ESE's works engine tuner

[sonic_v]

That's interesting. I was quite amazed at the importance of how you represent the intake with Mota, it seems to be where many people fall flat.

Sorry, you have lost me there. Could you elaborate more!


The graph of the engine power, some details on it would be interesting.

[gav]

Heres what the rules say about using a 24mm carb for your F4 bike.

F4 2 stroke engines over 104cc are restricted to carburation equivalent to a single 24mm carburettor,

Typically vague and ambiguous, but if you modify the inlet so it flows like a 26mm (or bigger) carb, is the carb still the equivalent to a single 24mm carb? Its not, is it? Therefore would it be legal to run that modified carb?

[speedpro]

Yeah, and the motor is making power like a 150cc 2-stroke so it's not legal for bucket racing anyway, using the same logic.

The rule you quote refers only to a dimension so therefore the legality, or not, must be determined purely on that dimension. Hardly vague or ambiguous.

[gav]

Yeah, and the motor is making power like a 150cc 2-stroke so it's not legal for bucket racing anyway, using the same logic.

The rule you quote refers only to a dimension so therefore the legality, or not, must be determined purely on that dimension. Hardly vague or ambiguous.

Well, Im sure youre aware that the rules state nothing about the allowed power output, so not too sure how that applies to anything?
The rules obviously allow for a multi cylinder two stroke to be eligible, so instead of saying a F4 bike is restricted to a 24mm carb, they use a term "equivalent to a single 24mm carb". Does a 24mm flat slide flow the same as a 24mm CV carb? Are all 24mm carbs the same? Its the use of the word "equivalent" that allows interpretation, doesnt it?

[bucketracer]

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The size of a carburetor is measured at the venture choke that's right inside where the slide is, not at either end which is bigger and not all carbs flow the same as for some carbs their ultimate flow numbers are secondary to how they drive on the street.

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[speedpro]

F4 2 stroke engines over 104cc are restricted to carburation equivalent to a single 24mm carburettor,

This rule is written with the person in mind who would fit two carbs to an engine. It's a bit of bad luck for the Suzuki 125 twins but they seem to work OK with just one 24mm carb anyway. The rule was introduced at an MNZ conference at Taupo years and years ago and so far nobody has worked out a way round it.

If the rule read that "a F4 bike is restricted to a 24mm carb", then it could be interpreted that the max carb size is 24mm but you could run more than one.

There is no restriction on the carb type and in fact it is not mentioned anywhere. Neither is it mentioned anywhere about restrictions to mods you can do.

I do see your point about the word equivalent. In this case it refers to the size not the performance and that is how everybody has interpreted it so far. I'd like to see someone arrive at the track with a 28mm carb fitted and flow bench analysis to show that their 28mm carb flow wise is "equivalent" to some 24mm carb. The obvious question would be "why don't you fit the 24mm carb?"

[TZ350]

My experience with air cooled 125cc engines to get around the BMEP you are suggesting requires a carb size in the area of 28 to 30MM.

Have you found different?

Thanks for the dyno run.

I worked the time area figures at 12,000rpm for various carbs and it came out at 32mm for an inlet timing of 145/55 which is the std timing for a GP125 and about 28-30 for later closing.

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[bucketracer]

I can't claim responsibility for this engine, but (so far) the highest power I have seen from this capacity with a 24mm Carb is this series of runs.

That curve looks much like TZ's but at lower and more sensible rev's.

[TZ350]

Your carb looks a lot better than the original standard version, and thus I would concentrate on the downstream side. i.e diffuser.

As for Mota. Do you still have to estimate the exhaust gas temperature. It is a long time since I have used it. Can you model a diffuser in the intake or is it modelled as a step. i.e A jump from 24mm to 30mm?

Yes you still have to estimate EGT and need to resort to a bit of trickery to model a tube inlet tract.

http://www.bevenyoung.com.au/motaman.htm#_Toc504313324

MOTA inlet configuration for rotary valves. As I remember it, MOTA treats the carb as a venture tube, it asks whether the inlet is bell mouth or not, size, length to choke, dia of choke (carb), length to exit (flange) and dia. Then the dia of the inlet tract (carb flange), and length of the inlet tract to the disk face.

