The Mikuni TM38 in this pic has a pilot circuit.  The pilot jet itself is missing.  It belongs in the threaded hole offset towards us from the main jet.  The non pilot circuit TM's don't have that threaded hole.  That pressed-in brass tube near the airbox spigot end of the carb body leads to the air screw.  Both the pilot and non-pilot TM's have this.

 

 

This TM38 carb body is of the non-pilot type.  It is also missing the main jet in this pic (it would go in the threadded hole in the center). 

 

 

 

I have no experience with the chinese PWK copies on eBay (many of which are dishonestly labeled as 'genuine' Keihin carbs from Sudco).  This is a pic of real Keihin PJ series carb like I used on my 406.  They were on many Honda motorcross bikes and all TRX250R quads.

 

 

 

 

 

Here's some eBay listings.  Some are listings for used, genuine Keihin PJ series carbs.  Most are listings for new chinese copies of  Keihin PWK carbs.  The PWK is an evolution of the PJ.

 

https://www.ebay.com/sch/i.html?_nkw=cr500+carburetor

 

 

 

Edited February 7, 2019 by Eccentric

[Eccentric]

11 hours ago, HelenaHanbasket said:

That rear brake???? Wow. That's some funky chit. How well does it work?

 

Worked fine for me.  A little grabby.  That little disk has the advantage of gearing (for torque multiplication) as it's on the countershaft.   Supposedly, they had a habit of overheating and fading (which comes from the disadvantage of speed multiplication as it's on the countershaft).  That'd be more of an issue in high speed/heat desert riding.  The last couple years of these bikes had conventional rear brakes (without the ATK constant chain setup).

[Eccentric]

10 hours ago, Piney Woods said:

Sorry to hear about the neck issues but selling that bike will be one of your better decisions. They weren't on the sales floor very long for many good reasons. Nostalgia is an emotional thing, reality is reality.

Ehh....  Yes and no.  They often remained on the sales floor for extended periods collecting dust.   Much of the low-sales problem with the ATK's was due to a sparse dealer network.............and high prices.  They were a 'high end boutique brand'.  This was all long before the internet/eBay.  Only source for parts were the few dealers scattered throughout the country.  They also were 'odd/unusual/not like the Japanese bikes'.  Left hand kick (which I still am more comfortable with, as the majority of my bikes including the 1983 CR250R were LH kick), air cooling, expensive parts, non-Japanese frame geometry, etc.  The European bikes (including KTM) still suffered from low US sales at this point for many of the same reasons.  Many younger riders probably don't even know that KTM wasn't always orange............and that Husky wasn't always owned by KTM (and using the same engines as the KTM's).  The reasons for low sales of these machines (especially the higher sticker prices) aren't really a detriment to what the OP was looking to do with the bike.

 

ATK never sold many of the 250/406 air cooled 2-strokes.  Most of their sales at this time were from the Rotax 4-stroke powered machines.  Those were some of the first 4-strokes to be relatively light and powerful.............AND to be available with the magic button.  Everything Japanese (2T anyway) and most Euro bikes were liquid cooled at this point.  Low sales numbers (no help from the economy of scale), the higher cost of US labor, and the cost of 'premium' components (Magura controls, WP suspension, Answer bars, and even nickle plated frames for a few years like my 1990 406) all raised the sticker prices for their bikes.  Towards the end of ATK, the Rotax 4T powered models remained, while the air cooled 2T bikes were replaced by 250/260cc liquid cooled Rotax powered models.

 

I don't see anything in the OP's posts that indicate that he was looking to use this bike as competition for a modern Japanese or Euro machine.  As a low investment bike to have some fun on, it'd be fine.  He obviously has the mechanical skills and the inclination to deal with the minor quirks that this bike has.  Yes he could sell it and buy something like a used Suzuki DRZ400 with electric starting and other 'modern' luxuries.

Edited February 7, 2019 by Eccentric

[Patrockyj]

17 minutes ago, Eccentric said:

Ehh....  Yes and no.  They often remained on the sales floor for extended periods collecting dust.   Much of the low-sales problem with the ATK's was due to a sparse dealer network.............and high prices.  They were a 'high end boutique brand'.  This was all long before the internet/eBay.  Only source for parts were the few dealers scattered throughout the country.  They also were 'odd/unusual/not like the Japanese bikes'.  Left hand kick (which I still am more comfortable with, as the majority of my bikes including the 1983 CR250R were LH kick), air cooling, expensive parts, non-Japanese frame geometry, etc.  The European bikes (including KTM) still suffered from low US sales at this point for many of the same reasons.  Many younger riders probably don't even know that KTM wasn't always orange............and that Husky wasn't always owned by KTM (and using the same engines as the KTM's).  The reasons for low sales of these machines (especially the higher sticker prices) aren't really a detriment to what the OP was looking to do with the bike.

