2 stroke tuning. Dyno? Sunshine Coast QLD

[skypig]

My RM125X project.

The original carb, a special Mikuni, made for Suzuki as far as I can make out. (Possibly only minor differences, like front mounted vent to clear the case... Possibly.) was discarded by the PO.

A generic brand new Mikuni has been fitted.
I've shortened it slightly, I think mimicking the original.
Jetted it as close to stock as possible. Inc NOS needle (another Suzuki special)
It runs pretty good WFO and plug chops look ok. (50/50 Avgas PULP)

Trying to get the midrange, (ANY midrange!!)  a bit better I've tried the clip position from top to bottom. Not much difference. A bit "fluffier" full rich. (I think I'm an insensitive test rider)

I'd like to put it on a dyno, preferably with a "sniffer" up the pipe. (Can this work with smokers?)
I heard there was a specialist near Woodford QLD (Sunshine Coast Hinterland) but can't track him down.
Anyone know of anyone?
Any other tips? (Apart from buying a 250/465 which I might be able to ride... 18yo Simon didn't need no stinking midrange!.... )

[Nathan S]

Based on my experience with my RM125Z, have a look at the ignition timing.

02 sensors in 2-stroke tail pipes give "useful" rather than "sure fire" information. Carefully watching header pipe temps with a fast response gauge is supposed to be a useful tuning tool, but I've never done it.

[Lozza]

My RM125X project.

The original carb, a special Mikuni, made for Suzuki as far as I can make out. (Possibly only minor differences, like front mounted vent to clear the case... Possibly.) was discarded by the PO.

A generic brand new Mikuni has been fitted.
I've shortened it slightly, I think mimicking the original.
Jetted it as close to stock as possible. Inc NOS needle (another Suzuki special)
It runs pretty good WFO and plug chops look ok. (50/50 Avgas PULP)

Trying to get the midrange, (ANY midrange!!)  a bit better I've tried the clip position from top to bottom. Not much difference. A bit "fluffier" full rich. (I think I'm an insensitive test rider)

I'd like to put it on a dyno, preferably with a "sniffer" up the pipe. (Can this work with smokers?)
I heard there was a specialist near Woodford QLD (Sunshine Coast Hinterland) but can't track him down.
Anyone know of anyone?
Any other tips? (Apart from buying a 250/465 which I might be able to ride... 18yo Simon didn't need no stinking midrange!.... )

A few things why run 50/50 mix? Because an unleaded setting and avgas setting run in opposite directions. Best is either one or the other.
Next is the O2 sensor, there is no faster way to confuse yourself than with one of those. Here's why, if yo get missfires a few cycles of unburnt air will go through the engine, thus setting the O2 sensor off, you see that as a "lean as hell" spike, so you richen it up which leads to more misfires and a bigger lean spike, so you richen it again which leads to more misfires.............see the pattern?
An Exhaust Gas Temp gauge is the best tuning tool but I don't think you need that just yet.
The lack of mid range will be combination of pipe/ignition/compression/ports..........easy fixed by starting with again  a TF/TS cylinder

[TT5 Matt]

arnt rm125x's watercooled and ts/tf's aircooled? and there way different motors?

[skypig]

Thanks for the replys.

I'll check the ignition timing. It's basic timing, all CDI.
Yep, water cooled. (I wasn't sure what TS/TF cylinders meant)

I won't be putting a cylinder from anything else on it. I'm hoping my cylinder hasn't been madly/poorly ported. I haven't had the jug off (it was rebuilt before I got it, can see a brand new piston). Looking in the exhaust/inlet, it looks like it has been at least "cleaned up", maybe.

It has the obiquitious DG chamber and silencer fitted.

I'd heard a mix of Avgas and PULP recomended. Some lead, which is good for engines, bad for the environment. Higher octane to reduce the risk of detonation, especially while "tuning". But greater density than Avgas alone. (Which is made for low performance Aircraft engines.)

It also has the GP replica air box. More flow. Impossible to access air screw and idle screw....

[Lozza]

arnt rm125x's watercooled and ts/tf's aircooled? and there way different motors?

Yes silly me I got confused with the air cooled engines

Thanks for the replys.

I'll check the ignition timing. It's basic timing, all CDI.
Yep, water cooled. (I wasn't sure what TS/TF cylinders meant)

I won't be putting a cylinder from anything else on it. I'm hoping my cylinder hasn't been madly/poorly ported. I haven't had the jug off (it was rebuilt before I got it, can see a brand new piston). Looking in the exhaust/inlet, it looks like it has been at least "cleaned up", maybe.

It has the obiquitious DG chamber and silencer fitted.

I'd heard a mix of Avgas and PULP recomended. Some lead, which is good for engines, bad for the environment. Higher octane to reduce the risk of detonation, especially while "tuning". But greater density than Avgas alone. (Which is made for low performance Aircraft engines.)

It also has the GP replica air box. More flow. Impossible to access air screw and idle screw....

Try a standard pipe will be a lot better all round power, the cylinder on the RM isn't too bad. Just be careful of exhaust ducts that have been enlarged that drops mid range power.

Unleaded requires a completely opposite set up to avgas, you could run either in a standard engine and be hard pressed to pick the difference.  When tuned on the limit unleaded makes more hp with a bit narrower sweet spot, leaded gives a greater margin for error. 

[DR500]

it's a 125, so it's' all or nothing.In other words full throttle and loads of gear changing.

[skypig]

it's a 125, so it's' all or nothing.In other words full throttle and loads of gear changing.

Yeah, there could be a lot of this in the problem.
It just seems worse than I remember. (35 years, and maybe early onset dementia.)
I might not be reving it out quite enough - it falls off the pipe each gear change.

I don't have a standard pipe, and I think good ones are hard to come by.

I'd just like to get the jetting as good as it can be - hence the thoughts towards professional help.

As suggested I'll check the timing.

It's all fun.

[Nathan S]

I got that advice about my Z, too... if you think it might just be because it's a 125, then get someone else with VMX 125 experience to ride it before you tie yourself in knots.

But if you think it's wrong, you are probably correct...

[80-85 husky]

you've got a std carb setting but an after market airbox and pipe. id bethinking it wants a bigger main jet at least??keh??. repack the muffler, can give a bit of assistance onto the main jet.

get the timing spot on, can make a big difference with the 125's.

[Lozza]

I might not be reving it out quite enough - it falls off the pipe each gear change.

I don't have a standard pipe, and I think good ones are hard to come by.

That is the pipe 90% and maybe 10% jetting/ignition/set up. Rev it until it doesn't accelerate.