1987 project questions

[bprolo28]

I’m new around here and I just picked this 1987 KDX up last week and I’ve got some questions for the smart folks here.

First: I pulled the pipe on this bike after I got it and the cylinder and piston look ok, and the bike has really solid compression according to the compression tester in my leg. That said, there is one vertical mark on the cylinder that caught my eye, and I think after this season I’m going to want to do a top end and re plate that cylinder. Most of the sources of pistons for these bikes say they’re the same for our c series bikes as the newer ones, is this right? I don’t want to stick the wrong piston in it, but I also wouldn’t mind a newer coated piston.

Second: I see RickyStator sells a 65W lighting coil for these bikes, would that get me into the range needed for a 12V conversion. My understanding is that these come with a 35W lighting coil from the factory? I assume a regulator is needed to do the 65W and 12V?

Lastly: The flywheel magnets. Seems like I’m going to want to address these sooner rather than later. Looks like I should be encasing them in epoxy, does anyone have any pics of this process from when they did it? Is it really just as simple as filling the voids between the magnets and calling it good, or is it more involved than that?

Anyways, glad to be part of the air cooled kdx crowd!

[KDXGarage]

Welcome to kdxrider.net. Congratulations on the '87 KDX200.

As far as Wiseco pistons, 1986 - 2006 are the same.

Ricky Stator once told me that they sell a regulator to go with the updated stator. It was 12 volt, so headlight and taillight would need to switch I guess.

There is a post here from a Mr. Swinehart, I think. May he RIP. He actually had some magnets made. I think his posts showed the encasing of the magnets.

Again, congratulations on the '87. Grease the swingarm and linkage fittings!

[Kipsy]

I have no experience with the Regulator Rectifier ignition kit, but I plan to buy this when I get to the motor portion of my KDX build. It comes with an 11 oz. flywheel. What was the stock weight?

It also has a 60 watt lighting coil. Nice feature. Again, though, I don't know of anyone who bought this so I have no idea if it all actually works. It would be nice if it does...

https://www.regulatorrectifier.com/prod ... r-cdi-coil

Nice bike. I have an 87 and an 88. The 87 putters around the property just fine. I ride it in first and second gear with my 5 year old on his little electric dirt bike. It has beautiful putting manners! An 85 KX250 seat puts the ground even closer. It'll get restored some point further down the road, with an 88 KX cartridge fork and 86 KX rear disc set up I have sitting in a corner. My 88 KDX is white and is completely disassembled on my work stand, as it has been for years. Progress is slow, especially since an 84 IT200 shoved it's way in line and is getting refurbished first.

Ask any questions you have and good luck with your build. These bikes are a fun piece of history, and although they are not as fast or well-suspended as a newer bike, they have a friendly low-to-the ground light-weight feel that is great for tight trails or riding with 5-year olds.

[Kipsy]

PS - the magnets are still on ebay I think, listed under the title of "Tecate" magnets I think.

[KDXGarage]

I have no clue on the flywheel weight.

Thank you for mentioning that about the magnets. It is great that she is continuing with them.

https://www.ebay.com/itm/235151245802

[bprolo28]

Bike has been running nicely, starts easy and pulls hard. I do have some fine tuning to do though and have a couple questions. When the bike is cold, idle is very high on choke, I’ve been turning choke off right after start up. This may be normal, not sure. Idle is still a little high when cold off choke, but settles down when warm. However, when it’s good and hot, the bike idles high coming off of a rev(maybe 500rpm high) for a few seconds, then comes back down to normal. It isn’t really a rev hang, as it comes down off the rev pretty normal, but just sits a little high for a few seconds after.

For reference, I’m running 32:1 amsoil interceptor, 91 no ethanol. Stock main and pilot, needle all the way lean. If the needle isn’t all the way lean it doesn’t like to rev out, although it seems odd to me that it’d need to be on the last needle clip. I have not checked float height as I can’t find the spec(if anyone has a pdf of the c series service manual let me know). This seems like a lean condition to me, but I’m no jetting expert. I have checked for air leaks as well and found none. I did try a 310 main(stock is 320), and I liked the 320 better.

If anyone has some wisdom let me know, otherwise I’ll just keep fiddling.

[KDXGarage]

I just turn the choke off as soon as it is running. I let it warm up for a few minutes before rolling off.

On a "new to you" used 37 year old bike, you need to check everything. Carb wear, reed wear, engine wear, etc. can all be a factor. It's not like it was running perfectly for years, then all of a sudden, something changed. It is tough to diagnose a "I just got this" bikes over the intnernet.

[KDXGarage]

I just turn the choke off as soon as it is running. I let it warm up for a few minutes before rolling off.

On a "new to you" used 37 year old bike, you need to check everything. Carb wear, reed wear, engine wear, etc. can all be a factor. It's not like it was running perfectly for years, then all of a sudden, something changed.

