450RRR
450R Veteran
Location: Central Cali
Posts: 10,711
Most of you agree there are THOUSANDS of some type of "jetting questions" on the Org....
and I have spent my share of time trying to answer many of them....
So, what I purpose, is a PINNED thread, which will allow most people to understand jetting, determine jetting needs, view what the most 'common' jetting is and/or questions, and if all else fails, give proper guidelines as to the INFORMATION (including proper terminology) needed for us members to post ACCURATE jetting information for those who need answers..... lets hope this works... lol
Lets start with the basic/stock jetting: Before we begin, at this point in time, there are basically TWO different machines when it comes to jetting. The stock 04/05 machine which utilizes a 42mm Keihin butterfly/slide carb, and the 06/newer machines which utilize a 40mm FCR (Flat CR style carb). Let me also say the 04/05 machines suffered from a bit of a 'restrictive' style intake and filter... while the 06/newer machines work very well with their factory intake and filter. Hence the reason for the massive changes in jetting between all corked up (stock) and uncorked (lid removed or modded) between these years.
04/05 came with 118 main jet, #48 slow jet (aka Pilot jet) and an adjustable needle. There is no removable Leak Jet (aka Acc bypass jet). the FUEL SCREW (aka Pilot Screw.....NOT Air-Fuel or Air screw or A/F screw) should be set near 2 turns out to begin...
04/05 HRC jetting is 185 main jet, stock slow jet, special 'opened up' HRC style LID. thats about it....
06/newer came with 120 main jet, #42 slow jet, non-adjustable NHHU needle, 2 3/8 turns out on Fuel Screw, #70 leak jet...ignore the #75 starter jet...
06/newer HRC jetting is 162 main jet, stock slow jet, NGPR needle on 3rd groove from top (all adjustments on needle are considered from the TOP and/or ROUND (not pointed) portion of the needle), #55 leak jet, turn fuel screw 1/2 turn IN from stock (1 7/8 from seated position) and turn acc timing screw (1/2 turn OUT from stock) both of these screws are a special 'D' shaped head, so you need the appropriate tools and/or modifications to these screws (such as cutting a slot in them) in order to adjust them....this requires the LID to be REMOVED or highly modded.
Ok....lets start with some basics:
from Idle or starting to WOT application. Idle jetting is controlled with Slow jet and Fuel screw, along with the choke mechanism (most know what the choke is for so I will skip the details)....common rule is to adjust your idle setting (not speed, which is adjusted with the black idle speed knob) first using the fuel screw. open screw up to about 3-4 turns out and begin turning this screw IN/CLOCKWISE slowly while listening to the RPM of the engine. once MAX rpm is obtained, back this screw out about 1/4 turn (based solely on my experiences). This is usually about as close as your gonna get depending on other issues. If you find the Fuel screw at less than ONE turn out from lightly seated position (go with next size SMALLER slow jet), and if out more than THREE turns, go with next size LARGER main jet. Then start this procedure over until the fuel jet is adjusted correctly, and it falls between 1 and 3 turns out from seated. this adjustment is usually performed in the garage.
Off idle and/or Mid range adjustments can best be handled by the Needle, but since all of the carb circuits tend to overlap, the fuel screw, slow jet, and main jet, will have a small effect on this. both the needle taper (so choose your needle wisely) and needle 'clip position' alter this jetting. Take the bike out for a decent NO LOAD, CRUISE speed at about 1/2 throttle (steady), 4th gear. Listen for POPPING/SAGGING/CHOKING.... not an easy task unless you know what to listen for. If she tends to Pop Pop Pop or you feel the engine SAG off, then pick up again, then SAG off again (like Lunging forward/back)... your probably LEAN, and you need to Raise the needle by LOWERING the clip position. If you feel your bike coughing/spitting, she is probably FAT and you need to LOWER the needle by RAISING the clip position (when giving or reading tuning advise, be very careful to note whether you want to RAISE/LOWER the NEEDLE, or RAISE/LOWER the CLIP, cuzz they have the opposite effect. Most people refer to raising/lowering the NEEDLE, info only.
