MOPED ARMY

One of the bikes had a destroyed drive belt (over 7,000 miles!). We have not been able to find an exact match for the belt, as it is different from the Hobbit / Urban Express and is no longer in production. Here are the listed part numbers from Partzilla.com:

BELT A, DRIVE (BANDO) - 23100-187-004

BELT A, DRIVE (MITSUBISHI) - 23100-187-003

Gates BX27 belt

I purchased a Gates BX27 belt today and will update on how it works out. After researching, it appears users have tried multiple belt types, however we were unable to find a consensus on what worked the best.

Here are the specs on the Gates BX27:

(edited)

Does the mega performance thread come in other colors?

Really most urban express information is identical. The differences are in the belt, the final drive ratio, and the wheel size. Aside from that nothing is really uncharted territory. I ran a BX27 and it worked fine. I also had a 14" wheel on it though and the combination of the BX width belt and the taller final drive made for a dog of a bike below 20mph and a rocket ship well past 40.

So we have one of these bikes in Toledo, we added a Bing 14, which is actually pretty easy, use a stock tomo header (a35 since they are smaller 18mm) bolts directly onto an Urban or other express intake, which fits on the SR motor and is larger has better flow then the SR version, and spigot mounted a Bing, sure you could use any carb, thats just what we had laying around, we welded a biturdo to the stock header, and with the stock pipe that got the bike to 36 with pretty good bottom end

We then swapped to the thicker belt, and it just couldnt rev out and only did 32ish

Sorry I was gonna type more, but Im at work, ya it was the bx belt, it was just to much for the stock cylinder, it really ran better with the stock belt, so we put a kit on the bike....then got a flat, and havent touched it in a few months

As far as the carb solution, Ill check with another Zero and see if I can find some pictures for you!

Well I had the engine on an NC50 so yes the front wheel was larger as well. Even with super light weights the base ratio was just so much that I couldn't even get into the pipe before 18-20. An aftermarket clutch would have helped but it would have to slip pretty hard for an extended time to do a lot better.

good stuff!

I had a chance last night to compare the PA50 cases to my NX50. It looks like the only major differences are the side transfer shapes, and the top transfer on the NX50 has a way smaller "flow area" (final two photos). See below:

I feel like the NX has the better stock transfer design, looking at the two of them now.

Got my crankshaft back today. Just to recap, the conrod installed into the NX50 (Express SR) crankshaft was from an aftermarket 'stuffy race crank' for a PA50 / Hobbit. I forgot to ask if any material needed to be shaved from the halves to accomodate the extra thickness of the conrod (aftermarket rod uses thrust bearings, stock does not).

I would still like to have / make adapter pieces to just use the PA50 crankshaft, however I wouldn't have access to the machinery myself for a few more weeks at minimum, and the guy on MA who made his own adapters hasn't yet made additional sets available for purchase.

Here's a pic:

If you are going to have a race you gotta invite richy rouser to the party. He's got a solid little Sr build. I have one as well but it's bone stock... For now. One suggestion I haven't seen posted yet is get a gy6 clutch. There aren't any clutch springs for the stock clutch. Best thing to do is get a good aftermarket clutch. I put a stock gy6 clutch in with red springs but the stall speed was still pretty low. The clutch shoes are just really heavy. Stage6 and others make nice clutches with lightened clutch shoes.

Wanted to post an update-- it's been awhile, fam. Photos to come later.

I have assembled my engine and was able to start it for the first time. It runs surprisingly well! The throttle is responsive and the pipe sounds nice. It idled without having to tweak the carb, that was a nice feeling. I set the HPI timing to the default setting, according to the instructions that came with the ignition kit. I will dial this in at a later time.

Speaking of a later time, I am unable to test ride right now. Weather aside, my 'MLM reinforced radiator' from Treats had a defective + bent neck and leaks coolant, despite swapping caps and attempts to level the sealing surfaces. I am also waiting on my voltage regulator / rectifier in the mail. I have an electric AC Delco water pump ($45 from Amazon) that runs off of 12v, currently powered by a cheap little scooter battery instead of the HPI.

In terms of replacing the defective radiator, I researched for another with an inlet/outlet matching the spigots on the Treats radiator. The Treats one has matching inlet/outlet ports of 16mm / .63". I settled with a Mishimoto closeout model for a KX450F for ~$30 that I'm waiting on in the mail. In the future I will not be buying another Treats radiator due to price and quality control issues. (EDIT: I see the Mishimoto has had a price adjustment / restock to $120. Ha!)

The stock vacuum petcock will not work without vacuum on this bike. I deleted my vacuum lines, so I decided to buy a chinese replacement with the same thread specs (16mm x 1.5mm). I attempted to drill a hole through the vacuum diaphragm in the stock petcock and accidentally drilled through the whole thing. Schwoops.

Regarding the intake / carb, I chose to use the stock plastic reed spacer, however this puts the carb really close to the frame. To avoid issues when the frame moves (shocks), I made intake spacers + gaskets for the carb to push it out a little. This is not intended as a permanent solution.

The pipe fits, but the bracket hole for the crankcase is not in the right spot. I hacked off my electric start section of the crankcase to fit the H95 pipe, so I was a bit salty when I discovered that the pipe doesn't fit without modification, esp since it costs nearly $300. (the NU50 motor, what this is intended for, has case holes in the same spots as the NX50, so it's a quality control issue with MLM). I drilled a hole in my case for the pipe bracket and just made it work.

To fit the Hobbit HPI, I had to drill/ tap two holes for the backing plate bolts. This took maybe 5 min, but I had to buy a cheap tap set (grumble, grumble). It just worked the first time I started the motor. I was genuinely surprised.

***GENERAL SPECS***

- 70cc Malossi H20 cylinder Kit (no porting)

- H95 NU50 MLM Expansion Chamber

- .4mm Carbon Reeds

- Mikuni VM20

- MLM VM20 NU50 intake

- Conrod from stuffy PA50 crank

- Hobbit HPI mini rotor

***LINKS***

Mishimoto Radiator

China Petcock Replacement

AC Delco Water Pump

Cheap $12 TDC Tool

NU50 Battery (wrong size but fits in battery tray, really need NX50 battery)

So this is your setup but you're going to race your brother who has a wizard kit? I feel like I can predict the outcome of this race. Need pics. Where'd you put the radiator? That's been my dilemma with an h2o kit

I don't understand this question. But really, at this point, I'm going to automatically lose. There's going to be no comparing / contrasting the two. It'll be like comparing a Honda Civic to a type r Civic. They're completely different bikes at this point. If you think an air cooled kit with minor mods / meh pipe is going to keep up with a bike that Doug has put $1500 into, think again.

I disagree with this statement. While I have invested more in parts, seals, bearings, gaskets and whatnot, I think most of the performance things I bought are overpriced crap. Assuming gearing stays the same, the only factors that really matter between the two bikes in a drag race is horsepower and weight. Your expansion chamber is about the same size as mine and you have the same carburetor, and aftermarket reeds. At least for me, this will be enjoyable to compare.

Also, Money != Linear performance. Based on the parts used, I don't think i have a significant advantage. We'll just have to find out!

If I could go back Jawanna, I'd stick with a DR!