(Before we get into the how-to - you may want to check out Carburretor's 101: Carburretor 101: <!-- m --><a class="postlink" href="http://www.motorcyclecarbs.com/jetting/carbs101.pdf">http://www.motorcyclecarbs.com/jetting/carbs101.pdf</a><!-- m -->) Carburetor Balancing Thanks to Trevor for this awesome information. To stop any troubles I'll point out now that you should only perform this method of carburetor balancing when the carburetors are off the engine. Reason for saying this is because we don?t want any of you guys/girls to have to try and take the ball bearing out of the engine because it when through the carburetors. To balance the carburetors, Trevor was told a way which works if the carburetors are OFF the bike. He made a stand to hold the carburetors at the same angle as on the bike out of some scrap wood. You could always hold them the same way but using your own method. He then took two ball bearings from a broken bearing housing and put them into carburetor one and two. (The balls must be about 6 mm's as if it is too small, it gets tricky.) Open the throttle arm slowly while keeping an eye on the balls. If they don't go through the butterflies at the same time, adjust the screw until they do. Now do this with carburetor two and three and then three and four. Trevor found this method better than vacuum gauges, as the needle tends to vibrate a lot for him. Trevor has also tried with 4 ball bearings and he told us that it?s not easy watching all 4 go through simultaneously. Also another bit of useful information is with what Trevor has done with his air filtering. Trevor has replaced the original air filter and the gigantic air box with 4 K&N filters. He has also changed the main jets to size 100 to go with the increase of air the K&N filters are providing. Thanks Trevor for your information, I?m sure many people will find it very useful.
Additional Info Above there is information on balancing the carbs, but this does not necessarily mean tuning. Below is some info from Jarmizz (that he posted previously) on tuning the carbs on the FZR: ******** Post #1 ************* If your bikes running rich then tune the carbs. The main mix screw should be three turns out. And then balance th carbs and that should sort the fuel problems. As with Dyno runs, it is possible to dyno a bike but what would you be looking for as our bikes are carburetors and not fuel injection so you dont have any sensors to tell you whats happning. But it would be good to see what power the beasts are pumping out after 12+ years of thrashing. ********* Post #2 ************* I think the BB's trick would be great, but I use the dial way. The reason why Trevor liked the BB way was because his dials moved alot while we was trying to read them and set the carbs. I didnt have this problem because the dials I used had a tap in the vac line so that you could stop that dial movement. So i would say a real perfect carb balance is always needed. Jets should all be unscrewed and with hi presser air and carb cleaner, cleaned. Set the carbs to 3 360 degree screws out from right in. The way I do it is, take the carbs off the engine and spray them down with carb cleaner and wipe clean. Then I would check the floats and spray them with some carb cleaner and air just to make sure that all the crap has gone. Clean the jets by the method I said above and screw back into place. Put the float bowls back on and make sure screws are tight so that no fuel will leak. GOOD HOUSE CLEANING IS IMPORTANT!!!!! CLEAN HANDS AND WORKING AREA IS NEEDED!!!!!!!!!!. Then from then on as you have said you have had a bit of expernce in carbs, just clean the rest of the carbs, make sure you are not to unbolt them into singles because that can introduce leaks that are a bitch to fix!!. Put the carbs back on the bike, do carb balance and then install air box and filter. Like I said before BE PERFECT WHEN WORKING WITH CARBS, NOT DIRT OR GREASE OR ANY SUCH SHOULD BE NEAR THEM> CLEAN THEM TO PERFECTION
Carb Floats Below is some information that Ciaran posted (see <!-- l --><a class="postlink-local" href="http://www.fzr250.com/viewtopic.php?t=924">viewtopic.php?t=924</a><!-- l -->) ***************************************** Here are a couple of pics of my carbs just before I cleaned them up and replaced a few seals. The first one is from the rear and the second one is from below. In the first picture you can see the four float bowls of the carbies. They are held on by only two screws each (except for the one on the far left that has had the screws taken out already). I am not going to go into what it does but all you need to know is the bottom part fills with petrol that the float sits in. The screws that you can see that are at a 45 degree angel are the drain screws. As said by Dave, if you open them the petrol in the float bowl will drain out. So we have the two screws holding on the float bowl and the angled one to drain it, what does the other screw below the float bowl do? It’s the idle mixture screw, if your bike is running fine don’t touch it. As for the leak, check all the drain screws are done up tight. If that fixes the problem good. If not the leak is probably coming from the rubber seal between the float bowl and the rest of the carburetor. To check, you will have to take off the float bowl by removing the two screws that hold it on. If the carbs haven’t been worked on for a while they won’t come out easy. As you can see by the pic, I eventually had to use an impact driver to get them out. Once they are off check the rubber seal. If it is old looking, flat or broken it will need to be replaced. They will set you back a bit less than a new set of spark plugs. Replace the seals and float bowls, do them up tight. These are the only two seals to the outside world for the float bowl. If it still leaks check all you fuel lines are in good order.
