ESE's works engine tuner

[Niels Abildgaard]

The Garelli looks nice and it is a shame that twins were not allowed to compete against the 125 singles.
Two 50ccm cylinders could have ca 10% more blowdown time area than a single125 ccm but of course also 10% more combustion chamber area so ultimate power would have been more or less the same.(Aprilia 54 horsepower and two Kreidler27 horsepower?)
Engine and transmission of the twin lower mass than a single with balance shaft and much nicer two stroke sound.

[Frits Overmars]

I'm not sure where to introduce myself in this forum, which I've been following for a while. I own several classic motorcycles, including a 125cc Garelli twin-cylinder from 1985 that I've just finished restoring. I now want to disassemble the fork, but I don't know how. Perhaps Frits, who is on this forum, knows this type of fork and could help me.

Bonjour Bruno, I actually worked on that front fork myself. Back then we called it ‘White Power’, the original Dutch company name, but because certain groups started using the same name for racist activities, the name became tainted, so nowadays it’s called WP.
At the time, I focused on the hydraulic stop, which was designed to prevent metal-on-metal contact when the fork was fully compressed.
The problem was that the hydraulic stop worked in both directions: when fully compressed, it also impeded rebound. I remember milling a couple of slots, which solved the problem. But unfortunately now, forty years later, I no longer have any documentation regarding this fork or my modification.

[MINGRET01]

Bonjour Bruno, I actually worked on that front fork myself. Back then we called it ‘White Power’, the original Dutch company name, but because certain groups started using the same name for racist activities, the name became tainted, so nowadays it’s called WP.
At the time, I focused on the hydraulic stop, which was designed to prevent metal-on-metal contact when the fork was fully compressed.
The problem was that the hydraulic stop worked in both directions: when fully compressed, it also impeded rebound. I remember milling a couple of slots, which solved the problem. But unfortunately now, forty years later, I no longer have any documentation regarding this fork or my modification.

Thank you for your reply.
Do you remember how to disassemble it?
I can't figure out how to remove the tube from the sheath.

[Frits Overmars]

Do you remember how to disassemble it? I can't figure out how to remove the tube from the sheath.

It might be a hex socket screw from underneath, but I’m not sure anymore. As I said, it's forty years ago and I have done a lot of other things since then.

[Wos]

Dear Specialists

What are the reasons for doing a ignition curve like the orange one?
There is advance added at higher reves? Look at the red circle !

Picture borrowed

Thanks! Grüße!

Wolfgang

[JanBros]

my guess : a soft rev limiter

[Frits Overmars]

my guess : a soft rev limiter

A soft rev limiter can be an option, but there is also another possibility.
Delaying the ignition timing at high revs is intended to increase the exhaust gas temperature in order to bring the resonance frequency of the exhaust pipe into line with those high revs.
However, a late ignition timing, sometimes even after Top Dead Centre, means that combustion pressure development above the piston becomes less effective, sometimes so much less that it no longer compensates for that adjusted exhaust resonance. In that case, it is better not to ignite even later at those high revs, but rather slightly earlier again.

Below are the power curve and the ignition curve of a 100cc direct-drive kart engine that delivered its maximum power at 18.200 rpm but would only reach its maximum speed of 21.000 rpm by setting the ignition slightly earlier again at that speed.
It should be noted that the exhaust system of this engine – which had no centrifugal clutch and no gearbox – was deliberately designed not to be very efficient in order to avoid the notorious torque dip at two-thirds of the maximum torque rpm.

[wobbly]

Adding advance back in over the pipe has been used for years in JetSki racing, where the max rpm is limited by cavitation in the pump.
It is used to achieve the same effect as adding advance up the front side at low rpm.
The pipes reduced efficiency at clearing out exhaust residuals means the combustion flame speed is also low, and the extra timing pulls the peak cylinder pressure back closer to the mechanical optimum of near 15* ATDC.
At rpm past the pipes most efficient range ( around peak torque ) the same thing occurs, so adding advance past peak power means a longer pipe can be used and the extra timing allows overev to the hard limit of the pump.

[jonny quest]

Hello, I'm Bruno from France.

I'm not sure where to introduce myself in this forum, which I've been following for a while. I own several classic motorcycles, including a 125cc Garelli twin-cylinder from 1985 that I've just finished restoring.

Attachment 358033


I now want to disassemble the fork, but I don't know how. Perhaps Frtis, who is on this forum, knows this type of fork and could help me.

Attachment 358034

Bests regards

Bruno

Pull off dust seal, look for a snap ring. Remove top cap, unscrew from damper rod. With snap ring removed you use the two tubes as a slide hammer and pull apart. Use a heat gun to warm the area by seals. There's bushings in there.

[jonny quest]

A soft rev limiter can be an option, but there is also another possibility.
Delaying the ignition timing at high revs is intended to increase the exhaust gas temperature in order to bring the resonance frequency of the exhaust pipe into line with those high revs.
However, a late ignition timing, sometimes even after Top Dead Centre, means that combustion pressure development above the piston becomes less effective, sometimes so much less that it no longer compensates for that adjusted exhaust resonance. In that case, it is better not to ignite even later at those high revs, but rather slightly earlier again.

Below are the power curve and the ignition curve of a 100cc direct-drive kart engine that delivered its maximum power at 18.200 rpm but would only reach its maximum speed of 21.000 rpm by setting the ignition slightly earlier again at that speed.
It should be noted that the exhaust system of this engine – which had no centrifugal clutch and no gearbox – was deliberately designed not to be very efficient in order to avoid the notorious torque dip at two-thirds of the maximum torque rpm.

What are some of the causes of this dip?

Obviously many possibilities, let's say on a engine that has had some time spent on jetting and a good ignition curve.

[wobbly]

The torque hole is not jetting or ignition curve related.
There are an infinite number of port timing/tuned length combinations that will work in a specific rpm range.
The more efficient the pipe design, combined with port resonance, giving good superposition over the desired rpm range - the more " out of sync " that combination will
be at around 2/3 torque peak rpm.
That effect can be very much ameliorated by a PV, as that changes the effective port timing, but without this band aid, the better your design combination is - the worse the effect becomes.
You see the effect in EngMod, where no matter what you do there is a drop in TubMax that is impossible to " tune out ".

[Wos]

Specialists
Thanks to you!

If we bring back some more combustion pressure to camber and cylinder by adding advance in overrev. Think

Isnt there a danger of overheating and Detonation?
Specially if we put in to much added advance to early?...at a pipe that is not yet completely out of its effective rpm Range?

Dankeschön!

Grüße Wolfgang