Kymco Stryker 125 Rebore Advice

[craig6398]

Hi all,

I seized my bike last week, so I have enlisted a knowledgeable friend to help me repair it. I suggested re-boring it whilst we're about fixing it. He seemed to think it pretty straight forward and I know he's done it before. Not too worried if it goes wrong and is irreparable. If the repair & re-bore work I'd like it all to have been done properly though.

However, I don't like to just take him at his word without knowing a bit myself. So I have the following questions:

I would like to go from 125cc > 150cc, is this going to be possible with this bike? Is there anything I should look out for that may make it impossible to go up to 150cc? And what other parts/operations need to be taken in to consideration?? If it's not possible to go to 150cc can anything be achieved instead?

What kits should I be looking at and where best to buy/enquire (UK)?

I'm not trying to belittle my friends skills but is there anything else I should be asking him or watching out for?

Oh the bike's a Kymco Stryker 125, 2003, 12k on clock, 2 Stroke. The engine is apparently modelled/similar to Honda CB 125. It's slow, lucky to get 60mph downhill at full revs.

The reasons I want to rebore is I'd like it to do at least 70-80mph, mainly because of being stuck behind lorries. Been told only a rebore is going to give significant power increase. And I don't have the cash to buy anything bigger atm.

Thanks all for reading and giving your advice.

Craig.

[P.]

The Kymco is a 4 stroke.

Unless you have a full licence, you cant go up to 150cc.

A rebore up 25cc would be impossible I reckon. You'll possibly get an oversize piston for your machine...but I personally dont think so.

Just find a used engine on ebay and slot it in, dont forget to change and check the oil regularly and it wont seize again

[DrDonnyBrago]

It's not worth spending much money on mate, fix it up as cheap as possible (probably a new engine) and enjoy it for what it is (a cheap, albeit slow method of learner legal transport).

[Rogerborg]

Forget it. There are 150cc head and piston kits available for the 156/157FMI engines, but the bore and stroke on yours is slightly different: I very much doubt you'll be able to get a piston to fit, even if you do get it bored out accurately.

And even if you do, going to 150 isn't going to give you a "significant" power increase. A few mph, tops, and that's if you re-jet to suit, maybe muck around with the exhaust and air filter.

Then of course you'd "have" to register it as a 150, can't ride it on a provisional, tell your insurer, all that jazz.

Anything's possible, but you'll just be pouring money down a hole. You say you can't afford anything bigger, but I'm not sure that you can afford the bike you've got.
____________________
Biking is 1/20th as dangerous as horse riding.
GONE: HN125-8, LF-250B, GPz 305, GPZ 500S, Burgman 400 // RIDING: F650GS (800 twin), Royal Enfield Bullet Electra 500 AVL, Ninja 250R because racebike

[whitedevil]

I had a kymco stryker, it was a bag of wank. struggled to do 50mph and i snapped a conrod trying. Sell it as scrap and buy jap.
____________________
GPZ500 sold ~ CBR600FS-2 sold ~ ZX6R sold ~ Street Triple R

[Teflon-Mike]

They will go 150 as said, but only with a new barel that has enough steel in it to take the bigger piston. Bore yours that big and you will cut through the steel cylinder into teh aluminium of the cooling fins, which will be rather soft and not last long with piston rubbing up and down inside it!

It will STILL be slow.

Bike is slow becouse it doesn't make very much power.

Power = Cylinder Pressure x Cylinder Capacity x Engine Revs.

Cylinder pressure comes from burning petrol in air.

25cc on 125cc = 20% best you could hope for will be 25% more power, on 10bhp motor an extra 2bhp.....

You wont get THAT becouse the engine is strangled by its cam timing, carburettor and exhaust.

You can get around 15bhp from a 'good' single cylinder four stroke 125..... so fact you are 50% down on that or more, suggests that YOUR engine isn't getting enough charge into the pot to fill the full 125cc it has....

So if it cant get a full 125cc lung full of 'bang' into the pot, it ent going to get 150cc lung full in to make a bigger bang, is it?

Wast of time and money..... it's a dog, it has always been a dog, it will remain a dog, no matter how much you groom it! Never going to be a glamour model!

Cut your losses; stick money you might spend, and its a seriouse amount; rebuilding your chinky-fake-away engine, and stick it towards a better bike...... or simply bodge it back together as cheaply as you can, live with teh sub-sub-standard performace and ride out whatever value you can get from it.....

They are not WORTH 'saving', let alone 'tuning'!
____________________
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Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?'

[chris-red]

Basically don't bother.
____________________
Well, you know what they say. If you want to save the world, you have to push a few old ladies down the stairs.
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[craig6398]

@Paddy, mistake on the 2 stroke there I did mean 4!! I don't have a full license and understand it would be illegal to drive at 150cc.

I was on the way to buy oil when it seized less than 1m from the shop.

Thank you all for your input, it all seems pretty unanimous. I will heed it and just try to repair or give the thing up for scrap

[humanbeing]

Tries the sprocket(s) mod 1st. Onroad with that "stock" ratio is wasting energy.
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ANY of these "kits" are direct fits on this bike:
common chinese type:
Jialing 156 (same bore & stroke as early CRF150F) 63.5mm
https://item.taobao.com/item.htm?id=10144327048
Jialing 145 (sam bore & stroke as GL145 / GL PRO) 61mm
https://item.taobao.com/item.htm?id=7981976622
Stryker 150 (62mm piston) is the domestic model in Taiwan BUT Taiwanese "kit" is NOT cheap SYM "Wolf" series also use similar config.
Honda also fitted some 62.5mm in some S. American / Indian as 150 bike.
"Weirdo" 58.5mm "133" can also found in some chinese/ Taiwanese bike as stock.
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Rebore & use 65mm still within safety limit
https://www.ptt.cc/bbs/biker/M.1314811697.A.E75.html

[Rogerborg]

^^^^^^^^^^^^^

IME, this guy knows what he's talking about.
____________________
Biking is 1/20th as dangerous as horse riding.
GONE: HN125-8, LF-250B, GPz 305, GPZ 500S, Burgman 400 // RIDING: F650GS (800 twin), Royal Enfield Bullet Electra 500 AVL, Ninja 250R because racebike