> I've run into a bit of a problem in tuning my flat slides that I hope > you can help me with. I've been using your tuning guide for guidance, > and it's a big help in that regard, but I've run into a problem. I found > a local shop that has a Dynojet dyno, but the guy who runs the place > really doesn't have a clue how to use it. I went there last Friday to > try and get my 400 sorted out and I was all but on my own as far > as running the dyno. All he did was push the start and stop buttons > for me while I ran the bike. They have no exhaust gas analysis or > eddy current power absorber, just a plain-Jane Dynojet and a Windows 95 > PC to collect power data. And unfortunately, this is the only dyno > I've found in my area so I can't go somewhere else. Put it this way, > I had to show him how to make the plots read out in engine RPM instead > of road speed, and this was the first time I've laid a hand on the > software. > > The problem is I have no clue what I'm doing. OK, I have a slight clue, > but that's about all. He told me they could do 4th gear roll-on tests or > a run through the gears. I tried 4th gear roll-on tests, but I had a huge > hole between about 5k and 9k, which I'm guessing was due to opening > the thottles at such low speeds and with such a large load on the engine. > > I don't have any idea where to go from here. I still have some things to > get sorted out in the bike and on the dyno seems to be the easiest and > quickest place to get it done, compared to trial-and-error at the track. > If you can give me some pointers on how to test this thing, I'd be most > grateful. Actually, if you'd like to write a book on how to dyno test a > bike, I'll buy the first copy. :-) > > Seriously though, if you could give me some tips on the whats and hows > of dyno testing, I'd really appreciate it. And my currently blubbering 400 > will thank you too. I realize this is like asking someone to summarize > world history in three paragraphs or less, but I'm hoping you can at least > give me some pointers on where to start. I'm just trying to at least get in > the ballpark with the jetting. I had it there before and that formula you > gave me worked like magic, but I've since replaced the bottom end and my > settings are no longer correct for this "new" engine. > > Thanks in advance for any help you can provide. Don't bother with the test where you shift through the gears. That test was really designed as a way to quantify changes in slide damping in CV carbs. It will show you how the engine picks up after a shift, so you may be able to find a problem if the accelerator pump isn't adjusted correctly or if the needles are really a mile off, but the accelerator pump is the last thing you're going to play with since the jetting has to be finalized before you can get any meaningful feedback with accelerator pump changes, and there are better ways to test the needle taper and position. So you'll be doing roll-on tests. Don't bother fiddling around with 4th gear; put the bike in top gear for testing. You want to load the engine as much as possible, and have it spin through the rev range as slowly as possible, to have any hope at all of getting an idea why it's running badly. If you run the bike in a low gear and it just goes "WOOOOIIIIP" through the revs, then you won't have enough time to listen to the engine at various speeds. If it does something funky, you'll have nothing to go on but one squiggly power output line on the graph. One of the neat things about a brake dyno is you can just run the bike at one speed and listen to it as long as you like. So try to make the inertial dyno as much like a brake dyno as possible by running with as little mechanical advantage as possible, which is top gear. On your 400, it won't be spinning fast enough at the top of sixth to hurt anything (guys spin their R1s and XXs up to the top of top gear on the all gear test, so…). If the dyno has a brake to slow the drum down after a run, that'd be nice so you don't have to let the 400 bring it back down with engine braking and its little bitty rear brake, but if that's what it takes, then… you might be buying some brake pads. ;) I forget if you're running 32mm or 33mm FCRs on that thing, and I haven't any idea if it's a 400 with kit cams or a 560 with stock 400 cams, or what, but even a crazy 400 with big carbs and cams and stuff (within reason) should be able to take full throttle before 9k rpm, unless you've got an exhaust system from hell that's creating a really nasty reversion problem in the midrange. The engine might be a slug under 9k, but it should at least run without bucking and misfiring at full throttle and, say 6k rpm or so. If the mixture is a little bit rich or lean, the engine will be down on power compared to perfect jetting. That's pretty obvious. What might not be obvious is that if it's a little more rich or lean, it'll misfire a bit, which you'll be able to hear as a bit of roughness, and feel as hiccups in power delivery (with some experience, you might be able to put your hand on the bike's frame during the run and actually _feel_ the misfires). If it's _really_ rich or lean, it'll be obviously popping, sputtering, and maybe even bucking around a bit. So if the bike is misfiring at WOT in the mid revs, but runs pretty cleanly up top, then the main air jet is probably wrong, which means the air:fuel ratio isn't remaining sort of constant through the rev range. For example, if it's too small, the high rev range and full throttle might be okay with little main fuel jets, but in the midrange at full throttle it's too lean, which would delay when you could open the throttle, so you'd have to go bigger on the main fuel jets to richen things up across the board then go bigger on the main air jets to lean things out as the revs rise. That's all in my little tuning guide, but I wanted to reiterate it since it strikes me that this may be the case with your bike. One thing that's not in the tuning manual is, unfortunately, the FCR main air correction circuit really sucks. It doesn't respond at all well to changes in the air jet. While some carbs will noticeably change the fuel curve with only a 5% or 10% change