FZRSupport: the FZROnline Archive

ok i know for sure my problem is related to the carbs. because i put my brothers keihin fcr's on my bike and it ran exceptionally well.

1. my bike runs like poo until about 3.5k, like it is hitting on 3 cylinders. after that it runs fine up until about 8k and crackles sputters. again like its running on 3 cylinders. all this happens if you give it 1/4 to 1/2 throttle and take it all the way through the rpm range. if your wot the bike runs fine.


2. the idle is eratic after you come off the throttle. once you start the bike it will idle fine but after driving the idle will be erratic.

3. after i synched the carbs it idles on 3 cylinders. im positive its 3 cylinders because everyonce in a while you can hear the fourth cylinder come in.

4. the bike back fires alot out of the exhaust after a rev to 10k.

like i said im positive the carbs are cleaned. im positive the carbs are synched. i have brand new rubber boots that connect the carbs to the head.
and i know its a carb problem because i put my brothers carbs on my bike and it ran perfect.

the rubber diaphrams in the carb on the top of the carb. i believe are vaccum operated to open. well mine have little bitty dry cracks in the outter edges of each rubber diaphrams. if that makes any sense....could this be my problem?

the bike has 12,xxxx miles recent rebuild, recent valve shim, less then 800 miles on them. full yoshi exhaust.

try this, do the slides DROP after you let them go? i saying open up the diaphram sid of the carbs and lift the slider up and lift off the diaphram, then let the needle slider fall down, all four of them must drop like a qulotine. if any of diem dont drop instantly and go THUD you have a problem. its easy to ignor this step in carb cleaning. i dont think a carb can do anyting intermittently like drop and then catch up a cylinder normally.i know you say the carbs are cleaned but.....ahh... are the carbs clean?? sorry i had to. so everything works at wot? all four pots? hmmm... but not at 1/2 or 1/4? hmmmmmmmm...... hmmhmmhhmmmmm.....checked float level? idle mixture screws?? they should be at 3 turns on all four.how many times have you had the carbs apart for cleaning?

well
here we go, assuming the carbs are perfectly clean, synch'd, and there are no air leaks in the boots
1) if the diaphragms are leaking air, then you will never get decent main circuit response. Just the pilot circuit. So-- as you grab a handful of throttle, the vacuum behind the slide spikes, and attempts to draw pressure from the upper diaphragm chamber, and in turn lift the slide. If that chamber is leaking, then then slide will oscillate in a long slow frequency, or in a quick short frequency. The oscillation in turn causes abnormal pulses of charge to be withdrawn from the main circuit. So--if there are any cracks in any rubber, then that component needs to be replaced. period!
If this is your only problem, the bike will start and idle fine, but ANY throttle will cause rough running.

2) are the emulsion tubes (needle jets) worn? I cannot recall if the emulsion tubes on the 1000 are combined with eh needle jets like they are in the 600. Essentially, the needles hang from the slide down into the needle jets, which sits above the emulsion tube (or sometimes is combined into one piece) which in turn sits above the main jet (which hangs down into the pool of fuel in the bowl). Down draft carbs wear them out since the loose hanging needle rubs in and out on the "downwind" side of the needle jet/emulsion tube as you open and close the throttle over the years. This wear makes the perfectly and precisely made hole less round and slightly egg shape-- allowing for excess fuel to sneak around the very precisely tapered needle. You can tell if they are worn by looking at them from the top of the carb after removing the slide -- they will have a slight egg shape. -- Factory Pro has some good photos of worn ones.

3) Since you have thoroughly cleaned the carbs, i assume all the o-rings were soft and without cracks...?

Lastly, you are positive the enrichner (choke) is working properly on all 4 carbs? The tips of the plunger can sometimes prevent fuel from passing, or allow it when you don't want it to.

Even if you have all of these problems and fix them, you will still need to tune your carbs. But the result will be fantastic. Factory Pro has a great tuning guide on their website. Replacing the items in 1 and 2 will cost you close to 200 bucks, but they will make a night and day difference (IF THEY ARE THE PROBLEM).

Hopefully that will be a decent start for you.

Good luck!

coreo19 wrote:ok i know for sure my problem is related to the carbs. because i put my brothers keihin fcr's on my bike and it ran exceptionally well.

Ok, so what carbs are you having the troubles with? Stock or a different set of FCRs?

kiki231 wrote:I cannot recall if the emulsion tubes on the 1000 are combined with eh needle jets like they are in the 600.

400, 600, YZF750, and 1000 are designed pretty much the same way.

the problem is with the stock 38mm carbs. i belive my air/fuel mixture screws are out 2 3/4 turns out. i have tore the carbs apart about ten times and cleaned them. you can say there not clean all you want but i honestly believe they are clean. the last 8 or 9 times i have cleaned them i have found nothing wrong with them. i have not checked the emulsion tubes which i will tommarow thanksgiving day. the needles def. look like they have some wear but nothing extremely major. i will check the emulsion tubes and needles closer tommarow and let you guys know. i will also try the slide drop thing.

the mixture screws are not the problem here. They may need to be tuned, but the pilot circuit (which includes the mixture screw) has effect only until 3rd throttle, then the main circuit gradually takes over.
Pilot jets and mixture screws do not use the main circuit, and are to keep your engine running during idle and slow-speed. They feed into a series of drillings behind the throttle plate. Adjusting the screws allows more mixture or less. But once you crank the throttle, and the slide lifts, the main circuit passes MUCH more charge than the pilot jet could ever.

