求高手帮忙翻译一下英文文章，谷歌跟百度翻译的太不正确了~~
The biggest misconception is that getting the jetting wrong will instantly destroy an engine, on the contrary, you'll know it's wrong before you even have a chance to run the motor long enough to do any real damage because it either won't start, won't idle, or will just run appallingly! This is by no means a guarantee that you won't blow your motor up though if you really don't have a clue as to what you are doing! If you are in any doubt, have the carb's jetted by a reputable tuner. Hopefully this section will give an insight into the basics of jetting, what each part of the system controls, and offer a little encouragement to get you started. You must have confidence in your own abilities when it comes to jetting, as once you have made changes you will need to deal with any consequences arising from getting carried away! This means that, although you seem to have a set-up that performs as you intended, more intensive testing is almost definitely going to be required. Jetting and re-jetting needs to be performed after ANY modification, no matter how small. The best case scenario of not re-jetting is missing out on a possible performance gain, the worst case scenario is seizure! Although a fairly straightforward procedure, jetting involves very fine adjustments, the replacing of very small components, and a large amount of patience! So if you are in any way in doubt whether to adjust the factory settings-DON'T! Make sure that you have ingested the previous carburation section, and familiarised yourself with the various components and our abbreviations for them. NSR-WORLD.COM Jetting Terminology. · AS - Air Screw · SJ - Slow Jet · MJ - Main Jet · PWJ - Power Jet · JN - Jet Needle (or simply, needle) · WOT - Wide Open Throttle Jet Kits. HRC, Jha, and Factory are the three most common names covering jet kits for the NSR series, and a guide to actually installing these kits can be found in the carburation section. The Jha kit is the most comprehensive, with fitting and set-up instructions available in English. Purists will want the genuine HRC kit, just to be able to say they have it, but if you don't have HRC expansion chambers and an HRC delimiter etc., what's the point?! The HRC kit is often much more expensive than Jha's too. Besides, most of the Jha kit comes in HRC packets anyway!! The Factory kit is much less common, and rarely found outside Japan. Watch out for custom NSR-WORLD.COM jet kits in the Marketplace... available soon! A base setting. A base setting is usually supplied by an after market parts supplier. The problem here is that this setting is often based on a standard machine fitted with their item only. For example, when Ethos supply an exhaust system, they also supply 2 MJ's to suit. This is fine if you are replacing your stock chambers only. Now, let's assume you are to fit a Daytona free flow filter, and the instructions recommend a different jet size, you need to account for your previous MJ increase due to the expansion chambers! (You also need to consider that although the filter flows air more freely, the expansion chambers help extract exhaust gasses more efficiently, so is it just a case of adding the increase in MJ size from stock to the increase in size already present after the chamber installation?) Next you are to fit an M-Max speed derestrictor, but the instructions call for larger MJ's again and you can't read Japanese! Do these sizes relate to a standard set-up, a "piped" motor, or a bike with both filters and pipes already installed? They may even be recommending jet sizes to compensate for the higher sustainable top speed that will become available after fitting the part! "...Confused? You will be, after the next episode of Soap!!" Undoubtedly, a basic understanding of what's going on inside your combustion chamber, and of how each component interacts with the next is very important! If you are with me this far, read on!! A table of manufacturers recommended settings and the set-up that they apply to can be found in the previous carburation section. View the manufacturers recommended settings table. |
Where to start? Start by noting down your current settings! If everything "goes to pot" you can always revert to your initial setting and start again!! As mentioned in the carburation section, NSR's came from the factory with a variety of configurations, probably due to both model evolution and climatic conditions. (Areas of Japan are very mountainous and because of this, bikes sold at higher altitudes could've come fitted with adjustable needles etc.) The three main areas to cover when jetting are the idle and slow running, the progression, and top end, and each is as important as the next. Without all three areas being optimised, you will never begin to appreciate the full "fun" potential of the NSR! The slow running is metered by the SJ and AS, the progression by the needle, and the top end is governed