 

ATK never sold many of the 250/406 air cooled 2-strokes.  Most of their sales at this time were from the Rotax 4-stroke powered machines.  Those were some of the first 4-strokes to be relatively light and powerful.............AND to be available with the magic button.  Everything Japanese (2T anyway) and most Euro bikes were liquid cooled at this point.  Low sales numbers (no help from the economy of scale), the higher cost of US labor, and the cost of 'premium' components (Magura controls, WP suspension, Answer bars, and even nickle plated frames for a few years like my 1990 406) all raised the sticker prices for their bikes.  Towards the end of ATK, the Rotax 4T powered models remained, while the air cooled 2T bikes were replaced by 250/260cc liquid cooled Rotax powered models.

 

I don't see anything in the OP's posts that indicate that he was looking to use this bike as competition for a modern Japanese or Euro machine.  As a low investment bike to have some fun on, it'd be fine.  He obviously has the mechanical skills and the inclination to deal with the minor quirks that this bike has.  Yes he could sell it and buy something like a used Suzuki DRZ400 with electric starting and other 'modern' luxuries.

Correct this was never a project meant to compete with any modern bike, or compete at all. But with the prices of some of these modern bikes,  and I know a lot of people that can't afford them. I bet a novice rider, could hit the trails for fun, for years on this bike, and never be unhappy. It would need basic maintenance, and that air-cooled 2-stroke engine, will probably last another 20 years. I mean my total investment is in the hundreds, low hundreds.

[Patrockyj]

16 hours ago, breakwellmz said:

That`s a shame mate.☹️ 

You have ridden it i hope, what`s it like? I`d forgotten about some of the unusual `features` it had until reminded by your photos- countershaft disk brake, constant chain tension, (early) USD forks. It looks good.

Taking her for a ride this weekend, hoping to get some video. I'll be forced to be hold the camera and let somebody else have the fun

[Patrockyj]

I find it amazing that some of the factory parts on his bike are stamped KTM, apparently atk did use some ktm parts.

[Eccentric]

2 minutes ago, Patrockyj said:

I find it amazing that some of the factory parts on his bike are stamped KTM, apparently atk did use some ktm parts.

Yep.  IIRC, the front wheel/hub/brake are KTM parts.  Possibly the forks and tripple clamps.  Been too many years for me to remember for sure.  Somewhere........I have the Dirt Bike magazine review of the 1990 406 packed away in a box of 'vintage' magazines I kept from my youth....

[Patrockyj]

3 minutes ago, Eccentric said:

Yep.  IIRC, the front wheel/hub/brake are KTM parts.  Possibly the forks and tripple clamps.  Been too many years for me to remember for sure.  Somewhere........I have the Dirt Bike magazine review of the 1990 406 packed away in a box of 'vintage' magazines I kept from my youth....

Front fork is definitely a KTM, that's how I found seals for it.

[Patrockyj]

2 hours ago, Eccentric said:

 

That looks like the Mikuni that originally was on my 1990 406.   With the float bowl off and the floats removed, you'd be able to see if it has a pilot circuit or not.  The main jet is in the center of the bottom of the carb body.  The pilot jet is smaller and offset from the main.  Both are brass.  Main has a hex head, while the pilot has a slotted head.  If it has a pilot circuit, I'd use it.  If it doesn't...........I'd replace it with a Keihin PJ or PWK carb. 

 

The Mikuni TM38 in this pic has a pilot circuit.  The pilot jet itself is missing.  It belongs in the threaded hole offset towards us from the main jet.  The non pilot circuit TM's don't have that threaded hole.  That pressed-in brass tube near the airbox spigot end of the carb body leads to the air screw.  Both the pilot and non-pilot TM's have this.

 

 

This TM38 carb body is of the non-pilot type.  It is also missing the main jet in this pic (it would go in the threadded hole in the center). 

 

 

 

I have no experience with the chinese PWK copies on eBay (many of which are dishonestly labeled as 'genuine' Keihin carbs from Sudco).  This is a pic of real Keihin PJ series carb like I used on my 406.  They were on many Honda motorcross bikes and all TRX250R quads.

 

 

 

 

 

Here's some eBay listings.  Some are listings for used, genuine Keihin PJ series carbs.  Most are listings for new chinese copies of  Keihin PWK carbs.  The PWK is an evolution of the PJ.

 

https://www.ebay.com/sch/i.html?_nkw=cr500+carburetor

 

 

 

Thank you for a very complete and easy to follow guide.

[Piney Woods]

Much better seals can be found at a bearing supply house, at much better prices also. It will be a fun bike to play on. I thought maybe you might go the restore and race route. Have fun.

