Honda Express Muriatic Acid Wash / Seized Cylinder Repair

How To perform a Muriatic acid wash on a Honda Express NC50 DR Racing 70cc (46mm) cylinder jug.

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Honda Express Moped nc50 1978 engine cylinder repair using Muriatic acid wash technique. Highly caustic and dangerous! Will even dissolve iron. This amateur attempt is used to repair a multiple soft-seized Honda Express Moped cylinder jug. The object is to use the acid to remove the aluminum left by soft-seize on cylinder jug wall. DO NOT ATTEMPT. DO AT OWN RISK. NOT LIABLE FOR ANYTHING SHOWING IN VIDEO.

With all that being said... Here are links to the items I used to perform this Honda express cylinder jug repair:

• Crown Muriatic Acid = $7.29 at Lowes
• Chemical resistant rubber gloves = approx. $7.00 at hardware or automotive store
• Goggles
• Facemask
• Rubbermaid bin
• Baking soda
• Shop towels
• Q-tips
• Water
• Honda hobbit UPGRADE DR 70cc 46mm replacement piston = $60 at Treatland.tv

Feel free to leave feedback and suggestions on video, process, and/or any questions.

Honda Express Moped Engine Soft-Seize Cylinder Jug Piston Seizure : Woops!

Honda Express moped... 

"Houston, we've had a problem here"

Back on Mar 28th 2014 I had taken out my newly "upgraded" honda express nc50 noped for some test riding. The prior weekend I had take in out as well and experienced some technical difficulties... ie. It died on me. Once fully assembled with the following parts, I was able to start the honda noped first-shot. It was great. Now, keep in mind, I used the following stock express moped Mikuni carb settings on pilot run:

DEFAULT MIKUNI VM 20MM SIDE BOLT INFO: 

• Idle : 22.5 
• Main : 185 
• Needle setting (clip position) : default 

The "low end" throttle was very poor, being sputtery and slooooow on the go. But, when I was in the 15-20 mph range... the moped FLEW! Because I was breaking in the new setup and honda carb, I never had the throttle more than 1/2 and kept the speed to 30-35 mph (measured by the Trail Tech vapor speedometer).

The moped ran excellent for 30+ miles and unfortunately my Trail Tech vapor temperature gauge is not installed correctly, so I was running without and monitoring of engine temp. On my way home there was a half mile or so of flat open back-roads and I decided to test max honda nc50 acceleration. I was probably between 35-38 mph and the honda noped began to "buck" (like I was jamming on the breaks) and then finally the engine died and I cruised to the edge of the road.

At the time, I didn't understand the problem. I thought it might be electrical or perhaps something went wrong with the carburetor and the engine lost fuel. As see in this mopedarmy.com forum post, I experienced a Honda Express Cylinder Jug Soft-Seize. As you can see for the honda express parts photo at the beginning of this post, I had soft-seize the engine a few times 5-10. After the piston and piston rings had melted to beyond functionable, I was unable to start the moped because I lost all compression I had.

I thought the cylinder and piston were shot and I would need to drop at least $150+ for a new engine kit. Some suggestions I received included:

• Honing the cylinder
• Having the cylinder bored and adding a big-bore piston w/ rings
• Using a Muriatic Acid cylinder wash technique to remove the aluminum from the icon cylinder jug

Of those options I choose the Muriatic Acid Wash technique, because is was the least expensive. $60 for the Honda Dr 70cc 46mm upgrade piston. $7.29 for the Muriatic Acid. Some chemical resistant gloves, baking soda, Rubbermaid tub, goggles, air mask, paper towels... all things I already owned.

Next post reveals the video documentation of the process.

Steps For NC50 Honda Express 1978 Moped Performance Tuning

The steps For NC50 Honda Express 1978 Moped Performance Tuning are as follows:

1. Clean and make sure everything stock is in order... then begin. (ie: clean the carb) 
2. Make sure good new honda nc50 battery. 
3. All new oils and gas. 
4. (supa' cheap start) Honda Moped Muffler Modification 
5. (got some $$$ then go straight to new pipe) : MLM Muffler Sidebleed Exhaust Pipe from treatland.tv (wait for sale :) 
6. Upgrade your engine CCs : Honda DR 70cc racing kit from treatland.tv
   You should be around 33mph (at weight 165'ish lbs) 
7. Premix and remove the honda express stock oil pump
   Note: 1978 nc50 has the oil mixing and going directly into the stock intake. You would need to cap off the stock intake. I have seen some people fill the old oil reservoir with pre-mix as well (run at least 50:1 mix, especially when kitted engine) and use a plastic fuel-rated "Y" connector with the main fuel line and get a little "extra" gasoline storage. 
8. Replace your reeds with Boyesen Dual Stage Reeds from treatland.tv 
9. Replace your honda express weak-ends custom nc50 intake 
10. Upgrade your honda express carb to a Mikuni VM 20mm carburetor
11. Tune the carb (I'm still working on this one). Get some Mikuni VM 20mm jets : Mikuni main jets from treatland.tv
12. (be cool and measure metrics on your noped like speed, temp, tach, etc) : Get a TrailTech Vapor

I hope to have a full "How To" video setup in the coming months. So... subscribe to me :)

Rear Fender 1978 Honda Express Modification

Rear Fender Honda Express Moped NC50 1978 Modification. For those of you who have decided to upgrade your honda express muffler, but would like to keep your stock rear fender... this post is for you. Simply use a grinder, hacksaw, Drummel with metal disc, or something else equally effective.

Honda Express Fender Modification Closeup

You can see I cut one of the two honda express fender braces (the one on the right-hand side of the moped scooter). Using the stock bolt brace that connects to the air intake and the other rear brace that connects to the drive gear box on the left-hand side of the noped.

Left Side Honda Express NC50 1978 Fender Modification

NC50 Moped Fender Mod Full View

Honda Noped Fender Modification To Fix Upgrade Full View

 I would suggest using a locking washer or "lock tight" on the bolts to keep them from falling out. There will be a lot of vibration without the support that connects to the honda muffler.

Before 1978 Noped Honda Express Stock Fender/Muffler

Happy trails!

Motion Left Moped Honda NC50 Express Sidebleed exhaust pipe muffler

Motion Left Moped Honda NC50 Express Sidebleed exhaust pipe muffler is here. This part is one of the few scooter parts I have left to complete my honda express moped "build". Still planning on LED headlight setup and perhaps some jets for my mikuni 20mm VM round slide carburetor (bolt on) for my 1978 honda express noped model nc50.


This is an amazing USA hand-made moped muffler that is excellently crafted. MLM honda muffler pipes are hand crafted with eighteen gauge steel metal and are welded using a TIG (tungsten inert gas). This honda moped muffler pipe is built to last with removable end-cap silencer and coated using a rugged 1,500 degree high temperature powder coat. The muffler exhaust flange is 1/4 in thickness and the rear muffler bracket is 3/16 in size with a 1 1/4 inch slot for mounting... no hassle here. Visit MLM muffler online.

You can find the MLM honda express NC50 & NA50 people's sidebleed pipe on the www.treatland.tv website. Current the muffer retails for $190 so buy it now before the prices goes up... or they sell out!!!

Do you need some more NC noped muffler references? Well, here are some similar moped constructions using the MLM honda express people's sidebleed pipe:

Stay tuned for more Honda Express NC50

modifications coming soon...