I read deiter's commentary and so have re-written this to get it easier for the german-language translation.
Thank you deiter for the translation summary.
Progress [Updated at 1700CET 13.AUG]:
Photo is of returning from the market
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I don't know how important it is to 'blank' out the license. Image is not displaying... Now it is. Thank you for the tip, dieter.
It goes a strong 23-25kmph with a passenger, less with wind resistance, up hill, etc. Again there wasn't so much an interest in speed, as in power, so it doesn't sputter-out on small bridges, etc.
The airflow un-restriction method used:
1. The first method posted to remove the most restricted flow area posted on the http://spartamet.forum2go.nl forum, which yoekio referred to [thank you], was for 1a. drilling ~6 large ~10mm holes in the round plastic which surrounds the air filter - and thank you very much to the author [prutser2009, administrator of http://spartamet.forum2go.nl] who did the research and measurements of the air-flow passageways.
Links: 1a. http://spartamet.forum2go.nl/luchttoevo ... 92-15.html and 1b. http://spartamet.forum2go.nl/luchttoevo ... n-t92.html
2. Additionally, by the same author there was a method which required a drill press, and a bolt extractor bit, to rectify the artificial restriction of the main passageway in the vergaser. These tools are expensive items, and for many who only have a bike and simple power tools, such as a ubiquitous cordless drill, there may be too many obstacles. Purchasing the drill press for a single use is impractical. Taking the bike off-line while a machinist does the work, more practical but still overly inconvenient for most.
Links: http://spartamet.forum2go.nl/opboren-ca ... e-t28.html and http://spartamet.forum2go.nl/post6665.html
This modification to step 1a are less-invasive physical changes to the SACHS cover on the back, with simpler tools. There are some small cuts and holes to make with simple household tools.
The modification for 1b continues to require a slight modification of the second piece of plastic with the same tools. It is only necessary to make two short cuts with a hacksaw blade through soft plastic and then snap off the tab of plastic. Takes about five minutes and almost anyone can do it themselves.
With the only change to #1b being that the modification and recommendation to only go about 3/4 of the indicated depth. Everything else is the same for #1b as per the original author.
1a. The newer methods [here] of steps 1a and 1b, continue to remove artificial airflow restrictions around the round plastic and air filter, with the additional desire to keep the noise level low. So, e.g. by the first version of 1a method direct, large ports for inflow of air to the surface of the air-filter. These would be directly adjacent to the metal air intake port on the vergaser block. This is believed to project more noise to the surrounding, as now the round cover serves almost no purpose in reducing noise to the outside environment. Engineering it so the plastic round cover for the air-filter played a greater role in reducing noise was important, as well as simplifying the operation as many people have a simple hacksaw and the material is a soft plastic. Even only the hack-saw blade is enough, no handle required. A 10mm HSS drill bit is less likely to be had, and while only about 6EUR it would only be used once, and still there is the noise factor. So the purpose was to use slightly more common tools everyone is likely to have access to, and continue to keep all the modifications to twenty minutes total, and place the cover directly back on the bike to put it immediately back into operation.
The method tested and in use for 1b, was by cutting 2 slots with an ordinary, thin metal-type (fine tooth designed for metal) hacksaw blade, about 3/4 of the length shown in the original photo on the dutch forum. Then simply snap the tab of plastic off.
The method tested and in use for 1a, was by cutting many slots, from the base of the round plastic shroud, with additional small ~2mm holes drilled near the top in the same round shroud. The slots were spaced about 1cm apart, and no wider than the thickness of the round shroud's plastic, and cut on an angle.
The purpose of cutting the slots at an angle, was so sound travelling from the intake port would be interrupted by the edges of plastic. See photos below.
A few additional holes ( ~6 to 7), were placed on the bottom of the 'SACHS' cover, with an ordinary household kitchen sponge cut and glued with instant glue, above the holes, to reduce noise, and unwanted dust/moisture from entering.
2.
This modification of #2 increases the main air passageway diameter to slightly over 8mm (thank you dieter for the corrected measurement) without removing any components from the vergaser, using common tools probably everyone has, plus Proxxon bit package 28781, in a 3x package. ~3 EURO. It also requires the #46 jet, which can be picked-up on ebay.de with a set of jets, #46, #48 and #50 for about 23EUR. Note: The package I picked-up does NOT have the connector for the fuel filter basket, but I haven't needed it.
Increasing the vergaser neck diameter:
The #2 original method of relaxing artificial airflow restrictions required removing the fuel tube with a bit extractor, then using a large machine, a drill press, to make the hole increase to 10mm. Most are not going to have a drill press or a bit extractor, or feel comfortable with the level of skill required to do it properly. And the cost of making a mistake is also expensive, so the effort is to minimize chances of doing-so remain.
The method used to protect the fuel tube while also increasing the carburettor (vergaser) to a modest 8,1mm (from 7,3?) so the engine breathes better was a Proxxon bit 28-781 attached to an ordinary cordless drill, at medium-low RPM, with the bit set in the chuck and the aluminium block removed from the bike, as if you were going to do a normal jet cleaning or swap (#42 -> #46). The jet has already been upgraded to a #46 and the unrestricted ignition module is in use, though there is a slight noticeable 'dampness' in the mixture (slightly too rich) with the existing 7,3mm throat. The zundkerze is an IX4RX.
Place the aluminium vergaser block on a flat, solid surface at waist-height (normal table height). It is not necessary to remove the fuel tube, jet, or the throttle or choke. Just exercise normal levels of attention and this will go ok.
With the vergaser on the table, lightly tighten the Proxxon 28-781 inside the chuck (the teeth of the drill), so that by pushing on the bit, it can slide all the way into the drill. Bring the bit back out so only a few mm of the shank are inside the chuck. Now, pointing the drill straight down, press the bit down inside the hole and it will self-align with the main passageway, and the bit shank will slide into the chuck. Now, lift the drill straight-up and out, and pull the bit out about 1-2mm, then tighten the chuck completely. 'Drill' medium-slow down, into the vergaser, and this will mill out the inside of the throat 1-2mm along it's length, and then automatically stop when the drill chuck can go no further.
Remove the drill, and loosen the bit, and repeat the process. When doing it several times, and approaching the fuel tube, just be watchful; use closer attention to the amount you are going to grind, in max 1mm increments. Eventually, the drill will be 'pushing' a crescent-moon shaped piece of aluminium out of the block, directly next to the fuel tube. Watch for this moment. Go slowly and there is no doubt in my mind if ye are careful, it will go very well.
The only limitation of this method is if you want to make the throat or neck, more than 8,1mm open, it would be necessary to find a grinding bit which is 9mm, 9,5mm etc, that has a flat face. Although I can say, I am very happy with the performance and strength of the bike. I feel the intent was to make the bike run in the most environmentally-friendly way, closest to the design characteristics of the engine, without silly limitations which actually make the engine run worse, and the ride less enjoyable.
There was some debate as to going with the NL version of the engine, a different gearing, however the DE version means more power over all speed ranges due to lower gearing. If it was geared to go faster, this would reduce the power to something unusable.
Photos:
The foto below is with the front seat removed. It can be used this way without second rider. The pilot sits on the rear seat.