WOT and/or MAIN circuit. Easy enough to fix, simply change the main jet. The difficult task is knowing which way to go, and how far to go. Same as with adjusting the needle, except running at WOT, preferably under a load, for as long as you can. Try and get a sense for what a lean condition feels like vs a rich condition. If the bike is VERY LEAN, she will sag a bit and 'lunge' a bit but she will sound very 'clean' if you know what I mean. If the bike is VERY RICH, it probably wont ever 'clean' out, and you will hear/feel a coughing/spitting sound, not to mention she wont want to reach max RPM. Go smaller number on the main jet to LEAN her down or go larger number to RICHEN her up.... another method is the plug cut, but this can become costly if using the stock Iridium tipped $20 plug. A cheap alternative is a typical $3 NGK BR8S or similar suitable plug JUST for this test. Put in NEW plug, take bike out for a short trail ride to put a LITTLE color on the plug, then proceed with WOT for as long as you can hold it. Do not allow bike to decelerate or idle, simply hit the kill switch and let coast to a stop. Remove plug, cut away the threads and look at the inner porcelain area. This is where you coloration comes from. you want a TAN or LIGHT BROWN color. darker = too rich, and lighter = too lean. Blisters on the plug indicate WAY TOO LEAN and/or detonation issues. Soot or thick black carbon usually indicate your burning some oil... typical for a high mileage machine with old plugs... last but not least is the Dyno... probably the very BEST method w/o a doubt, but it is costly, time consuming, and not all dyno operators are created equal....I would prefer having an Air/Fuel meter on the dyno, but again, I know not to RELY on this meter for tuning my machine. It should be used as a REFERENCE once your machine is TUNED, in order to have a set goal for the NEXT TIME you need some adjustments.... the reason being is simple, this is not one PERFECT A/F ratio for each machine, and it certainly is not anywhere near the 13:1 standard line they have on their graphs (at least not in my humble opinion). So use the dyno for what it can do best, measure HP and TQ. run your machine to WOT and adjust your main jet to obtain MAX HP and TQ, simple. then, once all said and done, note the A/F ratio on the graph so you can match that number next time you need a tune up or have made some major changes to your machine. This issue with most, not ALL, dyno operators is that they are really in business to make money, and there is NOTHING wrong with that.... but, as you know, TIME is $$$. And even though I wanna believe that most must know the proper method for tuning a machine, they simple take short cuts in order to get you in and out of their shop. There are however some excellent dyno tuners that will spend as much time you like to dial your bike in, and they are well worth the money.... One item to mention when dyno tuning is this. RPM does not = CARB POSTION.... and this is where so many dyno tuners fail. For those who have put your machine on a dyno, how long did the bike run once the operator started this operation? 2-3 seconds? max. There is no way you can adjust your idle/pilot or mid range circuits with this type of dyno "pull". Even though the graph/rpm will start out at 1000rpm (or so) then travel up to 10,000+rpm, the throttle position was put at WOT. This is simply how a dyno pull is done. Do NOT confuse the 2000-3000 rpm range on the graph as the Pilot Circuit, and do NOT confuse the 5-7000rpm range as MID RANGE. Cuzz they are not, the entire "pull" was done at WOT, and the only circuit being utilized by your bike was the MAIN CIRCUIT... the rest was just playing 'catch up'. So, if your gonna perform a dyno tune, do it correctly, and you will be very pleased. Let your bike run on the dyno with almost no load, idle to 1500 rpm, and adjust the pilot circuit accordingly. then bring her up to about 5-6000rpm, and adjust your mid range (needle) accordingly. Then, last but not least, WOT, and adjust your main jet for MAX hp/tq.... DONE, and your bike is now fully dyno tuned.....