by the MJ (and PWJ if used). The following diagram shows which system is in operation at each throttle position. The slide governs the primary airflow through the carb into the crankcase, and is directly proportional to the throttle grip position. A description of each other part of the system follows. Main Jets. The MJ is usually the first item set, but not necessarily the most important, especially for street riders! The reason for this is that the majority of riders will only ever be riding, for most of the time, on 1/2 to 3/4 throttle, and the more powerful the bike, generally the less throttle that gets used! This doesn't mean you can neglect the main jet though, far from it, it just means that you don't have to worry quite as much as you'd be led to believe by those "elite" tuners who are after all your setting-up money!! This therefore takes the worry out of the first, and biggest myth of jetting, "If you get the main jet wrong, you'll blow your engine up!" Why? Because, if you look at the above diagram, and couple it to the last statement, you will see the largest part of the setting up process will be devoted to the needle type and position! If you estimate an MJ setting and it's even only vaguely close, you could ride around town all day without the engine going bang! In fact, as mentioned right at the beginning of this guide, you will only encounter problems at this stage if you get carried away thinking all is well, and blast off into the distance on your favourite stretch of road without extensive refining! Don't let this detract from the overall importance of the MJ though, or the first straight you come to, with the throttle wide open in any gear, the engine will seize quicker than you can say, "new rings, please"! Two things to understand about the MJ are first, fuel is 'sucked' through it, and second, bigger is not always better! Air is drawn through the carb by the vacuum in the crankcase created by the upward motion of the piston. As this air passes over the top of the emulsion tube, fuel is "sucked" from the float chamber up through the MJ, into the emulsion tube where it starts to atomise with the airflow, this 'mixture' is then drawn into the crankcase. This can mean you need to consider two things: 1 A free flow filter (or filters) can allow the crankcase to suck harder, actually drawing more fuel through a given jet size; you have to decide if you really need a MJ as large as you originally thought!! This is because although you are flowing more air (making you think you need a bigger MJ to compensate), you can also be drawing more fuel than you thought, through your existing jet size! Go up jet sizes slowly!!
2 The larger sizes quoted by Jha and HRC are for use with pre-mixed, race octane rated fuel.* *Normally the oil is injected by the pump downstream of the emulsion tube nozzle, but with pre-mix, the oil is in the float chamber, already mixed with the petrol (gas). This means the fuel passing through the MJ is weaker than normal (oil is now making up 3.2% of the volume @30:1) and so a larger size is needed to compensate. Don't even bother trying to run Jha's base sizes until you've removed the oil pump and thrown away the airbox, it'll run like shite!! *The same can be said for using the #45 SJ's recommended once again by Jha and HRC, as exactly the same principal applies! We have had a number of enquiries in the past as to why, when these settings have been used, the bike runs so poorly, and this is often the reason! *For more details on the benefits of higher octane ratings, see the Fuel section later in this guide. Jha's and HRC's settings and parts are intended solely for racing purposes. Both companies naturally assume that along with the removal of the oil pump, all other race modifications have been carried out! Both HRC and JHA recommend the plugging of the PWJ's, preferring only one variable, the MJ, for full throttle fuelling. A section covering this is included on the carburation page. Slow Jets. The slow running and progression are a lot more complicated than you may think, with a number of variables to account for. As the throttle is opened, the slide is lifted, and as the slide raises, more air is allowed to flow, 'sucking' on the SJ. (The straight section of the needle effectively blocks off the MJ at minimal throttle.) Along with the raising slide, small pre-drilled passageways within the carb body, called galleries, assist the SJ in metering fuel from idle to 1/2 throttle. (Unlike the MJ, SJ's are only available in a limited number of sizes.) These galleries are developed over model evolution to iron out carburation flat spots, and modifying these is something even the most proficient tuner will only undertake very cautiously! (If you make it to the stage of modifying these you'll be wanting a job with Erv Kanemoto anyway, and this page won't be of much use to you!!) These galleries are often more apparent in 4 