The nozzle needle sits in the middle of the carburetor and is mainly responsible for the partial load operation of the engine. That is why it is also called a partial stylus. In older carburetor engines, the nozzle needle in everyday life has a significant impact on performance, fuel consumption, clean acceleration and the engine standstill under load. Interestingly, this component is more important in engine tuning than the main nozzle, because only very few constantly go full throttle at the stop. But how is a nozzle needle adjusted - and is the right needle installed at all?
> The prehistory
> What happens with a three-quarter throttle?
> Install the correct nozzle needle and set it correctly
> Learnings on nozzle needle on two-stroke for me
> Determine the correct nozzle needle size and position by driving tests
> My carburetor setting of the BING 84
My starting position in summer 2018:
- An almost 50-year-old MZ ES 250 / 2, which came on tours on hot days only coughing at the traffic lights
- a built-in "modern" BING 84 carburettor from the 80er years
- an increased "summer gas mileage" by 0,5 liters, which did not disappear even by gentle driving
- a dark gray, almost black sparking face
- as well as a slightly oil-damp exhaust with a clearly perceptible two-stroke flag - at least with the nose
In winter it went with the age-old > MZ from 1969 quite good, but on hot summer days the engine started to accelerate at the traffic lights to four-acts and was difficult to get up to speed. The BING carburetor I had bought new 2010 and meticulously adjusted with different nozzles (main and idle nozzles) for hours. It was at the end of the Original nozzle needle swapped for a greasy needle as the engine rang slightly on the highway at three-quarter throttle. Thanks to the non-original BING 84 carburettor, I had to work hard before the engine ran clean in all performance areas after the restoration of the MZ. Since then, the carburetor but since tens of thousands of kilometers quite inconspicuous his service. So far 8 years - completely without disassembly! The fact that the MZ always ran a bit cleaner in colder temperatures than in summer, was for me at first reassuring proof that the engine was set a little too fat and thus worked in the safe, jam-free area. For this you need some prior knowledge:
MZ engines were delivered in GDR times but factory a bit too lean to score with low fuel consumption and to meet the emissions of export countries. Experienced MZ pilots from the East therefore immediately exchanged the main nozzle for a larger HD and immediately put the part stylus one position higher after acquisition. Then a MZ ran even under difficult conditions - for example, with bad fuel or bad oil very reliable: If necessary, even with cheap four-stroke engine oil. Many MZ engines are still regarded as extremely robust, because the liter performance of the Zweitakters compared to other brands was low (extrapolated from 250 ccm max 84 horsepower per liter). Unknowing bikers from West Germany were therefore surprised by the frequent Kolbenklemmer when buying ex works on the Otto shipping or Hein Gericke. Many pilots also simply hung the nozzle needle in the carburetor after the first piston clamp one step higher and then drove completely problem-free.
For high reliability, the BING 84 carburetor is also known. MZ has built it in the last model years before the bankruptcy even in the 250er and 300er two-stroke models. Originally an 28er BVF carburettor "Berliner carburetor factory" from GDR production was installed in the MZ. However, this was so much ausgegeneltelt that the throttle valve idling rattled, also he held by a design flaw idle, which annoying at every red light with a vintage motorbike. The old BVF carburetor still has a soldered brass float (also at SIMSON). In this, the float level must be set exactly before you can start with the spraying. The precisely balanced float height is a mandatory prerequisite for all BVF carburettors with brass float (SIMSON). Likewise, at full load enough fuel must be able to flow out of the tank. With clogged fuel filters or a fuel cap with a clogged ventilation duct, the engine will lean dangerously at full load. In the past, even a tank bag has sometimes caused a major engine failure, as it likes to hermetically seal the small vent hole of the old MZ original fuel cap. In the tank, a vacuum is created in the long term, the engine is leaning through the lack of fuel and jams ...
For fear of a Kolbenklemmer on faster passages I drove over the past eight years with a slightly too high-caliber carburetor around, just to rule out engine damage. Instead of driving at full throttle, the experienced two-stroke engine usually simply takes away a third of gas and thereby spares the engine and fuel consumption on fast passages. In this gas position, the gasoline-air mixture is almost exclusively determined by the position and shape of the installed part-load needle. That's what makes them so important!
In the last third of the gas cock position, the consumption of two-stroke engines tends to double:
- With an old 250er MZ from the 60ern run instead of 5 liter mixture then 8-10 liters by the carburettor. Instead of 90-100 km / h you drive but then only 110-120 km / h top.
- With a SIMSON-SR50 scooter, it is suddenly 3-4 liters mixed with continuous full throttle instead of 5 liters. Instead of 55 km / h the engine runs good 60 km / h.