in the main air jet, FCRs need a big kick in the ass before the WOT fuel _curve_ (think of WOT air:fuel ratio plotted against rpm) changes instead of sort of changing things across the board like the main fuel jet does. So you might have to go from a 100 main air jet all the way up to a 200 to get the effect you want, and if you're already at a 200, you might have to pull the main air jet right out and run the air correction circuit with no restrictor. And one thing I've noticed with the big body FCRs is that _most_ bikes run better with bigger air jets regardless of whether the fuel curve is right or not. I think it might have something to do with atomizing the fuel so it doesn't emerge from the needle jet into the venturi in a bunch of big incombustible blobs, but I'm not really sure. Anyway, I'm getting off-track. So let's go through setting the bike up on the dyno. Adjust the front wheel chock such that the rear axle is a bit forward of the dyno roller's axle, but not so much that when the bike's making power and the forks are compressed the tire hits the deck of the dyno. What you're trying to do is get the bike to 'wedge' itself into the dyno roller under power. If a bike is too far back, it may spin the tire and start to hop on the roller, though a 400 in top gear probably doesn't spin the tire hard enough to do that. Run whatever the max rated pressure for the tire casing is to reduce carcass flexing and heat buildup. I _seriously_ doubt an FZR400 on an inertial dyno will put enough stress into a tire to do any heat damage, but there's no sense in not taking such an easy precaution as setting the tire pressure. Strap the bike down and cinch it down just enough that the tire doesn't creep too much on the roller. Cinching it down just a bit more than the rider's weight should be plenty. Make sure the rear wheel is perpendicular to the roller, because if it's not, the bike will push to one side when you start putting some power down. I hope you have a starter in the engine or the dyno has a starter, because bump starting a bike every time you have to make a dyno run is a pain in the ass. Take the fuel pump off the tank, hook it up to fuel supply bottle that you can hang from something in the room, and run the bike without the tank cover or gas tank in place. FZR400 gas tanks, as you're probably well aware, are a royal pain in the ass to take out and put in and take out and put in when you're trying to pull the carbs apart after every test. So anything you can do to speed up the process is good. Don't worry too much about how the tank cover might change airflow to the carbs or anything like that. The effect is so minimal that it's not worth the effort of running the bike like that when you're hacking away at big problems like you've got. If you're running a carbon fibre can and you can put fans on the radiator _and_ the exhaust system near the muffler, that'd be nice so you don't burn it up. Anyway, so the bike's on the dyno and running. Get it spinning up into top gear, then adjust the idle stop in until the bike is 'idling' at some speed above which it wants to jump around like it's going to jerk itself out of the wheel chock and kill someone. With FCRs, you might have to take that little idle screw lock spring and washer off to screw it in that far. I'm not really sure about that one though. Let it warm up mostly to operating temp before trying to get any meaningful data. When you're really a mile off on the jetting, keeping the operating temperature a constant isn't too important, but when you start getting close to nailing it, you've got to keep the engine at the same temp for each test or you might fool yourself into thinking the extra 0.3hp you got was due to something besides the fact that the thing was running 160 deg F for the first test and 190 for the second, and it just happens to turn out that the bike makes more power at 190. Or whatever. Marc has this really nifty Raytek infrared thermometer to check the temp of the top of the radiator and maybe the oil filter, just to keep things comparable between tests, but the stock temp gauge should suffice. Just try to keep the bike running up around the temp you see when racing, while you're testing. If that means you have to throw a few runs away until the bike heats up, or let the bike idle for five minutes with the dyno fans going, so be it. Anyway, keep an eye on the temp gauge. DISCONNECT THE ACCELERATOR PUMP ROD from the throttle linkage during dyno testing. You don't want the extra fuel injected while you're opening the throttle to mask a lean condition or make it seem rich when it's not, and confuse you. It's a big hassle to pull that rod off then reinstall it, I know. But do it. When you start the test, open the throttle as soon as the revs allow. If it will accept full throttle by 5k rpm without acting like you just flipped the kill switch or bucking around like crazy, have the throttle open by then, even if it sputters a bit. Don't bother running all the way to the rev limiter during the 'getting it close' stages of testing unless you've got a big problem right near the shift point that has to be sorted out, since it's not strictly necessary to get data for the last 1k rpm or so while you're just hacking away at a problem in the midrange. Trying to tune an engine with a Dynojet is, as you've found, incredibly frustrating. That equipment really doesn't provide enough information from which to make an informed decision when changing jetting. I have a lot of respect for the guys who can get a bike running well on one of those things, because doing so requires ingenuity, a near mystical ability to listen to and feel a bike run and tell if it's still not perfect, and persistence, because they've got to really work for the information and then pull the bike apart a whole bunch of times to make changes that bracket the settings they're trying to find. What you've got to do (here's the ingenuity part) is find a way to artificially richen and lean the mixture on the fly, so you can run a test, let the roller spin back down, quickly change the mixture, then immediately make another run to see if the bike runs better or worse. You're not really