HONDA EXPRESS SR: Mega Performance Thread

Keegles (brother) and I recently bought matching blue 80's Honda Express SR scooters at separate auctions, by coincidence. We are in the process of rebuilding these bikes to do 40's - 50's and intend to have some sort of informal race.

I decided to start this thread to gather knowledge, since there doesn't appear to be a lot of documentation for these bikes. Granted, they are scooters, but they descend from the Hobbit crankcase engine design and are pretty fun. Factory kickstart, variator, and electric start... sweet!!

More to come.

Re: HONDA EXPRESS SR: Mega Performance Thread

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)

Re: HONDA EXPRESS SR: Mega Performance Thread

Performed a hillbilly-ish repair on some of the plastics today, "drift stitching".

Re: HONDA EXPRESS SR: Mega Performance Thread

Megasaurass wRexckses /

Does the mega performance thread come in other colors?

Re: HONDA EXPRESS SR: Mega Performance Thread

> Sçütaur Rackęt Wrote:

> -------------------------------------------------------

> Does the mega performance thread come in other colors?

The seat covers do!

https://www.ebay.com/itm/HONDA-NX50M-Express-SR-Seat-Cover-1981-1982-NX50-in-25-COLORS-PATTERNS-ST-W/162761572309?hash=item25e5587fd5:g:MKQAAOSwwn9ZedzH&vxp=mtr

Re: HONDA EXPRESS SR: Mega Performance Thread

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.

Re: HONDA EXPRESS SR: Mega Performance Thread

> DPC Ryan Wrote:

> -------------------------------------------------------

> [...] nothing is really uncharted territory.

I was unable to find a consensus on aftermarket belt usage, among other things, and felt a centralized space for information may be beneficial to others. Let's promote knowledge sharing!

Interesting about your belt width / final drive affecting top speed. Did you also change front wheel size as well?

Re: HONDA EXPRESS SR: Mega Performance Thread

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

Re: HONDA EXPRESS SR: Mega Performance Thread

> Toledo Riot Wrote:

> -------------------------------------------------------

> We then swapped to the thicker belt, and it just couldnt rev out and

> only did 32ish

The Gates BX27 belt, or a different one? Did you guys save any pics of this bike / creation? Sounds fun!

Re: HONDA EXPRESS SR: Mega Performance Thread

> Doug Wilhelm Wrote:

> -------------------------------------------------------

> > Toledo Riot Wrote:

> > -------------------------------------------------------

> > We then swapped to the thicker belt, and it just couldnt rev out and

> > only did 32ish

>

> The Gates BX27 belt, or a different one? Did you guys save any pics of

> this bike / creation? Sounds fun!

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!

Re: HONDA EXPRESS SR: Mega Performance Thread

We have failed you Doug

zerosstuffs.jpg

Re: HONDA EXPRESS SR: Mega Performance Thread

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.

Re: HONDA EXPRESS SR: Mega Performance Thread

Kinda same here. I never got too into it, but the stock belt was better than the bx27, but there's no other options. Sucks cuz the belt was probably the best upgrade to the urban express but its a downgrade to the sr.

I'll just share my whole story briefly. Got one - all seemed to work. Kept it mostly stock til the belt started stripping apart and it was mid 30s.

Swapped the belt to bx27 and it was more restricted on top but it was the best or well at least basically the only one you can buy. I tried some others but I don't remember what, they all slipped or revved out without getting decent speeds.

I was still running the oil injector. Injector died. 3rd time I learned that lesson, but I thought hey it's working and Honda is good. Nope. Don't trust oil injectors. It got screaming super hot and started detonating and revving uncontrollably. Wow.

Put on a 77 iron kit, or nah, was stockoshocko. all else stock but jetting and the belt. Even pipe. Mid 30s. Stocko is useless except as a stock replacement. There's no shocko in there, but it was a cheap new cylinder. Mighta changed weights I forget. But I reused the circlip cuz I'd ordered 10mm clips and got 12s so I reused the old ones. 2nd time I learned that lesson. Don't reuse circlips. Buzzz BUZZZZZZ. ZZZINK. Womp womp.

Replaced with a DR, way better feeling, more power all around, low-mid 40s regular. But HOT, no matter how I geared. Put on a jammy pipe, almost zero performance gain- useless pipe, but flowed more and let the heat out and it overheated a lot less. Custom mounted the pipe and it pointed up. Sold to my sister in law and the pipe pointed up and filled with water. It's been sold and ended up somewhere in Pittsburgh

Re: HONDA EXPRESS SR: Mega Performance Thread

Jack Rutherford /

good stuff!

Re: HONDA EXPRESS SR: Mega Performance Thread

Will_D and Andy, thanks for the info and stories!! I love the wheelie photo.

I debated on the DR kit and ended up purchasing the Malossi 70cc liquid-cooled kit for my build, still in the mail. I'll be using an electric automotive water pump. Keegan installed his Wizard kit last night without any issues, except his base gasket spacer from Treats was bent.

Looking into final drive gearing, does anyone know if the NU50 gears will swap with NX50, and vice versa? I'm also looking for a specific tooth count in the final drive transmission assembly. (My knowledge on gear ratio tuning is limited)

Here's what I found from the service manuals:

Service Manuals

http://www.motorscooterguide.net/Manuals/Honda_NX50_Service_Manual.pdf

http://qt50.net/wp-content/uploads/2016/01/nu50-geninfo-lub-maint.pdf

Re: HONDA EXPRESS SR: Mega Performance Thread

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:

Re: HONDA EXPRESS SR: Mega Performance Thread

huh! neat! this is good stuff. I always thought they were basically the exact same inside but that appears to not be the CASE!! hahaa lol pun intended

Re: HONDA EXPRESS SR: Mega Performance Thread

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

Re: HONDA EXPRESS SR: Mega Performance Thread

Keegan Wilhelm /

Hola! I am doug's bro with the other express. The plastics are in rough shape, but mechanically, it is solid. I just installed a kit on mine, and wanted to post an update on it.

