Two-stroke performance tuning?

[SS90]

It would be nice to move this in to the "Mainstream" section of this site, and I hope we can do this shortly, however, "Good things take time", and some co-operation is needed.

Let's all get together and start a "Two stroke tuning" thread that rivals others in the world, as, we are all Kiwi's, and as such have an amazing pedagree (particularly when it comes to high powered racing Two stroke engines (Kim Newcome for example, & the often forgotten B.S.L Team, and it's conceptor, Brian Buckley)...........

Looking at the current NZ bucket racing rules, I see the potential for developing a very special type of engine.

A 125cc, Air cooled Two Stroke, limited only by it's capacity, (and), a 24MM carb............

I am unsure of the rules you can apply when starting a thread, but one I would like to place is that no-one is allowed to

"use words bigger than their I.Q"

What I mean is, lets try to simplify it, so that EVERYONE can contribute

......... many effective solutions have been discovered by in-experienced observers, simply because they applied logic that the rest of us missed , because we where "too involved".........

So.... lets Begin......

[SS90]

Since the Japanese started putting "real effort" into Air Cooled 125cc two strokes, it was around the end of the 70's that they gave up, and started to water cool them (and as such, started releasing "real power")

With the current rules in Buckets being the way they are, this gives rise to a "re-emergence" of developmental skills.

The biggest problem facing the 125cc class (air cooled rule not withstanding) is the limitation to a 24mm carb.

Does any-one here have a 125cc air cooled engine they want to develop?

Post the current port timing specs, and "Lets get started!
"

[saxet]

Well I'm looking at building a new Suzy GP125 bucket race motor hence my interest in other threads on K.B. My existing motor is the same thing developed according to John Robinson's specs in a Performance Bike article from the 70's but not taken as far as him. This was my first attempt at tuning a 2 smoke and all in all was pretty successful. Approx 17hp, rideable and very reliable but I'm under no illusions that it's any where current in terms of design. It was based on 70's technology.
I've recently just got an inkling as to how far behind the times it is..still I came 4th in the Bucket GP. As much due to the fact that several of the faster bikes didn't last.
Quite a lesson in reliability vs. power.
Recent reading as led me to the TSS500GP macine developed by Wayne "Wobbly" Wright. a N.Zer engineer for GRand Prix(unsure as to which teams he's worked for).
The porting pics have intrigued me as has the toroidal head.(only just heard about it-Yeah we all have to learn how much we don't know)
I'm guessing some of this could be applied but thats getting many steps ahead of myself.
I suspect some of the bucket tuners have applied some of this as one 50 cc bike seems to have more power than most 100's or 125's.
Will post origina ltiming specs for GP100 motor that I have laying on the bench when I get them sussed(was planning to strat by boring to 125cc but will hold fire for thr moment).Also in the middle of a house renovation project.

Anyone wants basic 2 stroke answers ..I'll do my best.

[Skunk]

I have two (and I've watched TZ350's thread with interest) - one is a cast iron rotary Kawasaki F6 and the other an alloy rotary Suzuki TF125. At present both are in the barely running stage so a little early to post specs. But I will.

[quallman1234]

I have a 100 I'd like to develop. As the chassis is starting to get into shape and has real potential. It is a Highly Ivanised Aprilla RS50 Frame. Sorry Ivan.

Could be a start? Its pretty bog stock. I have access to Lathe's/Mills/everything you can imagine. And some friends who can actually use them accurately and like beer... Well bourbon.
I have two barrels. One completely stock, the other slightly widened by none other than the infamous Ivan Juggins.
Two heads. One what has a slight squish on it. The other bog standard.
One Barrel is stock 50mm the other 0.5OS. Also have a spare new piston kit for the stock barrel.
Its got some old YZ125 chamber donated kindly by Skunk works. With a TZR250 header, welded up by Glen.
The main problem is the 4 speedbox. So i'd need something wide and fat. (The power curve that is). To make the most of what i have.

The biggest gain would obviously be a purpose built chamber, at this stage. But why not do everything at the same time?

Meh, if your specific to a 125. Then thats fine, ill just pod along doing my own thing .

Admittedly its got no spark atm. But thats minor. I hope.

[tri boy]

Ixion will cream his undies when he stumbles on this thread.
(unless he operates commando style)

[saxet]

Hey Quallman1234 probably gonna need the engine model, is it a GP100?. If so you might be lucky, I've got one here I'm planning to bore to 125 but before I do I'll measure it up so there's a base point to start from.....Hopefully within a couple of weeks.

[bucketracer]

Let's all get together and start a "Two stroke tuning" thread that rivals others in the world, as, we are all Kiwi's, and as such have an amazing pedagree (particularly when it comes to high powered racing Two stroke engines (Kim Newcome for example, & the often forgotten B.S.L Team, and it's conceptor, Brian Buckley)...........

I understand TZ350 worked for Bill Buckly at Buckly Systems during the time they were developing the BSL500. If your unsure about anything you could ask him. Just a thought.