- Interestingly, a straight-line two-stroke engine reaches more than half of its top speed even at quarter throttle.
For this reason alone, in both cases, the gas tap is closed again even at high speed by responsible driver / inside to half to three quarter throttle. And just then, so in this actually gentle driving style, two-stroker like to suffer the infamous "three-quarter throttle", caused by a wrong geometry or adjustment of the nozzle needle. This phenomenon occurs in all two-stroke cubic classes, for example also in SIMSON mopeds with only 50 cubic centimeters.
What happens with a three-quarter throttle?
The engine is in the partial load range due to too thin adjustment of the nozzle needle - too much air and too little gasoline - too hot, just rings a few seconds (sounds like a coffee grinder, but at high speeds under the helmet often barely noticeable) then goes abruptly, the rear wheel is locked and in the best case one pulls the clutch very quickly in fractions of a second and with luck may continue after cooling down, albeit almost always with less power. In less severe cases, the surprisingly blocking rear wheel may cause a fall from a higher speed, or a hot cranked rod bearing quits the service by distributing its parts in the engine in small pieces of metal and thus causing a major engine damage.
The engine can run so much too lean at three-quarter gas despite the fat main nozzle. The two-stroke engine, for example, you notice that when spontaneously turned up 3 / 4 gas while the intake noise is significantly louder, the vehicle but not properly accelerated, because the fuel is missing. The main nozzle engages in the carburetor only in the last power range, before that almost alone part needle including installation height is responsible. The cooling gasoline is missing at three-quarter gas, if the part-load needle is not also set fat enough. The air then takes over, a component such as the piston gets very hot, expands and blocks the engine. With good results, many screwdrivers simply change the position of the nozzle needle. You hang the needle a notch higher, the engine is running through it in the middle to higher range fatter and is not so hot by the cooling gasoline. The fuel consumption increases thereby somewhat, but for the engine starts better in cold temperatures and naturally runs a bit better in winter. As already described above, this simple measure alone is often sufficient to obtain a reliable motor - even in borderline areas.
Personally, I did not have 2010 Klemmer with my vintage MZ, heard the engine on the highway but at three-quarter gas often ringing clearly. At full throttle, the ringing stopped immediately and the candle image was then as it should be in two-strokes: Rehbraun on the electrode, black on the ring of the threaded socket. In addition a dry exhaust. It was clear to me that there was still need for action immediately to avoid a major engine failure. I really wanted to drive a vintage car that was suitable for everyday use and not always at the limit. My diagnosis at the time: The nozzle needle of the BING 84 simply had to be hung one position higher!
Install the correct nozzle needle and set it correctly
The "higher hanging" of the nozzle needle had the effect on me, however, that the 250 two-stroke engine altogether ran much too fat and turned up only lazily grumbling: He "four-stroke". A nozzle needle with a different geometry was needed. One that provided a richer mixture only in the upper part load range, until the main nozzle took over the top performance. The carburetor manufacturer BING has something for the > 84 BING carburetor in the program: The partial load needles are different for different engines and purposes (eg Siberia or southern Spain, flat country or mountains, moped or ultralight aircraft) pronounced, so that the carburetor in all load ranges can be tuned clean. That's when I got a BING 8E1 partial needle from a BING expert and swapped it for the original BING 4E1. The ringing on the highway was gone and I did not worry about three-quarter throttle anymore. At that time, I hung it in the second notch from above, exactly in the position in which the original part-load needle of the BVF carburetor also hung. That went so far fabulous 8 years good. Until this extremely hot summer 2018.
The engine of the MZ ran too fat, the oil dripped out the back of the exhaust, the spark plug was almost black, at the traffic light, I could barely start. Idling, Abtouren and full throttle were ok. Aware of the fact that after days of hiring the new carburetor at the old MZ for days, I might have given up too early, I hung the nozzle needle a notch deeper. For this purpose, it is sufficient to loosen only two screws from the outside and with a little fiddling the needle to set an annular groove deeper. After that, the bike literally ran as clean as ever. No more smoke banners after the cold start, hardly any smell, clean gas passages in all areas. If I were not a true two-stroke hares foot, I could have left everything at least until the cold season. Fearing to drive a bit too lean, I ordered the intermediate size 6O1 of the nozzle needle, which I could hang again a notch higher. If you want to understand this scheme, you can download a PDF from BING > BING84 nozzle needle, Even so, the MZ was still almost perfect, even at 28 degrees Celsius - but just with reserves for the colder months and under stress.
