Aprilia RS 125

[2TInstitute]

Been working on a RS125, was a much abused example from a very dumb or brain dead po. Like rode 5000km with the PV wired open, was to dumb to find that a $100 odd had a brand new on off ebay.
Anyways the bugs were ironed out before the tuning started, began with a 34mm Delorto VHSB, V Force 2 reed block, TYGA pipe and a Zeeltronic.
Dyno run after rejetting got 28.83HP at the wheel and a very ridable power curve.One odd thing was removing the 'restrictive' airbox snorkel showed a 2 HP loss and about 5 HP on over rev.
After a trip to the drags at EC (ran a 14. made some seroius bottom end noises. Strip down saw the big end knackered. A uprated big end bearing was found, so with the crank back from CRS and some more cylinder work it back and alive. Intial reports are positive and a trip to the dyno is on the cards very soon.
(I'll edit this with a few youtube clips)

[Jeram]

interesting

was that the same rs125 that you were working on for the young fellas some time ago?

28.8 aint bad for such a conservative dyno

those fools claiming 32hp after simply derestricting must be smoking the good stuff?

14.8 is very swift for a 125er

[2TInstitute]

Yes, a terminal speed of 86mph hoping to get closer to 95mph, but you know more about drags than me. Owner reckons about low 14's a quickshifter and a good launch might see a 13.
Only ever seen 1 30+HP dyno graph, hopefully this will be the next.

[2TInstitute]

Delight to ride on the road, few sensible mods has them going hard and being able to tootle around through school zones. Often overlooked as just a learner bike, but miles of fun on the twisties. Track days will require a suspension upgrade(on the cards next) with the aim of a sub 2 min lap of EC.

[Jeram]

well to put it into perspective,

a kid on a modified CBR250RR with wheely bars, lowered gearing, and lowered suspension was cracking 14.8s back a few years ago.
and he had 40hp+

The secret to a low ET is usually a quick 60ft time, not a high terminal speed
so if he lowered his gearing a tad to get off the line quicker, he will cross the finish line reving the tits off it in top gear, I reckon 13s would be on the cards for sure!

[graham]

14.8 on a 250............

Well eons ago....1968 when I had all my hair and had just turned 20, I put a Bultaco 250 engine......A Mettise TT the forerunner of the Astro engine into a Frame similar to a BSA Bantam..... the whole lot weighed 70 something KG

On Methanol.....39BHP @ 8200

Well after a bit of development my best time was 12.68 at 99MPH
It made the CB750's which were the latest thing at the time look very slow.





A few years later......1981..... 2 X YZ250H engines on methanol, about 85BHP and 115KG all up this thing went 10.77 @ 132MPH....



Nothing like a dragstrip to develop a twostroke........

Graham

[graham]

I forgot to add.....

Beware TwoStrokes are a lifelong addiction.......

Graham

[2TInstitute]

I forgot to add.....

Beware TwoStrokes are a lifelong addiction.......

Graham

Ain't that the truth

[DOC03]

So Graham, is that you on the bike ? Fantastic Pics !!!
Reminds me so much of "the Worlds Fastest Indian"

[graham]

yep, that,s me......

If you ever get a chance to see the doco that was made in 1968 that they based the Fastest Indian movie on, (it came in a 2 Cd set with the Movie) You will see Bert running his Velo sprinter when it broke the barrel flange off during a sprint meeting in Southland...... in the background you will see my bike at the same meeting......and me in a duffel coat with hair that was a lot longer and darker, and thicker than now......

Back before Insurance and liability was an issue.....and drag strips were un common, it was easy to get permission to close a public road for a few hours to run a sprint or hillclimb..... and it was the only way to quantify development on a motorcycle...... very difficult to get access to a dyno back then so we did what we could to develop stuff.....

ie circa 1972 we took a TR2B......an air cooled 350 production racer (pre TZ) out to a sprint meeting with 4 sets of pistons with progressively larger grooves cut into the crowns in the transfer port areas..... we went from 136MPH up to 146 to 151MPH and back down to 144 with 0.25mm steps....

I learned more from a day at the strip than at any race meeting.....

There is of course the egg dyno that we used to develop a bike we could use on a public road.......I could tell you about that if you're interested...

Graham

PS...... things weren't better back then than now......you have more good parts at ridiculously inexpensive prices now and more quality info......and a lot of bullshit as well......you just have to be able to sort between the two...

An RZ350 on 28mm carbs, well setup with a mild tune using only Yamaha bits, running in road ridable trim produces more power across a wider range than any TZ350 from the mid 70's era.......

Just like a Proton!!! 1600cc in 24hr Production trim, laps Bathurst 3 secs faster than the best Falcon GTHO time...... and the Chase wasn't in the way back then...... tell your Ford mates that and watch them cringe.....

[DOC03]

Very cool Graham, Yes would love to hear about the Egg Dyno !!!
I reckon theres a lot of guys that would love to hear about any of that stuff, especially us that remember having more hair.
I know the Doco but havent got a copy of it, might just have to track one down now.

[2TInstitute]

Hey I'M the only one who is allowed to hijack threads

Anyway as promised a youtube of the RS125.

http://www.youtube.com/watch?v=SBomHoWaJwc

As Jeram said "no need to dyno a drag bike the strip IS the dyno"

[graham]

yep I guess we have got off topic a bit.....

The egg dyno sort of evolved from a search for a method to accurately measure modifications. It started by trying to gauge where for example the distance travelled to reach a particular speed was obtained.

In Drag racing the speed obtained at the end of the strip is a direct indicator of horsepower..... whereas the time is related to traction, gearing, weight transfer, rider ability and many other factors....(as well as power).

So ignoring the time and only looking at the speed, we can gauge if we have increased horsepower reasonably accurately.

Extending this a bit, the shorter the distance it takes to reach a fixed speed, the greater the power.

Now how to judge where you actually are when you reach that speed..... we tried distance markers and tried to estimate where you were whilst looking at the speedo at the same time......not repeatable enough...then we figured that we could just drop something from the bike at the exact time we reached the speed......something that would stop immediately, not slide or roll, something that would mark the exact spot where the speed was reached.........

Bearing in mind this was done on a public road, at quite err.... reasonable speed, and if err.... official persons turned up to see what was happening, there was no evidence other than a few splats of dropped egg on the road

So each time the egg trail got closer to the start of the test run, you knew that your mod had worked.

Today I would buy a GPS device that I could push a button when the speed was reached, that would tell me the position within a meter or so. The eggs got us to that sort of accuracy 45 years ago

One problem was that after a while we were having to avoid Crows and Magpies.........

Graham

[DOC03]

Sorry Lozza, pretty cool though. Maybe someone should start a thread about "Old" two strokes / events / pics / memories etc - pretty cool subject !! and would be great place to pass down / preserve / share some great knowledge and experience..

[Jeram]

yeah, definitely do that.