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tuning mbx50


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If your bike has a reed valve it will almost certainly use a steel reed as standard. Using a more flexible fibre reed will give instantly noticeable improvement in acceleration. This is due to the reed opening sooner and allowing more charge into the motor. Matching the reed stiffness to the engine takes considerable development. Hy-tech's experience in reed valve design ensures you get a reed that will perform well. Simply replace the steel reed petals one for one with the Hy-tech reeds and re-assemble reed block. No other modifications are necessary except on bikes where pilot mixture may need richening to improve easy starting. Also now available from HY-TECH are a range of CARBON FIBRE petals utilising the latest manufacturing techniques with this versatile material. Please note : Some of the 'STANDARD' versions of these reeds may become superseded by their 'CARBON FIBRE' counterparts throughout the year.

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Taken from Visordown site

Blimey, trying to make an MT-50 go quicker takes me back exactly 21 years!

I was 16 and had an MB50 (same engine as MT50) 100 days before my birthday, my 3 best mates at the time 2 x MT's and an MBX 50 between them.

By the time mine was on the road it had been heavily, but sensibly modified.

I got it up to 61mph downhill with the wind behind it on one occasion, but it was still only good for 46mph on the flat.

When you see what I had to do to it to get it to go that even that fast, you'll wonder why I bothered :

Head skimmed, paper head gasket, exhaust port raised, inlet ports opened up, restricting lugs cast into barrel removed and reed valve stops opened up, hi-tech racing reeds fitted, Lintek aftermarket exhaust (looked standard but was unrestricted), cut the back skirt down on the piston to increase the inlet port duration, jets raised to correct mixture (jetting on it's own does not raise power as quite a few of my less mechanically aware 16 year old peers believed).

I also seem to think that Matt went to 15:36 gearing; bigger on the front and much smaller on the back - (how do I remember this shit after 21 years? - oh yeah thats right, it's cause for a whole year having the fastest moped was the only thing that I worried about)

second stage of mods which made it a bit more punchy and fun to ride but didn't seem to add dramatically to day to day top speed - drilled an extra port above the inlets (we saw a big bore kit with a port there, so Matthew Blackstone and I had to have them in our respective MT-50 and MB-50 barrels), skimmed a load off of the top of the barrel and made a 1mm thick aluminium base gasket to increase the port heights of everything (we couldnt raise the transfer ports any other way as we couldnt find curved riffler files that could get at them - which really bugged us). I also got a really weird looking Jama exhaust which sounded great and really helped it run clean.

I added a CB125T carb to mine which was much bigger, this made it run like a dog unless you were revving the tits off of it and ultimately contributed to the engines lack of reliability - ooh dear, and was it a dog by the time I finished with it.

The effort expended on this as you can see was considerable, as was the expense although most of the tuning type stuff was done at home or through the back doors of friendly engineering companies.

After all this the MB was barely faster than a stock RD50 with a Micron, slower than an S50 simpson (MZ produced pile of shit, but bugger me they were fast) and AP50's with pipes were still out of reach.

things I know now : the restriction is HEAVILY in the CDI box. I did a moped endurance race in 1999 and there were whispers about honda Melody CDI boxes being plugged straight into MT/MB 50's and making them go like rocket ships. Fact is you can do all you want to it, but the igniter box is the thing that rules. they just dont rev high enough to make good power with the standard CDI.


If I were 16 again, I'd start with the ignition (Honda melody CDI) and then go throught the other bits likes reeds, porting, exhaust. Despite the rumours the box is unlikely to work on it's own as restrictions abound on the MT and MB.

I would NOT get a bigger carb, I would probably get a big bore although when I was 16 that was cheating

anything MBX (even 50) will NOT fit an MT-50 a H100 however will (moped endurance racing on an RD50 against H100 engined MT50's taught me that)

Or just do the decent thing and buy an RD/DT50 and get a micron/gianelli.

blimey, thats taken me back a bit.....

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