Chief's 1998 XR 70 Build Thread
Posted 02 September 2011 - 09:09 AM
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!!
Posted 02 September 2011 - 09:10 AM
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 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!
Posted 02 September 2011 - 09:30 AM
Posted 02 September 2011 - 09:30 AM
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
Posted 02 September 2011 - 09:31 AM
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?
Posted 02 September 2011 - 09:59 AM
Posted 02 September 2011 - 10:10 AM
Awesome! Thanks for the links and the info.
Check it out. http://tboltusa.com/...5a6a7f81d331080
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!
Posted 02 September 2011 - 11:38 AM
Posted 03 September 2011 - 12:56 PM
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!!
Posted 03 September 2011 - 02:01 PM
Posted 03 September 2011 - 02:25 PM
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
Posted 06 September 2011 - 07:26 AM
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!!
Posted 13 April 2012 - 10:07 AM
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?
Posted 02 May 2012 - 01:26 PM
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
Posted 02 May 2012 - 06:20 PM
Any recent pics?
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.