[bprolo28]

Totally understand. I figured there wouldn’t be an end all be all answer to that issue, but I thought I ought to ask just in case it sounded to someone like I was missing something simple. I’m relatively new to two strokes, so it’s a little tough to know when I need to dig further, or when it’s a surface level issue that I haven’t learned how to identify yet.

For reference, the carb and reeds are in good shape, and I checked the top end as best I could from the intake and exhaust ports, and while it isn’t spectacular, nothing jumped out at me as being an issue. I do plan to do the top end in the semi near future though. I believe this is a relatively low hour bike though, just from the condition of everything else on it. While I have the motor apart, I think I will do crank seals as well, just to be safe.

[Chuck78]

I’m new around here and I just picked this 1987 KDX up last week and I’ve got some questions...

...there is one vertical mark on the cylinder that caught my eye, and I think after this season I’m going to want to do a top end and re plate that cylinder.

Most of the sources of pistons for these bikes say they’re the same for our C series bikes as the newer ones, is this right? I don’t want to stick the wrong piston in it, but I also wouldn’t mind a newer coated piston.

Anyways, glad to be part of the air cooled kdx crowd!

Although Wiseco are nice pistons, I especially prefer the Wossner forged pistons for our bikes, as they have coated skirts, whereas Wiseco does not coat the skirts on the KDX pistons unfortunately, despite other pistons that they manufacture having coded skirts.

This is my recommendation, 1986-2006 KDX200 C, E, & H series:


https://wossnerpistons.com/collections/ ... ducts/8093

I did just notice that it shows they are out of stock on the A, B, and C size for stock bores, which is unfortunate. That was the other bonus of going Wossner instead of Wiseco. Wiseco seemed to only offer a 70.00mm bore size KDX220 piston, and a 66.00mm bore size piston for an '86-'06 200, no A/B/C oversizes to compensate for bore wear in the stock cylinder bore size.
Wossner shows 66.50mm bore +0.50mm oversizes & 67.00mm bore +1.00mm oversizes available. I'd inquire with them also check with Wiseco to see if they offer the A, B, and C stock bore sizes (66.00mm, 66.01mm, & 66.02mm sizings for "stock" bore).

[Chuck78]

It'll get restored some point further down the road, with an 88 KX cartridge fork and 86 KX rear disc set up I have sitting in a corner.


Ask any questions you have.

These bikes are a fun piece of history, and although they are not as fast or well-suspended as a newer bike, they have a friendly low-to-the ground light-weight feel that is great for tight trails or riding with 5-year olds.

Kipsy, are you saying that a 1986 KX (125? 250???) swingarm will swap onto these '86-'88 KDX200's, in order to have a bolt-on rear disc upgrade?


Or does the swing arm require some modification?
Regardless, that's very good news to my ears.


I don't own an 86-88 yet, but if I did, I would consider selling my 1977 Suzuki PE250 in order to have and even more usable vintage air cooled woods bike.
I truly believe that the 86-88 KDX 200 is the absolute pinnacle of all air cooled vintage woods bikes. Awesome suspension linkage design which is mounted above the swing arm to keep it out of the way of logs, rocks, and obstacles, as well as having grease fittings installed from the factory. The shocks could use hard anodizing internally and a Race Tech Gold Valve and a new hose, sealhead, etc, but then they will be up to spec of basically any modern shock.
They're perhaps the only air-cooled bike that I know of that ever came with a power valve assembly, which makes them very unique and give them a bit of an advantage for some in terms of woods riding and reliability.
They have a plated cylinder, and while although the original plating was not up to modern standards, any bike of that age is likely due for a replating which will be done in Nikasil which will last for a very long time...
And...they had a front disc brake!

The 1988 or 1989 KX forks would have been a really awesome factory upgrade on those things, the ones that were 46 mm cartridge forks that were right side up. Those came out at the end of this model run though, and unfortunately were not used on any other bikes other than that one or two years of KX. I thought it was 1989 but I could be mistaken.







If I had an '86-'88, it'd get some kind of rear disc setup, and Showa 43mm conventional forks from a Honda XR400R (.40kg or .41kg springs stock) or '96-'98 Suzuki DR350 43mm forks (.39kg springs stock), with Race Tech Gold Valves. Those forks will bolt directly into 95-06 KDX triples which will bolt directly onto the C Series 200.... Add disc brake and donor wheel/axle offof the fork donor, and you're really set up... Tubliss, gummy tires, aftermarket pipe, probably have the cylinder board out 1 mm and have some mild porting work done to it, and possibly whatever aftermarket pipe offering is available, I believe Dynoport, Gemco, or another semi custom pipe maker offers a pipe for these bikes. I probably make a custom skid plate from delrin or perhaps a cutting board from a thrift store...
Add a Lectron HV series carb, or perhaps a SmartCarb SC2 36 or the upcoming SC2 35 that they are talking about designing specifically for the KDX, or a Lectron Billetron Pro Series (these and the smart carbs will have the choke on the incorrect side for the air-cooled KDX).

These bikes are absolute woods weapons when set up properly.