Now, lets start with some of the ISSUES associated with tuning... and the most common is the dreadful BOG/BAWG associated with the typical 4-stroke machine. Unfortunately for you 04/05 guys, there is no 'direct' fix for this on your carb, so you have to steal from Peter to give to Paul so to speak.... if the bike does in fact BOG (while riding, NOT IN NEUTRAL), then you probably need to increase fuel into this circuit. Raising the needle is the most common for 2-strokes (which have no acc pump circuit), next comes increasing the pilot circuit fuel by going with next larger Slow Jet and/or a combination of both. For the FCR guys, you can simply alter the leak jet. Smaller jet = MORE FUEL (the leak jet is a 'bypass jet' meaning when you depress the throttle, the plunger in the acc pump forces fuel out of the float bowl (plunger bowl area) and into the venturi of the carb, however, there is a 2nd path the fuel can take, and that is to BYPASS the venturi and be squirted back into the float bowl via the leak jet. So, the smaller the leak jet, the less fuel can be 'bypassed' and more fuel gets dumped inside the venturi. Stock was #70, HRC is #55, some go down to #30-35, but I do not recommend soldering this jet shut or going with a plug. This jet serves two purposes... allows for an ADJUSTMENT for the acc pump not found on the older 42keihin carb, but it also allows a release in pressure inside the acc pump diaphragm in order to reduce any DAMAGE that can occur. Remember, fuel/liquids do not compress easily, so you can easily rupture a diaphragm disc if depressing the throttle too quickly and not allowing for some of this pressure to ESCAPE via the leak jet (info only).... another aspect of this 'bog' issue is the acc pump TIMING.... Many people have cured this headache simply by turning the timing screw out 1 1/8 turn as recommended by HRC... Also, if you find your down to #30 or #35 leak jet, and you still have a dreadful BOG when accelerating, you can also raise your needle or increase your pilot circuit fuel. This is not a 'direct' fix, and yes, it does cause these circuits to be a bit RICHER and required, but it will help to reduce a bog if you cant cure this bog via the leak jet alone. the 04/05 can benefit from aftermarket pump covers such as Boyseen. These covers over a larger 'bowl' of fuel so more fuel can be squirted into the venturi. They are certainly not needed on the FCR carbs in MY opinion.
Lets talk about "popping on decel".... a quite common term heard often on the Org. Popping on Decel is caused by a LEAN condition inside the combustion chamber while the butterfly/slide is in the closed position. It can often be 'cured' by increasing fuel in the pilot circuit (1/2 turn out on fuel screw or next size larger pilot). The issue is that this is not the proper procedure for tuning your machine and it is more like putting a band-aid on an injury than actually fixing the problem at hand (if there is a problem). Commonly, you will notice this effect when changing your exhaust. A less restrictive exhaust allows a larger volume of cool air to be 'sucked' backwards via the exhaust pipe and into the combustion chamber past the exhaust valves. The REASON for this on Decel is simple. Your engine is still turning at a rather HIGH RPM, yet the carb slide/butterfly is CLOSED. Since the opening and closing of the valves is a mechanical one (via timing chain/gears/cam/etc), you cannot just STOP the engine from wanting to SUCK air into the combustion chamber. So, since it can no longer SUCK enough air thru the carb because it is closed, this excessive 'vacuum' tries to suck air from wherever it can....and yep, the exhaust is the next logical target. So although any small leak in the crush gasket would go unnoticed during normal operation, during DECEL it becomes quite prevalent. This cool/incoming air causes the lean condition and hence, POPPING. There is absolutely nothing wrong with your jetting, so if you begin enriching your pilot circuit, your jetting will now be richer than required during normal use. Sometimes a failing header crush gasket is to blame for allowing air to enter the system and a simple replacement can cure the popping. If however, this popping is a result of a new pipe system, and all components are sealed, you only have two choices. One, you increase the jetting in the pilot circuit as mentioned to help combat this issue, or, you do nothing, and live with the fact that this is a COMMON phenomenon and in NO way alters your jetting. The choice is yours. If you have a hard time believing this can be 'normal' and/or 'properly jetted', just watch some good ole NASCAR races. You can easily view the popping and/or FLAMES shooting out the tail pipes (side pipes) of these machines as they begin to enter the corners, then it disappears during the exit of the corners because the driver applied his throttle. Some of the cars will have flames, some will just pop, and yet others will do nothing. Trust me, each of those vehicles is tuned by EXPERTS in the performance industry and you could not tune them any better. bottom line...some mechanics leave the tuning alone and let the cars POP on DECEL, and others might want to eliminate the popping and add a lil extra fuel in the pilot circuit because this popping CAN cause issues with the exhaust valves (I really dont know their individual reasons, I am just speculating based on my experiences) Not very common nowadays, but old school days you could 'crystallize' a valve if running un-corked headers on a track that required the use of DECELERATION to slow ya down. Never an issue at the drag strip however....lol
Next, lets talk about proper jetting and why so so so many people continue to go with larger and larger jets, yet never smaller. If any of you have read some of my posts, your probably familiar with MY opinion on jetting, which is this: WAY WAY WAY TOO MANY PEOPLE believe MORE FUEL is BETTER. This includes major performance companies and tuners alike. The reason is simple. Most people have the 'belief' that if you "need" more fuel, then you have somehow increased the performance of the machine. And, to be honest with ya, that is quite true. What most people do not identify with is that JETTING has LITTLE to do with the 'amount' of FUEL, and most specifically, the fuel REQUIREMENTS, UNLESS your jetting the exact same machine, with no changes to the engine, intake, pipe, volumetric efficiency, etc.....if everything ELSE remains the same, then increasing or decreasing the jet sizes will alter the Air to Fuel ratio:
But, here are some "myths" if you will. "I just bought a new brand X pipe, and they recommend larger main jet and slow jet"....conclusion: this new pipe flows MORE, therefore requires larger JETS, therefore making more HP. WRONG!!!. again, JETTING has very little to do with fuel REQUIREMENTS. The manufacturer of this pipe had to make a decision. They could either be honest and lose money, or be deceitful and make money, Ill let you guess which. Because the overwhelming MAJORITY of customers honestly believe that by needing a larger jet they are making more power, the manufacturer had almost no choice, but to recommend larger jets. And since this 'free flowing' exhaust is more than likely going to cause some type of 'popping on decel', they again had no choice but to recommend larger jets for the pilot circuit, simply to reduce the number of COMPLAINTS or QUESTIONS coming into their company....both of which are 'wrong' but allowable....
