RS 125 jetting? please help!

[arsco77]

I'm in the process of de-restricting my 2009 RS 125, but am slightly unsure on the carb settings.. I've got the Dell'orto VHST 28mm carb, can't really afford the 34mm at the moment! :/

I have got:
- a full arrow system fitted
- powervalve and solenoid fitted
- drilled CDI
- free suction lug on the airbox and closed off secondary air tube (as in the derestriction guide)
- BR10 spark plug
- also put on a 17 tooth front sprocket

I have looked through some forums and the aprilia guide, but am still slightly confused on the carb setup!

Is the 185 main jet too rich?
Do I need to get the size 50 throttle valve over the 45? What are the differences?
D53 conical pin with S45 min. jet?
If I keep the 45 valve, do i keep the U36min jet?

Would appreciate some help!
Cheers, Max

[arsco77]

After doing some more research, I've come across this setup:

Main Jet: 178

Min Jet: U36

Conical Pin: D53

Throttle Valve: 45 (is that standard?)

And will this be ok for the bike??

[Kickstart]

Hi

More to a plug chop than that (need a decent hill to keep enough load on the engine to keep high revs and throttle for a bit), and a grey colour would suggest it is running VERY lean.

Not sure on the jetting of that. No knowledge of the late RS125s with that strange carb. However if you are playing with jets work on the basis that they are cheap and that rich is safe. Go too rich and you will just use more fuel and lose a bit of power (and long term increase wear a bit). Go too lean and a good chance of a seizure.

All the best

Keith
____________________
Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[arsco77]

Thanks for the advice,

Max

[satelliteone]

on my delorto 32mm VHSA standard.

Main jet 148
Tube 262FL
slow running jet 38

Thats for a tzr125r, but i would expect a full power rs125 to be simular. still a 2 stroke. and very close compression values.

IF i change the the airbox to a cone filter, and then rebore say to 1mm oversized, the main jet would increase to say 155-160, but a plug chop would see if it would be right.

slow running may increase a little to say 40.


have you got the standard data on your carb?.
____________________
Honda XLR125R - Project
TZR125RR Belgarda 4DL - Sold
Chinki Project done n Dusted/sold** DTR125 2003 - Finished/sold

[Kickstart]

[satelliteone]

the dtr uses the 28mm mikuni`s.. but have the power thingy doofers and the main jet is 240. , but i cant remember the the size for the non power versions.

i think if i can remember, the air fuel ratio is 14:1 on any rev range, some one put me right please. I think this what your trying to achieve. Any weak air mixture in that, will cause flat spots, most problems are air fuel ratios, at the mid-high rev ranges, this is where your center pin comes in, tapered to effect. also ironing out flat spots. The air pressure around you also effects mixture, but we are trying to find a balance here.

If you running weak at the top, the engine will get hotter, and blow a hole in the pistion as the mix is weaker, and centers in the middle of the piston.


back to the carbs, you say 150 main jet, sounds about right for a CC value of a 125. on a 32-34mm


also depends on the size of the venturi that equates to the main jet sizes,

from experience 125cc, the slow running jets, always sits around the 38-40. Its the mid range to high thats the key size.


if you have the standard data on the 28mm, then go from there, just increase the main jet slightly. depending on your intake airbox or cone filters. piston size..etc..

just another thing, is that the vespa community, use the delorto carbs as a custom upgrades and as standard. and there is plenty of data on the net for these 150cc and 125cc engines. That might give you some idea of jetting.
____________________
Honda XLR125R - Project
TZR125RR Belgarda 4DL - Sold
Chinki Project done n Dusted/sold** DTR125 2003 - Finished/sold

[Kickstart]

[satelliteone]

good info here, and i stand corrected. 12:1 ratio



https://twostrokemotocross.com/2009/12/carburetor-theory-and-tuning/

and here for the rotax engines


https://www.karting1.co.uk/new-ThePreparation&JettingoftheRotaxCarb.pdf
____________________
Honda XLR125R - Project
TZR125RR Belgarda 4DL - Sold
Chinki Project done n Dusted/sold** DTR125 2003 - Finished/sold