I bought the *70cc wizard kit, dual stage plastic boysen reeds, **vm20 w/ intake, and ***technigas Q-tre pipe. I also purchased a butt plug for the oil injector. Take that trash off and hang it on your xmas tree, or jam it in your drywall and use it as a coat hanger.

*On treats site, they recommend using a base gasket spacer so the piston clears the exhaust port. I used the .8mm base spacer, and 2 base gaskets, one on either side of course. Also, when tightening the exhaust bolts down (if you dont use studs), make sure you have the correct length bolts! If you don't you'll be drilling them out like I had to. An M8 tap works perfect with a 9/32 drill bit.

**The intake I purchased was this one from treats. (https://goo.gl/ieVx22). While it did bolt up, the intake hole is in the wrong spot on the reed cage. About half the hole is covered up by the gasket and reed cage. As of this post, I did order the correct intake, which is the one for the urban express, but it hasn't arrived yet. (https://goo.gl/YDT9Yc). The vm20 comes with a 185 main jet. With my current setup, it will scream allllll the way to 30-35mph, and start fuel starving real bad. Again, ordered parts, but haven't arrived yet.

***I orignially bought the q-tre pipe for a scooter I have, but I gave it to my friend when I got the express. I hacked the header off and welded on the header from the express pipe to make things simple. I have it mounted upright (pics later), but may reorient it later.

Re: HONDA EXPRESS SR: Mega Performance Thread

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:

Re: HONDA EXPRESS SR: Mega Performance Thread

I'm late to this thread but super stoked about it! I'm the guy with the SR in toledo and man those bikes are fun. as andy said, 14 bing and the biturbo were cool enough, and the bx27 belt ruined it. treats has a b26 gates belt that is advertised for NX50 but i have yet to try it. i popped my rear tube and havent gotten a replacement yet so havent been too gung-ho on working on it. i threw some hobbit kit from Dos cycles on it as well.

Re: HONDA EXPRESS SR: Mega Performance Thread

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.

Re: HONDA EXPRESS SR: Mega Performance Thread

will you gotta get on that stack flapper tech yo. keeps your pipe from fillin' up with water. duh.

Re: HONDA EXPRESS SR: Mega Performance Thread

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)

(edited)

Re: HONDA EXPRESS SR: Mega Performance Thread

Mikey Antonakakis /

Which regulator/rectifier are you using? I assume your stator is single-phase? I've had great success with the trail tech unit on my Peugeot, although I still dream of converting to 3-phase some day...

To get the most performance out of your setup, you will probably want a pretty high clutch engagement and tune your variator slightly higher than that. Just from pics the Malossi kit doesn't look to have too crazy of a blowdown area, so this might not be a huge issue. But if you are looking to pump your top speed, obviously your lack of gearing tunability will be an issue - your speed increase will come from higher revs.

If you have a chance, measure the exhaust and transfer timing. If you get exhaust timing up in the 180-190 range (if it's not already there), the kit looks to have good enough transfers to make really good power, albeit way up high in the rev range - but that's the beauty of a CVT, hence my suggestion for focusing strongly on clutch/variator tuning once you get the bike running solidly. That pipe + some exhaust porting should get you some really awesome performance.

Re: HONDA EXPRESS SR: Mega Performance Thread

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

Re: HONDA EXPRESS SR: Mega Performance Thread

> Which regulator/rectifier are you using?

I chose this over-priced model from Treatland. I wanted one with a rectifier built in since I will be charging a small battery to run my accessories from. I read that I will have to modify my stator to have a floating ground.. not stoked or anxious for that process.

> I assume your stator is single-phase?

From my understanding, yes. I have this model HPI from Treatland.

> lack of gearing tunability will be an issue - your speed increase will come from

> higher revs.

Ah ha! This is where I can disagree. I have purchased a set of NU50 rims-- they are considerably 'taller' and will allow me to play with gear ratios :) The wheel spline is the same, I'm not yet sure about the brake pads. Still waiting on the rims in the mail.

> If you have a chance, measure the exhaust and transfer timing.

Will do!

> you're going to race your brother who has a wizard kit?

Haha...... yeah. Our bikes are so completely different. It's alright. It will be fun to contrast / compare.

> Where'd you put the radiator?

I currently have it ziptied to the handlebars. Classy, right? I plan to make a bracket to attach near where the front grocery basket sits, such that I can keep my upper plastic bodywork. I should have the replacement Mishimoto radiator tomorrow.

Right now, I had to remove the lower bodywork in favor of BMX pegs because one of the kit water ports interferes with the metal frame for the bodywork (but is removable... RE: swapped for BMX pegs). I plan to investigate modifying this frame to keep the lower bodywork as well. Yay plastics.

PICS INCOMING LATER

Re: HONDA EXPRESS SR: Mega Performance Thread

Keegan Wilhelm /

> you're going to race your brother who has a wizard kit?

>

> Haha...... yeah. Our bikes are so completely different. It's alright. It

> will be fun to contrast / compare.

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.

Re: HONDA EXPRESS SR: Mega Performance Thread

My bike is sooooo minty. I'd like to go h2o but I don't want to drill any holes in the bodywork. May have to stick with air cooled

Re: HONDA EXPRESS SR: Mega Performance Thread

> It'll be like comparing a Honda Civic to a type r Civic

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!

Want to post in this forum? We'd love to have you join the discussion, but first:

Login or Create Account