Author Topic: Mini thumper  (Read 378 times)

johnr

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Re: Mini thumper
« Reply #15 on: May 26, 2020, 09:27:22 PM »
new head and valves, cant get bigger than these or else they would be clattering each other. cam has a lot more duration too, sham i didnt get pics of it.
once the head was on and times up, the new carb went on the old manifold and after a few mods, the original airbox. studying the multitude of supposedly tuned step thru hondas out there, mostly fitted with big exhausts and big carbs but nothing else inbetween, i decided not to go for thee silly air filter as it would cop all the water from the front wheel in the rain, which might restrict performance somewhat.

johnr

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Re: Mini thumper
« Reply #16 on: May 26, 2020, 09:31:44 PM »
and thats pretty much all there is to it, some funky new non pogo stick shockers on the back.

tin of satin black paint and a few screws and bolts to secure a motley selection of bargain panels and thats it really, at 150cc its hardly a thumper, but it sounds bloody lovely for a step thru and the satin black sleeper look apeals to me...

johnr

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Re: Mini thumper
« Reply #17 on: May 26, 2020, 09:33:39 PM »
completed, all told this rebuild has cost me about 200 quid and the mods arent yet completed, ive a little oil cooler kit to figure out how to plumb in next, but im gonna leave it till i can get it mot tested and insured so i can sort the jetting out right.

johnr

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Re: Mini thumper
« Reply #18 on: May 26, 2020, 09:38:34 PM »
and thats all the pics i have for now. im missing one small panel and im going to have to try and find some sort of aftermarket ignition because the stock unit has advance and retard controlled by a microswitch thats built into the carb itself, obviously the new carb is much bigger than the stock one but doesnt have the microswitch, but thats a problem for another day.

themoudie

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Re: Mini thumper
« Reply #19 on: May 26, 2020, 10:59:25 PM »
OOO! Looks like fun John!  ;)  The lump hammer head next to the valves, could give the wrong impression!  ;)

The advance and retard could be a bit of a conundrum and I look forward to your ingenuity at resolving that.

Thank you for posting.

Good health, Bill

johnr

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Re: Mini thumper
« Reply #20 on: May 26, 2020, 11:30:39 PM »
well its not a massive issue. these bikes are designed to be incredibly user friendly and civilised, so the stock carb as well as having the mocroswitch on it also has an electric heater element to prevent any risk of icing up when its cold, but in reality the thing wont be getting commuted so can do without that. plus, the microswitch is not a huge problem. most mechanically triggered ignition advanvce and retard units have the ignition set advanced for starting and then using mechanical weights retard it at higher speeds. but this engine is set to be fully retarded whenever the microswitch is closed by opening th throttle, in short the ignition has full retard all the time and gets advance by the throttle being shut and triggering the switch. so as it is, without the microswitch its got full retard all the time, which only makes it a bit lumpy at the bottom end when its cold. once its warmed up, it runs ok, and these bikes dont really get run round on closed throttles too much, theyre either off or flat out.
till i can get it on the road and givee it a thrashing about i wont know if its 100% but it sems ok for now, and the ignition advance and retard are negated somewhat by the fact that its also got a whopping carb compared to stock, so wont be running super lean as they are built by honda.

mthee

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Re: Mini thumper
« Reply #21 on: May 27, 2020, 10:39:02 AM »
Love this! It's easily got to be the cheapest and biggest power increase using brand new parts - 9 to high teens? Looking forward to the road test report... ;D

johnr

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Re: Mini thumper
« Reply #22 on: August 23, 2020, 09:11:24 PM »
just as an update to this, ive been messing with this on and off for a few weeks now. it took from june to august to get the v5 back, but its here now and the bike is now mot'd and taxed. ive been faffing with thee jetting till i got it close to right. took me several plug chops but its now as close as im going to get it, main jet is up from .95 to 115 and it now starts ticks over and revs cleanly. it pulls well through the gears and a blast up the local bypass shows that even with my lardy 20 stone sat on it, it pulls through to an indicated 75mph which isnt bad for a semi auto step thru commuter. im sure i coud get more from it, but i quite like that its stil rideable in traffic with the ability to trickle along at low speed without getting all wooly or overheating. so, as it is right now, its staying like this. i think a genuine 70+mph step thru isnt to be sniffed at. ive been told by the neds of the internet that their stock innovas did 75-85mph on the standard engine pipe and carb, which i find implausible for a 9bhp step thru, but its not a problem, if i ever meet them, im sure they can show me a clean pair of heels. me and the mrs are off to the lakes next weekend for a couple of days backlane fun so lets see how it copes for a couple of hundred miles, but for now, its bang on, and it still looks like a ratty old step thru.

johnr

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Re: Mini thumper
« Reply #23 on: Today at 04:28:26 PM »
so ive been pottering round on this little thing for a few weeks, and this last weekend we decided to give it a bit of a run out, so saturday saw us run up the coast from silverdale to carlisle travelling on only b roads and unmarkd tracks, the full coastal route was 185 miles, and the little honda didnt miss a beat, sunday saw us put another 135 miles on up the scottish coast of galloway and then back to carlisle. today we ran back down the last 95 miles of the a6 to home. 415 miles under the wheels and not a beat missed. average fuel consumption was still about 110mpg on the honda in spite of its state of tune, though sues gs125 averaged 150mpg. theres a lot to be said for touring on small engined bikees. you see more and enjoy the journey more than something big and fast. i could have done the whole trip in a day on the bmw, butwheres the fun in that.