ESE's works engine tuner

[Flettner]

So the slower/later timing softened the " hit " making it easier to control tire spinup, and the shorter gearing made it accelerate faster due to the torque multiplication.
A better set of compromises, in that application.
Yes, MX is a special case with a special set of requirements to be fast, but you gotta realize the vast majority of members on here don't give a monkeys what happens well under the pipe.

I give a monkeys,

[jonny quest]

Wobbly, I know you know power off the pipe is always beneficial. Always.

The moral to my story (which was brought up because of Airstriker mention) mechanical gearing advantage in my case trumped all out power.

Bottom end power, strangely, is more beneficial the bigger an engine gets for faster lap times.

[F5 Dave]

I know I was dribbling on about Enduro bikes before which are largely used below peak, off pipe. Yesterday I was out on the Trials bike. Still good clean 2 stroke fun. . . but I don't think it has any on-pipe power

[Larry Wiechman]

Wobbly, I know you know power off the pipe is always beneficial. Always.

What if my monkeys think like kart racers and use a slipper clutch that gradually engages just before peak torque? On a small displacement motor (Freetech 50 or Bucket), that would help cover up gearbox ratio gaps and the power dip at 2/3 RPM.

[jonny quest]

What if my monkeys think like kart racers and use a slipper clutch that gradually engages just before peak torque? On a small displacement motor (Freetech 50 or Bucket), that would help cover up gearbox ratio gaps and the power dip at 2/3 RPM.

Every motorcycle with a gearbox and clutch has a slipper clutch. It's your left hand. Good offroad riders constantly slip clutch in corners.

[diesel pig]

KTM used Keihin carbs from MX Suzuki RM 250 for semi mass production Red Bull cup, when they was on the right way with 2T Al frame 125. Original PJ and TPS, but working must be different from MX.

Of couse. The Red Bull bikes were mean to be all the same ( I am sure some here would let us know if that was actually true or not) So they all should here been giving up the same amount of power with all them having the same bad carburation. So what Wobbley posted still holds water I think.

[ApolloMotoMoto]

Every motorcycle with a gearbox and clutch has a slipper clutch. It's your left hand. Good offroad riders constantly slip clutch in corners.

1000X this.

My Single-Speed Direct-Drive Kart track racing machines have a manually operated friction clutch. A carefully manuplated clutch hand converts this into a slipper clutch. All the fastest racer are apply controlled slip in certain areas around the course to maximize drive and generally keep the engine within its useful power-delivery band given my use has NO TRANSMISSION of any kind.

Yeah I care about "under the pipe" features, but only because our engines and vehicles are not yet really optimized for the use case.

We keep changing gearing to shift the RPM range relative to vehicle speed "UP" such that we can get the bike "above the torque hole" comming out of the slowest corners.

As it stands right now, we still have to use RPM's that are below 2/3rds of the torque peak, which means accelerating through the 2/3rds torque hole.

Everything that addresses while still requiring the vehicle to operate in this band is mostly a band-aid.

Really, gear ratio must be such that the vehicle never drops into that 2/3rds of peak torque "torque hole" band, with an effective power range wide enough for the application;

That means in my case, if I am going to make peak torque between 9-10k PRM in a ~90-100cc engine, I cant really be using RPM's below 7k RPM's, and with a required power range for single-speed direct-drive of 3.0+ (ideally more like 4.3-3.6...) that means this engine needs to have usable over-rev to 20k RPM's, or I am going to be forced to use the dreaded "torque hole" range.

As it stands right now, our setups are not optimized, over-rev to 15k is barely consistently achievable, engine RPM comming out of the slowest corners is 4-5k RPM's, and there is a LOT of 'manual slipper clutching".

Its mildly interesting how much of a race is decided on "cltuch games" VS. the other elements of the competition; clear evidence that the setups have quite a bit more optimization required.

It can be deceptive how much better a bigger rear sprocket can be. You think you are going to give up terminal velocity, be the way the engine is loaded will allow over-rev to extend further than intuitionally expected when you slap the bigger rear sprocket on the bike, and the torque multiplications wins everywhere else can produce an unexpected range of ideal gearing if these larger rear sprockets are never fully explored.


This is a persistent argument within my own race team and across the paddock, and everytime we put a new "biggest ever used" rear sprocket (or smaller front sprocket, or anything else that drives the ration in this direction) lap times come down, and we dont loose the terminal velocity we would expect to loose given the change.