MOTA assumes a pie slice configuration of the port window and asks the dia to the bottom radius, the dia to the top radius, port arc and corner radiuses. My GP has a round port not a pie slice port so I made the corner radiuses 12mm (for a 24mm port).

Whenever I reduce the radiuses to 4mm and hence a bigger port, MOTA predicts a power gain. This would be encouraging if MOTA knows that the inlet tract was changed from a tube to a divergent cone.

In first setting up MOTA you need to know the torque curve as well as the other data so you can adjust MOTA to fit the curve then it will more accurately predict changes to the engines configuration.

When Thomas first setup the base files for our GP125’s we only had the max hp, torque and revs of a std GP125 but no graph. Now that we have a good torque/revs graph we can dial in MOTA better.

We will update the file and then explore inlet tract changes and see what MOTA comes up with.

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[F5 Dave]

F4 2 stroke engines over 104cc are restricted to carburation equivalent to a single 24mm carburettor,

This rule is written with the person in mind who would fit two carbs to an engine. It's a bit of bad luck for the Suzuki 125 twins but they seem to work OK with just one 24mm carb anyway. The rule was introduced at an MNZ conference at Taupo years and years ago and so far nobody has worked out a way round it.

. . . Well there is a bit of a way around it but it isn't really worth the effort.

In general it is a good rule in that it is simple. I do wonder whether 26 would have been more fair, but there you go.

Nice inlet tract TZ. Lets see you fit that to a race bike. I have seen a GP run with a carb on the end of a long tube, but I can't imagine the throttle response wouldn't be cacked up,.

[bucketracer]

Nice inlet tract TZ. Lets see you fit that to a race bike. I have seen a GP run with a carb on the end of a long tube, but I can't imagine the throttle response wouldn't be cacked up,.

I think he is going to put a wheel on it and go side car racing.

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[bucketracer]

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Hot Rods web page, Search by application, part type, dimensions or model to find the parts you need.

Put in the rods center to center distance and find the rod you need for your bucket. Great heavy duty rods for 4-strokes too.

http://www.hotrodsproducts.com/index...roducts.search

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[Bert]

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Hot Rods web page, Search by application, part type, dimensions or model to find the parts you need.

Put in the rods center to center distance and find the rod you need for your bucket. Great heavy duty rods for 4-strokes too.

http://www.hotrodsproducts.com/index...roducts.search

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Thats really useful bucketracer... I've been looking for something like that.

[TZ350]

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Now that we are getting into carb setup and tuning this might be helpfull.

Carb Tuning by Eric Gorr:- http://www.cyclewerksracing.com/Carb%20Tuuning.htm

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[TZ350]

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Ignition system number three. Had to make a small mounting adapter ring for it. With these KX80 ignitions the stator needs packing up 8mm so I used a piece of 10mm plate and stepped the stator into the ring 2mm and it all worked out very well.

Setup like it is the trigger coil fits neatly into a recess in the crankcase and the original ignition timing marks still line up, so there should be no problems with getting it running, just need to dial it in on the dyno. I like it, it all fits in very nicely.

It is an older KX80 (I think) ignition I got from F5 Dave, I am unsure how much retard or what its curve is if any. I think it has some retard but it was not enough for F5 so hopefully it might be the 5-7 at 10,500rpm I need and not 15deg like the RM one.

Whatever, it has a trigger coil so if it does not work out I will be able to try my JaCar programmable ignition again and if there is no joy there I will get one of those digital units that K14 told us about.

The blue line that drops off at 11200 is the 17deg BTDC fixed ignition. The green line is the RM ignition with 15deg retard (aprox). It is setup to advanced between 7500 and 10500 and is losing power but retards to the right point about 11000 for a very use-full 500-750 rpm over rev. With an ignition that has less retard or a programmable ignition I think I can have the best of both the blue and green lines.

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