As i mentioned, the needles, which are stainless steel, hang down into the emulsion tube/needle jet combo. On downdraft carbs, they are on their side. So the needle rests on the lower rim of the tube. Sadly, the tube is brass (ie. very soft metal) , and the in and out of the needle, and the slide vibrations during idling wears a little cradle in the otherwise round tube. this in turn opens up a crescent shaped crack on the opposite side of the tube. Remember-- this is VERY precise stuff.

Add to this the leaky diaphragms -- i bet you have your culprits.

Now-- as always-- check the other obvious stuff-- make sure there is no problems with the throttle linkage-- etc etc -- sometimes big probs have simple solutions.

here is a graphic form my website earlier this year.

Looking down on a needle from above. Upper is a healthy needle jet (emulsion tube) , bottom is severe wear. Not only does the extra gap cause a rich condition , the needle will oscillate and flop around in the too-large hole, causing erratic flow and negating all the benefits of a tuned and tapered needle

ok checked today. the emulsion tubes are circle and no where near egged shaped. the slides when lifted fall normally. i cleaned the carbs once again today so i guess ill just put them on and see what happens. one thing that i never payed much attention to before. the number 1 and 4 cylinder main jets are 140's when i believe the mains on a stock carb are 125's would this cause any of my problem. i know im running rich now which i believe the jetting is the culprit to that.

sounds like the jetting was the culprit... were the stock insides 122.5? stock filter? I seen you said full exhuast, you will lose out on bottem end and some midrange. it'll be a bog if you dont know how to completely dial it in for right sea level. Even then I wouldn't put it past an actual Exup to even pull better but using a full system will make your top end scream, thats why a lot are used on race bikes as the RPM's are always up along with a lighter system..

Throw an exup header and go to stage 1 jetting or dial in the stage 3 the right way.

Cheers

coreo19 wrote:ok checked today. the emulsion tubes are circle and no where near egged shaped. the slides when lifted fall normally. i cleaned the carbs once again today so i guess ill just put them on and see what happens. one thing that i never payed much attention to before. the number 1 and 4 cylinder main jets are 140's when i believe the mains on a stock carb are 125's would this cause any of my problem. i know im running rich now which i believe the jetting is the culprit to that.

the Exup carbs are staggered at 125 for cylinders 1&4 and 122.5 for 2&3. 140 sounds a bit big but that could be a Dynojet jet as opposed to a Factory Pro or Mikuni Jet. Dynojet has their own numbering system. Either way it seems you've gotten to the root of your problem.

alright. i put what i believe is a 124 dyno jet in there. from some cross reference sheets i found on the internet it comes out to be around a 116 mikuni jet. which would be very lean considerin my full exhaust and some cheap ebay pod filters. but still puffs some black smoke when you hit wot. i did install the carbs tonight and so far so good . but wont know for sure until i get to ride it on the road which may be a while considering the weather is really crappy here in kentucky right now

thank you all for your help so far

I'd contact Mikuni and order the correct size MJ's. the best way to gain performance or see where your bike sits is to return to stock. 2 125's and 2 122.5's should run you to much money, return to stock float height if messed about with and go from there. also the best way to check your emulsion tubes is hold them to a light source and peak through, its not going to be incredibly ovaled but the slightest bit will drastically turn the bike around...

You say you have no exhaust, well that with a not properlly tuned carb set up will result in poor running conditions as well..

Do you know what altitude you're at?

Black smoke? are you burning oil? how many miles on the bike?

not positie of the altitude...but i rebuilt the motor 1000 miles or less ago....the only time i burn any oil is at start up because the valve seals are goin bad. and i believe black smoke means your running rich?? correct me if im wrong.


12,xxx on the bike

Wait so why'd you'd rebuild the motor if it had 12k on it????? Worn stem seals doesn't seem like a culprit at that many miles BUT that is excatly what happens on old bikes... I hope you rebuilt it with brand new gaskets and made sure timing is spot on.. shoulda done the stem seals while in there. Worn stem seals over time will result in your guides getting messed up..

Black smoke doesn't just mean rich.. could be when you get out it oil is seeping by the rings and getting burned up... my bike let's out a cloud at around 7-8 grand but the motor is eattingg oil so I'm not worried and it seems to have decent compression as she pulls like a raped date...

I'd still look at your carb set up... easiest way is to go to stock n work from there. Use noaa.gov and find you're altitude, do some math and then fiddle with the right jetting and floating height if you truely want to go with a stage 3 kit...if not call factory pro. Get their 1.1 ti kit do that..


-Ant

McFizzer wrote: Black smoke doesn't just mean rich.. could be when you get out it oil is seeping by the rings and getting burned up..

I could be wrong here (not the first time for that) but black smoke usually denotes a rich fuel mixture and blue smoke denotes oil being burned.