[slotracer577]

I had one of the later ones with normal brakes. The brake pads were Suzuki rm, forks were WP. I had to replace the rear brake rotor as the factory ones were from really soft metal. Used a cut down rotor from a Kawasaki street bike. A huge improvement in wear. The head had also been welded and recut to have a more modern squish band. Great bike until it grenaded a piston. Took out the crank and cylinder. Far to expensive to replace, so it got donated to another 406 owner for parts.

[Singletrack_rider]

I just picked up a 96 ATK 406 a couple days ago. It's probably going to be parted out. Bike is mostly complete but needs a piston. I have no idea of the bottom end condition.  I would get it running but don't really see a point. There's no value on the used market for these bikes. I bought a pile of bikes from a guy for next to nothing otherwise I would not have bothered.

[Patrockyj]

16 hours ago, GreenMT_Rider said:

I just picked up a 96 ATK 406 a couple days ago. It's probably going to be parted out. Bike is mostly complete but needs a piston. I have no idea of the bottom end condition.  I would get it running but don't really see a point. There's no value on the used market for these bikes. I bought a pile of bikes from a guy for next to nothing otherwise I would not have bothered.

It's actually worth more than Parts because it is a 65 + horsepower 2 stroke in a 210 lb frame, whereas a 2019 CRF450R has 10 less horsepower and weighs 35 lbs more just saying (updated)

Edited February 9, 2019 by Patrockyj

[Patrockyj]

On 2/1/2019 at 10:20 PM, Patrockyj said:

I'm reviving a 91 Atk 406 mx that was left for dead, in the snow of Colorado. So I have found a few repairs that save this bike from scrap as parts are super pricey. This is not a restoration, this is intended as a bike to be ridden and 100% functional with not spending tons.

 

1st the kickstart knuckle is not hardened steel, and strips easily. I searched for this part and only found them in the $400 range. Easy permanent fix, that maintains serviceability of the clutch. Simply drill the Kickstart knuckle 5/16ths bit see pictures attached, and tap with a 3/8-16 tap, the use a 3/8" x 3/8" Allen set screws for less that a dollar. The only hard part is, now drill a 3/8" in the Kickstart shaft 1/4 inch deep, any deeper and you will hit the gear shift shaft. Pictures attached. This works exceptionally well as the setscrews are hardened, so is the shaft so it does not cause damage. And can be removed very easily. 

2, the viewing window on the master cylinder was cracked and I could not find, new factory part was $180 the $3 fix on this is to take out all of the plastic and clean it exceptionally well, cover the hole from inside of the cylinder with single piece of duct tape, stuff the master cylinder with paper towel to support the tape. make some one minute epoxy, and fill the hole with a little bit over full to cause a bubble see the attached pictures, I have used this trick over gluing a nickel or dime in its spot, when this dries it's clear enough that you can see the brake fluid level and will not corrode. I have done this for years never had a leak.

Fyi I was a ASE auto mechanic with over 20yrs experience, but not a bike tech, so take the advice or not. I just hate seeing vintage bikes go to the dump cuz the rider can't afford or find parts.

 

I hope this helps at least one person that cannot find parts.

 Update on the master cylinder, the epoxy fix was 100% no leaks, but the brake, did not feel right, meaning strong pull at first then one out of 30 was too soft. I won't ride, or put a bike on the trail, if I don't have 100% confidence in the brakes. Brakes are priority #1, so I searched for the factory part and hell no, $390. Found one with the same banjo fitting, for ktm, which, this bike used for the caliper Fork front wheel and rotor from the factory, so I ordered it, for $45.  I figured if everything else on the front was KTM let's just finish it off. Lol. And that is the last part everything else is done. I'm hoping to post a video of her running shortly. P.s. I am shocked coming from the automotive world, and doing bikes as a hobby. In the difference that repacking exhaust really made. WOW, and I learned, never to adjust anything with the timing or carb, unless you have repacked the silencer on a 2 stroke 1st. After repacking (I drilled the rivets out and replaced with sheet metal screws to make the silencer very easily serviceable. The end of this one was damaged. Now its easy). The 8$ repack was better than a tuneup, it will now be the first thing I do on any bike I get.

Edited February 9, 2019 by Patrockyj

[2 Stroke Boogie]

I néed to do the silencer on old Frankie. Thanks for the reminder.

Looking forward to a video of that beast! ?

[Patrockyj]

10 minutes ago, HelenaHanbasket said:

I néed to do the silencer on old Frankie. Thanks for the reminder.

Looking forward to a video of that beast! ?

Np, btw at my house amazon prime offers FMF 2 stroke exaust packing for same day free delivery ($7.99) I am afraid I am becoming a prime snob, I can get my dirt bike parts, gold prospecting gear, and my 16 yr old daughter's magnetic face mask (whatever that is, sounds cool) all delivered same day lol

Edited February 9, 2019 by Patrockyj