RS125 Polini Big Bore Kit - Gearing Change?

[Loud]

Hi All,

I'm giving serious thought to purchasing a Polini 154cc Big Bore Kit for my RS125. I've read that 37bhp is acheivable given the other mods I've already done, and this sounds appealing.

From all that I've read this is going to introduce additional stresses to the bottom end - after all it is a touch over a 20% increase in capacity. I gather this will see me needing to rebuild the crank more often in order to replace the rod and big end bearings. Feel free to interject if I haven't considered everything I need to please.

My question is regarding the gearing of the bike though. Should I gear the bike taller, or will this introduce even more stress?

[Goldmember]

I wouldn't bother with the 154cc bore kit just not really worth it...

i don't know about the gearing though

[Loud]

Thing is that I have to buy a cylinder and piston for another bike anyway - not mine this time! So I'm thinking about spending the modest extra amount and doing a swapsy

[Gangus]

Depends if the barrel shifts your powerband.
Do the mod and run it.
Dont do the shifty though!

[Loud]

Dont do the shifty though!

No shifty, all above board - the other bike is one I'm buying to get running again!

[aaronmvrider]

with that power change i wouldnt thing gearing it different will be of benifit.... 37 hp not a big deal for gearing

[pesty74]

why dont you just change the exhaust and put a bigger carby on your bike 35 mm it could go pear shaped need to tune it right and there is no 1 here that will touch your bike since it's a 2 stroke i only found 1 that will

[Loud]

with that power change i wouldnt thing gearing it different will be of benifit.... 37 hp not a big deal for gearing

I would have thought a 40% increase in power over stock was substantial enough to look at a gearing change, but I'll do as Gangus suggests and run with the existing gearing setup to see how it goes.

[aaronmvrider]

i guess it will also depend on your riding needs... long distance or short squirts around town

it will be more punchy but i still wouldnt expect massive power

[pesty74]

you might have to re-program your CDI unit if your going to use a big bore kits Zeeltronic Handheld programmer but you will only get alittle more torque when comming out of corners there are a few sites to look at and which they specialize in 2 strokes and will give you the info you will need try this site they are in germany which i have brought a exhaust and carby from Internetseite von Fischer-KFZ

[Gangus]

Torque will make it punchier and faster. You could take a tooth or two out to increase your top speed etc. But the real issue is if it lifts or drops your operational window. I added a tooth on my track rs which killed the basin as with a 42 rear I'd drop 2 gears pull through the apex and drive up the hill. With a 43 I was at 11k by dropping 2 gears! Useless! Dropping one gear I would be at 8 something and wouldn't get a hard drive up the hill and this cost me 12kmh top on the back straight! Gearing will make or break a 2 banger!

[Loud]

I've read a bit about people changing both the front and back sprockets, eg down one at the front and up one at the rear - This sounds to be a means of a more incremental increase than simply changing the front or rear. Plus they come in gold...

Peaty I go through PJME and have done so for my carb, filter, reed block, exhaust, piston, cylinder, head, clutch, etc etc. Have you had someone local dyno tune your Mito?

[Gangus]

I want a 14/44
same roughly as 13/39
the link book has a table in it

[Goldmember]

Gearing Commander: Motorcycle Speed, RPM, Chain & Sprockets Calculator

[Gangus]

I had them add the vj22 Simon

[pesty74]

i havent taken my bike to any one as yet to dyno tune it but spoke to some one who races and told them what i want to do and what im getting so they will help me out and tune it properly for me but talking to the guy from germany and he said with the add on's im putting on should get about 40hp same when i spoke to a guy from the UK about more power and same thing about 40hp max over wise 1 hp =$1000 i asked about getting a big bore 170cc and he told me he tried and got a friend who races to ride his bike they told him its not worth it so he sold the kit and went back to a 125cc on his cagiva sp ex- factory bike only had slight bottom end power out of corners and top speed was down

[EEKNOWS]

An RS 125 been playing with pulls 17/44 have it up 175k's now.

[pesty74]

i rang most of the dyno's in perth and told them i have a 2stroke and they say they are not interested

[510_go_kill]

Hi guys, I owned an aprilia rs 125 and just fitted a 34mm carb, if you guys interested on getting two strokes dynoed, call these guys!

Witch Cycles
Motor Cycles, Parts & Accessories-Retail - Rockingham, WA
Cnr Day & Dixon Rds, Rockingham WA 6168, Australia
(08) 9527 2398

I haven't done any with them but I just called them and confirmed if they do 2 strokes, and they do!

any of you know if a single curve CDI unit in PJME worth buying? or should i just get the zeeltronic with the remapable module?

[Loud]

Thanks for the tip there, it's nice to have an option - although it's a bit further than the Welshpool shop that's apparently now allowing two-strokers to use their dyno.

What year is your bike? And what else has been modified, aside from the carburettor? The ignition is a fair way down the list of things to do...