I like to start a thread for whichever bike I am building at the time. I've done this on other forums and it has turned out well.

I recently picked up a 1998 XR 70 to use as a pit bike so I can get around the paddock during track days I do on my R6. I got the bike for $300! It's was in decent running condition.

I will be posting all of the work I do to the bike, how I did it in some cases, etc. I hope that eventually this thread will be a tool for other 70 owners to refer to, etc.

On with the pics!!

She smokes a LOT, but runs strong!


When I got the bike, the front end wasn't the straightest. Looping it in a second gear wheelie only made it worse.

The day I picked it up!



Here she is doin her job at the first track day I brought it to. It's a long walk to the john!!

Mod list:

• Long shifter
• Adult sized rear spring
• Cylinder breather tube setup
• Skull and cross bones sticker on number plate
• 24 mm Mikuni Carb
• 24mm Intake manifold
• Aftermarket throttle cable
• Aftermarket 40mm cone filter

Info about the carb upgrade I did on it:

This is the reason I started this thread. I was getting fuel pissing out of the overflow hose on the carb.. It was pretty annoying having to turn the gas off all the time, etc. This occurred after transporting it 3 hours to the track. I pulled the carb off in my garage, and the bowl had some grit in it, etc. The float wasn't mounted to the float needle correctly, so I fixed that up quickly. I see it had a new float needle, but apparently wasn't in the groove right.

After cleaning out the emulsification tube, main jet, and pilot jet, I reassembled the carb and put it back on the bike. I still wasn't getting great performance at all. The bike would only reach 50% RPM unless I put the choke on. I had already ordered the 24mm Mikuni from an Ebay vendor in CA.. When it came in I realized I needed a larger intake manifold. That is shown in the image below next to the carb. So I ordered that up too!


Next I quickly realized that the OEM throttle cable has the carb cap attached to it.. So I started looking on ebay again and ordered a throttle cable.. I also located a cone filter for it in 40mm for like $11.. I wish I had known I needed all this to begin with! Woulda had this pig running last week! I was browsing an ebay store and saw intake manifold gasket kit, so I ordered that also.. <sigh>

So for the bigger 24 mm Mikuni carb kit you need:
Compatible throttle cable
Intake manifold
Intake manifold gasket kit
40mm air filter
24 mm Mikuni Carb

The intake manifold is angled to the left, so that the big ass carb has clearance. Otherwise, it wouldn't fit under the frame! The carb is as big as the cylinder!! LMAO


The carb came with an adjustable needle in it already. I set it 2 lines from the top. It was set two from the bottom, and I felt like on a stock motor, it would be WAY too rich. I am not too sure if that's the case, cause without an air filter, it would bog badly. I covered the carb opening with a rag and two fingers to restrict the flow a bit, and it revved up SO strong! My air filter will be in today. I'll install it and get to tuning the bike properly for epic wheelies in my street!

More updates to the Carb project coming SOON!

Reserved for future updates.

I just had the flywheel on a XR100 lighted by 12 oz. I recommend doing that to your 70. Makes a world of difference for about $60.

Anyone have any fork suggestions? I am pretty sure that's what's bent up front. I would like something stiffer of course. All I find is forks for 50's..

Honestly, I'd really like to put motard tires and rims on this bike with a disk brake setup and some good suspension.

I have already been in touch with the guys at fast50's about a motor kit. This thing blows quite a bit of blue smoke, so I assume it's just valve seals, but with the age of the bike, etc, I am thinkin about a rebuild. Fast50's will give me a GREAT price on the trail master 88cc kit since I already have a carb setup, it will be $285.

I love how everything is SOOOO cheap for these bikes. I'm used to my R6 and spending a damn fortune on that build! You can check that bike out here

fletchman919 said:

AWESOME!!! Thanks for the heads up bro! I am up for anything. Do you have any links or info on where you had it done, etc?

www.firepowerminis.com does the ultralight flywheel for $55 shipping included back to you... I went to a local machine shop and told them what I wanted. I had it back in an hour. Check your local guy first! The XR's with manual clutches have heavy flywheels so that kids don't stall them out as easy. I'm not sure about the auto clutches, but I'm thinking that they are heavy too to reduce the snap.