Let me start over with this bit of information... as an engine becomes more EFFICIENT, specifically the volumetric efficiency (identified with the symbol Ve in the industry) the need for larger jets becomes less. Now remember, and here is the TRICK (if you will) to jetting but remember the difference between needing larger JETS and needing more FUEL. The actual Air to Fuel ratio has remained the same, but because whatever MODS were done to the machine, the air flow into the carburetor has become LESS, and therefore, by simple physics, you must increase the jetting in order to maintain the SAME A/F ratio. This is the KEY to all the BS behind jetting. If you increase the bore or stroke or Ve (by porting usually: Ill discuss CAMS in a minute) or have a BETTER (not MORE) flowing exhaust, etc....then you have just increased the Ve of the engine. This means there will be a larger influx of air through the carb. As the AMOUNT/VOLUME of air increases, using the exact same carb diamter, then in order for this larger VOLUME of air to pass through the venturi of the carb, it must INCREASE IN VELOCITY to do so. Think of a river as it cuts a path down the mountain. As the area where the river widens, the flow slows down, but as the river reaches a NARROW path, the same VOLUME of water wants to continue flowing, so the SPEED of the river must increase as it narrows. Ok, back to this carb, as the air increases in velocity, the ability of this increased incoming air to SUCK fuel UP from the float bowl becomes GREATER. Ok, lets stop for a second and talk about the effect of an airfoil (wing). as air travels over an airfoil it splits and becomes separated. the air traveling over the top of the wing wants to meet up with the same air traveling over the bottom of the wing. the airfoil is designed in such a manner (in MOST occasions) so that the air particles traveling over the top of the airfoil must travel a longer DISTANCE than those traveling over the bottom (FLAT on high lift aircraft). So the air traveling over the top must INCREASE IN SPEED in order to reach the end of the airfoil and keep in line with the bottom air. This increase in speed causes a lower pressure on the top of the wing than on the bottom. It is this DIFFERENCE IN PRESSURE that causes lift. The venturi of the carb is no different. It is shaped in such a way so that incoming air must INCREASE in speed when traveling through the smallest portion of the carb (Venturi/Center). As this air increases in speed it looses PRESSURE, so that the rather stagnant air inside the float bowl can push the fuel UPWARDS towards this low pressure area inside the venturi (consider typical atmospheric pressure at sea level is close to 14.7psi) (and trust me, Barometric pressure, weather changes, temperature, altitude, etc, play a HUGE role in jetting...and im actually kinda knowledgeable in this realm, but that would require another 10 pages of typing..sorry...lol)....so, I will often use the term SUCK and/or DRAW fuel into the carb, but in reality, and if you remember this for the rest of your days, you will have a much CLEARER picture of how to make HP (specifically in the intake area) but fuel is not SUCKED from the carb, nor is air SUCKED into the filter/intake/engine...buth rather it is PUSHED into the filter/engine/venturi by atmospheric pressure inside the float bowl (what this means is if you have a clogged float bowl vent, your gonna run VERY VERY LEAN) (also, if your float level is LOW or HIGH, this will effect the ability of the fuel to be PUSHED upward into the venturi) (and dont even get me started with pressurized intakes such as PRE-CARB nitrous or TURBOS, cuzz they become a PITA). SOOO, if you actually INCREASE the Ve of your engine, although your Air to Fuel RATIOS become the SAME, you have increased the ABILITY for fuel to enter the venturi via a lower pressure inside the venturi. This means you must REDUCE your jetting, not increase it.... now a pipe manufacture may claim you need more fuel, but if they built the pipe correctly, that would be doubtful at WOT applications. However, they can easily recommend a larger pilot jet based on the fact their pipe probably POPS a lot more on decel and they simply are trying to correct this 'issue' without a lot of complaints and/or phone calls..... larger bores and longer strokes tend to increase the incoming air and therefore require smaller jets. Porting SHOULD do this, but not all porting is equal, so it is difficult to recommend jetting not to mention if you port for max HP, you will probably need a smaller main jet, but more than likely larger jets in the pilot circuit, cuzz that is simply the nature of the beast (you either get better low end, mid range, or top end). This brings me to bumpsticks. Chances are if you using a top end oriented cam, this cam will produce the best results in the upper rpms (more flow) but at lower rpms, you will actually have LESS FLOW, so at lower rpms, you will probably need to increase your pilot circuit fuel requirements to compensate, while your top end fuel requirements (actually jet sizes) will become less... remember, all bumpsticks are different and I would never presume to know how to tune them all, just giving out some BASIC tuning guidelines...