Incidentally, I could hardly judge the spark plug on the spark plug of the brand new spark plug. Unfortunately, the addition of alcohol and the fully synthetic oil of modern unleaded fuels leave almost no trace even after kilometers traveled by 100. But the exhaust is now dry and the engine pulls clean even on hot days without gas orgies at the traffic light again. Consumption is likely to decrease slightly in the long run.
Learnings about nozzle needle on two-stroke for me
In retrospect, I was amazed how drastically the nozzle needle alone can affect the overall engine characteristics. The character and position of the nozzle needle often has the most important influence on the engine characteristics in everyday traffic:
- The very few miles you drive really full throttle, but almost always between eighth and three-quarter gas
- The influence of the nozzle needle is clearly noticeable even in the lower power range
- A fine-tuning and / or your own summer and winter setting is therefore worthwhile, at least for old two-stroke
- The exhaust gases are by a well-adjusted carburetor also on vintage engines considerably cleaner, it smells better
- The exhaust no longer settles as the mixture burns clean
- The added amount of oil can probably be reduced somewhat, since the engine is well cooled by the gasoline even at partial load. I will go with my two-stroke mixture of currently 1: 60 with good, fully synthetic oil on 1: 70 (no guarantee for imitators!)
Oldschool instructions: Determine the correct nozzle needle size and position by driving tests
According to the cult book "Make Better" by the post-war two-stroke guru Carl Hertwick, the correct main nozzle size must first be determined for each carburettor setting. A new spark plug, unprocessed original nozzles, the original air filter with unchanged intake, an original exhaust and a > Halfway set ignition are required to set a two-stroke carburetor from scratch to clean. Unfortunately, the process is quite complex. For this one drives (on a test track) full throttle with the fattest main nozzle and determines with ever smaller main nozzles the one that provides the best top speed. All measured values are meticulously recorded, so that the tests do not have to be performed several times. Thereafter, the next larger nozzle is used again, so that the engine is still full throttle resistant even in worse conditions 100%.
For the partial load range - ie for our nozzle needle - the throttle valve is blocked with a tube exactly on half of its normal slide path. An 28er carburettor is thus blocked by means of a stop at exactly 14mm, so that the gas cock can only be opened halfway. Again, the optimal nozzle needle (of course, there are several part-load needles to choose from ...) and the best position determined by the maximum speed reached. The same thing happens with a tube at quarter or eighth gas position. Even after that, the nozzle needle is again hung a position fatter or fetter selected so that no three-quarter throttle can arise. Are bad gas transitions in the lowest performance areas between steady and quarter gas are still different needle nozzles tried. The needle nozzle is responsible in connection with the part load needle for the lower part load range. Incidentally, the same procedure also applies to the idling nozzle and idle air screw, which are initially set according to the manual. Here, the throttle must be artificially blocked at a 10tel its normal stop. Do not worry, the moped is still driving with it.
Then you have a fully gas-proof moped with maximum performance and the necessary reserves. It's easy to imagine how much time this type of carburetor tuning costs: without a dynamometer and experienced engine experts, it can take several days. By the way, a two-stroke engine has the highest performance in a slightly too lean tuning. Unfortunately, it makes it very hot and has no more reserves of mountains, on cold days, with a passenger, full throttle downhill, in the lee of trucks ... it's the game with the fire. That's why I advise everyone prefer to give up the last horsepower and describe a two-stroke engine as described deliberately a bit richer than absolutely necessary.
Modern engines today use a lambda probe, which constantly analyzes the current gasoline-air mixture and regulates accordingly. The best ratio at which the fuel burns completely results from a ratio of 14,7 kilograms of air to 1 kilograms of fuel. Where λ = 1. This requires complex control mechanisms, which can usually only be realized with an electronic injection. In times of 3-Wege-Catalysts, AdBlue and Chiptuning no longer governs the nozzle needle on the mixture preparation in the engine, but the software and its developers or the group managers.
My carburettor setting of the BING 84 at the MZ ES250 / 2 Year 1969, 19 PS
- Main jet 125er (an 124er would probably be even better for optimal top speed)
- Partial needle "BING 6O1" in the 2. Notch hung from above, so second-leanest setting (original equipment was BING 4E1)
- On hot summer days, even the leanest, first notch from above (I test just in midsummer), the engine rotates even cleaner in the lower rpm range
- 45 idling nozzle, idle air screw approx. 1,5 revolutions opened
- fully synthetic two-stroke oil 1: 60 to 1: 75 (no guarantee for all imitators!) - 1969 was a simple two-stroke oil 1: 50 recommended
- Electronic VAPE 12V ignition with fixed ignition timing > Details on Simantik.de
- Details on > Installation of the BING 84 carburetor in the MZ ES 250 / 2