Any one put RG150 chamber on a GP125?

[Triplenut]

Hi All,
I'm finally about to enter the fast paced world of bucket racing to help fill the boring gaps between postie races.
A mate and I have gone halves in a GP125 which we are mildly tweeking and is nearly ready to go.
TZ350's ESE thread is a great source of info but i'm only up to page 60 of the thread, 300 pages to go!!

Our GP is running the stock pipe with the guts cut out of it which I doubt is doing the power any favours.
I've tried finding an RG250 or RM125 chamber as I understand these are suitable but no luck.
I've seen a an RG150 chamber on tardme it looks to be similar, any one tried one on a GP125 ? or any thoughts on whether its going to be better the a a gutted stocker?

Appreciate any thoughts from the experts.

Cheers
Red

[koba]

Hi All,
I'm finally about to enter the fast paced world of bucket racing to help fill the boring gaps between postie races.
A mate and I have gone halves in a GP125 which we are mildly tweeking and is nearly ready to go.
TZ350's ESE thread is a great source of info but i'm only up to page 60 of the thread, 300 pages to go!!

Our GP is running the stock pipe with the guts cut out of it which I doubt is doing the power any favours.
I've tried finding an RG250 or RM125 chamber as I understand these are suitable but no luck.
I've seen a an RG150 chamber on tardme it looks to be similar, any one tried one on a GP125 ? or any thoughts on whether its going to be better the a a gutted stocker?

Appreciate any thoughts from the experts.

Cheers
Red

Sam Van Oosteram (Spelling?) from up Auckland way had a GP125 engine in an RG 150 frame. He used the RG pipe too.
It went quite well, about the same as a standard FXR or a little better.
I'm not sure if anything else was done to the motor or not.

[jasonu]

Hi All,
I'm finally about to enter the fast paced world of bucket racing to help fill the boring gaps between postie races.
A mate and I have gone halves in a GP125 which we are mildly tweeking and is nearly ready to go.
TZ350's ESE thread is a great source of info but i'm only up to page 60 of the thread, 300 pages to go!!

Our GP is running the stock pipe with the guts cut out of it which I doubt is doing the power any favours.
I've tried finding an RG250 or RM125 chamber as I understand these are suitable but no luck.
I've seen a an RG150 chamber on tardme it looks to be similar, any one tried one on a GP125 ? or any thoughts on whether its going to be better the a a gutted stocker?

Appreciate any thoughts from the experts.

Cheers
Red

Pretty much guaranteed to be better than the stocker.

[Triplenut]

Thanks for your input Gents, I'll give it a crack
Cheers
Red

[Buckets4Me]

Pretty much guaranteed to be better than the stocker.

you would say that but back before I inherated old #9 my stock engine and stock exaust (did get a full rebuild and clean up first. and the exaust was choped up a bit. mainly for groundf clearance) went as fast as any of the other E.S.E bikes
I wasnt going to change anything till one of them was faster (and then I stole the fast one 19 h/p with rg250w chamber). Now I'm waiting to rebuild that second engine and get up near 30 h/p

[Pumba]

.......Now I'm waiting to rebuild that second engine and get up near 30 h/p

Why bother. It has been a couple of seasons since I have seen it on the track

[koba]

you would say that but back before I inherated old #9 my stock engine and stock exaust (did get a full rebuild and clean up first. and the exaust was choped up a bit. mainly for groundf clearance) went as fast as any of the other E.S.E bikes
I wasnt going to change anything till one of them was faster (and then I stole the fast one 19 h/p with rg250w chamber). Now I'm waiting to rebuild that second engine and get up near 30 h/p

Ruapuna may be different though. Sam's one was frustratingly just a little bit faster than the FXR I was on.

[TZ350]

Now I'm waiting to rebuild that second engine and get up near 30 h/p

Why bother. It has been a couple of seasons since I have seen it on the track

Its been sitting at work for a while waiting for an upgrade, it might be time to get it sorted, as it could be a real weapon.

[TZ350]

I've seen a an RG150 chamber on tardme it looks to be similar, any one tried one on a GP125 ?

Sam Van Oosteram (Spelling?) from up Auckland way had a GP125 engine in an RG 150 frame. He used the RG pipe too. It went quite well, about the same as a standard FXR or a little better. I'm not sure if anything else was done to the motor or not.

Yes Sam and his Dad, Chris Van Oosterum, (they are from Hamilton) tried an RG150 pipe on their GP125 engine it went OK'ish but Chris says it was much better when they fitted a pipe from an Aprilia 125 road bike which is what they used with some mild Ex porting and both pipes were very heavy compaired to a purpose built chamber.

[Triplenut]

Hi TZ350, thanks for all the great info on your ESE post, very inspirational.

The guy I purchased the bike off gave me a template for a chamber that is suposedly ideal for the stock motor ( first pic) I'm hoping I can modify the RG chambers to closely match this rather than build a new one from scratch.
For now I want to keep motor largely stock for reliability.

2nd pick is the RG150 chamber just purchased from Petersales.

3rd pick is the beast, just finished rebuilding brakes/lines and forks, fork brace, crash protection. Next job rearsets, frame/swing arm bracing, stiifer shocks/ride height and seat.

This is probably a stupid question ( this is the first two stoke I've owned in 20 years) , does an expansion chamber usually require rejetting like a performance 4 stoke pipe would? or is it just more efficiently using what is already there?

Cheers
Red

[TZ350]

does an expansion chamber usually require rejetting like a performance 4 stoke pipe would? or is it just more efficiently using what is already there?

Almost any change to anything requires a look at the jetting, when we ran Std GP carbs, over the different bikes the jetting ranged from 97.5, 105, 107.5 and 110 main jet. We used KX80 ignitions with no curve and the static timings were 20, 26, 23 and 16 deg BTDC and the fastest bike didn't have the bigest MJ or most advanced timing. The settings for each bike were sorted out on the dyno, so they were pretty close to the optimum in each case.

A common thing we find when dynoing friends bikes are engines with over advanced timing and jetted up to compensate, these feel fast on the track as they are peaky but a better setup with more hP and better curve feels flater, but on the track its faster.

Another trick we did with the GP's was to space the carb cover off by 4-5mm or the thickness of a 5mm nut. This was good for a hP in itself on our early bikes.

[Buckets4Me]

Another trick we did with the GP's was to space the carb cover off by 4-5mm or the thickness of a 5mm nut. This was good for a hP in itself on our early bikes.

not my one it lost topend power but gained more down low

[Buckets4Me]

Why bother. It has been a couple of seasons since I have seen it on the track

shut up. Now go change a nappy or something will ya Wait till you have 4 of them and the oldest steals your bike

[TZ350]

Another trick we did with the GP's was to space the carb cover off by 4-5mm or the thickness of a 5mm nut. This was good for a hP in itself on our early bikes.

not my one it lost topend power but gained more down low

Yess odd that, all that we can say is, all were pretty much made to the same formula but no two ESE bikes worked out the same on the dyno .....

[Triplenut]

Carb spacer has been made and fitted thanks for the info.
And will definitely run the bike on the dyno to tune the jetting and timing. Last thing we want is to seize it on its first outing.

My partner in this bike has never ridden on the track so the broadest power we can get will be helpfull to his learning process (and probably mine).

I need to check out the carbs and rotary valve, I think this bike was a GP100 now fitted with a 125 head. Not sure if the previous owner changed the carb and valve as well as the head.

Cheers
Red