fine-tuning so much as just finding a direction to go with the next jet change. A nifty way to do this is gather up all the float bowl vent tubes into a small manifold in which you control the ambient pressure. In English, that means buying three T or Y vacuum hose fittings and a few feet of vacuum line, running carb float vents 1 and 2, and 3 and 4 together, then left and right together, and then either getting fancy and using some sort of hand pump with a pressure/vacuum gauge like maybe a Mighty-vac if you've got one, or maybe running one more T fitting in the line and hooking up some sort of pressure gauge like an automotive fuel pressure gauge and using some sort of syringe or pressure bulb or something to control the pressure in the float bowls. You're not going to be pumping 2psi of air in there (the stock fuel pump only puts out something like 3.5 psi); it'll be more like a quarter psi or something like that, just a few inches of mercury, however that works out. You could just blow or suck on the hose to get the proper effect, but I never told you that. ;) So when you increase the pressure in the float bowls, more fuel will squirt through the jets, so the mixture will richen, just like with ram-air bikes. Well, they pressurize the float bowls to keep the mixture constant when the pressure in the airbox increases, but you get the idea. Then if the bike runs better, you know you've got to pull the carbs apart and put bigger jets in it. If you manage to hold a steady pressure for the whole test, and power gets better in the middle but worse on top, then you know you've got to find a way to richen the middle without richening the top, so you'd put in bigger main fuel jets _and_ bigger main air jets during the change. If it got better everywhere, then you'd just put in bigger main fuel jets. The other way to richen things up is to just tape over the mouths of the velocity stacks or tape up a bunch of the air filters (I'm assuming you're running open stacks or indvidual filters, not an airbox, but if you are, then you'd just tape up the airbox entry). With the tape deal, you've got to make big changes. If you want to make things richer, don't tape up 10% of the area and expect to be able to tell the difference on the next run; tape up half or two thirds of the area then run another test. Unfortunately, the tape-things-up method doesn't allow you to lean the mixture, it's not linear through the rev range (more effect at higher revs), and it's pretty useless for part throttle tests, so you have to sort of extrapolate that if the bike runs poorly and you tape things up and it runs even worse that it's probably already too rich and needs to be leaned out, but you'd have to use a whole lot of tape for a 1/4 throttle test to choke off the air supply enough to make a difference. But you can be pretty damned sure that if it runs badly at full throttle, you tape up a bunch of the air intake area, and it makes _more_ power, then it's _got_ to be lean. Once you've got the full throttle jetting nailed, it's time to figure out stuff with the needles. Use a felt tip marker like a Sharpie to mark closed, 1/4, 1/2, 3/4, and full throttle on the throttle grip right by the housing. The way I do it is to twist the grip enough to take up the slack in the pull cable, then put a mark on the grip right next to the parting line for the upper and lower halves of the throttle housing, then go to full throttle and mark that, then just eyeball 1/2 throttle, then 1/4 and 3/4. So now just go back and make pulls at 3/4, 1/2, and 1/4, doing the same thing as you did with the full throttle testing until the bike pulls smoothly and cleanly at each throttle position through the whole rev range. Yes, do pulls at 1/4 throttle, even though it takes forever and a day to spin up. If you get the thing running well at 3/4 throttle, but have to use a different needle clip position to get it to run well at 1/4 throttle, then you know you need a needle with a different taper. Of course, it helps to have a whole bunch of needles handy. Once you've got the needles sorted out, it's time to play around with the slow fuel and air jets. If you're buying jetting parts, call up Sudco and get the screw in slow air jets. They're worth their weight in gold (which is a good thing, because I think that's how Sudco figures their price) in the time they save trying to get that circuit sorted out. Run the thing up to whatever rpm you think you're going to use while just cracking the throttle open mid-turn, and work around there. Spin it up over that rpm, then let the roller spin down to speed, then crack the throttle open and slowly roll through the closed to just barely cracked open area, listening and feeling for the bike to pop or die or sputter or whatever. Do what you have to to get that part right, which is a REAL bitch, because the needle root diameter, start of taper, slow air jet, slow fuel jet, and fuel mixture screw all mix it up there, and it's super easy to really botch things up with everything being a band-aid for the next. If you're running open stacks, you might try peeking in there while the bike is running and seeing where the straight part of the needle starts changing to the taper as you pull the slides up and the needle comes up through the needle jet, to get an idea where the problem might be. If you have a problem at, say, 4k rpm with the throttle just cracked open, but it's different as you run at the same throttle position and 9k rpm, then fiddle with the air jet. If it pops and stuff on closed throttle decel, then play with the mixture screw and slow fuel jet. And beg, borrow, or steal a filter mask with hydrocarbon filters. And spend the ~$25 on some Howard Leight Thunder 29 hearing protectors, or whatever the spiffy headphone looking things are that MSC has. Don't skimp on those. Then wear earplugs under them. At the end of the day, you'll be glad you did. And take notes. Write down your thoughts. Write down 'sputters' or 'bogs' or whatever you want, as long as you put your ideas down right then and there. Don't try to remember what it did five runs ago. If nothing else, they'll look cool in your notebook when you go to the racetrack.