[wobbly]

Quoting different Apple and Oranges scenario's, like direct drive karts, Gyrocopters, MX/VMX or whatever are all special, specific cases where off the pipe power does matter.
And the people doing those things imho are in the minority on here as a group.

All I am saying, for example, is that if you take any MX 125 engine where power under the pipe is so important that people even clutch the things off the slowest corners, then fit that engine to a kart the
fastest setup then needs no power at all below 9500, but has to run the shortest gear possible and thus it needs to rev to 14500 and beyond.

In this case having a carb that has fantastic throttle connection at 4500 is completely useless, especially if that carb wreaks the front side, peak and overev power.
Thus I would never use that carb in a Roadrace or LSR end use.
Same with FreeTech 50's, the fastest bikes in video's I have seen will easily rev to 16,000, and they never drop off the pipe, or if they do they get beaten by correctly tuned engines that dont.

Bucket racing, that this forum was initiated because of , is in the same category.
If you are off the pipe or slipping the clutch, a correctly tuned/ well setup bike will blow your doors off.
Quite happy to be corrected on that.

[Flettner]

Quoting different Apple and Oranges scenario's, like direct drive karts, Gyrocopters, MX/VMX or whatever are all special, specific cases where off the pipe power does matter.
And the people doing those things imho are in the minority on here as a group.

All I am saying, for example, is that if you take any MX 125 engine where power under the pipe is so important that people even clutch the things off the slowest corners, then fit that engine to a kart the
fastest setup then needs no power at all below 9500, but has to run the shortest gear possible and thus it needs to rev to 14500 and beyond.

In this case having a carb that has fantastic throttle connection at 4500 is completely useless, especially if that carb wreaks the front side, peak and overev power.
Thus I would never use that carb in a Roadrace or LSR end use.
Same with FreeTech 50's, the fastest bikes in video's I have seen will easily rev to 16,000, and they never drop off the pipe, or if they do they get beaten by correctly tuned engines that dont.

Bucket racing, that this forum was initiated because of , is in the same category.
If you are off the pipe or slipping the clutch, a correctly tuned/ well setup bike will blow your doors off.
Quite happy to be corrected on that.

In Vinduro, it's extremely difficult to be 'on the pipe' all the time. In fact the only place 'on the pipe' is used is between sections, but, I don't want to lose that between sections top end power.
So I want best top end I can muster with electronic devices to enhance the mid (and some bottom end) as best I can. Clearly powervalves, sliding gib and my vairable rear cone 'device'.
Would be EFI also, if it wasn't outlawed. Quad injector TPI would have been my choice.

[husaberg]

Mmmm., I suggested the Carbs of the mx bike primarily as a source of parts rather than raiding a somewhat limited supply of Honda RS125 parts.
TBH I never looked into the air striker thing meant I assumed it was additional air bleeds and those funny wings?

He looks at pics

^^^^^^^
SPJ as in RS125 NX4 $$$$
Actually looks even shorter than the PWKS?
a lot of difference also in the slide config (looks more Mikuni)

is it the same slide as a PWM?




^^^^^^^^^
KX125 arround 99 PWK short with a TPS and E PJ



^^^^^^
above what is called airstiker PWK in short with tps but no E PJ or to the right as totally bare no TPS or E PJ

[wobbly]

Its the " funny wings" that generate extra venturi velocity at low slide heights, but they also completely wreak the rest of the powerband.

[Wos]

I know I was dribbling on about Enduro bikes before which are largely used below peak, off pipe. Yesterday I was out on the Trials bike. Still good clean 2 stroke fun. . . but I don't think it has any on-pipe power

The needs of trial bikes is to have torque and driveability from deepest rpms...

Big cross or enduro 2t bikes need a compromise between trial and road race...yes

Big 300 cross and trial bikes often use ex timing under 185 degree and ignition timing curvr is Completely diffrent from road racers, for example to avoid hard hitting response on short geared bikes

Think its an advantage to know best of every diffrent world ...

Grüße Wolfgang

[JdG]

I have a jetting question: Say that you go from 2% oil in the fuel to 4%. For instance after seeing Frits’s RS125 data that says 4% Elf HTX909 was being used by world champion bikes.

Should you then blindly jet 2% richer to compensate for the fuel that is displaced by the oil that burns less good and to maybe prevent detonation? I can imagine that the higher oil percentage lowers the octane value of the mix and that the oil in the mix makes the engine “see” a leaner mixture.


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[JdG]

RS125 should be RSA 125. Sorry Frits


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