[bucketracer]

Hey Quallman1234 probably gonna need the engine model, is it a GP100?. If so you might be lucky, I've got one here I'm planning to bore to 125 but before I do I'll measure it up so there's a base point to start from.....Hopefully within a couple of weeks.

Im working on a GP100 myself, unfortunatly you cant bore a 100 to 125 but you can fit a 125 barrel head piston to a 100 bottom end. They go straight on. The rotary valve and valve cover are a bit different but can be modded. Look at the ESE thread for details.

[bucketracer]

Does any-one here have a 125cc air cooled engine they want to develop?

Post the current port timing specs, and "Lets get started!
"

I have a GP100 but would like to run it as a 125.

Scraped from the ESE thread.

Suzuki GP100/125 Covers and Rotary Valves.

Std. Suzuki GP100 Inlet Opens 135 BTDC Closes 45 ATDC
Ex Opens 94 ATDC Transfers Open 123, 125, 126 ATDC.

Std. Suzuki GP125 Inlet Opens 145 BTDC Closes 55 ATDC
Ex Opens 91 ATDC Transfers Open 122, 122.5, 123 ATDC.

[quallman1234]

Hey Quallman1234 probably gonna need the engine model, is it a GP100?. If so you might be lucky, I've got one here I'm planning to bore to 125 but before I do I'll measure it up so there's a base point to start from.....Hopefully within a couple of weeks.

Hey its an AX100 (yea yea i know).
3 petal reed valve. Standard.
I have a 6 petal reed valve sitting around. A V-type reed valve. Could mod it and make it fit.

First Question of the day! What advantages and Disadavantage's are there with larger reed blocks?

p.s
Its' kyle the kid who lent you a back protector at taupo.

[saxet]

Hey Kyle

With Bigger reed blocks I'd say..advantages-more fuel/airflow.
Disadvantages-too peaky-too much fuel.
So far I've learnt everything is a comprimise and finding the limit where comprimise becomes liability is the trick.

If I'm off track someone say so.

[SS90]

The more the merrier!

With the Ax100, there is a small problem with tuning, well, that is, they look like "crankcase induction" (like Mb100's, CR125's etc for example), but the reed block location ends up making quite a torturous path through a "piston window", like say an RZ250 (except the RZ intake is mounted directly on the cylinder, and far better in this respect!)

The intake rout is fairly poorly designed (in as much as performance goes), and it could perhaps be considered wise to simply "go bigger" (and try and develop your intake system to simply "flow more", to help compensate for this...........

Personally, with out having one in front of me, it's difficult to say, BUT, I think it may actually be a good idea (in this case), and some good gains could be made!

Does anyone know of an AX100 with a bigger reedblock fitted?

Also do you have the cylinder off the engine?

I found these pictures, so you can see what I mean about the inlet.

[SS90]

Well I'm looking at building a new Suzy GP125 bucket race motor hence my interest in other threads on K.B. My existing motor is the same thing developed according to John Robinson's specs in a Performance Bike article from the 70's but not taken as far as him. This was my first attempt at tuning a 2 smoke and all in all was pretty successful. Approx 17hp, rideable and very reliable but I'm under no illusions that it's any where current in terms of design. It was based on 70's technology.
I've recently just got an inkling as to how far behind the times it is..still I came 4th in the Bucket GP. As much due to the fact that several of the faster bikes didn't last.
Quite a lesson in reliability vs. power.
Recent reading as led me to the TSS500GP macine developed by Wayne "Wobbly" Wright. a N.Zer engineer for GRand Prix(unsure as to which teams he's worked for).
The porting pics have intrigued me as has the toroidal head.(only just heard about it-Yeah we all have to learn how much we don't know)
I'm guessing some of this could be applied but thats getting many steps ahead of myself.
I suspect some of the bucket tuners have applied some of this as one 50 cc bike seems to have more power than most 100's or 125's.
Will post origina ltiming specs for GP100 motor that I have laying on the bench when I get them sussed(was planning to strat by boring to 125cc but will hold fire for thr moment).Also in the middle of a house renovation project.

Anyone wants basic 2 stroke answers ..I'll do my best.

Cool!

does anyone have some dyno curves available for, say, a tuned Gp125 (or similar)
It doesn't have to be a GP125 as such, but a competitive disc valved air cooled two stroke with a 24mm carb to see what can be done

I see that Suzuki only claim 9.5 P.S, originally and I cannot find a curve for a tuned one.

I am interested to see what sort of power they are making with 24mm carb...... I think that 17 P.S would be heading towards the most you would see.....but I truly don't know!

[quallman1234]

The more the merrier!
Does anyone know of an AX100 with a bigger reedblock fitted?

Also do you have the cylinder off the engine?

I found these pictures, so you can see what I mean about the inlet.

Skunk's has a bigger reedblock fitted .

Yes i know what you mean about the inlet.
Its going to be difficult getting a v-type reed block in there as well.
Might have to move the reedblock back. What would this effect?