Anyone got experience with big bores for the NSR125?

[jimbo]

Summer is fast approaching. Exams are over in May. And a young man's thoughts turn to...

Big Bore Kits!!!

The bike needs a good overhaul as it will hit 30,000km soon, and while i'm at i'm thinking those of little extras that can improve one's spiritual and emotional well-being. Such as more cc's.

Can anyone who has actually fitted, ridden, crashed a big bore NSR125 give me an idea what they're like and what's available?
There's a 140cc kit around, but then there's the 170cc and 180cc kits too.
Also does the Asian market nsr150 barrel fit a European nsr125?
Is it worth keeping the stock pipe with a bigger bore?
Do the kits come with a new carb jet or does that have to be sorted out separately?
Can the stock engine cope with the extra power or do the crank and big end bearings drop out after 3 months?

Any nsr experience would be really appreciated, but pleeeaase not the amazingly helpful "i have a big bore on a [50] [80] [250] [400] [1000] [1300] [Goldwing] [Ford Escort] and it goes fast" crap.

Cheers, jimbo

[Scouse]

Hi

My NSR was apparently as I was told bored out. I'm sure that they told me that it was a 160cc though. It doesn't really make that much difference to the bike, apart from the obvious slightly quicker (but not too much more than) the 125's. I had fun with mine racing 125's and would advise getting it done.

[MarJay]

There's a guy who comes on here sometimes who has a 180cc kit fitted to his NSR125... He was having trouble in that it didn't feel any more powerful than the stocker.

TBH my would be buy a bigger bike. Big bores are okay on four strokes, but two strokes are something of a black art. If you are going to get some work done then get Stan Stephens to have a look at it, that might do you more good.

Still a waste of money on a 125 IMO, better to spend the cash on a bigger bike.

{EDIT}https://www.stanstephens.com{EDIT}
____________________
British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F; Cheap project: CBR900RR FireBlade
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.

[Danny]

If you fit a big bore kit your bike is likely to blow up soon after. So don't bother doing it.

Do you test and get a much faster and bigger bike.

[Ste]

Two strokes with big bores go bang regulary, needing lots of rebuild. Not worth the time and effort IMHO.

As per above, do your test, sell the NSR, then buy a new bike. You'll then be amazed that you considered spending £££ on a big bore kit for your NSR.

[dainesefreak]

I've had a 180 big bore kit on an Aprilia before, quite a while ago now. They garage told me it was going to take a couple of months to get original parts from Italy and they had some big bore kits in stock and it would cost less. So I did it and it was great for about a month, then it went pop.

I had a similar problem to Ste with the garage, CAB, trading standards involved, talk of the small claims court, etc. At the end of the day if you're willing to take the risk and haven't got the cash to do the test then it might be worth doing.

[Danny]

If you've got enough money for a big bore kit then you've got more than enough to do your test.

[jimbo]

Thanks a bunch for the help, the general opinion seems to be kind of negative, so i'll probably skip it.

[stevo as b4]

Big bore kits on a 2 stroke can work ok, but they also have their drawbacks. Any motor designed as a 125, will have a crank and bearings only designed to take the load/torque that the std motor is capable of producing. If you do fit a big bore you are definately shortening the life of the bottom end, even if it can take the extra load. many MX bikes can be converted to bigger cc's but its usually 135-145cc on a 125cc, and 270-300cc on a 250cc, even KX500's can have a 540cc, (why?). Small increases in cc are less of a strain, but again, its putting more stress on the bottom end and transmission. With many big bore kits, if the port timings are not altered, or even if they are sometimes, you end up with more midrange, but can have a shorter powerband, as the pipe will now not be the right volume/tuned length for maximum power. The std carb will usually work fine if re-jetted to suit, but the airbox/filter may become restrictive if the motor needs alot more air. Dont bother with a race pipe, as they will all be suited to a 125cc cylinder, so you wont get any advantage except for weight savings. Sometimes there are problems with cooling and lubrication on big bore motors, so that you could end up needing a bigger rad etc? My KMX200 is really a bigger bored version of the 125, but Kawasaki have designed the bottom end to be tough enough to cope, however it runs the same sized rad as the 125, and so it gets hotter quicker, and there were more overheated KMX200's than 125's for this reason. The power isnt really that different either. The 200 has midrange and gets away quicker, but the KMX125's more peaky powerband makes it feel quicker even if its not.

[jimbo]

Cheers stevo as b4 .That's seriously helpful. I didn't think the cooling system would need to be uprated, because my bike always runs cool (piddly weather here). It sounds like it would become a high-maintenance liability either way. Ta muchly