My point is this... rarely does anyone suggest LEANER jetting when modding these machines.... quite the opposite, too many give out suggestions indicating the need for larger and larger jets... and in MY humble opinion, falsely so. Remember, HRC gives you a #162 main jet and actually require you to turn your fuel screw IN (leaner) 1/2 turn with their jetting. and Honda still warranties this product. So if they were way too lean on their suggestions, dont ya think Honda have issues with this warranty? Trust me, if anything, Honda recommended slightly RICHER jetting than optimum. So if your at sea level, cool ambient air, high pressure system, etc... your probably fine with this jetting. BUT, if your above 1000 foot level, hot humid climate, low pressure system, etc.... you probably need LEANER jetting to be optimum.... they "myth" that lean jetting will blow up your machine vs rich jetting is just that...a MYTH (it CAN happen, but requires a certain set of circumstances including LONG/WOT application for the most part)...How many times have you read on the ORG where a guy removed the lid (cuzz he read that somewhere) and never changed the jetting. Yet the only complaint was poor performance. and that is a HUGE lean jetting issue, not just a few jet sizes..... now 2-strokes are a bit different, we are only discussing 4-bangers and specifically the 450R for now.....
a few facts: Cooler air is more dense and requires richer jetting: Higher Elevation is less dense and requires leaner jetting: Dynajets work just fine, but have a different numbering system, so make sure you know what your comparing them to when reading jetting information. My information is based solely on factory Keihin jets.
Ok...lets talk about information needed for accurate jetting. If you have to ask about jetting, please include the year machine, any carb mods, your intake system, filter type, (stock vs intake eliminator type) whether lid is ON or OFF or MODDED (very important) pipe mods, bore/stroke, cam, ELEVATION and ambient air temps, etc.... this information is very helpful when trying to determine proper jetting.... dont just say modded lid, we need to know how was the lid modded (size and number of holes, etc)... hint: if your gonna mod the lid, make sure you cut large enough holes so as to not have any RESTRICTIONS when using the lid. a couple of small 1" holes will only confuse the jetting issue, because it will flow enough in the pilot/mid range circuits, but will be restrictive at WOT, so the jetting will be off....also, if you complaining of a BOG, indicate whether this is during riding or sitting in the garage blurping the throttle.... and last but not least, make sure all other mechanical/electrical issues have been fixed/evaluated. I cant tell you how many electrical/stator/ICM issues can act just like JETTING. OH...do not use the term "I have a stage II jet kit"...not even if you know the brand "sparks vs FMF vs Dyna, etc". We need to know the actual BRAND of JETS and their SIZES.... Keihin vs Dyna vs Mikuni, etc....
Now let me say this... I am NOT the tuning expert on the Org or anywhere else for that matter.... there are literally hundreds of much higher qualified tuners than myself on here. I am only giving you information based on a long time enthusiasm for building/tuning/racing a wide variety of machines. So, with that being said, you will not STEP ON MY TOES if you disagree with me. Any information is welcome.....
If you have any questions or information you think could be useful, please ask....ill do my best to answer them and make it a part of this pinned thread.... Thanx
And I apologize for the length of this thread, sometimes I just dont know when to STFU....
JMHO...Greg
Oh well we have moved on from there now.
You must be an expert at whipping the carbs off, making changes and putting them back on by now.
It'll be interesting to see the results of your latest set-up 
