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Author Topic: Hyosung 165cc Big bore kit  (Read 8538 times)

dowensy

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Hyosung 165cc Big bore kit
« on: January 25, 2012, 03:31:53 PM »

I think I'm the only person on here who actually has bored their Hyosung out and I'm going to list every problem and thing I've had to do to fix this bike to try and get it to run right.

I bought the big bore kit and thought would be too hard, cylinders bored straight through exhaust system and up jet and racing airfilter, should be all I need, oh how I was massively mistaken!!!

Firstly don't even try and attempt this if you have less than 1000 to waste. First problem arose when the bike was bored and the engine was ran in. I then realised the bike was no matter what jet configuration I tried wasnt running right, so I've had to fit larger 250cc carburetor, which still gave a wrong fuel mixture and had to be rejetted to not run lean, This then put larger amounts of stress with the power through my chain and sprockets causing the chain to sheer, so had to buy a SUPER HEAVY DUTY X-ring chain. After this found out the bike was running a too retarded a ignition system, which meant my valves have been burnt to a crisp as a result needs a full set of valves which when you bike has 8 of them turns out isn't that cheap. Next step is overheating, due to the increased cc the bike runs dangerously hot! so you need to get a 250cc+ oil cooler to help keep the oil temperature down. Still not finished yet, The final step is getting your valves timed correctly (not manufacturers timing) so you can achieve maximum combustion. I will keep this thread going if I come across anymore problems and if any one wants a running total of costs for me so far feel free to ask. All in the name of SPEED and PERFORMANCE :D
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Spidey

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Re: Hyosung 165cc Big bore kit
« Reply #1 on: January 25, 2012, 04:35:35 PM »

What kind of performance boost are you actually getting tho?

Like for example:

0 - 100km/h times - before and after
Top speed - before & after
More power through the revs?
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dowensy

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Re: Hyosung 165cc Big bore kit
« Reply #2 on: January 25, 2012, 04:47:56 PM »

I've never actually been able to test it, as once I sorted one thing something else has happened straight away. but it has A LOT more torque, you can actually feel it now, before I got it bored my bike did 96mph which is about 155-160km/h. Still haven't had time to get the compression up on the bike as I still haven't fitted the valves and now have to wait for an oil cooler from a 250 to arrive from Australia as because the bike runs that hot it melted a oil line which then managed to leak oil which somehow caught fire. This boring out and tuning process has taken me over 4month to get to this stage, but the bottom end torque is amazing now compared to what it was. you can actually feel a power band and it feels like it wants to move from about 4k rpm instead of being so heavy and sluggish, but like I said I haven't had the chance to fully test it yet as I'm the first in the UK to do this to a Hyosung so I've been told by the tuning company which supplied the parts for the modifications. They said to expect a dramatic increase in torque characteristics of the bike and with the right set up to break the 100mph mark or (175km/h estimate) mark.
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Spidey

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Re: Hyosung 165cc Big bore kit
« Reply #3 on: January 25, 2012, 04:56:19 PM »

Thats an impressive number...

IF you can sort out the cooling issues...

Good luck with it!
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dowensy

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Re: Hyosung 165cc Big bore kit
« Reply #4 on: January 25, 2012, 05:10:22 PM »

Yeah just ordered a Racing 250 oil cooler from Auz so lets hope this help lol other wise this is one futile endevour and a waste of A LOT of money
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dowensy

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Re: Hyosung 165cc Big bore kit
« Reply #5 on: January 31, 2012, 04:05:37 PM »

Other things ive just found out as I had the boring done "professionally" just tore apart the engine to replace the valves and found out the travel on the old and new pistons is difference so it looks like I will have to get the cylinders skimmed by about 2mm. So hopefully should be pumping out even more power than what I had before, this also might mean I have to play around with jetting it right again :(
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dowensy

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Re: Hyosung 165cc Big bore kit
« Reply #6 on: February 19, 2012, 06:34:25 PM »

Still havent finished this bike as the person who bored it out fitted the OE gaskets instead of the larger ones and has lost them so I've had to order a new full set of gaskets

Eth
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adamk

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Re: Hyosung 165cc Big bore kit
« Reply #7 on: February 20, 2012, 09:55:54 AM »

Hmm.
I know of a few people running 125 oil coolers and 125 carbs with the 250 engine, as the parts manual also states the GT250 and Gt125 share the same carb part number, its safe to say their is no difference in carbs, just jet sizes...



I also have had some confirmation that the GT250 engine will run fine with a 125 oil cooler, maybe a little warmer, but not enough to worry about (i am in the cold uk weather tho) and i can confirm this is true, Sim Simma on here will confirm this too.

Also when increasing any power i would have said you would need to upgrade to 250 chain and sprockets its a no brainer..., i would say 520 x 112. Just getting a better quality chain wont stop it stretching eventually.

And tbh, there is a reason nobody else on here bores out the 125R... its easier and cheaper to buy a 250 and drop it in, thus having less hassle, less money to spend, less problems and more power.

I have seen someone on here bore a 250 into a 300 using Suzuki 150 pistons which worked out well for him with no additional parts needed.

I think you have jumped into the 'lets bore it out' bandwagon too quick without reviewing the options of a 250 engine.
Also if you had just 250'd it you end up with a spare engine to sell or put back in when you sell.

I now its abit late now, and congrats on getting the job done, but imo you have wasted alot of cash to gain very little extra power, on a dyno i would be amazed if you have gained more than 6-7hp as the 250cc is only 15hp more than a 125 engine.
« Last Edit: February 20, 2012, 09:58:15 AM by adamk »
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Re: Hyosung 165cc Big bore kit
« Reply #8 on: December 27, 2013, 03:53:02 PM »

Hmm.
I know of a few people running 125 oil coolers and 125 carbs with the 250 engine, as the parts manual also states the GT250 and Gt125 share the same carb part number, its safe to say their is no difference in carbs, just jet sizes...



I also have had some confirmation that the GT250 engine will run fine with a 125 oil cooler, maybe a little warmer, but not enough to worry about (i am in the cold uk weather tho) and i can confirm this is true, Sim Simma on here will confirm this too.

Also when increasing any power i would have said you would need to upgrade to 250 chain and sprockets its a no brainer..., i would say 520 x 112. Just getting a better quality chain wont stop it stretching eventually.

And tbh, there is a reason nobody else on here bores out the 125R... its easier and cheaper to buy a 250 and drop it in, thus having less hassle, less money to spend, less problems and more power.

I have seen someone on here bore a 250 into a 300 using Suzuki 150 pistons which worked out well for him with no additional parts needed.

I think you have jumped into the 'lets bore it out' bandwagon too quick without reviewing the options of a 250 engine.
Also if you had just 250'd it you end up with a spare engine to sell or put back in when you sell.

I now its abit late now, and congrats on getting the job done, but imo you have wasted alot of cash to gain very little extra power, on a dyno i would be amazed if you have gained more than 6-7hp as the 250cc is only 15hp more than a 125 engine.

Sorry to resurrect this old thread, but could you by any chance post a link to the 300cc thread? tried googling it and searching on the forum as well but didn't find anything, I was curious if it was done and wanted to see how it turned out.
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adamk

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Re: Hyosung 165cc Big bore kit
« Reply #9 on: January 18, 2014, 08:35:12 PM »

http://korider.com/index.php?topic=9730.0

Naza Blade 300cc, using 150cc Suzuki Pistons + Bore.
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