an excellent site for carb tuning (may not be for an fzr - but same principles apply) <!-- m --><a class="postlink" href="http://www.cr-x.org/cbr250/forum/topic.asp?TOPIC_ID=26849">http://www.cr-x.org/cbr250/forum/topic. ... C_ID=26849</a><!-- m -->
Please do NOT us the ball bearing method as the method has many serious flaws invloved in setting just clearances rather than considering the basic priciple of mechanical wear and fluid dynamics and the intake tract as a whole system. By balancing the carbs you are trying to achieve uniform fluid flow (air) primarily through the venturi inducted by the action of the piston/valve train during the intake stroke, not a uniform clearance at the throttle bodies. If all things were equal and the tolerances between the individual carbs were close to 1000th of a mm in ever aspect and each cylinder was in exactly the same condition and the cam wear was identical and the valve seats and valve profile were identical then this method would be near enough. Since the possibitliy of all the throttle bodies wearing evenly with respect to the throttle valve position, piston ring wear, cylinder lubrication, valve seat reccess, cam profile etc is next to none, you are actually in need of calibrating the the 3 intakes in the case of an FZR250 to the reference intake tract. That is why a vacuum gauge is used because it doesn't discriminate between throttle body wear, valve wear, cylinder wall/piston ring wear, fouling etc but provides a total vacuum in each intake tract that can be accurately calibrated to the other 3 as a SYSTEM, not just a throttle plate clearance. The reason the adjustment is made at the throttle plate is due to ease of adjustment, and it being the first point of metering for the intake system. You may well find that the throttle plate clearance may be all over the place compared to the vacuum pressure, but hte vacuum pressure is the correct calibration.
Umm would anyone have any step by step photo's of hwo they do this? and using the vacuum method to the ball bearing method? What sort of vacuum would u need? sounds very different to car carby tuning as u dont need one usually.. Cheers,
Photos will be added in a few days to the new thread on the subject. You don’t need a vacuum you need a vacuum gauge. The engine creates the vacuum in the intake manifold as the piston draws air and fuel into the cylinder.
Thanks for that Ciaran, I have taken some photos fo my carbys for anyone who wants to use them for a reference or anything. They shouldnt be off for too much longer hopefully.
I balanced my carbs on my 3LN1 in an unusual way. I did it by undoing the 4 bolts on the exhaust headers underneath the bike, In-between the engine and exup valve. first I had the bike up to running temperature and had it idling about 15-20% faster then factory settings, then I listened to the sound of each cylinder firing coming out of each hole, putting your finger near each hole helps by feeling the pressure and hearing the note it's making, you can hear if one or more cylinders are firing harder or softer or not at all. If it helps you can put a ice-cream container filled with water under it, it will show the different pressures by how far the water gets blown down Once you figure out which cylinder/s are firing harder than others you need to know which screws to turn to open and close down each butterfly valve, clockwise opens the next valve & anticlockwise closes it. cyl 1,2,&4 all get adjusted around cyl 3. I started by adjusting cyl 2 & 3 by using the middle screw. (Turning it clockwise will open cyl 2 & 1) Once you have cyl 2 & 3 the same you can move to ether cyl 1 or 4, if cyl 1 sound about the same as cyl 3 then as much as you turn the middle screw one way or the other to adjust cyl 2 you need to move the left screw in the opposite way equally to keep cyl 1 the same. Just keep turning the screws 1/8 turns till it sounds and feels even. After each adjustment turn i blip the throttle. After all cylinders sound even lower the idle down as low as you can without stalling it and see if it still sounds even if not keep adjusting till it does. You may need to raise the idle a bit. When its idling it shouldn't sound like a rotary engine idling it should sound smooth & even, it helps also by listening to the exhaust note at the tip as engine noises may put you off. Diagram: Left side of engine{1*2*3*4}right side of engine. (1,2,3,4, = cyl. *= adjustment screws) If you look at the simple diagram imagin cyl 3 is fixed and if you turn the middle screw you can see that it would turn cyl 2 & 1 at the same time. cyl 4 is easy, just needs to be the same as cyl 3. I know this is not the correct way to balance the carbs but it worked for me my bike runs sweet & idles nicely, before i fixed it wouldnt idle properly and then would cut out after 5 seconds. Before you attempt this your carbs and valve clearances should be in good order, and you may need a fan to prevent the engine overheating.
That's a fairly unusual way of balancing the carbs. If it works then that's great. Doing it by vacuum is not always easy.
hey guys Just bought myself a Carbtune II- new for $180. If you can stretch it, I consider it a worthwhile investment. Very easy to use (on the carb models like FZR- connect to the tune screws in the intake manifolds). Also, it uses stainless slugs instead of mercury in tubes- so doesnt matter about tipping it up, sucking mercury into the cylinder etc. First time I used it had the throttle bodies (same principle, same process as carb) on the CBR synched in around 20 minutes- and this is with figuring out how it all works, finding balance ports, adjust screws etc. The best thing its a precise measurement of vaccuum- providing the system is tight between the butterfly valves and the cylinder. Food for thought.....
Wanna come balance mine <!-- s:o --><img src="{SMILIES_PATH}/icon_surprised.gif" alt=":o" title="Surprised" /><!-- s:o -->
gday mate, Funny you should ask- I am organising a couple of garage days in the near future. First will be this or next weekend, the next will be soon after. The idea being bring your bike and any bits to be fitted/ servicing to be done, get a hand from someone else, then give a hand where you can. The first one is predominantly for Track day entrants on the 12th August, but anyone is welcome. Likely held at Moorooka for the first one, second one likely northside. Turn up to either and I am happy to have a look (bearing in mind I am a backyard boy). Also holding a group buy for bits (HID's, chain/ sprockets, braided lines etc) to be fitted at the garage days. <!-- e --><a href="mailto:bradcad1@hotmail.com">bradcad1@hotmail.com</a><!-- e --> if interested. Brad