stroke carburettors. A modification more regularly seen in the past on 2-stroke carb's, are small holes drilled in the slides. These provide additional airflow when the throttle is shut. Most modified NSR's with a free flow filter(s), modified airbox, or open carb's can run #38 (stock) or #40 SJ's; use #40 or #45 with pre-mix. Air Screws. Air screws are the final element of the idle and slow running circuits, they are often referred to as idle mixture adjusters. Due to the limited sizes available for the SJ's, some form of finer adjustment is needed, and this is where the AS's come into play. The AS's are a tapered, well, er, screw! As shown in the above diagram, an auxiliary air gallery is cast into each carb body, and the taper on the screw, depending on its position, allows extra air to bypass the opening created by the slide, weakening or richening the mixture. Screws are available with a finer taper than stock, giving a much more accurate method of fine tuning, but really they're over the top for our needs! Needles. The needles, along with the emulsion tubes, sometimes referred to as needle jets, take care of the progression phase. The progression phase is the transition from the slow running circuit and 1/4 throttle, to the MJ (and PWJ if used) and full throttle. Needles are available in different grades, usually denoted as A, B, and C type, with profiles suitable for both leaded and unleaded fuels. In the NSR's case, the A type is the richest, i.e., the slimmest profile, allowing the greatest flow of fuel, and the C type is the leanest. As mentioned before, B needles have a profile extremely similar to the non-adjustable needles found in the vast majority of stock carburettors, and are usually suitable for most applications. The adjustable needles have 5 grooves machined into them, and a circlip is inserted into one of these grooves to vary the height at which the needle sits. Raising and lowering the height of the needle allows you to fine tune the amount of fuel released from the float chamber at part throttle, therefore allowing the fuel/air ratio to be altered for a specific throttle opening. (Unlike the MJ or the SJ, where the fuel/air ratio is constant.) Food for thought here, a GP mechanic was once quoted as saying that he had 2000 jet/needle combinations at any one track to play with... so if you think this is a lot to take in, think again! Fuels. Often overlooked, the type of fuel used can regularly effect the jetting process, particularly on a 2-stroke engine. Japanese sports bikes have been designed to run on unleaded fuel since the mid '80's, and a stock NSR will happily run all day long on it without any adjustment. JHA and HRC advise the use of 100+ octane race fuel with their kits, which accounts for, in part, for their choice of base setting of the MJ's, SJ's, and pre-mix ratio. Even higher (than regular) octane fuel such as Super Unleaded can adversely effect the jetting on a modified motor, and will often necessitate the richening of the mixture. You will not necessarily notice a difference in feel when using the higher octane fuels, especially on a stock motor, and consequently wonder if it's worth the extra expense over regular leaded fuel, but a higher octane will allow you to run both more compression and more ignition advance over stock without as much fear of detonation. This is a point worth noting when an HRC or equivalent ignition delimiter is used on an MC21, or the HRC harness, card, and flywheel conversion, is used on the MC28. NSR-WORLD.COM recommends the use of 97+RON Super Unleaded
by virtue of it's detonation prevention characteristics,
as a general precaution against premature piston and cylinder failure. NOTE: DETONATION CAUSED BY HIGH COMPRESSION/HIGH IGNITION ADVANCE & LOW OCTANE FUEL HAS TO BE RATED AS ONE OF THE QUICKEST, IF NOT THE QUICKEST KILLERS OF A 2-STROKE ENGINE... BE WARNED!!! | Using the higher octane fuels will make reading a "plug chop" harder, as the fuel burns more fiercely and less residue is left on the electrode. |
Finally, also consider the fact that as Super Plus unleaded is more highly refined than regular unleaded, it is therefore cleaner. This can only be a bonus as you are less likely to encounter blocked jets, especially the small PJ's, another 2-stroke killer. Remember though, that most fuel nearly always comes from the same refinery, so it doesn't matter where you buy it from! The Jetting Process. Everyone's opinion of the jetting process will vary, so as mentioned throughout our pages, this is only our guide! This jetting information is based on one of NSR-WORLD.COM's MC21's, fitted with dry Ramax foam filters (dry filters require different settings to oiled filters), a full Jha jet kit,
