The 50

[cotswold]

There seems to be a resurgence in the 50cc ranks so I thought I would post up how I am going about mine ( Johns ).

John Steer got hold of the ugliest Honda MTX50 you would ever wish to see, it was a rescued beach toy and was very neglected. John put an FXR front end in and also modified the original swinging arm to accept an FXR rear wheel.
The first trip to the track we found it was restricted in 5th and 6th gears, the culprit was traced to an electrical jobbie that was rotated by the gear change inside the case. It was a simple job to remove it and plug the hole. We just had to rotate the unit until it would rev out in all gears.
The next time at the track I entered F5 and finished a nice solid last as it is very slow, I did have race long battles with a Honda 100 foul stroke to keep me interested.
I have a mb100 on my shelf that is donating it's reed block and it's carb ( a nice 28mm pwk ) and I have gotten hold of a couple of MX pipes to try and cobble up a less restrictive exhaust.
I have just lucked across a spare engine and the cylinder looks to be ok ( it is 1mm over though ) but the crank needs a rebuild as the big end is shot.
I have plans to try make a Scitsu type frame ( lego bike for you Dave ) and have a contact in UK who is hopefully going to give me a bit of help with the dimensions.
Like all my plans it will probably never happen and I'll be the new Ivan, but you never know.

[cotswold]

This is the starting point

[F5 Dave]

I would have loved to have that when I was racing my MB50. It's all about the piston though. The MB had 1.5 mm rings that used the clean tips off if you revved them much past 11. What are these? I ran RD pistons but it wasn't a simple conversion.

[speedpro]

I ran RD pistons but it wasn't a simple conversion.

You ran "LONG" brand rods for a bit as well didn't you Dave???

[F5 Dave]

Yeah they became 2 shorter ones

[cotswold]

Been around to the local 2 stroke tuning specialist this morning. I took my new cylinder as I thought it looked like it had been attacked with a porting tool already. lucky I did as the exhaust port is as wide as you would want to go, the transfers do need a little work as does the inlet. Gives me something to do. I am thinking of putting it on with some of the mods for next weekend as it is bound to be better than the standard one.
Is a 28mm pwk too big?

[mr bucketracer]

let the dyno wars begin (-: 28mm is the biggist you would want to go , my gt50 runs a 28mm carb and my old rd50 had a 25mm

[F5 Dave]

Actually I'm thinking of trying bigger one day. 28 should be ok, smaller might be better on slower revving engine

[speedpro]

Rob is making 30+hp with essentially a 24mm carb. I've just had a motor simulated at 29hp with a 28mm carb. Do it right and you probably will be fine with a smaller carb. The simulation for 29hp was tested with a 32mm carb and made no more power.

[cotswold]

The 28mm will have to stay as it's all I have . I may swap it out if it is a dud on the bike.

[F5 Dave]

I have a nice almost new flatslide 24mm Mikuni I'm going to list on TM one day when I get my act together. $50 would buy it.

[Gigglebutton]

Im using a 24 on my RG. Only 10hp but not peeky at all

[mr bucketracer]

Im using a 24 on my RG. Only 10hp but not peeky at all

whats the hp with nitro

[cotswold]

Im using a 24 on my RG. Only 10hp but not peeky at all

I can only dream of 10hp

[cotswold]

The job for today was to measure where my ports are timing wise. The target was 80* ATDC for the exhaust and 118* ATDC for the transfers.
The cylinder had to be lifted to get 86 and 116, I used penny washers under the cylinder to achieve this.
The exhaust port needs raising and the cylinder needs a bit skimming off to get where I have been told I want to be.