Re: HONDA EXPRESS SR: Mega Performance Thread


Did some of my wiring last night. Per Trail Tech instructions, I "floated the ground" on my HPI CDI for the light coils so that I could use the Trail Tech voltage regulator / rectifier with my battery. I had been putting this off because I thought it would be hard or I might damage my coils, but it took me about 10 minutes from start to finish.

Items Needed

- Soldering iron

- Solder

- Small heat source (for heat shrink)

- New length of wire

- Wire strippers

- Wire cutters


1. Cut ground from light coils with wire cutters

2. Place heat shrink tubing on wire

3. Strip 1/8" of insulation from new wire

4. Solder new yellow wire to old ground wire from light coils

5. Use heat source to shrink the shrink wrap over the exposed solder joint / wire

6. Route new wire next to current wire harness

7. Ensure new wire does not rub the flywheel

8. ????????


Both yellow wires will now attach to the yellow inputs for the regulator / rectifier:

Here is the result:

Re: HONDA EXPRESS SR: Mega Performance Thread

As he said, the emulsion tube may be different. Same idea for a bing where your jet will be greatly effected by an atomizer change.

Also, glad I got my HPI years ago when it came with both yellow leads floated. All profit.(edited)

Re: HONDA EXPRESS SR: Mega Performance Thread

Keegan Wilhelm /

What makes you say that the vm20 is too big? saying that a 19mm port means i cant go bigger than a 16mm carb doesnt make any sense...

Re: HONDA EXPRESS SR: Mega Performance Thread

Keegan Wilhelm /

What carb and jet would you recommend then...?

Re: HONDA EXPRESS SR: Mega Performance Thread

douggie is the homie but im rooting for keegan on this one. im diggin the zero fucks factor. if you want to completely obliterate use a speedfight kit. party on

Re: HONDA EXPRESS SR: Mega Performance Thread

Miss ya Marvin, I hope all has been well!!

Update, I earlier deleted the vacuum petcock for

this one from Amazon. Spoiler alert, it's way too big. I instead purchased a Magnum petcock from Treats

, which they claim is 16mm x 1mm. Psych, it's actually 15mm x 1mm, which was also too large for my NX50 tank. UGH.

I actually measured the fitting on the NX50 tank and it measured at 14mm (thread diameter) x 1.0mm (thread pitch), the same as the MB5. I purchased an

MB5 petcock

, now to wait on it in the mail. Petcock #3, awwww yeaaaa boiii. Serves me right for not measuring my shit.

In the realm of carburetion, the bike runs pretty well for not toughing it. I exchanged the 180 stock jet for a 160, and while it seems to run better, I did not have time to incrementally make changes and effectively dial it in. I have a feeling I will need something around the 90's, but we shall see!

Re: HONDA EXPRESS SR: Mega Performance Thread

If it needed a 90 it would not even get moving with a 160.

Re: HONDA EXPRESS SR: Mega Performance Thread

> DPC Ryan Wrote:

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

> If it needed a 90 it would not even get moving with a 160.

This thought occurred to me, however it is very curious that most 70cc build specs I have seen using the VM20 have sub-100's main jets. Strange.

Re: HONDA EXPRESS SR: Mega Performance Thread

I would guess that as well. The question may then become one of a possible air leak but you will know better when you get the idle and transitional throttle positions sorted.

Re: HONDA EXPRESS SR: Mega Performance Thread

Jack Rutherford /

and . . .

Re: HONDA EXPRESS SR: Mega Performance Thread

Yeah I want to see more! I just picked up an Urban and SR for 75 bucks today!

Re: HONDA EXPRESS SR: Mega Performance Thread

Jack Rutherford /

Ok, I'm going to pick up and carry this thread farther although I'm not going to invest the same amount of dough in this bike as the previous authors.


My friend's SR on the bench. It's missing quite a bit of plastics.


Stock belt seems to be the best option from what I can tell and this one seems to be in fairly decent shape.


Kick stopper return is broken but it doesn't seem to be as big a deal as in the urban.

Re: HONDA EXPRESS SR: Mega Performance Thread

Jack Rutherford /

It hasn't been ridden since my friend bought it so we have no baseline for stock performance. Well, there was no stock exhaust so we don't even have that but we do have:


the Big Shitter pipe. Stock header is welded on to this and it came with the bike. It doesn't ride as low as the picture makes it seem. Loud as hell! So I attempted to muzzle it some.


It came with a mounting bar but I couldn't figure out how the previous owner had mounted it. It looked like it was meant for the Express SR in the way they welded it together. I could be wrong. Anyhow I did a temporary mount for now.

I have no brake cables or levers right now so I don't think I'll try to ride it yet. Went down to 30 ounces in the variator.

Anyhow, that pipe is probably overkill, if it even does anything, for the stock cylinder but we shall find out soon. It sounds impressive enough just wear ear protection.(edited)

Re: HONDA EXPRESS SR: Mega Performance Thread

Jack Rutherford /

Anybody know the belt length on the stock belt. I guess I can take mine off and measure it. I did locate that it was 14mm wide which translates to 0.55". No wonder you can't find that belt anymore. It's either 1/2" wide or 5/8" wide and nothing in between. Is there a consensus on the best replacement belt? 5/8" would be 15.87mm wide. 1/2" is 12.7mm. I found 4 belts for cheap so I'm going to give them each a try.

Re: HONDA EXPRESS SR: Mega Performance Thread


I've put a ton of miles on my water-cooled Express SR. The Malossi H2O cylinder kit has held up impressively well; I'd buy another one in a heartbeat. The bike has served mostly as a loaner at rallies for others who don't have a bike to ride.

Current Parts List

Malossi H2O Hobbit cylinder kit

MLM H95 NU50 exhuaust

.4 mm carbon reeds

24mm Mikuni TM24 flatslide carburetor

K&N air filter

Bosch water pump

Trail tech regulator / rectifier


I trashed the MLM oil pump blockoff plug, the JB weld holding it in place finally failed. I chose to instead reinstall the factory oil pump with the input shaft cut off (reduce drag on the crank, I premix anyway). I had to get my MLM pipe re-welded (Thanks Devin!) when the baffle ripped off. I've chased down several fuel leaks and ended up using an OEM NOS 1988 Yamaha DT50 petcock + inline fuel shutoff (since the petcock is inaccessible with the battery installed). My AGM battery stopped taking a charge when the bike was crashed last year + wiring shorted out; I've since installed a small fuse block to prevent any more electrical fires. Ha.

Last night, I noticed I no longer had spark, for some reason. I think I might have fried my CDI box after doing an extended tire burnout the other week at the Spicy Boys moped rally (lots of friction, and probably, static electricity buildup). I will be trying a spare CDI box tonight.

Most recently, I've decided to follow my brother's trend and install knobby tires (NUBBIES) since the bike is extremely torquey / a blast off-road.

I think next modifications will be a better rear shock (RIP my current spinal column), look into better forks, replace the battery, run a snorkel from the carb (them water crossings tho), and I plan to rebuild my NU50 bottom end (it's longer than the NX50 crankcase) with a forged crankshaft + move my top-end parts over to that (it will allow me to run a larger diameter rear wheel in the future).

Re: HONDA EXPRESS SR: Mega Performance Thread

Jack Rutherford /

Thanks for the update. We went with a proma on ours, SHA carb, stock cylinder, wider rear tire (3.5"), gy6 clutch, stock belt flipped inside out, and 31 grams in the variator. Just shooting for 40 with stock cylinder but can't quite get there. I think I also shaved the boss narrower as well. We're still working on it.

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