NSR-WORLD.COM wire-splice, Ethos SP expansion chambers, but before the HRC top head conversion. The bike was originally jetted at approximately 100Mtr above sea level, with an air temperature around 20ºC. Using the manufacturers table as a guide, choose a base setting. The Jha and HRC settings are for use with open carb's, pre-mixed fuel, expansion chambers, and delimited ignition. The biggest difference for most of us will be the use of the oil pump, so disregard the #42 SJ's and go with the stock size (#38), or #40's. Use the #40's if running open carb's, and keep the #38' if using a filter(s). The Jha/HRC AS base setting is a good one, for any modified set-up, so go with it... 1.5 turns out from the fully closed (commonly referred to as TOFFC or TOC) position. To adjust the airscrew, set the engine to normal idle speed, 1250rpm +/-50rpm, and then adjust each screw until the maximum engine speed and throttle response is achieved. Again, as mentioned before, the HRC "b" needles are extremely similar in profile to the stock needles, and as such, a good place to start when jetting. (If Honda found "b" needles to be the best compromise for the stock road bike, there's obviously something in it!!) Don't forget to use the HRC needle holders with the adjustable needles, as they have a small brass insert for more accurate location of the needle. To give a similar fuel ratio to the stock needle, start with the clip in top groove. The HRC emulsion tubes MUST be used in conjunction with the adjustable needles. If not, and the needle clips are set in the top groove, they will jam in the main jet when the throttle is closed! The HRC emulsion tubes are also more efficient, with more holes in them for better atomisation and are consequently richer than stock. Optional extras included in the Jha/HRC kits are the air solenoid jets, i.e., the + and Y joints. Opinions differ regarding the validity of using these on race bikes, let alone road bikes, but we have run with them trouble free for many years now! PJ's have become increasingly popular in GP's again over recent years, after a brief respite, but they were done away with on the NSR by both Honda and Jha for ease of tuning by the amateur racers! The air correction solenoids, coupled to the RC Valves and the PGM engine management are responsible for the near legendry NSR mid-range tractability. The solenoid jets are still utilised in the Jha and HRC kits but now modify auxiliary airflow through the carb's. The Y joint is a direct replacement for the standard piece, with the straight side going to the solenoid closest to the frame. The + joint should have the rubber cap removed and the side with the jet left open to air. The 2 smaller joints go to the carb's, and the last joint goes to the pipe adjoining the Y joint. Initial start-up and Slow Running. Using the above settings, start the bike up. Very little change will have been made to the slow running circuit so the idle should be close. Start the motor and set the idle to run at 4000rpm. If the revs drop, and then continue to rise and fall a little, then the mixture is rich. Adjust the airscrew position, turning it out, 1/4 turn at a time. If the number of turns out exceeds 2 full turns, decrease the SJ by 1 size and reset the AS to 1.5 turns out. If the engine holds steady at 4000rpm, "blip" the throttle around 4000-6000rpm to prevent loading the spark plugs, allowing the motor to warm up to around 30º. Once warmed up, do the same between 4000-7000rpm. If the throttle response is very quick, and you can only feel a little pulsing from the exhaust gasses, then the mixture is lean. Try adjusting this out with the airscrew first, screwing it in to richen the mixture. If you need to screw the AS in more than ¾ a turn from the base setting of 1½ TOFFC, go up 1 size on the SJ's. If the throttle response is poor, and heavy pulsing can be felt from the exhaust gasses, the idle circuit is too rich. Try adjusting this first with the AS, turning it out to a maximum of 2 TOFFC. It is extremely unlikely that you will need to go down a size on the SJ's unless you are using the #40's or #42's. Blip the throttle 4-5 times, to around 7000rpm. The throttle response should be crisp, and the exhaust gas pulses should then fade away with the bike settling down to a clean idle. Main Jet and Needle. With the temperature at at least 50º, hold the throttle at a constant 7000rpm. If the tacho wonders up and down, the mixture is rich. Either decrease the MJ 1 size, or increase the needle diameter 1 rank, i.e., raise the clip 1 groove (lower the needle). If you try to hold the throttle at a constant 7000rpm, but find the revs keep rising 1000-2000rpm, then the mixture is lean. Increase the MJ 1 size or raise the needle 1 groove. If the tacho seems to hold steady, but then drops a little, you are slightly rich. Try adjusting it out with the AS's, but if that doesn't work either reduce the MJ 1 size or again, lower the needle 1 groove. Once the revs hold steady the MJ setting is good. Steadily open the throttle. Rev the engine smoothly from 4000rpm to 9000rpm. Anywhere the engine revs quickly it is lean