Honda MT50/H100 project

[Fladdem]

I have recently passed my mod 2, like all teenagers with a full motorbike licence I couldn't wait to hop back on my old moped. Or should it have been onto a 250? Never mind. For reasons unknown, I am back on the MT5. Recently, I bought a H100 engine to throw in it. What else will I need to get it running nicely, I reckon a h100 carb and maybe get a Honda MT80 exhaust to cope with the bigger engine. I don't want to rush into this and muck it all up, any advice would be great.
Thanks in advance.
By the way, I am trying to do this legally so I will inform my insurers and change the logbook, would it be a honda mt100 now?
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Current:1991 Honda MT50 (Soon to be a H100/MTX/MT5 hybrid), 1976 Honda Cub C70, 2005 Honda Varadero 125, 1993 Yamaha TTR250 Open Enduro , 2010 Road Legal Stomp YX140, 1994 Honda CRM 250 MK III, 1999 Cagiva Mito 125, 1992 Honda CB400 Super Four, Stomp T4 230, 1984 Honda H100s, 2009 Sym XS125K
Past:2003 Aprilia RS125, 1982 Kawasaki GPZ550(FREE BIKE!)
I'm having more fun than a well-oiled midget.

[dangerousdave]

hi - sounds like a fun project.

for performance you'd be better off using the h100 exhaust, the mt80 exhaust isn't going to work too well on the 100cc engine. its not a high-rise exhaust like the MT pipe but engine will go a lot better.

use the h100 carb like you say, although the airbox of the mt5 wont work well with the bigger engine. consider using a clamp on air filter, but be sure to check the jetting in the carb. These carbs can make the motor run a bit lean if the jetting isn't checked.

yes, you'll need to update the logbook and send back to DVLA for this to be logged. Let your insurer know when you make the change as the bike will no longer be standard & will be classed as modified.
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1988 Kawasaki KMX 200

Previous: Yamaha YZF1000, ZZR600, KMX200, DT50, KX80, CG125, PF50

[Fladdem]

Actually, at the moment the bike doesn't even have an air filter, I took the air box out to clean the air filter because I thought that a year of riding means he filter needs cleaning and I looked inside the airbox, nothing, put the lid back on and took it off again incase I was hallucinating, still nothing. So I am in the market for an air filter anyway. It runs perfectly, surprisingly, as instead of playing with jets when the exhaust was emptied of everything one of the 3,000,000 previous owners must have taken the air filter out to compensate for the lack of exhaust stuff.
I am hoping to use it on green lanes, so thats why I thought of the mt80 exhaust as 80cc is closer to 100cc than the standard 50cc pipe and still high up.
50cc.nl has pretty much everything I will need, would a clamp on airfilter be usable in muddy conditions? I was thinking of getting like a high performance foam one.
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Current:1991 Honda MT50 (Soon to be a H100/MTX/MT5 hybrid), 1976 Honda Cub C70, 2005 Honda Varadero 125, 1993 Yamaha TTR250 Open Enduro , 2010 Road Legal Stomp YX140, 1994 Honda CRM 250 MK III, 1999 Cagiva Mito 125, 1992 Honda CB400 Super Four, Stomp T4 230, 1984 Honda H100s, 2009 Sym XS125K
Past:2003 Aprilia RS125, 1982 Kawasaki GPZ550(FREE BIKE!)
I'm having more fun than a well-oiled midget.

[cb1rocket]

read all of this, that is all, or get an H100S2 like I did

https://www.mb5.co.uk/12.html

[dangerousdave]

If you have a mt80 exhaust hanging around then it could be tested with the 100cc engine.

However, i doubt it would run as well even as a standard H100 because it will alter the pressure wave back to the cylinder as the pipe has different internal dimensions to the correct pipe for that engine.

You may be able to modify a Dt100 or ke100 pipe if you can find one, both are high rise abs match the motors capacity at least.

Wouldn't recommend running without a filter ever as all sorts of dust and crap will get into your engine, even when used on the road.
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1988 Kawasaki KMX 200

Previous: Yamaha YZF1000, ZZR600, KMX200, DT50, KX80, CG125, PF50

[stevo as b4]

check the header pipe diameter from the exhaust port on the cylinder. If the H100 downpipe ID and the MT80 pipe ID is the same or nearly the same then it should run reasonably well.

The MT80 pipe we assume is different and has a bit more chamber volume than the MT50 pipe does. If so it's a closer match to the 100cc engine, and also as the H100 engine never really had a tuned expansion chamber style pipe, it should be easier to re-jet for using with an 80cc pipe.

Lastly i agree that for road or off road use you need an airfilter asap! For serious off road use you want a well sealed airbox and hose coupler from airbox to carb. If you havn't already go an airbox if personally try and source a std MT5o airbox, and adapt the hose adapter or use a silicone hose section to joint it to the H100 carb.

[Fladdem]

Right then, cheers for that information.
Just to clarify, I wasn't the one who removed the air filter, when i discovered it was missing I stopped riding the bike but I fear the damage is already done, and it partly explains why it ran horribly.
I will have a look at the inner diameters of the exhaust port and exhaust and see what it is like.
On my MT50, the exhaust is rusted to the studs and the studs are rusted to the cylinder, I tried penetrating oil and i went to undo it, it is an allen key style stud, I put the allen key in and turned and now its a circle. How do I get the exhaust off now?
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Current:1991 Honda MT50 (Soon to be a H100/MTX/MT5 hybrid), 1976 Honda Cub C70, 2005 Honda Varadero 125, 1993 Yamaha TTR250 Open Enduro , 2010 Road Legal Stomp YX140, 1994 Honda CRM 250 MK III, 1999 Cagiva Mito 125, 1992 Honda CB400 Super Four, Stomp T4 230, 1984 Honda H100s, 2009 Sym XS125K
Past:2003 Aprilia RS125, 1982 Kawasaki GPZ550(FREE BIKE!)
I'm having more fun than a well-oiled midget.

[moonzoomer]

For your intrest both the mt/mb 50/80 and the H100 were based on the older cr80 motocross engine which will bolt directly into either bike, difference is a lot more power @16 bhp. Exhaust systems etc of a cr80 might be usefull if you can find one.

[Fladdem]

hi, does anyone know what the jetting is for a honda h100a? I have got the carb but none of the jets have come with it and I don't know how I would go about getting the right stuff.
Any help would be fantastic.
____________________
Current:1991 Honda MT50 (Soon to be a H100/MTX/MT5 hybrid), 1976 Honda Cub C70, 2005 Honda Varadero 125, 1993 Yamaha TTR250 Open Enduro , 2010 Road Legal Stomp YX140, 1994 Honda CRM 250 MK III, 1999 Cagiva Mito 125, 1992 Honda CB400 Super Four, Stomp T4 230, 1984 Honda H100s, 2009 Sym XS125K
Past:2003 Aprilia RS125, 1982 Kawasaki GPZ550(FREE BIKE!)
I'm having more fun than a well-oiled midget.

[bladerunner]

On the plus side the mt50 frame is loads stronger than the original H100 item and it is worth trying an 80 exhaust as tbh the std h100 one is crap with zero expansion chamber effect....maybe even Bodge on a dt100 or km/ke100 to try if you can find them. Having bolted on a ar80 micron to a yb100 motor years ago I didn't expect it to do anything due to very poor transfer ports..4 speed box and very low tune porting as std but with a bit of header length shortening....it fair flew to 70 and for what it was quite shockingly quick! Would be worth doing the same with the h100 engine it was after all aimed at the same market back in the day, half the fun is in experimenting with these things
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Current bikes...cbr929, KDX200's, Rd125lc mk2, RGV250's