BTW, you can buy a beefy aftermarket engine complete for around $300-$500. I've not used them, but I've read about many that have. At that price, you can just keep buying new engines.

Check it out. http://tboltusa.com/...5a6a7f81d331080

fletchman919 said:

Awesome! Thanks for the links and the info.

fletchman919 said:

Thanks for this link too! I may consider that. I did see motors on ebay for cheap too. I'm curious about the reliability, etc. I do know that these honda motors are literally 100% copied and produced in China and I assume thats what those are. I'll check into it for sure! At the same time, I am kinda looking forward to trying to rebuild the top end myself with a pal. I think it could be  areal fun project.

Thanks you SO much for your help and all this great info!

No problem. There's guys here that know a lot about your bike. I would check out the XR70 forum and get some expert advise.

fletchman919 said:

Thanks!!

The k&n type air filter is too high flow and the bike just bogs horribly at low RPM. I set the needle as rich as possible and put some tape over the filter to restrict it a bit for now just so I could ride it a bit. It definitely pulls a couple thousand more RPMs and does great wheelies in 1st. And now 2nd gear does a million miles per hour.. Third isnt happening in the neighborhood. LOL Gonna need to regear it ASAP!

So I'll be ordering a foam filter ASAP!

And the carb is a 22mm not a 24. Did some searching on here last night and came up with that. Don't know where I could get a new jet for it. I would love to change the jet for he K&N to work! It's so LOUD now too!!  

FWIW, a baseline setting for the 22mm Mikuni-clone carb at sea level is to use a #17.5 pilot jet, a #100 main jet, the jet needle clip in the 3rd or 4th notch from the top, and a fuel screw setting of 1-1/2 to 1-3/4 turns OUT from seated. Being that is a fuel screw, you turn it OUT to richen it, IN to lean it.

dirtbkr188 said:

Thanks so much for the info! Where would I be able to purchase jets for it? I didn't think I saw anything on this carb other than a idle screw for the throttle idle position. Sounds like it's clearly not a great mikuni carb like I had hoped.  but it does idle smooth, have a working choke, not pee gas out either! LOL

Thanks!

The carb uses genuine Mikuni jets, you can get the main jets HERE, and the pilot jets HERE

The fuel screw is located in front of the float bowl, under the intake side of the carb, and circled in red below...

dirtbkr188 said:

Thanks again!! I just ordered a foam filter for it and will see if I can work the fuel adjustment screw a bit. I will definitely look into the jetting since I'm sure it'll be necessary, even with the foam filter vs the k&N type. And it's certain I'd need a rejet if I did a top end kit on this pig..

The key thing is accomplished tho. No more peeing fuel, no more crappy idle and unpredicatable running. I should be able to get to the bathroom double the speed I did before when I'm at the track now!!

My bike started running REAl crappy. I figured I'd replace the spark plug on it. I have no clue how this thing even ran! This is the most carbon I've EVER seen on a spark plug.


I am looking for some straight forks for this bike. Anyone know of any aftermarket ones that are affordable and sprung for an overweight adult?

Well, the bike runs GREAT after a new spark plug. Still needs to be jetted differently, but runs good!

I'm still getting smoking, and am sure it's valve seals. Anyone have a service manual download link?

Also, I popped the tube in the rear from wheelies with all the new found power and low tire pressure. LMAO

Cool update,you need some taller bars.
Any recent pics?

Bonefrost, on 02 May 2012 - 04:20 PM, said:

Cheers

Any suggestions where to get it? I'm gonna need longer cables then too. Let me know some suggestions. My brake cable is shot, so is the lever. Can  I get tall bars in standard sportbike diameter?! If so, maybe my extra R6 clutch lever can act as a brake to pull the cable. Oh, and drum brakes are AWFUL!!! :lol

I am into sport bikes so I don't know about all the parts for these little beasts. Can I get bars in the same diameter as sportbike bars? I need a new clutch and have a few for my R6's

Edited by ChiefSmokeDawg, 02 May 2012 - 06:24 PM.