at that point, if it hesitates, it is rich at that point! GP tuners are at a distinct advantage here, as they can utilise needles with custom profiles, we have to make do with the three sets that come in the kit so this will have to be a best compromise. The rest of the setting up needs to be done on the road or track! Riding the bike. This section is slightly trickier! You really need a good "feel" for what your bike is doing, but the trouble is, most of us, myself included, can't really tell the difference between the minor changes!! The easiest thing to do is a "plug chop". This involves running the bike flat out in top (6th) gear, near the "red-line", i.e., 12000rpm, for at least 10 seconds, preferably slightly uphill so the motor is under slightly more load. Two things to note here, firstly, that if the bike won't pull cleanly to 12000rpm, there is something inherently wrong with the MJ or needle set-up, and secondly, to accurately gauge a "plug-chop" you need fresh, clean plugs! Also, allowing the engine to run off of full throttle for only a second will give a false plug reading. NOTE: It is harder to "read" a plug if Super Unleaded (i.e. higher octane) fuel is used over leaded fuel, as it burns more fiercely and therefore more cleanly. For more information on this see the Fuel section earlier on this page. So, at the end of a long enough straight to run flat out for 5~10 seconds, pull the clutch lever in sharply, flick the kill switch, and coast to a halt. Remove the spark plugs, and check the colour of their respective electrodes, noting which cylinder each plug came from. They should be a light tan colour if your settings are good. Too dark, or black, and it's rich, if the plugs are grey you are too lean, and if they are near white, you are dangerously lean!! Two main areas need looking at in this section. The plug chop takes care of the wide open throttle down the straight scenario, but what happens when you're mid corner?! Advanced Section: High radius corner, 1/4 throttle setting. Symptom (1/4 throttle lean). Revs not bad, but engine feels week.When opening the throttle, the engine revs too quickly.Snap the throttle open, and the revs fine, but has no torque. Test. Open throttle slowly; this symptom still occurs. Solution. Close up AS.Reduce needle diameter 1 rank (raise needle), orIncrease SJ 1 size.Increase MJ 1 size.* * Only change the MJ if attempts to rectify the problem with the AS, SJ, and needle fail. Symptom (1/4 throttle rich). Engine revs poorly, when opening the throttle there's a sudden drop in revs.Engine power "surges" and feels like the bike is punching.Engine feels like it's stalling. Test. Open throttle slowly, the condition becomes worse. Solution. Open up AS.Increase needle diameter 1 rank (lower needle), orReduce SJ 1 size.Reduce MJ 1 size.* * Only change the MJ if attempts to rectify the problem with the AS, MJ, and needle fail. Advanced Section: Medium radius corner, 1/2 throttle setting. Symptom. Engine has torque, but revs slowly.When downshifting, engine revs poorly, and the throttle response becomes poor.When downshifting from partial throttle, engine braking is heavy. Problem. Partial throttle rich. Solution. Raise needle clip 1 position.Reduce needle taper. (i.e., replace "b" needle for "c" needle) Symptom. In a high speed corner, the bike won't hold its line and drifts wide.The engine seems like it has power, but detonates even with large MJ's.Until full throttle, bike has poor speed, and the engine has no torque. Problem. Partial throttle lean. Solution. Lower the needle clip 1 position.Increase the needle taper. (i.e., replace "b" needle with "a" needle") One last check again is the MJ. If the bike has no high speed power, you are running lean. Increase the MJ 1 size, and perform another plug chop. Jetting Guide - Quick Reference. Conclusion. Jetting is no black art, but it is time consuming! Every time you want to adjust something, you need to pull the carb's off, which obviously means removing the tank and the airbox (where applicable), draining fuel, and reassembly and testing. This is easy enough on a race bike... no airbox, quick release fuel tank, etc., but can be a real pain on a road bike, but is absolutely essential if ANY modification has been made!! A worthwhile investment is dyno time. After careful setting of the carb's, exhaust gas analysis is an added comfort! You will also receive a power vs. torque graph where you can assess gains and losses throughout the rev range; invaluable down the local bar with your mates for added horsepower!!! Make sure you use a dyno engineer with considerable 2 stroke experience as the engines characteristics are vastly different from that of a 4 stroke's. Patience is the ultimate virtue, but once you have a technique down, you'll be considered with high regard, and be able to save yourself a awful lot of money to boot!!
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