honda h100s tuning

[salem1987]

Hi, just acquired a h100 as part of a deal to play with over winter.
I own other bikes and want to see how much I can actually get out of the little two stroke for a bit of fun!

I've heard the inlet is rather restrictive and have seen this reed on wemoto which could make some improvement to start with... https://www.wemoto.com/bikes/honda/h_100_sg_sj/86-93/picture/reed_valve_-_performance/

Next I have read getting a proper expansion chamber exhaust and bigger carb will help?

And finally does anybody know for sure if the mb8 Athena 125 kit is a direct bolt on?

Thanks for any advice

[cb1rocket]

[bladerunner]

Contact mick abbey regards porting and pipe! He's been grinding ports for longer than I can remember and at a reasonable cost for his skills!
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Current bikes...cbr929, KDX200's, Rd125lc mk2, RGV250's

[salem1987]

thanks, that helps a lot. Porting is definitely something i will look into also.

Also thinking of changing the gearing a bit, put the front sprocket from the standard 15t it is now to a 17t, as it is reving its guts out at indicated 65mph!!

[_Iain_]

Gearings fine.

A standard crank/rod shits itself at around 13,500rpm-14,000rpm & you'll be lucky to make it hit 10k on standard porting.

Before improving on stuff i'd sort out what you've already got. Get onto grampian motors, get a piston kit,little end and a few top end gasket sets. Check the plug is an 8 & not a 7 - mine heat siezed on a top speed run as previous owner haddn't done this. Clean the existing expansion chamber out. Mine also ran a smidge lean after servicing as it had a DIY panel filter, upping the main to a 130 sorts this. Put good two stroke in it - currently running comp 2 plus in mine.

While the cylinders off get the files out, you wanna square the top of the exhaust port off - aim of the game is to widen it above the height of the transfers. Also raise the port height by around half a mil. Then out with the files & wet/dry to open the channel out of the head, & smooth it right off. It'll not do much, but it does shift the "pull" from about 5.5-to a 6k takeoff & noticeably goes at 7k.

However it still drops flat after 7 and a bit, so gonna try raising it a bit more when i've got it apart next, but that could be the pipe. I think an MB80 proma pipe will fit, but may want some tweaks & fettling.

If you're really up for a challenge the '82 CR80 motocross motors look to share the same mounting points. If you could get a h100 head on, or make up an adaptor, you'd have 16bhp off the mark to play with.
____________________
Please be aware that the above post may be full of complete nonsense.
Riding: '07 KTM Duke II, Baotian BT49QT-20 Driving: '88 Volvo 340

[cb1rocket]

[cb1rocket]

I will admit I'm having problems with mine but only as I have gone extreme.

Pictures and graph in this thread https://www.bikechatforums.com/viewtopic.php?t=279145
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Honda H100S2 Rebuild - https://www.bikechatforums.com/viewtopic.php?t=253852

[salem1987]

Thanks for the advice. The guy who had mine before has been running the bike without an air filter as it runs bad with one on. Jets are all standard which is odd. Carb is totally clean now too. The power on mine starts at 6.5rpm and seems to last until about 8. There's is absolutely nothing below 6rpm and it totally bogs at 5 and slows.

Plug is looking a good colour on various plug chops too...

The Athena head and the mb80 custom pipe is very tempting

[salem1987]

Could anybody recommend what piston would fit if I got a spare barrel borred to 125?

[cb1rocket]

I would just buy the 150 quid kit, you can get the pistons on their own, also I think the stock barrel bored out to 125cc will mean no liner left!
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Honda H100S2 Rebuild - https://www.bikechatforums.com/viewtopic.php?t=253852

[moonzoomer]

Drop an old cr80 red rocket engine in ( 17 bhp), it was the engine the MB/T 50/80 and H100 was based on.

[bladerunner]

Just don't expect it to pull long road gearing very well!
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Current bikes...cbr929, KDX200's, Rd125lc mk2, RGV250's

[moonzoomer]

[bladerunner]

That's not bad tbh! Shorter gearing to 70-75 helps ....but would expect 80+ with a tuned road bike motor......if that's really where you'd want to be on a H100
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Current bikes...cbr929, KDX200's, Rd125lc mk2, RGV250's

[moonzoomer]

[salem1987]

i thought it might be a bit thin with regards to boreing , but wondered if anyone had done it.


My next idea after sitting in the garage having a early morning coffee is fitting 17inch wheels. I have a spare front end and rear wheel with sprocket etc from a cd200 - bigger forks and better drum brakes...

Might have to have an experiment!

[cb1rocket]

[salem1987]

thanks yeah i am aware of that. I've had a go at the rear wheel anyway and (not suprisingly) it is not a direct swap. The CD200 sprocket carrier is about 1cm offset compared to the h100.

The front however looks more possible, the yoke stem and headstock seem to match after some quick measurements.

Another reason for this possible conversion is that i have clip on bars for the cd200 forks and a spare cafe racer hump seat.....

Had the carb apart again today and noticed the needle was on the top notch. With no airfilter foam in the box and the needle this low im surprised its not running dreadfully lean.

[_Iain_]

[salem1987]

Cheers for those Iain I've just got a filter now and read this! Just placed the cafe back end on to see how it looks...

[_Iain_]

Chef!

Where'd the clip ons come from & how on earth do you ride with them?
____________________
Please be aware that the above post may be full of complete nonsense.
Riding: '07 KTM Duke II, Baotian BT49QT-20 Driving: '88 Volvo 340

[salem1987]

Found them at an autojumble for a fiver! They are seriously shimmed though. Need to get some proper 27mm ones off eBay I guess.
It's not to bad riding with them. Just awkward when doing slow manoeuvres!!

[salem1987]

can't find anyone on the internet who has fitted a mb80 proma exhuast and payday is looming on friday.
https://www.vsmotoparts.com/proma-exhaust-honda-mb80

I'm mainly concerned about the pipe routing past the rear brake, foot peg.

I might take the gamble, from looking at pics of the mb80 the foot peg placement looks the same:

https://p1.bikepics.com/2010%5C04%5C23%5Cbikepics-1958333-full.jpg
https://www.motorstown.com/images/honda-h100-04.jpg


Will it go straight onto a h100 standard barrel??


The athena kit will have to wait a month, but a decent reed and general clean up of the exhuast port and piston will be done.

(plus the usual cafe racer add ons or take off's - bit of weight saving!!)

[salem1987]

after 2 days of research i have finally found a parts supplier with all the tuning bits for the h100!!!

https://www.50cc.eu/en/parts_3.asp?Hg=All&Km=&M=Honda&T=H100&TA=HonH100&I=1363&Ag=14


it took reading through 18 pages of an aussie forum to find but there is everything from exhausts to reeds to cdi's listed there.

[Kickstart]